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:
After that, I had a test drive and I am experiencing issues:
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? |
Originally Posted by B serious
(Post 24590884)
You must really be coming out of the roundabout at 10/10th's.
Originally Posted by B serious
(Post 24590884)
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.
And I am soon going to be supercharged so I need to solve this situation.
Originally Posted by B serious
(Post 24590884)
Did you get the alignment AFTER the install of all these parts? If not, that could easily explain your instability and over steer.
Originally Posted by B serious
(Post 24590884)
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. What is the relationship with the diff fluid 75W140 ?
Originally Posted by B serious
(Post 24590884)
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? 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. |
Originally Posted by pizzai69
(Post 24590872)
Full alignment with "UK settings"
|
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?
|
Originally Posted by Car Analogy
(Post 24591032)
Did you clock the bushings when all this work was done?
|
Originally Posted by B serious
(Post 24591004)
Imagine it this way:
If the car was already on the ground and you turned the perches upward....would the spring compress further? No. 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 ? |
Originally Posted by pizzai69
(Post 24591316)
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 ? 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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