Hmm: Doesn't S4 suspension geometry result in dynamic camber changes under cornering?
08-08-2003, 06:52 AM
#23
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Assuming you still have stock wheels...
If your offset changed getting bling bling wheels 
you may not have to change camber, or you may have to adjust it even more, and your dynamic camber is skewed even further...
Generally I increase neg camber by 1-2 degrees compared to stock, improves the handling and doesn't wear the tires all screwey. I have coil overs and I just drop the car the extra 1.5-2 inches at the track for the negative camber change and live with the castor. If you have Hoosiers you don't have to worry about castor too much anyways
Worked well for me so far, but its hard to judge increased wear on an R compound tire. Should I be doing anything different?
you may not have to change camber, or you may have to adjust it even more, and your dynamic camber is skewed even further...Generally I increase neg camber by 1-2 degrees compared to stock, improves the handling and doesn't wear the tires all screwey. I have coil overs and I just drop the car the extra 1.5-2 inches at the track for the negative camber change and live with the castor. If you have Hoosiers you don't have to worry about castor too much anyways
Worked well for me so far, but its hard to judge increased wear on an R compound tire. Should I be doing anything different?
08-08-2003, 07:11 AM
#24
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Actually, changing wheel offset only has the effect of a minor change in spring rate. --->
As for lowering at the track, you wont see any caster effects, but you will get some toe-out.
08-08-2003, 07:14 AM
#25
agreed, and to add, when you lower it, you are likely using a lot of bump stop...
...which acts like added spring rate. Most bump stops have a progressive nature to them so you really don't "feel" the bump stop hitting, so that added spring rate (though causing you to understeer more and lose ultimate cornering grip) does act like more spring rate which flattens the car out.
The key there would be to ride up at 25.5" height, and have more spring rate such that the flat ride quality is still there, AND you have bump travel for road inputs while loaded (like in a long sweeping corner).
But I ehco MichaelTM's comments, the B5 car responds very much to positive rake, and things like Toe Out will all change the behavior of the car dramatically, so looking at one aspect (ride height) without taking into account the rest of the car (alignment spec's at 25.5" vs. lowered), weight transfer with a higher vs. lower center of gravity, etc. all play into how it "feels".
The key there would be to ride up at 25.5" height, and have more spring rate such that the flat ride quality is still there, AND you have bump travel for road inputs while loaded (like in a long sweeping corner).
But I ehco MichaelTM's comments, the B5 car responds very much to positive rake, and things like Toe Out will all change the behavior of the car dramatically, so looking at one aspect (ride height) without taking into account the rest of the car (alignment spec's at 25.5" vs. lowered), weight transfer with a higher vs. lower center of gravity, etc. all play into how it "feels".
08-08-2003, 07:20 AM
#27
They may not exactly for every suspension...
...for example, say your coil over suspension reuses the OEM bump stop, which is extremely long, and you still want that 2" of exposed shaft for a net wheel bump travel of about 3", you may end up being higher than 25.5", possibly 26".
If you are using bump and rebound travel as your ultimate guide to setting ride height, it will be different on every threaded damper system.
I was terse in my final statement becuase most folks are running low, and many with OEM bump stops, so my generic "25.5" ride height was to point out that you need to get the car a bit higher, or make provisions such that the car has sufficient bump travel when lower.
But as a good rule of thumb, I would aim for 2" of expose shaft between damper body and bump stop to get you with a decent amount of wheel travel. As far as STaSIS Track Sport kits, that comes out to a ride height of 25 1/4" to 25 1/2" using the bump stop in that kit.
If you are using bump and rebound travel as your ultimate guide to setting ride height, it will be different on every threaded damper system.
I was terse in my final statement becuase most folks are running low, and many with OEM bump stops, so my generic "25.5" ride height was to point out that you need to get the car a bit higher, or make provisions such that the car has sufficient bump travel when lower.
But as a good rule of thumb, I would aim for 2" of expose shaft between damper body and bump stop to get you with a decent amount of wheel travel. As far as STaSIS Track Sport kits, that comes out to a ride height of 25 1/4" to 25 1/2" using the bump stop in that kit.
08-08-2003, 07:22 AM
#28
with fixed upper control arms, you will not be able to get negative camber back to OEM spec...
...or am I missing something in your post?
The front suspension has a lot of nice features (like the ability to affect caster dramatically), and while the gain in negative camber under bump is a huge bonus (as is the "zero-scrub" design), with fixed upper arms, ride height determines negative camber.
Although I'm guessing I missed your point/question.
The front suspension has a lot of nice features (like the ability to affect caster dramatically), and while the gain in negative camber under bump is a huge bonus (as is the "zero-scrub" design), with fixed upper arms, ride height determines negative camber.
Although I'm guessing I missed your point/question.
08-08-2003, 07:34 AM
#30
not sure about "spring loaded", but as far as the OEM bushings, here is what I do know...
...first off, they isolate a lot of road noise and harshness (which makes sense in a 40k luxury sports sedan). Secondly, they flex as much as 1/8" (not so great, but hey, it's still a luxury car). Which gets to corner balancing the car, many people say a corner balance is *essential* with a coil over (was that the BIRA guys that hate on coil overs?), when in reality, a true 50% cross weight is great, but once you lean the car, you're going to lose that.
NOW...
Take a race car with no rubber anything in it, and a 50% cross weight vs. 48% is noticeable by the driver, and it makes total sense.
But in a street car, tough to say. We've seen many coil over installs finish out with a cross weight between 48.5% and 50% with even ride heights without screwing around with anything, so we're inclined to leave the corner balance alone. Also, many places corner balance the car with the sway bars connected, which throughs everything off anyways.
Back to the bushings...
The other thing I notice, is that the rear damper upper mount has a very bizarre movement to it. It's clearly a tuned item in the car, as it moves vertically by 1/2", but not at the same frequency of the damper movement. When we moved to spherical bearings on the upper and lower rear damper, we noticed no loss in road noise surpression, but did notice the response. Though a valving change was done as well, so the direct comparison is skewed, but not by a ton.
Lastly, every suspension component that is isolated by a rubber bushing (which is pretty much all of them) do not like being torque'd to spec at full droop. This has shown definite changes to the alignment of the car, and has adversely affected handling as a result. Add to that the preload that the bushings are now under while at ride height, and the failure rate will likely increase.
My last comment on the bushings is to always torque them at ride height, on every one.
NOW...
Take a race car with no rubber anything in it, and a 50% cross weight vs. 48% is noticeable by the driver, and it makes total sense.
But in a street car, tough to say. We've seen many coil over installs finish out with a cross weight between 48.5% and 50% with even ride heights without screwing around with anything, so we're inclined to leave the corner balance alone. Also, many places corner balance the car with the sway bars connected, which throughs everything off anyways.
Back to the bushings...
The other thing I notice, is that the rear damper upper mount has a very bizarre movement to it. It's clearly a tuned item in the car, as it moves vertically by 1/2", but not at the same frequency of the damper movement. When we moved to spherical bearings on the upper and lower rear damper, we noticed no loss in road noise surpression, but did notice the response. Though a valving change was done as well, so the direct comparison is skewed, but not by a ton.
Lastly, every suspension component that is isolated by a rubber bushing (which is pretty much all of them) do not like being torque'd to spec at full droop. This has shown definite changes to the alignment of the car, and has adversely affected handling as a result. Add to that the preload that the bushings are now under while at ride height, and the failure rate will likely increase.
My last comment on the bushings is to always torque them at ride height, on every one.