Interior rear wheel lift after news bushings, Ohlins DFV and alignment
 

Hi,

I have a 2002 AP1 UK (RHD) S2000 since 2012.
Since 2013 I was riding "BC Racing BR-Rs" Coilovers (10/10kg springs), with 25mm (1") height drop, and had no major problem with it.

My compliance bushings were getting worn so recently I made modifications on my car:

• full MUGEN arm bushings (front inferior + superior arms, rear inferior (except the front big bushing which can't be bought) and superior arm + rear toe link)
  Info: When installing the arms back on the car, I did put a hydraulick jack under the lower arm, and jacked up until the car began to lift up (of the stand jack), before torquing the bushings bolts.
• Ohlins DFV coilover (MI20) with 10/8kg Ohlins springs. Settings: 25mm (1") height drop, Ohlins recommended settings (including rear 2mm preload)
• Replaced differential for another identical oem used one
• Full alignment with "UK settings"

I don't have any bumpsteer kit, but didn't have it either before the modifications and I was already at the same ride height.


After that, I had a test drive and I am experiencing issues:

• I feel the car much more oversteering when getting on the gas during a corner: the rear end of the car is more "mobile" than before, more "moving/placing" itself when going on the gas. It is not drifting, but moving due to the torsen action I think.
  Actually, I hoped theses mdifications would do the exact opposite: get more stability...
• in moderate speed hard cornering (such as a roundabout when I get fast enough to nearly drift it) : my engine is revving up because the interior rear wheel lifts up, and the it gives a grip when the wheels returns to the ground. This is not fluid at all...

I need your help and ideas because I can't imagine what could be the problem... Ohlins DFV are not supposed to generate these issues for what I read...
The bushings are supposed to be more rigid than oem ones, but I highly doubt this would generate such problems.

I am opened to hear your ideas :)

You must really be coming out of the roundabout at 10/10th's.

With 2mm of preload, I got tire lift at the track on very tight turns where I'd be demanding a ton of power to be put down on exit in like 2nd gear.

Did you get the alignment AFTER the install of all these parts? If not, that could easily explain your instability and over steer.

Its massively counter intuitive...but with a lot more rear preload (I think 15mm or something), the rear stopped lifting as much for me. FWIW, I also started using 75W140 fluid.

The preload will also make the suspension effectively softer...so you will definitely experience less over steer.

There's plenty of reading out there that will show that 2mm of preload pretty much puts you on the rear bump stop. Ohlins has later revised this spec. The whole kit has gone thru 2 additional revisions to deal with the limited rear stroke. Do you have the kit with improved rear stroke? If so, you may not need as much additional preload.

What is the full part number for your kit?

Sorry, but I don't understand what you mean here.

This is similar to my case: I am in the middle rpm of 2nd gear and asking for power.
And I am soon going to be supercharged so I need to solve this situation.

Of course yes :)

I thought this would be exactly the opposite ! I thought that increasing the preload would make it feel like "harder" ... :confused:
What is the relationship with the diff fluid 75W140 ?


I read a lot on s2ki about the rear preload. But actually, the few french S2k owners that I know who have the DFVs are happy with these 2mm of preload...
Increasing the preload won't reduce the stroke actually ? (if not, my understanding of this must be incorrect...)

I bought the Ohlins used, with about 1500 miles and 2 years old. I can try to check tonight the complet full part number if I have it...
What is sure is that I don't have a "Sakebomb" version of the DFVs.

Damn "UK settings"... In short, they're terrible. Way way WAY too much rear toe-in, which makes the rear feel *less* stable. Otherwise specs are nothing special, IMO you want more negative camber up front than it prescribes. But mainly you need to reduce your rear toe-in from UK spec down to about 0.2 degrees *total* rear toe-in, or 0.1 degrees toe-in per side. Even a bit less than that is fine. UK spec of 40 arc-minutes is 0.67 degrees, this is excessive and leads to handling weirdness, while also cutting rear tire life in half or worse.

The more I read s2ki and else, the more I think my problem is related to the preload/height/bumpstop.
I have a friend who rides the same Ohlins DFVs that me, but he is near stock height. I am 25mm lower, which is the Ohlins recommended setting however. He has no problem of rear wheel lift...

Preload can't make the suspension harder as long as there is weight on it.

If the shock is fully extended (wheels completely off the ground), then upon landing, the initial reaction of the contact will be harder. Once the spring compresses even 0.00000000001mm, it will act like a non-preloaded spring would.

Preload doesn't change spring rate. It changes shock shaft position.

Imagine it this way:
If the car was already on the ground and you turned the perches upward....would the spring compress further?

No.

The car would raise up. The spring would stay exactly the same length. Because the rate (hardness) is still the same.

On the Ohlins (or any full body coilover), you then lower the ride height back down using the lower bracket which is independent of the spring.

Did you clock the bushings when all this work was done?

He did, according to the original post

This trick works ! I understood your hole explaination :groove:

So the problem is that, with 2mm rear preload, my shaft is in a "low" position, so that when I drive my car I have very little rebund travel ? reason why my wheel would lift instead of keeping contact to the ground ?

Actually, less preload means less compression travel, but MORE rebound travel. More preload means the opposite - more compression, less rebound

So for that reason, one would think that adding preload would create more inside wheel lift for that reason.

But I think that with too little preload, on a hard turn, your outside rear corner hits the bumpstop....but the outside front corner keeps compressing, which pulls the inside rear corner up. Just a theory.

Again...its counter intuitive. But for me, adding the right amount of preload helped with wheel lift. I assume too much preload would cause inside wheel lift too.

How big is your rear sway bar?

Thank you again for those explainations. Not that simple ...

I have the oem sway bars, and my car is MY2002.
I found this on s2ki:

Summary of spring rate findings:

Front Rear Front Rear
Model Year Spring Spring Sway Bar Sway Bar
--------------+------------------+--------------------
2000-2001 219 291 393 427
2002-2003 246 309 300 396
2004-2005 262 278 300 311
2006-2007 262 269 300 311
2008-2009 280 294 354 311
2008-2009 CR 384 343 392 362

Maybe softer rear sway bar

And get 15mm rear preload..

I had no problem with my previous coilovers, so I will start by changing the rear Ohlins coilover preload to 15mm !
Maybe I will get Eibach swaybars (or else) in the future if necessary, I will see on track with the supercharger...

Thank you all for your help adn explainations, because over than the solution: I like to understand things.

Now my goal is: change the rear preload and re-adjust the height, in order to keep my alignment settings (brand new: done 1 week ago !)...
But it will be impossible to be sure, so I will pay again to check alignment I guess...

Examples on bias from one of our residents
https://www.s2ki.com/forums/s2000-br...1183541/page3/

Measure wheel from arch first ,then preload adjust, so counter adjust with perch adjustments.……..
then no need to pay again.

This is what I will do, but it is hard to get back to the exact same height. Even if I move my car in my garage, my heights change at the four wheels ! (only a few mm of course, but it is not easy to fix something in this situation...)

Only a few mm lower or higher wont change the toe angle much at all.
By the way did you have the exact same alignment figures with the Öhlins as your previous coilovers?
Show us the setup if you got a printout, maybe there is something that could be improved there as well.

This might sound stupid but, did you check the adjustment knobs to make sure they are on the softer settings? Also, I would maybe take the car to a different shop and re-check the alignment?

Add 13mm of preload (use turns, not measurement). Each 360 deg turn of the perch is 1.5mm.

Then lower the bottom bracket by 13mm to keep the same height.

Easy peasy.

I just reread First post. I'm not seeing where he mentions clocking them.

With the OHLINS I have the exact uk specs, except 0degre05' of toe in at each front wheel.
With previous coilovers I could not put the UK alignment because of seized bushing. I have only 0degre40' of front camber; the other values were uk ones.
Sorry I am on my smartphone now so can't post hole values.

I set the ohlins hydraulics to recommended 10 clicks from harder.

Will be doing this right now :)

Sorry but, what does "clocking the bushings" mean in other words? (Frenchie inside :D )

He jacked up the arms before torquing the bolts.

I am under the car and just finished preloading the rear coilovers. Going to put the car back to the ground. The problem is: I ride a 28mm height drop, which is 1.11", so I can only go up to 10mm preload and the the coil is "hurting" the bottom end of the thread.
I will try to ride with this preload tomorrow, I have a trio with a friend to see a Rallye race :)
I will see how it behaves on bumpy roads.

More compliant, assuming you were nearly on the bump stops before.

The other important thing to re emphasize is that you adjust the lower shock body to compensate for the added pre load so that your ride height/alignment is the same as before.

Oops...

You were almost certainly contacting bumpstops and thus the loss of traction. Add preload as so many others have suggested.

Softening the rears can also add more grip.

What did the alignment specs look like before you got the UK alignment?

Are you sure the front sway bar is reconnected at both ends? Most people disconnect it at some point during a shock install.

I had a problem and could not road test the car yet with the new preload: I have to replace a front upper arm bolt&nut , the thread is dead and I can't torque it so it makes noise and unscrews itself when I drive the car...

Alignment before modifications was:
Front
-0deg40' camber
Caster 6deg45'
Toe 0deg
Rear
-2deg camber
Toe -0deg25' /wheel

Now it is:
Front
-1deg camber
Caster 6deg45'
Toe -0deg05' /wheel
Rear
-2deg camber
Toe -0deg20' /wheel



I checked that: front sway bar is connected.