Leigh2

Tough to explain but when the pressures (and all else) is right the car slides smoothly. When the pressure are low the car feels rough when it slides...like slide/grip/slide/grip thunk thunk thunk..., it's very subtle but the butt feels it. Perhaps somebody else could chime in with a better description???

For camber watch the tire wear it's the best indicator but I haven't met a street car yet that didn't need at least -2.5 in the front with R compounds. rear generally less, but my guess is it will be a while before the effects of the rear wheel steering on camber is well understood....

Zulu Alpha

Ah, ok got you now. Right, so yes if the pressure is just right it should slide smoothly, but this is what the front does at 29, but the rear doesn't slide smoothly with higher pressures. As I understand, since there is a balance ratio of front and rear pressure since the tire sizes are staggered (meaning, to have equal pressure front and rear the pressures will be staggered as well), I might need to go up on pressure in the rear just a smidgen.

C.J. Ichiban

When I was running Michelins on my old RS I noticed the smoother yaw transition was with a stiffer setting on the rear sway bar. If you are feeling body roll as a component of the slide/release than a tighter rear bar will help keep the body from wobbling. Also higher pressures will definitely help smooth out the rear tires to a point, once they go too high they slide everywhere.

Michelins have a stiffer sidewall so you don't need to go past 36 but 34-35 is probably ideal.

Running low psi allows the sidewall to flex too much and it will alternatively dig and release which is probably what you are feeling. That combined with a looser swaybar can lead to an awkward handling car on the track.

Zulu Alpha

I'll take sway bar in to consideration as well, but I don't think roll is the factor here. Also, the car has a lot of rotation on turn in, and push on exit. I think you hit the nail on the head in your last paragraph about running low psi and sidewall flex. The front end of the car seems dialed in (I mentioned earlier that I increased a bit of camber in the front before this trackday), as soon as the rear slips this judder thing happens, and in that moment is does, the car takes a certain amount of time to settle and it doesn't settle predictably. I feel a lot of time is lost during the judder as it becomes distracting and I can't keep the car in that steady slip of 106% - 110% you may know what I'm trying to say.

Do you think camber is a factor as well? If I increase a bit of rear camber that the tire won't roll on the side wall and judder, instead roll on the carcass of the tire?

My thought process is there is not enough camber so the tire is leaning on the leading edge of the outer sidewall causing this judder, kind of like a digging in snowboard on the outer edge causing the rider to fall over (but in the case of the car it hops).

P.S. All the best to you and your team at Daytona!

Shahano

Hi guys, I had the same problem and I bumped up the tire pressure to 34/35 rear and 32 front hot. That solved my problem

Zulu Alpha

Thanks very much for the feedback all much appreciated. I'll go down the pecking order with your recommendations and try to apply until the issue is fixed.

Gt3Fan

Yeah, those pressures are way lower than what I found optimal for the MC2's. Hot, I found rears 35/36 and frot 31/32 to be spot on.

TRAKCAR

ideal for me was 30F 32R Michelin guys on track said, officially 32, some prefer as low as 30.

C.J. Ichiban

+1 on rears at 35.

something for OP and others to consider- when you start the tires too low it really is hard for them to ever properly get up to temp in what is generally a 20-30min DE session. race cars start at super low PSI because they have to run for 45-90 mins straight at 100%.

TRAKCAR

Is it me, or are these Mpsc2 just very hard to get up to temp / psi? Or was it the cold track experience?
Sometimes it took me 10 minutes because the first laps I had to take it easy 22/24 psi and it took 3-4 laps to just get them up enough to push..

Ur20v

Chunky= lumpy= judder you are experiencing

Zulu Alpha

I start off on street pressures, build the heat for a few laps, come in and bleed to desired pressures. Not sure if this is a correct method or what not. But I have no issues of building heat and pressure in those laps, and within a lap I have decent grip. Is it possible that it might be more difficult to build heat starting from low pressures, idk.


Sounds like an ice cream, haha! Thanks for the explanation. :thumbs up:

TRAKCAR

^^ or maybe warmer track surface and air?
It was cold in Europe and in long straights the PSI went down..

1965356

Drive smoother?

Manifold

Good comments and discussion.

To some extent, I think that behavior is inherent in this car (there are similar reports for the RS), so we need to adapt our inputs to keep the car stable, especially at corner entry. Not sure how much you're trailbraking, but you might try initiating braking earlier and doing less trailbraking, along with recalibrating your steering input so that the weight 'rolls' from the front to the side of the car at corner entry more smoothly and with more optimal timing. The rear stepping out too quickly can be indicative of not enough weight back there and/or rate of steering input being too high.

Tracks also make a difference. I find that the rear of the car wants to step out much more quickly in some turns of some tracks vs others. Pavement surface texture, track geometry, bumps, etc. can make a big difference.

But as others have said, do also make sure nothing's wrong with the setup of the car. Maybe recheck the alignment, make sure nothing's loose, etc. Hopefully, you don't have something like a bad damper. Your tire pressures seem reasonable; you can certainly tweak them, but I'm guessing that they aren't off enough to be a major factor in what you're experiencing.