mdrums

Hi Mooty, I was spinning the rear tires (dry mounted) basically all the way around on a 2 day DE and the front about half way around. This is at Sebring that has some high speed threshold corners. I had the CCW's bead blasted to take off the black matt powder coat where the tire bead sits. I have not had a chance to go back to the track since this mod to the wheels to see if this works. My RA1's on stock aluminum CCW's I use to have never spun much at all.
Yes, seems like 245 and 305 is all there is with the Toyo's. I can find the Nitto's in 255/35/18 and 305/30/18 and this keeps the front to rear ratio in check but over all diameter is much smaller than stock. I am confused if this screws up ABS though. I did try this size for 1/2 a DE in my 07 997 and it seems to work.

mark kibort

I dont think diamters matter, as most porsches have front and rear separate system. Can someone confirm for your porsche?

335, 305, 295, and 275 are also available in the toyos.

the rim spin thing is something. I guess we have to imagine 2400lbs of thrust force in 2nd gear (based on 400ft/lbs rwtorque / 6:1 2nd gear and 24" (1foot radius) diameter rear tire). Up front is much more believeable, underbraking as thats the direction the tires should slip. rear is under power and the opposite direction.

mk

mdrums

Hi Mark, I have been told I need to keep the diameter with in 4%...BUT I do not know if that is 4% of each tires diameter or 4% between the front and rear tires or it's 4% of both diameter and difference from fron tto rear.

Correct the rears spin one way due to accel and the front spin the other way due to braking.

mark kibort

Im sure you could go unlimited size greater front and rear together keeping the ratio percentage-wise front to rear. I dont know what the ratio of rear to front needs to be, as there might be a factor that modulates ABS If the rears are much slower than the fronts Just as if you change diameter, you rpm and MPH are usually not changed, even though the actual mph might change.
So, if the ratios are kept the same the car would never know, unless it speed input was GPS .

side to side changes is bad no matter how you slice it. by accident I did this on the fronts and was forced to do it on the rear. on the front, you pull to one side, and on the rear, you wear out the LSD and pull to one side as you accelerate.

mooty

drum, i can't help you on nitto's. i THOUGHT 255 wont work so i never bothered trying them. i know for a fact 245 and 305 RA1 works on the 997's.

mooty

I wonder why you are getting darty under braking? thats just weird. that can happen with a lot of toe out, but didnt think the tire could cause that. after all, ive run street tires and DOTs in races and haven noticed anything other than lack of grip and more noise.
==> we ran RA1, R888, R6 on that same car, same track, same day back to back session with me and tony c driving the damn car. it doesn't dart, it moves left or right (not left and right) when you brake. it was very consistent and ONLY on R888 full tread. one may argue that perhaps that particular set of R888 was defectively. but on another new set of full tread R888 on a different GT3 also had the same problem. both cars were just aligned and for sure rear had toe IN.


Again, I cant wait to run the R888s, just to see. Unfortunately, if they are not any good, that all Ill able to use due to my racing budget ($0).
==> they aren't bad. when i was chasing you and dave at the NCRC/ARC race at THill last year, i was on R888's.

333pg333

Stupid question, but what is the downside of a tyre spinning on it's rim say 180o over the weekend? Doesn't this mean that they're shifting in small increments at a time and therefore won't this be of little consequence? I get that if it shifted 360o during one race then you're going to be suffering but I wonder what a few mm's per lap might inflict upon us?

Peter Carroll/Toronto

Just for the record, I run R888s on my 600hp 930 as well as our E46 M3 and I absolutely love them. I used to run RA1s but prefer the feel of the R888s. You don't have to go through that squishy period at the beginning. And when they are well worn you still have tread in case it rains on the way home. The sidewall is also stiffer so they work well on cars with less camber. i.e. they are the ideal Driver Ed tire...

They do tend to lose grip before you hit cord. At this point they still have a bit of tread left. Another handy feature to get you home.

Veloce Raptor

The downside of having a much stiffer sidewall than the RA1's is that the 888's are MUCH more sensitive to hot pressures, and their sweet spot/oh **** range is tiny compared with the relatively broad range & forgiving nature of the RA1's. Thus, the 888's tend to go off more easily & suddenlyy, and are comparitivvely harder to bring back, than the RA1's.





Professional Racing and Driving Coach

Peter Carroll/Toronto

On the Turbo I run 37-38 hot. On the M3 we use 40 hot. Both are streetable track cars with lots of suspension and 2-2.5 deg of camber.

TedA

[QUOTE=M758;6748262]We also have been working on tweaking the set-up as the R888 take LESS camber then than the RA-1. Running RA-1 camber levels will overheat the inisde of the tire causing it to go off during a session./QUOTE]

Joe ...give up any secrets on camber with the 888s?. Also am running the 888s at 2 psi higher pressure than thr RA1s.

I continue to stockpile RA1s..my wife is not happy about it but she will get over it.

M758

This is EXACTLY what I have found as well. I could slide an RA-1 through a corner and it would stick fine in the next one. In fact it worked so well it became technique in some places. Just slide the car through that turn. Only If I went over the edge and starting a a "drift" routine did the RA-1 go off. Then I would need to back off for 2-3 corners before the tire came back.

With R888 one moderate slide and the tire goes off. Not bad at first and not enough to put you in the weeds, but it forces you to slow down for the next corner. This gets progressively worse untill you start losing multiple seconds a lap. So with the R888 you cannot casually slide the car and if you make a mistake and slide it you need to be easy on the tires and hope they come back in a lap. If you are lucky they do. If not you a dead meat.

For me reducing the camber seems to have lowered the inside shoulder temps giveing me a bit more margin to sliding. This way a small slide did not send the tires past the point of being able to bring them back during a run. I was running 3.5 and 2.5 on RA-1, but I am not closer to 3.0 and 2.0. I also adjusted sway bars to reduce oversteer tendancy to prevent rear end sliding. Now what is interesting is that those camber levels on RA-1 would have not been very good. I tired and found them to unacceptable on RA-1.

bb993tt

I think that would only be true if you were running viscous coupler type AWD (993 for example), in order to keep the VC from frying. I understand the 4% to be the difference in OD between the front and rear.

mark kibort

Thats how I understand it. (4% difference) again, what would it matter if all 4 were bigger. Nothing on the car would know if the proportions were the same, except a radar gun. Its all relative.

mk

mark kibort

Ive stockpiled them as well, but the will be gone by mid next season.
so, Ill be testing them soon! maybe November

mk


[QUOTE=TedA;6751526]