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VSS Tech Article - Shocks Info

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#2
Nice write up.

I really liked how Koni's FSD struts helped the ride in my '11 MINI. Their ability to be compliant on the pot-holed streets while firm on fast curves was great. I was bummed to find out they weren't planning to make an FSD variant for the ST. Are there any other strut manufacturers who have anything similar for the ST? what kind of strut would you recommend to handle rough road conditions while still maintaining most of there stock suspension's sportiness?

I was even wondering if standard Fiesta struts with ST springs might work. But I assume the standard Fiesta struts probably would be a bad combo with the stiff ST springs.

Thanks for the info.
 


OP
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Thread Starter #3
Nice write up.

I really liked how Koni's FSD struts helped the ride in my '11 MINI. Their ability to be compliant on the pot-holed streets while firm on fast curves was great. I was bummed to find out they weren't planning to make an FSD variant for the ST. Are there any other strut manufacturers who have anything similar for the ST? what kind of strut would you recommend to handle rough road conditions while still maintaining most of there stock suspension's sportiness?

I was even wondering if standard Fiesta struts with ST springs might work. But I assume the standard Fiesta struts probably would be a bad combo with the stiff ST springs.

Thanks for the info.
Stiff springs will be bouncy on a relatively untuned shock. The compression speed will be too low. The rebound would be fine over most bumps, but would overpower the valving on some.
 


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#4
Ok. That makes sense. So what kind of strut or spring/strut combo would be recommended to better handle rough road conditions while retaining a fairly sporty ride? I'm hesitant to try any of the coil over kits because I don't want to make the ride stiffer.
 


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Thread Starter #5
Ok. That makes sense. So what kind of strut or spring/strut combo would be recommended to better handle rough road conditions while retaining a fairly sporty ride? I'm hesitant to try any of the coil over kits because I don't want to make the ride stiffer.
Sorry for the late reply, I don't think I got a forum email or maybe it went to my spam box.

Here's a prescriptive method for improving ride quality. It's not just one thing, you have to think of everything as acting like a spring until it reaches you. When you hit a bump, EVERYTHING flexes. The tire, chassis, seat, your body, etc. However, most NVH that is perceived from a bump involves the rocking motion of the chassis because the tires hit at different rates. That being said, a stiff front is perceived less than the stiff rear when you involve harshness due to it's effects on passenger movement. NVH is hands down the biggest problem that OEM engineers face and let me tell you ... I get invited to about 50 different NVH gatherings a year. It never ends, LOL.

Here's what improves ride quality. You can take this and apply it towards your choices out there.

1. Taller sidewall tires. The Fiesta has really skinny sidewalls to allow Ford to install big wheels for aesthetics in a boring Fiesta wheel well along with the bigger brakes. Going up in sidewall allows the tire to flex more which dampens the hit and how much is pushed into the suspension over time. The tire acts like a spring when you run over things. A taller tire will also carry a higher load rating which means the car will generally handle at a higher G limit. The trade off is response, but the tire's attitude at limited slip angles is also greatly improved, so there's less sudden give at the limit.

2. Reduce unsprung weight. If you've ever driven a truck or a car with a live axle you'll notice that they are rough over bumps when the axle tramps up and down. This is because you've energized that mass and it's gotta be dampened. That vibration is pushed into the driver through the chassis. It also reduces stability over bumps and reduces tire to ground control. You can reduce wheel weight, tire weight, or brake component weight. The control arms and other items are only partially unsprung since their weight is spread between a sprung component (the chassis) and the outer spindle / hub.

3. Maximize shock stroke length. The longer the shock has to travel the less dampening force is required to slow the mass. This improves ride quality quite a bit but can cost in response if the dampening is too soft or you greatly increase stroke length. This is a major problem when you lower a car, especially a MacStrut as it greatly reduces the shock stroke at a ratio equal to the motion ratio. Aftermarket shocks take this into account and try to maximize stroke length by various methods. However, lowering the car by more than half to one inch can and will generally force the shock to have greatly enhanced dampening which makes for a rougher ride.

4. Spring rates. You want them to be increased at a nominal rate. Too many coilovers out there just JACK the spring rates because they know people are going to dump the car and perceive a tight suspension as a well handling car. If you are increasing spring rates by 100+% you need to be doing it for a very specific reason else you are likely going to have a covered wagon. If you are on street tires at a normal ride height you should only be increasing the spring rates by a moderate amount. There is a sweet spot for handling:comfort balance but it can be application specific.

5. Valving. My STI's Ohlins feature a dual flow valve that lets ultra-high speed pressure to be blown off and allow rapid movement of the shock. This lets the shock eat the hit and not force the tire to skid; within reason. You can't run over a speed bump at 40 MPH, LOL. The internal structure of shocks is very important as are the shim stacks and overall valving rates. Try to get shock dyno results of various shocks on the market. You are looking for the moderate to high speed regions of shaft speeds. Greater force equates to a harder ride.

Bilstein, Ohlins, and Koni tend to have good road manners. In fact, you'll often find Bilsteins and Konis on OEMs for this reason. Aftermarket companies like BC and others well ... your mileage may very. They CAN ride well, just have to work around it sometimes.
 


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#6
Great info. Definitely worth the wait. :D

I have already gone to light weight, 16" wheels. And that helped a bit. But I was looking to reduce the juttering the suspension had over some road irregularities.

Actually, I'm currently in the process of trying out some prototype matched progressive springs and adjustable struts on my ST. The spring rates are a bit softer than the stock STs but firmer than the standard Fiestas. So far, I'm pretty happy with the ride. The only downside is that the car sits a bit too low for my tastes, causing some minor scraping on driveways. But there isn't any rubbing or bottoming out so far. Still, im looking at adding spacers to get back some of the ride height. Maybe updated springs will be available in the future too. Anyway, I'm going to post more on the setup when I have things more dialed in.

Thanks again for all the info. Sounds like I'm on the right track.
 


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Thread Starter #7
Spacers on top of the struts won't fix it. The ride height is lowering due to the suspension compressing. You'll need to space the bottom or top of the spring. In fact, BMW used spring pads to adjust ride height and reduce NVH in the 90s - 00s BMWs. They need to be replaced from time to time, but you might be able to pick up a 20mm pad from a BMW and see if that works for you.

Not sure if you meant one or the other, but just wanted to add that.

In fact, spacing is a great idea. You're losing shock stroke length with the static compression due to the lowered shock pressure and spring rate. The spacer will push the body upwards and gain back the shock travel, assuming the spring you installed is the same length.
 


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Thread Starter #8
But I was looking to reduce the juttering the suspension had over some road irregularities.
Juttering, especially if you've downgraded the stiffness is likely due to insufficient dampening force and/or unsprung mass. Go to a two-piece rotor and up the high speed compression / rebound a touch.
 


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#9
Right. The spacers would go in the spring perch, not on the strut mount. The BMW pieces are a great suggestion. I was looking at a universal rubber spring booster made by Mr. Gasket. But the BMW pieces are worth a look, especially since some are available in polyurethane. Here's the Mr. Gasket piece.



The juttering was noticeable with the stock suspension before any of my mods. The updated suspension and wheels have pretty much eliminated the jutter.
 


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