Dead Serious

http://www.youtube.com/watch?v=aFsPDB2RKqY&t=8s

ottawas2000guy

Watched the whole vid. Good job keeping it together. hahah. To me it doesn't look shock travel related, as you actually don't have much oversteer during the high G load bumpiest sections of the track. I also noticed how much smoother your inputs became throughout that video so it appears you were certainly adjusting your driving style to compensate for your setup at that track. Seems like a combo of corner entry oversteer during off throttle/trail braking and some exit on throttle oversteer. I think the bar is going to help you a bit in both scenarios, but I would be double checking your rear toe, tire pressures and softening up the rear shocks if adjustable.. I'm sure you've either considered or addressed all of these already..

DanielB

It's hard to tell from just the camera, but it seemed like you were sliding the rear tires more on the opening two laps which might have overheated the rears. Once you adjusted how you added power on the corner exits on laps 3 and 4 it seemed that the oversteer became more manageable and you also went faster. Assuming alignment and tire pressures are ok, a softer rear bar might make a noticable difference after all when coupled with adjusting your driving style to use a bit less throttle on corner exists at the start of the session to reduce rear tire temps.

Another thought is to disconnect the rear for a session and see how much things change. It's not a big deal to try.

bgoetz

I stumbled across this thread trying to rid my car from that same demon. Watching the video I noticed one big similarity in the on throttle oversteer past mid corner. It is something that has bitten me several times to the point where that sound of hanging throttle makes my neck hair stand.

The entry oversteer to me is far less concerning because it is predictable and manageable whereas the on throttle exit oversteer is not. Oversteer on entry your weight is over the front wheels and your steering input causes a light rear to loose grip, you have two choices open the wheel and/or add throttle, the condition is typically corrected by a combo of the two. On mid-corner and beyond you have already transitioned the weight to the rear and by all accounts the car should be set, but it isn’t. Your option is really limited to a drastic countersteer which is tough if you are running out of track and is even more difficult to do without loosing time.

I have narrowed it down to two conditions one drive and the other car and am starting to think it is a combo of car and driver. You are on throttle very early in all of those on throttle oversteer situations, meaning you overslowed the car (I observed the exact thing in my instances). The car situation is that these cars have very short rear travel, so as the outside wheel runs out of travel the inside lifts causing power to all go to the outside rear, you can hear it happen. Additionally, we all know these cars loose rear toe and camber under these situations making things worse.

So to me that is the riddle, the fix I have not come up with except enter faster and apply throttle later, but that seems like only part of the solution.

ottawas2000guy

Interesting to hear about these issues, although I can’t say I’ve had any of them. I’ve now been running 255 square with Ohlins 10k/10k with stock ‘00 front bar (393lb) and Miata rear bar for 1.5 years on track and find the car extremely well balance. I would say it’s extremely eager to rotate but not a handful at all. I also recently rode with a very fast s2k driver at my local track who’s running all stock bars with 255 square and 13k springs all around. There was no real oversteer to mention on his car either despite what I expected.

Don’t know if this Instagram video work but here’s an in car video on my local track (Calabogie) earlier this year.

https://www.instagram.com/tv/Bz3Vj7n...d=83bo4z5z272y

Car Analogy

Interesting and enlightened observations. One thing though, with the stock torsen diff, if one rear wheel lefts fully off the ground, all power goes to that unweighted wheel, just like an open diff. A mild weakness in this diff design.

I'm thinking the additional oversteer you are observing when outside rear wheel travel runs out is due to exactly that. The suspension can't absorb undulations and this causes the additional oversteer.

One fix might be more rear travel. Either shorter rear shocks or just more rear ride height.

bgoetz

Ok well that is a good bit of information/correction to my statement. So maybe that is the cause of the “hanging” rpms the inside tire spinning for a moment before returning to the pavement. Which to me confirms the inside rear lifting, but eliminates the cause of the outside rear loosing grip as being power going to the outside unless it is once the inside returns to the ground and the sudden transition back to power on a fully compressed outside rear causes it. Or the lifting of that inside rear is causing the rear to loose toe/camber. Maybe it is the combination of the two.

So so how do you keep both rear wheels on the ground in a car with super short shock travel?

ottawas2000guy

Im not seeing the logic here for some reason. Inside rear wheel lifting and sprinting should not cause oversteer, that tire isn’t providing much grip already. Also, the outside rear tire compressing gains negative camber and toe-in both of which only help with grip and stability. I think there is something else going on with these guys cars. Of course we all know that over bumpy surfaces AP1’s can be a little skiddish because they have aggressive dynamic toe which will toe out the rear wheels when they droop after going over a bump. Corner exit oversteer is traditionally the easiest oversteer to control unless you’re really jabbing at the throttle and sawing at the wheel. So I think there is something else going on and I wish I knew what it was.

Car Analogy

I think you might be on to something there.

IRS. The toe or chamber of wheel in air which isn't doing anything to cars dynamics has no effect on tire that is on the ground that is affecting dynamics.

QUOTE=bgoetz;24625406]
So so how do you keep both rear wheels on the ground in a car with super short shock travel?
[/QUOTE]

Less rear swaybar, and/or less stiff rear springs, and/or raise ride height so there is more compression travel, and/or get different, shorter shocks (or modify shocks to be shorter, like the SakeBomb rear lower mounts for Ohlins DFV).

ottawas2000guy

Less rear swaybar, and/or less stiff rear springs, and/or raise ride height so there is more compression travel, and/or get different, shorter shocks (or modify shocks to be shorter, like the SakeBomb rear lower mounts for Ohlins DFV).[/QUOTE]


Ya, I should mention I do have the SakeBomb lower mounts so I might have slightly more travel depending on our ride heights.