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Bilstein Science Experiment
- Thread starter Fusion Works
- Start date
Over the holiday break, I purchased both the BILSTEIN 47167490 (Fiesta/Mazda 2) and the BILSTEIN 47242043 (Fiesta ST) kit to better understand their differences. This has been a debated topic for some time on this forum, and I aim to provide a definite answer.
Here is the executive summary :
Both kits are exactly the same except for the front struts.
Front springs have the same part number.
Rear springs have the same part number.
Rear dampers have the same part number.
Rear spring adjusters have the same part number.
Since we now know that the main difference between these two kits is in the front damper assemblies, let's dive in a little deeper.
The bump stops are the same exterior dimensions, but they have a different part number. The Fiesta kit has a 19 marking and the Fiesta ST one has a 34 marking. I could not tell the difference by squeezing them both in my had.
I have since returned the Fiesta kit. If you need more dimensions for the Fiesta ST kit, feel free to ask!
Here is the executive summary :
Both kits are exactly the same except for the front struts.
Front springs have the same part number.
Rear springs have the same part number.
Rear dampers have the same part number.
Rear spring adjusters have the same part number.
Since we now know that the main difference between these two kits is in the front damper assemblies, let's dive in a little deeper.
The bump stops are the same exterior dimensions, but they have a different part number. The Fiesta kit has a 19 marking and the Fiesta ST one has a 34 marking. I could not tell the difference by squeezing them both in my had.
I have since returned the Fiesta kit. If you need more dimensions for the Fiesta ST kit, feel free to ask!
OP
Thread Starter
#148
Thread Starter
#148
Now I need to measure my insert dimensions to compare. Wonder what made the base Fiesta use the shorter insert, since it didn't really have a "drop knuckle".
The 11mm shaft causes problems with getting an adjustable shaft. I have a set of B16s from an RX8. The rear damper is an adjustable insert installed in an inverted setup. I am still trying to figure out how to get the shaft apart. It has a 90deg adjuster on the shaft end because the bushing mounts on the end of the shaft.
Bilstein Germany says they won't sell me the parts inside a Bseries damper. So all improvements will have to be done with valving.
The 11mm shaft causes problems with getting an adjustable shaft. I have a set of B16s from an RX8. The rear damper is an adjustable insert installed in an inverted setup. I am still trying to figure out how to get the shaft apart. It has a 90deg adjuster on the shaft end because the bushing mounts on the end of the shaft.
Bilstein Germany says they won't sell me the parts inside a Bseries damper. So all improvements will have to be done with valving.
Interesting detective work!
So what I take away from this is that the ST version is as you mentioned, stiffer with the spaced sliders and the perch is slightly higher up. This might explain why I wasn’t able to make a 10” spring fit without a tender and still get the desired ride height I wanted on the standard Fiesta B14’s. With some of the limiters removed and the added droop, I needed a total of 10.75” of spring at full extension using the DNA upper spring perch.
Short of making the damper stronger for a rally machine, I’m not sure the increased stiffness will matter that much, given that just going to an inverted strut is already a massive increase over a standard upright. It looks like the ST used the longer body insert to fit the wider spaced bearings.
For the standard Fiesta damper, one side effect of the shorter body is the increased available travel vs the ST that you mentioned. They start the same length, but the shorter body means the bumpstop engages lower down. 15mm may not sound like that much, but it’s that much more travel keeping you out of the bumpstops
I could see a lot of philisophical arguments about which way to go
So what I take away from this is that the ST version is as you mentioned, stiffer with the spaced sliders and the perch is slightly higher up. This might explain why I wasn’t able to make a 10” spring fit without a tender and still get the desired ride height I wanted on the standard Fiesta B14’s. With some of the limiters removed and the added droop, I needed a total of 10.75” of spring at full extension using the DNA upper spring perch.
Short of making the damper stronger for a rally machine, I’m not sure the increased stiffness will matter that much, given that just going to an inverted strut is already a massive increase over a standard upright. It looks like the ST used the longer body insert to fit the wider spaced bearings.
For the standard Fiesta damper, one side effect of the shorter body is the increased available travel vs the ST that you mentioned. They start the same length, but the shorter body means the bumpstop engages lower down. 15mm may not sound like that much, but it’s that much more travel keeping you out of the bumpstops
I could see a lot of philisophical arguments about which way to go
I should have called it rod force. I measured the force it took to start to get the piston shaft moving from a ''standstill''. You could infer the internal gas pressure, however.
Gas force (lbs) / ((Shaft Dia. (in)/2)^2 x pi) = Gas pressure (PSI)
For the ST : 31.2 / ((0.433)/2^2*pi) = 91.74 PSI
For the fiesta : 36.1 / ((0.433)/2^2*pi) = 106.15 PSI
So they are right up to that limit it seems.
Gas force (lbs) / ((Shaft Dia. (in)/2)^2 x pi) = Gas pressure (PSI)
For the ST : 31.2 / ((0.433)/2^2*pi) = 91.74 PSI
For the fiesta : 36.1 / ((0.433)/2^2*pi) = 106.15 PSI
So they are right up to that limit it seems.
Last edited:
So the regular Fiesta kit front setup will allow for a higher static ride height than the ST kit, albeit still not to an ST factory ride height? ![[dunno]](/images/smilies/icon_smile_dunno.gif "Dunno [dunno]")
The main problem you’ll run into is that with both versions, the overall droop length is 25mm shorter than the OEM shocks, which means you’ll only have about 50mm of droop travel left, which is not enough to deal with normal roads unless you’ve got nice smooth pavement in your area or drive mostly on track. If you drive on any sort of back road, You’ll be lifting your inside front tire in the corners any time you’re on any pavement that’s a bit bumpy This is a problem with many if not all street/track coilovers (not counting something aimed at rallying)
This can be solved, at least on the on the Fiesta B14’s during revalving by removing 25-30mm of droop limiter inside the shock as there’s a bit of travel available without losing the bottom slider. But it looks like with the wider bearing spacing (+35mm), you may only be able to add 5-10mm of travel (even with the 15mm longer shock body). Maybe enough, but still less than than the OEM shock travel.
Following Dialcaliper's train of thought here and looking at what could be done with the ST strut to claw-back some travel.
The distance from the bottom of the strut base to the start of the lower slide bearing is (315mm-155mm) = 160mm (however this measurement was taken from the top of the seal, we need to add 2mm to compensate), so 162mm.
The distance from the insert top (thread going into the strut mount) to the bottom of the chrome surface = 363mm
Adding these two dimensions gives us a total length possible with both slide bearings making full contact at 525mm. Compared to the stock length of 515mm, this gives us 10mm of extra droop travel we could remove from the droop limiter.
This means that we could regain 10 of the 15mm travel difference between the Fiesta and the Fiesta ST kit. You would need specialized tools to degas & regas the strut to do this however.
I did not measure directly, but measuring from pictures I took, the slide bearings seem to be between 25 and 30mm thick each. Assuming it's safe to engage only half of the thickness of the bottom slide bearing at complete droop, we could add another 15mm of travel.
This would bring our total to 540mm of strut length. This would mean that we could extract 540mm-370mm (363+7mm, because we're measuring to the seal surface, where the bumpstop will hit) = 170mm of travel with no bumpstop and 134mm of travel until we engage a 36mm long bumptop.
That is 5.28in of total travel until the bump stop engages, which seems pretty good considering.
The ultimate configuration would be a Fiesta lower strut base and an ST strut insert. We could be at 545mm total length with full slide bearing engagement.
The distance from the bottom of the strut base to the start of the lower slide bearing is (315mm-155mm) = 160mm (however this measurement was taken from the top of the seal, we need to add 2mm to compensate), so 162mm.
The distance from the insert top (thread going into the strut mount) to the bottom of the chrome surface = 363mm
Adding these two dimensions gives us a total length possible with both slide bearings making full contact at 525mm. Compared to the stock length of 515mm, this gives us 10mm of extra droop travel we could remove from the droop limiter.
This means that we could regain 10 of the 15mm travel difference between the Fiesta and the Fiesta ST kit. You would need specialized tools to degas & regas the strut to do this however.
I did not measure directly, but measuring from pictures I took, the slide bearings seem to be between 25 and 30mm thick each. Assuming it's safe to engage only half of the thickness of the bottom slide bearing at complete droop, we could add another 15mm of travel.
This would bring our total to 540mm of strut length. This would mean that we could extract 540mm-370mm (363+7mm, because we're measuring to the seal surface, where the bumpstop will hit) = 170mm of travel with no bumpstop and 134mm of travel until we engage a 36mm long bumptop.
That is 5.28in of total travel until the bump stop engages, which seems pretty good considering.
The ultimate configuration would be a Fiesta lower strut base and an ST strut insert. We could be at 545mm total length with full slide bearing engagement.
So the regular Fiesta kit front setup will allow for a higher static ride height than the ST kit, albeit still not to an ST factory ride height?
The main problem you’ll run into is that with both versions, the overall droop length is 25mm shorter than the OEM shocks, which means you’ll only have about 50mm of droop travel left, which is not enough to deal with normal roads unless you’ve got nice smooth pavement in your area or drive mostly on track. If you drive on any sort of back road, You’ll be lifting your inside front tire in the corners. This is a problem with many if not all street/track coilovers (not counting something aimed at rallying)
This can be solved, at least on the on the Fiesta B14’s during revalving by removing 25-30mm of droop limiter inside the shock as there’s a bit of travel available without losing the bottom slider. But it looks like with the wider bearing spacing (+35mm), you may only be able to add 5-10mm of travel, even with the 15mm longer shock body). Maybe enough, but still less than stock (more similar to a B8 shock)
The only thing you might need to consider is that with the ST body, compared to the Base model B14, you’ll have both less droop (shorter shaft, shorter droop limiter to remove) and less compression travel (longer body)
Depending on your goals, that could be fine. One of the things I aimed for in my setup is to get as much travel as possible out of the B14. So far so good as the car is stable with less loss of traction and fewer bumpstop hits even when the road is rough.
The other thing I’ve been really happy with is much better front wheel traction and reduced torque steer under acceleration. With the same RE-71RS tires prior to getting the retuned B14 shocks back, very little feathering is required even in second gear even on the Dizzy stage 2. On the previous setups I was getting more wheel spin.
Depending on your goals, that could be fine. One of the things I aimed for in my setup is to get as much travel as possible out of the B14. So far so good as the car is stable with less loss of traction and fewer bumpstop hits even when the road is rough.
The other thing I’ve been really happy with is much better front wheel traction and reduced torque steer under acceleration. With the same RE-71RS tires prior to getting the retuned B14 shocks back, very little feathering is required even in second gear even on the Dizzy stage 2. On the previous setups I was getting more wheel spin.
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