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

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

 
Old 04-17-2019, 12:54 AM
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Default 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
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Old 04-17-2019, 03:13 AM
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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?
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Old 04-17-2019, 03:57 AM
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Originally Posted by B serious View Post
You must really be coming out of the roundabout at 10/10th's.
Sorry, but I don't understand what you mean here.

Originally Posted by B serious View Post
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.
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.

Originally Posted by B serious View Post
Did you get the alignment AFTER the install of all these parts? If not, that could easily explain your instability and over steer.
Of course yes

Originally Posted by B serious View Post
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.
I thought this would be exactly the opposite ! I thought that increasing the preload would make it feel like "harder" ...
What is the relationship with the diff fluid 75W140 ?


Originally Posted by B serious View Post
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?
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.
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Old 04-17-2019, 06:41 AM
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Originally Posted by pizzai69 View Post
Full alignment with "UK settings"
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.
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Old 04-17-2019, 07:05 AM
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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...
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Old 04-17-2019, 07:53 AM
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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.
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Old 04-17-2019, 08:40 AM
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Did you clock the bushings when all this work was done?
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Old 04-17-2019, 02:03 PM
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Originally Posted by Car Analogy View Post
Did you clock the bushings when all this work was done?
He did, according to the original post
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Old 04-17-2019, 10:03 PM
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Originally Posted by B serious View Post
Imagine it this way:
If the car was already on the ground and you turned the perches upward....would the spring compress further?

No.
This trick works ! I understood your hole explaination

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 ?
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Old 04-18-2019, 02:09 AM
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Originally Posted by pizzai69 View Post
This trick works ! I understood your hole explaination

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?
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