Newly Installed AST 4100 Rebound Settings (for Street)

[Dubbedown]

I know this is the "track" section of the forum but one thing at a time right? First DE isn't for another month and until then been trying to find the right setting on my newly installed AST 4100 (450f/550r) for street...

In the first few days, I found the ride to be a little bouncy. It rode over bumps great but on flat roads you felt the undulations. Thinking I need to dial up the rebound, I started with softest 1f/1r and worked my way up, but always had the fronts higher, ie 3/2, 4/2, 5/3. Nothing worked but someone then suggested I add more rebound to the rears instead. Sure enough at 2f/3r, the ride is more stable (hasn't fully resolved the issue but it's better) - why is that? Every thread I've read here mentions AST owners adding more to the fronts for the street - is that a function of higher spring rates (whereas I chose lower)?

Also anyone know what else might be contributing to the bouncy ride?

[The HACK]

Short chassis.

[lowflyer]

Not apples to apples but on my E46 M3 with AST 4100s and 550f/650r springs I usually run 3f/4r from full soft and works fine. I recently started 4f/4r and will probably leave it there. Definitely not bouncy. For autocross I use 8f/4r with good results after gradually reducing rear rebound to help put power down on corner exit. The higher front rebound helps a lot for slaloms and fast transitions. YMMV.

[Dubbedown]

Short chassis.

Hack - do you also run more rebound on the rears of your M coupe?

[The HACK]

Hack - do you also run more rebound on the rears of your M coupe?

Depends on the track. Problem with the shorter chassis, is that when you take the settings from a longer car, the end result is the frequency of the spring bouncing between the front and rear is changed and you get results that are not what you expect.

I typically start with the same settings front and back (about 1/4 turn off of full stiff on the Ground Control Koni's), and based on what I see during the first session, either soften the front or the back to get to desired result. And then I re-use those settings for future events at the same track.

I run 1/2 turn from full stiff up front at Buttonwillow. 1/4 turn from full stiff all around at California Speedway. But I'm staggered (245F/275R).

YMMV.

[Dubbedown]

OK so I think I figured out what else was contributing to the bouncy ride, aside from the rebound settings. It seems like the bounciness is also a function of front ride height.

When I had the car at its original lower height (and it wasn't slammed by any means), if I jacked one side up, I could easily raise the spring up and down because the gap between spring & upper perch was that big (say over 2"). If I raise the collar enough to just introduce slight load on the spring, the fender gap is much BIGGER than stock, I'm talking more than a fistful. So I ended up raising it to the point where there was maybe a 1" between spring & upper perch. That resolved any bouncy issue but as it currently sits, the gap is equal to slightly below stock.

I would think a helper spring in this case would be the solution but AST doesn't offer these nor do I see others with AST's use them as well. So the million dollar question, how do I lower the front without having the spring sit so low like in the first pix? I see guys here with AST's riding slammed but for me, seems like I need to keep the height at stock or higher, wtf?

(Car on lift, full droop)

Preferred ride height, but too bouncy and notice the gap between spring & perch





Brought the collar up, spring is closer to upper perch, bounciness gone, but fender gap is barely less than stock levels

[Potenza]

What is your front ride height in inches, measured from hub center to top of the wheel arch?

[Dubbedown]

What is your front ride height in inches, measured from hub center to top of the wheel arch?

As it sits based on the last picture above it is 13.5" from center of wheel to fender.

[benjlv]

what length spring is that? my car is 12.75" wheel center to fender with 6" springs at the top of the perch on my asts. I am using ground control camber plates, but that shouldnt matter since the stack height of vorshlag and the GC plates are very close if i remember correctly. anyways i need to go to a longer spring to maintain this ride height with full jounce travel. i currently coil bind before the shock hits the bump stop.

back on topic... another thing that can contribute to boncyness are soft rear shock mounts. Compliance in these is compliance that has to be taken up before the damper can dampen the rear suspension.

[Dubbedown]

what length spring is that? my car is 12.75" wheel center to fender with 6" springs at the top of the perch on my asts. I am using ground control camber plates, but that shouldnt matter since the stack height of vorshlag and the GC plates are very close if i remember correctly. anyways i need to go to a longer spring to maintain this ride height with full jounce travel. i currently coil bind before the shock hits the bump stop.

back on topic... another thing that can contribute to boncyness are soft rear shock mounts. Compliance in these is compliance that has to be taken up before the damper can dampen the rear suspension.

I'm almost certain I received the standard springs in their 4100 package which is 6" as well. The rates I'm running are 450f, 550r. Rebound is set at 2f, 3r (1=softest) and I find that to be the most compliant for street. I'm actually using the Rogue RSM's.

Maybe it's coincidence but like I said, the bounciness went away after I brought up the ride height. I am curious for those with AST who ride much lower than I do, are your collars that low where if you jack up the car, you can easily move the spring up and down the shaft?

[modernbeat]

I don't have an answer for your original question, but I did spot something wrong in your photos. That black plastic ring you have above the spring is ONLY supposed to be used when you are stacking springs. If you are using a single spring, take that double-spring adapter off.

Also, you can buy AST helper springs separately. I know we have them available on the Vorshlag site and they are in stock.

[Potenza]

As it sits based on the last picture above it is 13.5" from center of wheel to fender.

You really should talk to AST/Vorshlag if you're having any problems, they have great customer service.

edit: didn't realize this was a Z4.

[illinipo]

I suspect the z4 has a much different wheel arch so the ride height numbers are a little different from what people are used to...

For example, the H&R race, which are quite low indeed, ride at 13.25 front and 13.0 rear

[Dubbedown]

12.75" is the MAX recommened ride height for the front. Run any higher in the front and you risk damage to the shock because it tops out (oppostie of bottoming out). If you want to run higher you need to buy the droop travel spacer. You really should talk to AST/Vorshlag if you're having any problems, they have great customer service.

It is NOT my preference to run a height this high. The whole reason for this thread is because I DO want to go lower but when I do so, it translates into a bouncy ride. But unlike blown shocks where all 4 corners feel bouncy together, here the front and rear alternate.

I've reached out to both Terry and Matt via email/pm. But I'll follow up with a call during business hours.

I suspect the z4 has a much different wheel arch so the ride height numbers are a little different from what people are used to...

For example, the H&R race, which are quite low indeed, ride at 13.25 front and 13.0 rear

This sounds very plausible. I recall reading the stock height for a Z4 coupe on oem sport suspension was 14" from center of wheel to fender, which means I'm 0.5" lower than stock. I'm assuming the e46's are less than 14"?

edit: found the link listing ride heights

[illinipo]

That space goes away completely when you let the car down. And that harshness is probably the bumpstops.

When you take out the dual spring spacer it will get a little lower at the same adjustment setting.

[Dubbedown]

That space goes away completely when you let the car down. And that harshness is probably the bumpstops.

When you take out the dual spring spacer it will get a little lower at the same adjustment setting.

If you're referring to the first picture, I know the gap goes away once it's on the ground. I was just merely pointing out how much travel there was in relation to how much I had to bring up the collar to make the ride "better". But the ride was never harsh... it was the opposite as if there was no rebounding at all. However I will take out that spacer though...

[ThreeD]

I run 7F/5R on the street with 1 being the rebound settings in the softest/open setting. I am on 550/650 rates though, I find the ride to be firm but not harsh, well-damped on Z1 star spec tires at 38psi warm. I'm running a 12.25" ride height in the front and 11.5" in the rear. For 450/550 springs maybe you should run it a little softer....maybe 5/3 or so.

If you felt like you were riding on blown shocks you should increase the rebound.

[benjlv]

Rogue offers two different bushing sets. Make sure youre using the stiffer ones.

I am using the same rsms with the stiffer bushings... Pretty bouncy. But a have a different problem... one of my front springs turned out to be a 650 not 450. Getting that exchanged soon. Embarrassingly I didn't notice the incorrect spring during install...

[sh1ftgear]

I have 500/600 spring rates and I'm from 5F/5R, with 1 being full soft. Ride feels almost like my stock suspension.

[the Scholar]

On a side note, is anyone finding that the springs offered with the AST kits too short? I bought my kit from BW and they sent me 6" springs up front and 5" springs for the rear (rates of 500F/750R) and I believe they should have at least been an inch longer front and rear for the ride height range that I requested. A friend of mine also running AST 4100 (with a slightly less front spring rate than I am running, 450lb/in) is finding that he is running into coil bind before the bumpstop hits. By his measurements, he was thinking that he should be running an 8" long spring up front for his rates.

Just wondering if anyone else was thinking the same thing.

[jph28]

My E46 M3 kit came with 6", 600lb-in fronts and 5.5", 650lb-in rears, both support the ride height I wanted (~13.25"/12.75") really well. Fronts gets some free play on jack stands, but that's normal.

[scooper]

I'm on 4200s on e36 platform with 500 6" up front and 650 5.5" in rear. I think 5.5" is really the absolute minimum in the rear since my adjusters are all the way down and I'm almost slammed. I am thinking about getting 6" springs 650 in rear and moving down rates in the front for better ride on the streets. Staying with 6" in front.

[Dubbedown]

Managed to take out the spacer yesterday, well in actuality didn't really need to take it out. Once the car was jacked up, the plastic spacer had pretty much cracked/deformed so I pulled it out. Car drives fine now and this is how she currently sits:

[illinipo]

Question for you. Do your rear spring adjusters sit all the way up against the chassis?

The inner diameter of the AST adjuster is 35mm+0.3mm (that's a 0.3mm tolerance to the big side only) and the chassis stubs on our car are 36.5 and 37.5mm.

Terry says he has never seen this before so I'm trying to find out if it's an issue with all non-m z4 coupes or just ours.




Of course to workaround we will just run it on the bottom. But it is so much easier to adjust when it's up top!

[Dubbedown]

Question for you. Do your rear spring adjusters sit all the way up against the chassis?

The inner diameter of the AST adjuster is 35mm+0.3mm (that's a 0.3mm tolerance to the big side only) and the chassis stubs on our car are 36.5 and 37.5mm.

Terry says he has never seen this before so I'm trying to find out if it's an issue with all non-m z4 coupes or just ours.


Of course to workaround we will just run it on the bottom. But it is so much easier to adjust when it's up top!

I don't think that was the case but I'll check when I get home. Are you going to keep the upper spring pad?