Bilstein Science Experiment

[M-Sport fan]

Not necessarily. The OE shocks I dyno'd had 40Kish on them, they were fine. Bilstein builds some extrememly nice shocks from a component standpoint. They have one of the best seal heads in the business. A friend dyno'd a 20+yo Miata Bilstein and it was within a few percent of the Original specifications when it was built.

Like many OE type shocks, the Bilstein street shocks don't build enough force to really hurt the components inside. Now that all said the B6 and B8 dampers are a twin tube like the stock components and are built differently than the monotube and motorsport dampers. I see no reason if they aren't leaking that they should be worn out at 50K miles.

Given that superior internal componentry, would you expect the B6es to be more durable/long lived without leaking over the factory dampers (even if they are not as well valved for a/x road course use with higher rate springs) for rough roads, or in my case, working on bombed-out forestry roads on ARA rallies??

 

[Fusion Works]

The Front B6s are very similar construction to the OE setup. They crimp the top. They are vastly different than the B14s. The rears are a better design, probably hold up better.

The B6/B8s won't do a good enough job of controlling the springs at high shaft speeds, because they don't have the valving for that ("rally" type valving). I would build around the B14s in the front and just soften the springs and fix the valving. The inverted damper is much stiffer laterally for what you are doing.

Then start with a B6 damper in the rear and have it revalved, it will have a bit of extra length compared to starting with the B8 and B14 rear damper. You could also skip the OE rear damper all together and go with a B8 5100/5160 off road truck shock on the rear and keep your OE springs. The extra length and the extra size will give the damper more control and better heat dissipation capabilities. While swell you don't necessarily need the remote reservoir since there is a lot of volume in the damper body itself.

You want extra travel without sending your whole retirement to Reiger. I think I could comfortably build a setup like my front dampers that would have enough travel to work for a light rally application. The insert I have would be the limitation. I think once you get too far beyond OE travel levels things would get tricky. Would really have to measure and see where it all works out.

 

[Sam4]

In my case it's because my OEM dampers were shot after 70K miles in NEO.

embarrassed, disgraced, and THEN shot!

 

[kevinatfms]

The Front B6s are very similar construction to the OE setup. They crimp the top. They are vastly different than the B14s. The rears are a better design, probably hold up better.

The B6/B8s won't do a good enough job of controlling the springs at high shaft speeds, because they don't have the valving for that ("rally" type valving). I would build around the B14s in the front and just soften the springs and fix the valving. The inverted damper is much stiffer laterally for what you are doing.

Then start with a B6 damper in the rear and have it revalved, it will have a bit of extra length compared to starting with the B8 and B14 rear damper. You could also skip the OE rear damper all together and go with a B8 5100/5160 off road truck shock on the rear and keep your OE springs. The extra length and the extra size will give the damper more control and better heat dissipation capabilities. While swell you don't necessarily need the remote reservoir since there is a lot of volume in the damper body itself.

You want extra travel without sending your whole retirement to Reiger. I think I could comfortably build a setup like my front dampers that would have enough travel to work for a light rally application. The insert I have would be the limitation. I think once you get too far beyond OE travel levels things would get tricky. Would really have to measure and see where it all works out.

Wanna dyno a set of B8's off an early Focus? They are a 49mm monotube but are shorter than the factory B8's. Id love to see the valving on them compared to stock and Fiesta B8's.

I also have a set of KYB AGX's for a Focus that could be tested at full stiff. They are the correct length for a Fiesta rear.

If so, i can send them over. Let me know.

 

[Fusion Works]

Sure. Send them over and I can dyno them. I almost wonder if the B8s are similarly valved. The AGXs are twin tube.

Because of the rear length and travel, I would lean heavily towards building a truck based damper. That would get you all of the travel you could ever want.

 

[the duke]

I think we should note those fiesta ST Bilsteins (B6s and B8s) are just off the shelf fiesta unit and aren’t specifically made for the ST springs. I believe the KONI sports and oranges are the same issue.

 

[Fusion Works]

I don't think the Bilsteins are valved for anything in particular. This seems like Corporate Bilstein valving philosophy. Dyno'd some RX8 B14s that I put on and they had similarly soft valving.

Koni Oranges are basically Sports on full soft without any adjustment. They are probably not any better than the Bilsteins. Remember you don't want to get labeled as being "too stiff" in the aftermarket game where guys are just putting lowering springs and new shocks on their cars.

 

[Dialcaliper]

They are not "over damped", they are fine for the stock spring rates and even the spring rates of stiffer springs. They would be fine with the Bilstein spring rates. Do you want a Cadillac or a car that handles well. Can't have both.

The valving built into my new dampers is pretty much double the OE rates across the board. Also has a lot less bleed in the lower end of the curve than the OE or even the Bilsteins. It is definitely not a couch and 250lb springs feel harsh for street use, but on track they are magic.

The OE dampers are a compromise for the 90th percentile. They have to be. There is no reason for the Bilsteins to have even less control. That is just poor shock valve selection.

Why do you think the B6 damper will be better than the OE in a track application? It is softer, thus allow the vehicle to flop around more.



The Bilstein Techs barely know more than the part numbers and some basic tech data. They are not ride control engineers or shock valving specialist. I would never ask them for shock valving or setup advice (the people in Poway CA at the Aftermarket side of Bilstein).

Yes the Bilsteins are progessive. I can measure the springs, but I don't really care what they are beyond what Bilstein claims they are. They won't really be used in this application for this customer.

The OEM shocks are heavily overdamped in rebound intentionally, with heavy asymmetry over compression damping.

Part of what makes the ST feel so stiffly sprung is that ford has taken a page from Japanese import sports cars, and designed the rebound to cause the car to "jack down" on the stock MCU bumpstops, which are really "spring aids", and are engaged as soon as you enter a corner. I have some testing to do, but my first guess is that the linear ramp of the bumpstops front and rear add about 130-150 lb/in to the front spring rate, and about 100 lb/in added to the rear. In other words, the car is effectively sprung progressively with a ~300lb/in spring in the front, and a ~250 lb/in rear. The good part about this very common OEM tuning style is that it gives you a stiff car that feels "sporty" (because of the lousy ride on account of the heavy rebound damping), corners reasonably well, and because the front bumpstops engage and go nonlinear first, you get terminal understeer from a setup that otherwise starts with mild liftoff oversteer.

The Bilsteins through no coincidence, actually have a very similar or even softer spring setup at 278/228 to the OEM spring+bumpstop arrangement, but use less and more symmetrical damping as is typical of a "European" style of suspension tuning. Despite appearances, the springs themselves are not really progressive once they are on the car - the rear springs, like the Swift, have a built in helper/tender spring which binds up pretty quickly in cornering and aids in the angular tilt that occurs in droop travel, - this is why the "progressive" section of the Bilsteins is at the bottom, not the top like you'd expect for a true progressive spring. The actual progressive behavior of the Bilstein setup kicks in later on account of the long bumpstop/spring aid inside the front damper, which is typically a linear ~200lb/in foam bumpstop.

Bumpstops have been part of OEM tuning for a long time, yet most aftermarket lowering setups and most people who modify their cars don't really pay as much attention to them as they should. Most "street" coilover setups are basically in the same range of suspension frequencies as a stiff OEM setup, just with a linear spring and bumpstops that are short traditional bumpers rather than spring aids.

Neither philosophy is "wrong", but the OEM jack-down strategy has a few more drawbacks when it comes to real performance, but several advantages when it comes to convincing the average consumer that a car has "sport" suspension and decent handling, while still producing an understeer tendency for the lowest common denominator in driving skill.

I've been slowly putting together some spreadsheet models that are still a work in progress, but the early takeaways are that the OEM setup is solidly in the low end of sports car range of suspension frequencies (1.4F/1.7R Hz without bumpstops, 1.8F/2.4R Hz with), and would be pretty decent if not for the inherent flaws in the overdamped/jack-down damping strategy. For reference, maximum mechanical grip and road holding for a GT class race car with minimal aero is in the 2.0-2.5Hz range, which is about where you'll find most recent 911 GT3 RS. Any higher and you'll actually be giving up mechanical grip on all but the smoothest of tracks. The only reason you'll find higher frequencies on most racecars (especially in the front) is that in order for ground-effect underbody aero to work (functional splitters and diffusers), you need to maintain tighter control of ride-height, and the added grip from downforce outweighs the loss in pure mechanical grip.

The other interesting takeaway is that like you mentioned, the MacPherson strut suspension geometry on the Fiesta family is pretty terrible. The ST is basically already on performance lowering springs, 0.9" below a standard FIesta, and between 0 and 0.5" lower than that is the best you can get for reduced roll moment arm, with the front static roll center between 2-4 inches off the ground, which is a good starting point for a FWD car. Beyond that, where pretty much all aftermarket springs drop the car to, the roll center starts dropping faster than the CG, meaning that lowering the front suspension much actually makes things worse when it comes to body roll, not better. At about 1.5" below the stock ST, the front roll center is at ground level, and at 2" you've added 10% more body roll than running at stock height.

 

[Fusion Works]

The OEM shocks are heavily overdamped in rebound intentionally, with heavy asymmetry over compression damping.

Its not overdamped. At best it will come up with a bit more force than one inch of OE spring rate at 10in per second. At 2in per second the OE damper has at best half the OE spring rate (this discussion pertains to front dampers). I am not taking into acount any motion ratio to simplify the discussion. My ST lowering springs (172lb/in) are compressed 3in just to hold the car at ride height with a driver. So starting at ride height the spring force is 516lbs (again leaving M/R out of this). The rebound force becomes even less effective at that point. Add to that any extra travel in the corner as the body rolls and any extra force from the sway bar. The OE damper is nowhere near critical.

Part of what makes the ST feel so stiffly sprung is that ford has taken a page from Japanese import sports cars, and designed the rebound to cause the car to "jack down" on the stock MCU bumpstops, which are really "spring aids", and are engaged as soon as you enter a corner. I have some testing to do, but my first guess is that the linear ramp of the bumpstops front and rear add about 130-150 lb/in to the front spring rate, and about 100 lb/in added to the rear. In other words, the car is effectively sprung progressively with a ~300lb/in spring in the front, and a ~250 lb/in rear. The good part about this very common OEM tuning style is that it gives you a stiff car that feels "sporty" (because of the lousy ride on account of the heavy rebound damping), corners reasonably well, and because the front bumpstops engage and go nonlinear first, you get terminal understeer from a setup that otherwise starts with mild liftoff oversteer.

The OE setup doesn't engage the bump stops in normal aggressive driving, only in the worst mid corner bump or possibly a curb. (or massive chuckhole) This is not like Mazda's tuning strategy of keeping their cars soft and letting them flop all over the place and bounce of the bumpstops The OE damper has 1.5ish inch of gap between the bumpstop and the damper after 2in of bump travel. The rears are nowhere close to the damper except in all but the most heavily loaded trunk and heavy bump type situation. The rear dampers have so much travel you will have a hard time getting into those in any normal track situation.

The ramp rate on the bumpstops is pretty aggressive. I don't think I have my notes, but it heads north of 500lbs pretty quickly. Its meant to save the chassis, not enhance performance significantly. IF you contacted the OE bumpstops on track the spring rate will go up enough to wash the front end out, that doesn't help performance at all.
(scratch that, I found them in the trash, lol. The OE Fiesta and Mustang GT [I had a Ford kit I bought for the bumpstops] both start at 160-190lbs at 1in and go to 570lbs .5in later.) That is no way to tune a suspension setup. These are simply to protect the dampers from Northern roads.

The Bilsteins through no coincidence, actually have a very similar or even softer spring setup at 278/228 to the OEM spring+bumpstop arrangement, but use less and more symmetrical damping as is typical of a "European" style of suspension tuning. Despite appearances, the springs themselves are not really progressive once they are on the car - the rear springs, like the Swift, have a built in helper/tender spring which binds up pretty quickly in cornering and aids in the angular tilt that occurs in droop travel, - this is why the "progressive" section of the Bilsteins is at the bottom, not the top like you'd expect for a true progressive spring. The actual progressive behavior of the Bilstein setup kicks in later on account of the long bumpstop/spring aid inside the front damper, which is typically a linear ~200lb/in foam bumpstop.

Since I have the Bilstein springs here I can measure the actual rate and is ramp up of linearity. The rears are most definitely progressive and won't be in the linear portion at ride height. The front "progressive" portion is at the top of the spring mount.

There is MINIMAL assymetry in the Bilstein curve. They use a TON of bleed on the low end and generate almost no forces in the range you as a driver will feel them. They band aid that lack of damping with springs. If they didn't it would behave like a Miata. It might manage 50lbs of rebound and 40lbs of compression at 3in/sec. I am eyeballing my picture, not looking at the dyno computer.

Bumpstops have been part of OEM tuning for a long time, yet most aftermarket lowering setups and most people who modify their cars don't really pay as much attention to them as they should. Most "street" coilover setups are basically in the same range of suspension frequencies as a stiff OEM setup, just with a linear spring and bumpstops that are short traditional bumpers rather than spring aids.

Nothing wrong with bumpstops and tuning them to benefit your driving conditions, the problem is their quick ramp rates can make them a tricky tool to use. Most people don't use spring rates on track that are compatible with bumpstop tuning procedures used in other forms of racing. If you look at the Ford/Eibach dampers they use a solid type puck with little to no progressivity. It will simply save the dampers. Most Ricer coil overs do similar things and use a rubber puck as a bumpstop.

Neither philosophy is "wrong", but the OEM jack-down strategy has a few more drawbacks when it comes to real performance, but several advantages when it comes to convincing the average consumer that a car has "sport" suspension and decent handling, while still producing an understeer tendency for the lowest common denominator in driving skill.

Are we discussing race car or street car parts? There is nothing wrong with lots of rebound. You don't have enough force to "jack the car down". My current valving is basically double what the OE dampers are everywhere. Yep its stabilizes the platform but in no way will it "jack" the car down. That is a theoretical concept, but for the most part isn't happening with anyone's street dampers and most of the current philosophy race dampers.

I've been slowly putting together some spreadsheet models that are still a work in progress, but the early takeaways are that the OEM setup is solidly in the low end of sports car range of suspension frequencies (1.4F/1.7R Hz without bumpstops, 1.8F/2.4R Hz with), and would be pretty decent if not for the inherent flaws in the overdamped/jack-down damping strategy. For reference, maximum mechanical grip and road holding for a GT class race car with minimal aero is in the 2.0-2.5Hz range, which is about where you'll find most recent 911 GT3 RS. Any higher and you'll actually be giving up mechanical grip on all but the smoothest of tracks. The only reason you'll find higher frequencies on most racecars (especially in the front) is that in order for ground-effect underbody aero to work (functional splitters and diffusers), you need to maintain tighter control of ride-height, and the added grip from downforce outweighs the loss in pure mechanical grip.

Still disagree with your, "jacking down" assessment. There is no reason to run ridiculous spring rates if you can make the dampers behave like a mechanical device and stabilize the platform and tire as it transitions. Most cars that we are all dealing with make less than 400lbs of "negative lift" in reality. So everything we are dealing with here is mechanical grip and doing everything possible to increase that should be your focus.

The other interesting takeaway is that like you mentioned, the MacPherson strut suspension geometry on the Fiesta family is pretty terrible. The ST is basically already on performance lowering springs, 0.9" below a standard FIesta, and between 0 and 0.5" lower than that is the best you can get for reduced roll moment arm, with the front static roll center between 2-4 inches off the ground, which is a good starting point for a FWD car. Beyond that, where pretty much all aftermarket springs drop the car to, the roll center starts dropping faster than the CG, meaning that lowering the front suspension much actually makes things worse when it comes to body roll, not better. At about 1.5" below the stock ST, the front roll center is at ground level, and at 2" you've added 10% more body roll than running at stock height.

I agree, people don't understand how "the low life" affects the handling of their cars. Suspension geometry is a critical factor in a strut car and they have a very limited range in which they can operate. I have seen graphs of OE VW GT1 suspension, (probably MK1 or MK2) and 15mm of lowering DRAMATICALLY" affects the suspension geometry and its not good. Ford did us no favors in the ride height department and people need to stop treating these like a dual a-arm Honda application. If you want the low life, time to bust out the plasma cutter and welders to raise the pickup points. Its not worth it, buy another car.

I am sure I have glossed over a few things, but this is a good discussion.

 

[Dialcaliper]

Its not overdamped. At best it will come up with a bit more force than one inch of OE spring rate at 10in per second. At 2in per second the OE damper has at best half the OE spring rate (this discussion pertains to front dampers). I am not taking into acount any motion ratio to simplify the discussion. My ST lowering springs (172lb/in) are compressed 3in just to hold the car at ride height with a driver. So starting at ride height the spring force is 516lbs (again leaving M/R out of this). The rebound force becomes even less effective at that point. Add to that any extra travel in the corner as the body rolls and any extra force from the sway bar. The OE damper is nowhere near critical.



The OE setup doesn't engage the bump stops in normal aggressive driving, only in the worst mid corner bump or possibly a curb. (or massive chuckhole) This is not like Mazda's tuning strategy of keeping their cars soft and letting them flop all over the place and bounce of the bumpstops The OE damper has 1.5ish inch of gap between the bumpstop and the damper after 2in of bump travel. The rears are nowhere close to the damper except in all but the most heavily loaded trunk and heavy bump type situation. The rear dampers have so much travel you will have a hard time getting into those in any normal track situation.

The ramp rate on the bumpstops is pretty aggressive. I don't think I have my notes, but it heads north of 500lbs pretty quickly. Its meant to save the chassis, not enhance performance significantly. IF you contacted the OE bumpstops on track the spring rate will go up enough to wash the front end out, that doesn't help performance at all.
(scratch that, I found them in the trash, lol. The OE Fiesta and Mustang GT [I had a Ford kit I bought for the bumpstops] both start at 160-190lbs at 1in and go to 570lbs .5in later.) That is no way to tune a suspension setup. These are simply to protect the dampers from Northern roads.



Since I have the Bilstein springs here I can measure the actual rate and is ramp up of linearity. The rears are most definitely progressive and won't be in the linear portion at ride height. The front "progressive" portion is at the top of the spring mount.

There is MINIMAL assymetry in the Bilstein curve. They use a TON of bleed on the low end and generate almost no forces in the range you as a driver will feel them. They band aid that lack of damping with springs. If they didn't it would behave like a Miata. It might manage 50lbs of rebound and 40lbs of compression at 3in/sec. I am eyeballing my picture, not looking at the dyno computer.



Nothing wrong with bumpstops and tuning them to benefit your driving conditions, the problem is their quick ramp rates can make them a tricky tool to use. Most people don't use spring rates on track that are compatible with bumpstop tuning procedures used in other forms of racing. If you look at the Ford/Eibach dampers they use a solid type puck with little to no progressivity. It will simply save the dampers. Most Ricer coil overs do similar things and use a rubber puck as a bumpstop.



Are we discussing race car or street car parts? There is nothing wrong with lots of rebound. You don't have enough force to "jack the car down". My current valving is basically double what the OE dampers are everywhere. Yep its stabilizes the platform but in no way will it "jack" the car down. That is a theoretical concept, but for the most part isn't happening with anyone's street dampers and most of the current philosophy race dampers.



Still disagree with your, "jacking down" assessment. There is no reason to run ridiculous spring rates if you can make the dampers behave like a mechanical device and stabilize the platform and tire as it transitions. Most cars that we are all dealing with make less than 400lbs of "negative lift" in reality. So everything we are dealing with here is mechanical grip and doing everything possible to increase that should be your focus.



I agree, people don't understand how "the low life" affects the handling of their cars. Suspension geometry is a critical factor in a strut car and they have a very limited range in which they can operate. I have seen graphs of OE VW GT1 suspension, (probably MK1 or MK2) and 15mm of lowering DRAMATICALLY" affects the suspension geometry and its not good. Ford did us no favors in the ride height department and people need to stop treating these like a dual a-arm Honda application. If you want the low life, time to bust out the plasma cutter and welders to raise the pickup points. Its not worth it, buy another car.

I am sure I have glossed over a few things, but this is a good discussion.

In reference to “jacking down”, I’m referring to the stock setup, not the Bilsteins. Also, I’m slightly misusing “overdamped” in the technical meaning of the term. All suspension is under damped below “critical”, or it wouldn’t work at all. What I mean is that they have more rebound than is optimal for the stock springs and significant asymmetry between rebound and compression.

The OE front springs (using the 2014-2016 as an example) are ~12” in free state (preloaded to ~10.5” in droop). Spring install ratios for this car are near 1:1, except for the rear shock, which is actually >1 almost 1.2 (this is actually quite important as it means motion ratio approaches 1.5 in the rear - only for the shock, not the spring).

Stock front corner at about ~850 lb means 5.5” compression, which is 4” below full droop height. I just measured a stock strut, and we’re starting with only 4.25-4.5” of clearance to the bumpstop in full droop. So the car, stock springs and stock ride height is actually sitting a mere 1/4-1/2” above the nose of the front bumpstop at rest

Looking at your plot, the stock dampers have low speed rebound force at almost 1.5x the compression force. Needing that much extra rebound to “control a stiffer spring” is a bit of a myth. springs affect steady state cornering, and are effectively preloaded in a corner by weight transfer.

With the stock roll moment in a 1.0g corner I’m coming up with weight transfer of nearly 300 lb in front and 400lb in rear (stock), which would compres the front spring alone ~2” in addition to the static ride height, not including the damping effect. So very quickly, you’re into the linear nose of the front spring aid/bumpstop, on the order of 1” once you include it’s stiffness. That first 1.0-1.5” range of the bumpstop you mention is *extremely* important to the stock suspension tuning. The progressive ramp past that is the “save the suspension” zone you refer to.

With ~50-75lb of damping asymmetry at the knee, physics tells us the car will jack down another 1/4-1/2 inch into the bumpstop as the chassis oscillates. Even a “smooth” track has undulations which compresses the spring/shock and the dynamic response of the sprung mass with much more rebound than compression will have a “ratcheting” effect on the car body, until the added spring force balances the downward bias

Controlling the oscillations of a stiffer spring requires higher total damping, not just rebound. That much assymetry *will* cause jacking down as the spring oscillates, which acts to *keep* the car in the nose of the front bumpstop, and not come off it in a corner (not flopping around “bouncing off” the bumpstop) factory Miatas and the vast majority of factory “sport suspension” cars are tuned the same way.

With the struts in the front and nearly 1:1 motion ratio in the rear, plus aft-of-wheel dampers, the ST has much higher actual wheel rates than you’d expect for a given spring stiffness compared to a double wishbone car like the aformentioned Miata

Our rear damper mounted aft of center, as I mentioned before, has a motion ratio of almost 1.5x during chassis oscillation when it comes to forces generated at the wheel (the shock moves at ~1.2 the velocity of the wheel, which generates force at a higher point on the dyno plot, and those forces act back at the same 1.2x leverage at the wheel) so the massive truck damper travel you’re seeing in the rear is actually being used more than you’d think.

Most aftermarket lowering springs on stock shocks are basically sitting on the bumpstops, which is why they feel stiffer than stock despite the spring rates being the same or only marginally stiffer.

Obviously this changes once you swap in a different shock and spring design like the Bilstein or adjustable coilovers

 

[kevinatfms]

Did you get a chance to dyno the B14 front damper? Or was it just the replacement B6/B8 dampers?

 

[Fusion Works]

That was the B14 front damper in the picture. I didn't measure an OE rear shock only the B6 damper before I cut the top off and revalved it.

Dial, I will have to check and OE Fiesta ST, but my car with lowering springs still had 2in of bump travel at the point of lifting the chassis from that wheel with a jack. The car didn't ride around on the bumpstops stock or with lowering springs.

 

[thecman02]

Hey Brett, was wondering if you would be willing to post your after revalve dyno plots? I'm trying to figure out with what I want to go with. I've slowly been cheaping out on my suspension as I've gone through cars. I had Hotbits DT2's on my old Galant VR4. That was gloriously adjustable. The CTS-V got FEALS 441's. Part of the attraction of the FEAL suspension other than they do good work for the price is Odi, had a CTS-V and nerded out and did all the development work in making a great package. Its decently valved for spirited driving and I can tweak it some on track days to extract the balance I want.

I just got some B14's for a song. They are used, but seem be in good condition based on previous owner description of use and driving them. I feel like with the few hundred miles I've put on the setup that I want a tad bit more compression to slow down the g out effect I get on big dips. I feel like the spring rate is about what I would want. I haven't gotten into borrowing my friends scales and going through dynamics calculations. I'm assuming Bilstein spring rates are close to flat ride frequency ratio since I don't notice any pitching issues as far as comfort goes. I'm really trying to avoid nerding out and going head first into suspension (Mechanical Engineer major, and I did lots of work with our schools FSAE car). I already have too many hobbies and a young family that deserves my time.

Once I can iron out what I want from this suspension I'll bring my list of demands to a business in town that just so happens to specialize in Bilstein (https://deltavee.net/). One last concern on the B14's I was thinking about is changing out springs. I feel like having to max out preload to minimize drop to my preferred ride height isn't ideal. So I'd need to source linear springs in a slightly longer size and change spring mounting hardware.

Also completely off topic. Dialcaliper.... I'm assuming you kept your same screen name from the galantvr4.org forum days???

 

[Fusion Works]

Hey Brett, was wondering if you would be willing to post your after revalve dyno plots? I'm trying to figure out with what I want to go with. I've slowly been cheaping out on my suspension as I've gone through cars. I had Hotbits DT2's on my old Galant VR4. That was gloriously adjustable. The CTS-V got FEALS 441's. Part of the attraction of the FEAL suspension other than they do good work for the price is Odi, had a CTS-V and nerded out and did all the development work in making a great package. Its decently valved for spirited driving and I can tweak it some on track days to extract the balance I want.

I just got some B14's for a song. They are used, but seem be in good condition based on previous owner description of use and driving them. I feel like with the few hundred miles I've put on the setup that I want a tad bit more compression to slow down the g out effect I get on big dips. I feel like the spring rate is about what I would want. I haven't gotten into borrowing my friends scales and going through dynamics calculations. I'm assuming Bilstein spring rates are close to flat ride frequency ratio since I don't notice any pitching issues as far as comfort goes. I'm really trying to avoid nerding out and going head first into suspension (Mechanical Engineer major, and I did lots of work with our schools FSAE car). I already have too many hobbies and a young family that deserves my time.

Once I can iron out what I want from this suspension I'll bring my list of demands to a business in town that just so happens to specialize in Bilstein (https://deltavee.net/). One last concern on the B14's I was thinking about is changing out springs. I feel like having to max out preload to minimize drop to my preferred ride height isn't ideal. So I'd need to source linear springs in a slightly longer size and change spring mounting hardware.

Also completely off topic. Dialcaliper.... I'm assuming you kept your same screen name from the galantvr4.org forum days???

I have found with my valving, the car is pretty harsh on public roads even with a 250lb front spring. They have a LOT of rebound. (will get a pic of my damper curves). I have en-rounte some 162lb 8in Springs and I will swap back in the 117lb rear springs from my ST lowering spring set that hasn't sold. This well let me test a street setup. My setup is probably not the best for an average street user, especially one that drives on Michigan's bombed out roads daily.

You will have one problem, The Rear Bilsteins are probably crimped. That causes a problem for many shops. You may want to talk to your preferred shop and see if they are capable of dealing with a crimped rear shock.

What are you trying to do with the car? We already know the Bilstein doesn't have enough valving and they bandaid it with springs. I put their rear springs on my car and am not totally thrilled with the behavior. I haven't rated them, will when I get my new springs mounted. They are progressive and they block out pretty quickly which on the street makes my car too bouncy.

Preload is good. There is nothing wrong with preload.

 

[Intuit]

The other interesting takeaway is that like you mentioned, the MacPherson strut suspension geometry on the Fiesta family is pretty terrible. The ST is basically already on performance lowering springs, 0.9" below a standard FIesta, and between 0 and 0.5" lower than that is the best you can get for reduced roll moment arm, with the front static roll center between 2-4 inches off the ground, which is a good starting point for a FWD car. Beyond that, where pretty much all aftermarket springs drop the car to, the roll center starts dropping faster than the CG, meaning that lowering the front suspension much actually makes things worse when it comes to body roll, not better. At about 1.5" below the stock ST, the front roll center is at ground level, and at 2" you've added 10% more body roll than running at stock height.

I agree, people don't understand how "the low life" affects the handling of their cars. Suspension geometry is a critical factor in a strut car and they have a very limited range in which they can operate. I have seen graphs of OE VW GT1 suspension, (probably MK1 or MK2) and 15mm of lowering DRAMATICALLY" affects the suspension geometry and its not good. Ford did us no favors in the ride height department and people need to stop treating these like a dual a-arm Honda application. If you want the low life, time to bust out the plasma cutter and welders to raise the pickup points. Its not worth it, buy another car.

Base model Fiesta is reportedly banned from autocross situations due to rollover possibility.

Stock ST models reportedly don't have the same issues with autocross.

My assumption has been, the lowered center-of-gravity of the ST had more to do with this versus damping? Of course, for reasons others have mentioned, moving much beyond whatever stock is, is not necessarily better.

https://www.fiestastforum.com/threads/fiesta-st-autocross-accident.25828/

 

[Dialcaliper]

I have found with my valving, the car is pretty harsh on public roads even with a 250lb front spring. They have a LOT of rebound. (will get a pic of my damper curves). I have en-rounte some 162lb 8in Springs and I will swap back in the 117lb rear springs from my ST lowering spring set that hasn't sold. This well let me test a street setup. My setup is probably not the best for an average street user, especially one that drives on Michigan's bombed out roads daily.

You will have one problem, The Rear Bilsteins are probably crimped. That causes a problem for many shops. You may want to talk to your preferred shop and see if they are capable of dealing with a crimped rear shock.

What are you trying to do with the car? We already know the Bilstein doesn't have enough valving and they bandaid it with springs. I put their rear springs on my car and am not totally thrilled with the behavior. I haven't rated them, will when I get my new springs mounted. They are progressive and they block out pretty quickly which on the street makes my car too bouncy.

Preload is good. There is nothing wrong with preload.

Your ride is harsh because you're using a ton of rebound and going down on the bumpstops, not because of your main spring stiffness.

There are two "schools" of thought on suspension damping and neither is specifically "wrong" if you do it right but both have advantages and disadvantages. The stiff spring+light symmetrical damping setup is one, and it's not "old and outdated" like you've described and it actually works well for many setups. The second is what you, and most OEMs are doing with "sport models" using a lighter spring, and heavy rebound biased assymmetrical damping. The second one is designed to jack the car body down as it oscillates (basically "hunkering down to the road) until it contacts the "linear" nose of the multicellular urethane "christmas tree" foam bump stops that are pretty ubiquitous now. This creates a progressive setup that is stiffer than the spring you are using would suggest. Using a heavy rebound design means that you *must* pay attention to your actual bump travel and bumpstop spring rates, and how they add to your primary spring. OEMs use it because in straight and level driving, the softer main spring provides a more comfortable ride, and in cornering the spring aids come into play creating a stiffer setup.

@Fusion Works Are you using the OE bumpstops in the rear and the B14 internal ones in the front and have you trimmed anything? And how are you measuring your "bump travel"? If you're getting in there and measuring on the car, then yes. But if you're measuring with a jack until the wheel stops moving, then you are compressing the soft bumpstop nose until you've reached the "ramp" at the end.

For the OE front strut and spring, you can work out the bump travel pretty easily. At full droop, the front spring is compressed to just over 10.5" length, and the clearance between the 65mm bumpstop nose and strut top I measured at 4.25". Free length of the 2014-2016 spring is 12" and rate at 171 lb/in. For a stock front corner at ~850lb, that will compress the spring about 3.25" from full droop, leaving an inch clearance to the bumpstop. Going into a corner, combined with damper oscillation with rebound bias will hunker the car onto the bumpstop nose, and it won't come off until you exit the corner (which is as designed - coming back off the bumpstop is bad because it means a rate change. The rear, despite it's really long travel, acts similarly because of the aft mount (>1 motion ratio) and very tall bumpstop. I don't have a great measurement just yet

If you've lowered the car an inch (many lowering springs), then the bumpstop is basically in or very near contact with the nose just at static ride height. I don't have measurements for the internal bump travel on the B14 front (yet), but it's not going to be all that much different at a given ride height.


I just took some measurements on a few bumpstops kindly sent to me kevinatfms. Unfortunately I wasn't able to get ahold of the Instron at work, but I made do with a dial indicator and a shipping scale that reads up to 115lb.

You would probably get a better measurement squishing a bumpstop in the shock dyno you have access to, especially at the higher compressions where they do actually ramp dramatically

OEM MCU are 65mm front and a rather long 120mm in the rear.

The front is a progressive spring aid that has a light 40 lb/in initial rate that ramps to a "linear" section with 140 lb/in rate. I was able to measure to shy of 1.25" compression before maxing my scale, it then progressively ramps to a very high rate somewhere after that (probably at about 40-45mm compression (most MCU bumpstops will compress to about 1/3 of their initial height before going "hard"

I have confirmed this with a "bounce" test on the front suspension (at the time, I had mountune springs on OEM struts). I came up with a little over 1.4 Hz for very small motions (consistent with 181 lb/in front rate), and ~1.9 Hz for a larger displacement, which is consistent with the ~140 lb/in bumpstop engaged (for a total effective rate of about 320 lb/in in the front)

The rear 120mm (~4.75") spring aid/bumpstop has very linear behavior for at least the first 1.6" compression I was able to measure, and comes in at a rate of ~70 lb/in (slightly sloping). Because of the aft mounted damper, at the wheel where the actual rear spring is, it is effectively acting as ~100lb/in spring

This means the stock setup, in actual cornering behavior, is in reality behaving like a 310 lb/in front and ~250 lb/in rear.

The B14 internal stop is also 65mm and while I haven't measured it, the one bilstein usually uses is progressive and usually estimated as a 200 lb/in spring rate, which is how the B14 front is considered a "progressive" setup, even though the spring itself is linear (and the rear, like the Swifts, is basically using an integrated tender spring that blocks very quickly. But the B14 as it comes and as your dyno shows, does not use heavy jack-down rebound biased damping.

The B14's as delivered, with their light damping, are *not* a jack-down design, and so does not use the bumpstop as a primary spring aid. In reality, the B14 kit as delivered is a *softer* setup than the stock ST (274/228). Which makes sense because it was originally designed as a "performance" option for the base Fiesta/Mazda 2 (which are softer than the Bilstein setup)

I suspect that if you've gone with heavy rebound bias, you are turning the Bilsteins into a jack down setup, and engaging the bumpstops, which is why your 250 lb/in front springs ride horribly despite being softer than the B14's as delivered. You're engaging the front bumpstop, which could be providing as much as an additional 200 lb/in for a 450 lb/in front, which is quite stiff. You can confirm this with a bounce test (though your heavy damping will make it difficult to get an accurate result). 250 lb/in front would come in somewhere around 1.7 Hz. Adding in the bumpstop depending on where it's engaging to could put your front rate as high as 450 lb/in, which would give you ~2.25 Hz bounce, which is extremely stiff and not recommended for a non-aero car. Controlling ride height on a front splitter is really the only reason to exceed 2.0Hz front (I'm referring to a real undertray adjustable splitter, not just a fancy looking lip that you can buy from various companies). Your results will necessarily be a little off due to damping, (unless you were to actually fit the car with strut/shocks that have been drained of oil and seals removed)

I've been putting together some very in-depth geometry and suspension frequency calculations for the FiST. It's not quite ready to write up a big post on the forum (and its also a mathematical model with all it's imperfect approximations of reality), but if you're interested, send me a PM and I can share the draft with you, and if you give me some more detail on your setup and I have some spare time, I might be able to add a model in the spreadsheet for you that can give you an idea of where you are and what you're looking for a little more directly than just swapping out parts to see what works and what doesn't.

Below are my measurements of the Stock ST bumpstops up to 115 lbs (and also some Focus bumpstops kevinatfms sent me). I'd love to have measurements up to higher forces to see where the ramp starts, but I haven't had access to the proper equipment yet.

 

[Fusion Works]

I am not jacking down on the bumpstops. The car still has plenty of suspension travel and even bouncing the car over a curb the o-ring travel indicator on the damper shaft doesn't not show contact with the internal bumpstops. While I have't measured it, the rear is also not hitting the bumpstops even with the squishy 117lb/in ST lowering springs. Which only lower the car .6in lower than the stock setup (in the rear). (seems to be about the same height as I set the 250lbs springs since the ST spring is 10in and my Eibach spring is 8in with the added threaded sleeve.

I found my notes on the measurements I took with stock parts before I removed the ST LOWERING springs and stock dampers. The Front strut compresses 3.5in to hold the car at static ride height. (The OE spring setup has some preload, so add that to the increased ride height.)There is 5in of total shaft travel from ride height (without the OE bumpstops). 2.5in until you hit the bumpstops. The OE Dampers are not hitting the bumpstops in normal street driving unless there is a severe bump event. Also my measurement of an OE front bumpstop shows 160lb rate at 1.0in of travel and 570lbs of rate at 1.5in of travel. So your numbers don't jive with what I have measured on the spring rater.

I am also not using B14 parts in anything on my car. Everything on my car is custom built by me. I am using an inverted Bilstein damper similar to the B14, but about an inch longer. The rears started life as a B6 damper that I cut open and revalved. They are now probably similar in length to the B8 damper, though not sure as I didn't have them to compare when I built my setup.

I just rated a rear bumpstop.
.5in 50lbs
1in 86lbs
1.5in 118lbs
2.0in 200lbs

Rear bumpstop is no where near as aggressive as the fronts. I think Ford used them to augment trunk and passenger loads without creating a stiff setup for unloaded ride. If you added 300lbs of passengers (maybe two kids) and 100lbs of luggage, that would probably put the bumpstop close enough on a big dip to allow minor contact under loaded conditions. I doubt you get into the rear bump rubbers without using the curbs aggressively on track with a very high grip tire. The OE tires didn't generate enough grip like a modern RT660 or A058. I would need to pull the sleeves off mine and put a ziptie on the shock shaft and see how it behaves driving down the road. Maybe I will do that when I swap out the rear springs. I stuck the Bilstein rear springs in temporarily and don't like them at all. They ride about as bad as my 250lb linear spring rate on the street.

 

[Dialcaliper]

I am not jacking down on the bumpstops. The car still has plenty of suspension travel and even bouncing the car over a curb the o-ring travel indicator on the damper shaft doesn't not show contact with the internal bumpstops. While I have't measured it, the rear is also not hitting the bumpstops even with the squishy 117lb/in ST lowering springs. Which only lower the car .6in lower than the stock setup (in the rear). (seems to be about the same height as I set the 250lbs springs since the ST spring is 10in and my Eibach spring is 8in with the added threaded sleeve.

I found my notes on the measurements I took with stock parts before I removed the ST LOWERING springs and stock dampers. The Front strut compresses 3.5in to hold the car at static ride height. (The OE spring setup has some preload, so add that to the increased ride height.)There is 5in of total shaft travel from ride height (without the OE bumpstops). 2.5in until you hit the bumpstops. The OE Dampers are not hitting the bumpstops in normal street driving unless there is a severe bump event. Also my measurement of an OE front bumpstop shows 160lb rate at 1.0in of travel and 570lbs of rate at 1.5in of travel. So your numbers don't jive with what I have measured on the spring rater.

I am also not using B14 parts in anything on my car. Everything on my car is custom built by me. I am using an inverted Bilstein damper similar to the B14, but about an inch longer. The rears started life as a B6 damper that I cut open and revalved. They are now probably similar in length to the B8 damper, though not sure as I didn't have them to compare when I built my setup.

I just rated a rear bumpstop.
.5in 50lbs
1in 86lbs
1.5in 118lbs
2.0in 200lbs

Rear bumpstop is no where near as aggressive as the fronts. I think Ford used them to augment trunk and passenger loads without creating a stiff setup for unloaded ride. If you added 300lbs of passengers (maybe two kids) and 100lbs of luggage, that would probably put the bumpstop close enough on a big dip to allow minor contact under loaded conditions. I doubt you get into the rear bump rubbers without using the curbs aggressively on track with a very high grip tire. The OE tires didn't generate enough grip like a modern RT660 or A058. I would need to pull the sleeves off mine and put a ziptie on the shock shaft and see how it behaves driving down the road. Maybe I will do that when I swap out the rear springs. I stuck the Bilstein rear springs in temporarily and don't like them at all. They ride about as bad as my 250lb linear spring rate on the street.

Interesting. It sounds like I made an incorrect assumption about your front struts and they’re not the regular B14 type.

Just to clarify, are your bumpstop measurements listed force (lb) or rate (lb/in). Your force measurements may be more accurate than mine, because one thing I noticed testing was that once compressed, the bumpstops slowly “deflate” in static measurements, so my slower measurements may be coming up with a different force at a given position. The only way to get the “true” bumpstop rate is to test them at realistic damper velocities (for example squishing them between blocks set up on a shock dyno). would be great to see a full curve at operating conditions. MCU bumpstops make good spring aids in some setups, but do have both advantages and drawbacks compared to linear and progressive springs.

Something doesn’t jive with your notes on bump travel measurements for the stock front struts though. I’m measuring directly on a stock strut off the car (basically full droop/preload), and with the bumpstop all the way to the top, I’m measuring 4.25” from bumpstop to damper top. Spring seat to spring seat is 10.625”. I have a couple types of stock front springs off the car, and free length is right on 12” for the 2019 springs I have, and notes say 11.5” for the 2015 springs that are now on the car. Unless the stock springs are really non-linear, they have to compress ~5.75” to support the front corner of the car (~5.25” for the earlier models). Minus the 1.375” preload leaves 4-375” compression from full droop. +/- 0.5” for measurement inaccuracy

Your damper setup may be different, but I’m struggling to wrap my head around fitting more than a couple inches of additional bump travel over the stock setup in the front, especially with a bit of lowering tossed in.

On the rear, yes the bumpstops are soft, but the dampers are also mounted 20% aft of the axle which has an amplified effect on wheel rate/natural frequency of almost 1.5x. So even though they may seem soft, they’re effectively somewhat stiff given how light the rear end of the car is.


I tried to get a picture showing where the bumpstop is under the boot, but not sure if it is quite visible here

 

[the duke]

I can’t fathom you’re running into coil bind in the front, are you?

 

[Dialcaliper]

I can’t fathom you’re running into coil bind in the front, are you?

If you’re referring to the pictures I just posted, the front does not coil bind. The rear mountune spring next to it is progressive, which by definition involves partial coil binding in order to function