Bilstein B8 Rear Shock Tune Error?

[FiST Mag]

I had some new Bilstein B8’s sitting around for a year and I finally got them installed with Eibach springs. During the install process I like to compare the OE tune vs the Bilstein tune by pushing down on on each shock. The old squat dyno test…I noticed the Bilstein tune was very firm (slow) on the compression and very soft (fast) rebound when compared to the OE tune. The Bilstein rebound took 2 seconds were as the OE took over 6 seconds to reach full extension from full compression. It seems to me that Bilstein might have got the valving flipped by mistake. The car does not handle proper with these installed as it just bounces around. I put the OE rear shocks back on with the B8’s still up front and still running Eibach springs. The car handles 90% better. I chalk this up to a little miss match in shock tunes. I even noticed the rear end ride height dropped when removing the B8’s for the OE shocks. I’ll probably put the OE front struts back on if Bilstein does not come through with a replacement. Has anyone else noticed this problem with their rear B8’s?

 

[MagnetiseST]

I'm not a suspension expert by any means, but shouldn't shocks rebound quickly? Every time I've removed well used (40k+ mile) FiST shocks they are extremely slow on the rebound, sometimes they do not come up on their own at all. New Ford shocks aren't like that, they are noticeably faster. I know that lowering springs destroy OEM shocks, so I always attributed the slow speed to being heavily used / nearly blown / relying on the spring to decompress.

I had B8s paired with Swift springs and never noticed any bounce, but they were way too hard. The Swifts were designed to be used with the stock shocks and the B8s are designed to be used with lowering springs, it was not a happy pairing.

 

[FiST Mag]

I'm not a suspension expert by any means, but shouldn't shocks rebound quickly? Every time I've removed well used (40k+ mile) FiST shocks they are extremely slow on the rebound, sometimes they do not come up on their own at all. New Ford shocks aren't like that, they are noticeably faster. I know that lowering springs destroy OEM shocks, so I always attributed the slow speed to being heavily used / nearly blown / relying on the spring to decompress.

I had B8s paired with Swift springs and never noticed any bounce, but they were way too hard. The Swifts were designed to be used with the stock shocks and the B8s are designed to be used with lowering springs, it was not a happy pairing.

Thanks for the comparison info on new and old OE FiST shocks. It’s good information I will keep in mind. Im not an expert, but I like to think I know enough to be a novice. A shock tune is a specific recipe the manufacturer will come up with to control a specific spring rate. In my mind the OE damper should feel pretty similar to the Bilstein with a hand dyno test. There is a couple things that will play a significant role in suspension tuning, and it’s easy to mess up if someone doesn’t pay attention during the build process. One of this things is IFP volume and pressure. Too much of either will prevent the shock from reaching full depth off stroke and increased compression with faster rebound. The more I think about it, that’s what I think is wrong with my B8’s. Too much gas volume or pressure which will not allow room for proper oil displacement in the damper as the shaft compresses into the shock. The other thing that could be a problem is the shim valving at the piston could be set wrong or flipped. I’m thinking this is less likely.

 

[kevinatfms]

I'm not a suspension expert by any means, but shouldn't shocks rebound quickly? Every time I've removed well used (40k+ mile) FiST shocks they are extremely slow on the rebound, sometimes they do not come up on their own at all. New Ford shocks aren't like that, they are noticeably faster. I know that lowering springs destroy OEM shocks, so I always attributed the slow speed to being heavily used / nearly blown / relying on the spring to decompress.

I had B8s paired with Swift springs and never noticed any bounce, but they were way too hard. The Swifts were designed to be used with the stock shocks and the B8s are designed to be used with lowering springs, it was not a happy pairing.

The B6/B8 damper isnt specific to an ST. The shock shaft length is based on the regular Fiesta and not the ST model. The only Bilstein damper specific to the ST is the front in the B14 kit with the updated part number.

 

[FiST Mag]

The B6/B8 damper isnt specific to an ST. The shock shaft length is based on the regular Fiesta and not the ST model. The only Bilstein damper specific to the ST is the front in the B14 kit with the updated part number.

I can believe this. The B8’s don’t set the Fiesta ST in a way I agree with. I have explained the situation to Bilstein and they seem convinced nothing is wrong. Everyone tells me to just drive it a few thousand miles. IMO, I don’t think a damper should effect sag 10mm. I’d rather have something developed for the ST chassis.

 

[kevinatfms]

I can believe this. The B8’s don’t set the Fiesta ST in a way I agree with. I have explained the situation to Bilstein and they seem convinced nothing is wrong. Everyone tells me to just drive it a few thousand miles. IMO, I don’t think a damper should effect sag 10mm. I’d rather have something developed for the ST chassis.

Koni Sports are the same way but work with both non-ST and ST models(minus the mass damper). Nearly every OTS damper for this car compromises between the non-ST and the ST.

Also, pairing the B8 with an Eibach was a major mistake. The Eibach rates are initially softer than the OE springs. Pair that with the exceptionally stiff B8 damper and its a total mismatch. Still dont understand the reasoning behind Eibachs choice of initial and final spring rates on the ST.

Throw something stiffer into the mix and i think the feeling might change.

 

[M-Sport fan]

^^^AGREED!

Eibach is generally a decent spring company overall, why they could not have offered a minimally lowering spring with a higher LINEAR rate than the factory boingers for this platform, I will never figure out (save for that everyone wants to slam their cars to the ground, but still have a 'cushy ride' while doing so, two things which are totally incongruent to say the least ).

 

[faust]

I just installed b6s with my stock springs on my '15 FIST, and noticed exactly the same compression / rebound difference with the rears. The old ones did have 50k on them, so probably they had the condition MagnetiseST mentioned.

From what I can tell, this is a major upgrade from my stock shocks, which could have used more compression and less rebound. The ride around town is certainly improved, and it seems like the additional compression helps control body roll when cornering.

I did notice that my car appears to be sitting a bit higher with the b6s on. Bilstein has a FAQ somewhere on their site saying that this is common, and goes away after the shocks are used a bit more.

 

[FiST Mag]

Koni Sports are the same way but work with both non-ST and ST models(minus the mass damper). Nearly every OTS damper for this car compromises between the non-ST and the ST.

Also, pairing the B8 with an Eibach was a major mistake. The Eibach rates are initially softer than the OE springs. Pair that with the exceptionally stiff B8 damper and its a total mismatch. Still dont understand the reasoning behind Eibachs choice of initial and final spring rates on the ST.

Throw something stiffer into the mix and i think the feeling might change.

Knowing what I know now, I would agree that pairing the B8's with the Eibach springs was a major mistake. I just hope this thread helps keep someone from making the same mistake. I think if you want to run the the Eibach springs that sticking with the OE dampers are probably the best option. Which I'm going to try next and until I can get some two way adjustable coil overs.

 

[FiST Mag]

Koni Sports are the same way but work with both non-ST and ST models(minus the mass damper). Nearly every OTS damper for this car compromises between the non-ST and the ST.

Also, pairing the B8 with an Eibach was a major mistake. The Eibach rates are initially softer than the OE springs. Pair that with the exceptionally stiff B8 damper and its a total mismatch. Still dont understand the reasoning behind Eibachs choice of initial and final spring rates on the ST.

Throw something stiffer into the mix and i think the feeling might change.

I wonder it Eibach's recipe should include their stiffer sway bars? Having their whole pro kit paired with the stock OE dampers is the recipe they developed.

 

[Fusion Works]

You will most typically use more rebound than compression.

Bilstein probably didn't mess up the shock, its probably softer than the stock shock. The Fiesta has a lot of rebound for an OE car. If you want sent me the Bilstein and I will dyno it next to my stock rear shock and we can compare the curves from a real dyno.

Measuring a shock by hand is a worthless endevour. Its a quick way to test of damage to a shaft or something like that, but no way at all to determine shock forces.