Must be my driving style but even with stock suspension my car tended towards oversteer. At least on 1st/2nd gear corners.

The evos kind of lame though for that. The 12:1 steering ratio is so quick that it's too easy to correct it and end up going straight instead of sideways.

Now my e36 with like 16:1 steering ratio... You gotta be quick on the hands some times to catch it. Haha

 

dont put that hex on me man!

my net purchases are all my safety equipment.

 

I just had another thought.


I'd there any basic adjustment/thought process to what should be done with rebound settings in relation to the spring rate increase?

 

As requested, this is quite basic: in general you need more rebound damping as spring-rates increase because you're controlling more energy (for the same amount of movement).

 

ok, thats what i thought. the setup sheet for how the coils sit now has the fronts running what i feel is pretty tight (10 clicks back from full). i played around with it last year to see how going softer changed things and it was quite interesting.

 

Rebound vs. compression damping...

So the 2/3 of critical for compression and 3/2 of critical for rebound seems to be more of a "rule of thumb." In this case, the system you are considering is the sprung mass system where the chassis spring and the sprung mass are the dominant system parameters. This is the slowest responding system and has a natural frequency around 1.5 to 2.5 Hz for most setups.

However, isn't the way the system actually behaves slightly different then this? To me, this makes sense for compression damping as the unsprung mass system is much quicker to respond so the sprung mass reacts with the ground. 65% of critical damping here provides the mathematical "best response." There is your 2/3s of critical for compression number and it makes sense.

On the rebound action though, the car body reacts much slower than the unsprung mass and it seems like the damping should actually be setup in a manner that considers the car body a "pseudo ground" with the actual ground being the impulse response that you are trying to have the unsprung mass follow? From some numbers I've come up with, it seems the sprung mass has a 3 to 4 times higher natural frequency than the car body. Also in general, because the rebound motion really won't overshoot (because the tire will simply follow the actual ground) it's beneficial to have the damping coefficient much less than the "ideal" 65%.

The 3/2 makes sense here too if you consider a natural frequency of the unsprung mass to be 4 times greater than the sprung mass as you are essentially at ~30% of critical for rebound. Off the top of my head, I believe 25% of critical is about ideal for high speed damping. In the case of rebound however, the tire is always going to try and respond at the natural frequency speed since the ground is trying to escape the tire, this will be in the high speed range of the shock curve.

I guess my point to all of this though, can you get more accurate numbers for damping by calculating compression damping separate from rebound damping by considering them two different systems? Or is simply the 2/3C and 3/2R rule just close enough that it really doesn't matter?

 

you just went very far over my head in that post...

 

One hugely important point is missing from Post #81: the fact that the ground can push up on the wheel, but the ground cannot pull the wheel down.

 

I wouldn't say the point was missing. In fact, it was more or less the crux of the post.

But the vast majority of the time the tire will be in contact with the ground. Wouldn't this mean that the rebound damping is generally going to be controlling the forces generated as the previously compressed (outside) spring unloads in a turn? That's what you're damping 99.9+% of the time unless you're on a very rough surface.

 

Wow. That's the second time in a week that I've really missed someone's point. Sorry about that.

Anyhoo, yes. Rebound really only controls the energy stored in the spring, while compression controls the transmission of upward unsprung movement to the chassis.

 

well, in typical "im a dumb ***" fashion...it appears i over looked/screwed up a few things and the springs i got dont fit...

the swifts are measuring 61mm ID and my hypercos are measuring in the ballpark of 63mm, so the swifts dont sit all the way down on the perch.


i completely overlooked the helper/assist spring piece of this (i did not have helpers on the front)...*****.

 

Being that I sold you the springs, I'm sorry to hear this. These were originally for my KWs that use helper springs.

Not that it really matters, but they are listed as 60mm ID on the site.

 

yeah no worries, its totally my fault. i got misinformation on the original size of my springs or something who knows.

the real question is, why if both are supposed to be 60mm why are my hypercos bigger.

i think i should just be able to pick up a set of helpers.

EDIT: scratch that, dont fit the top hats either, thought they did initially.

 

I don't know anything about Hypercos, maybe someone with more experience can chime in. Do they tend to run larger than listed?

Swift has helpers if you are interested:

http://www.swiftsprings.net/products...r-springs.html

 

Your Hypercos are most likely 2.5" ID, which is 63.5mm.

From what I recall, you need 65mm ID springs for the Ohlins if you're going the metric route. The 60mm ID springs won't fit, as you noticed. Too bad it's too late.