bperry

Here are the specs:
OEM fronts 245/35/19 25.7od 808 revs/mile
OEM rears 325/30/19 26.6od 781 revs/mile

Toyo fronts 245/40/18 25.6od 812 revs/mile
Toyo rears 335/30/18 25.9od 803 revs/mile

OEM ratio: 25.7/26.6 = 0.966

Toyo ratio: 25.6/25.9 = 0.988

Looks like a difference of 2.2%

IS THIS MATH CORRECT?

Ran this combo on the track last weekend and the rear brakes came off smoking (literally) hot if I came in without a cooldown lap which I had to do on 2 occasions. SC was off; TC was on for most of the sessions. I only felt the TC engage once in 8 20 minute sessions. I had no instances where I had the dreaded ABS ice braking.

Is this combo okay or is it torching my brakes with TC on as the rears are turning 18 revs /mile more than the OEM fitment? Anyone else running this combo successfully? How would I know if it is triggering the ABS/TC since the light on the dash already comes on when SC is turned off?

Any advice on this matter is appreaciated!

bperry

Also with the SC/TC on driving on the Hwy no ABS or TC lights come on. The TPM light is on as I didn't put sensors in my Track wheels.

Carrera GT

I've run a lot of combinations of width and compound on the 2010 RS. If you managed to get that much heat in the rear pads, it's a matter of driving the car. Sounds like you're having run with the car and I've gone through similar experiments, but I can't stand to have the PSM intervene, so I treat it like a soft-spoken instructor trying to gently coax and coach me towards smooth and fast. I spent a three-day weekend at Laguna on heat-cycled 315's just practicing how to drive without relying upon the prodigious rear grip of the new RS. I wish I'd thought to take off the wing -- maybe I did think of it, but I wasn't that cavalier and I still think the 450 horses and phenomenal front grip deserves absolute respect.

In terms of "ice pedal" I've encountered that problem on stock Sport Cups and Hoosiers alike -- if the surface of the track is a bit slower than ideal and you're above the middle of the threshold limits, it's important to transfer weight forward and use a progressive pedal to get the weight on the nose before using the full brunt of the brakes. If you're as quick on the pedal as the tires and front springs would allow, the ABS doesn't keep up and goes into fits trying to figure out what's happening -- when you get ice pedal, just instantly release and re-apply the brake and all will be well because you'll already be much slower and you'll have a chance to do simple things like take any steering input out and let the car settle, then turn in on the line again and trail. Trailing will also prevent the smoking pads you're experiencing.

bperry

Thanks Carrera. No doubt I'm having Fun with the car. Have you run this particular combo? Anyway I do the math it comes out with btw 2.2 to 2.3 % change from OEM ratio. I know these cars are hard on rear brake pads but just checking there was nothing wrong with this combo before I order another set of tires for spares since they are less than half the cost of the MPSCs with very near the same performance!

Carrera GT

I don't know. I've run 265 fronts with 315, 325 and 345 rears mixing Sport Cups and Hoosiers doing hard laps or heat cycles, bedding in brakes or generally flogging the car around for fun. Even over the Corkscrew, there's a line and a throttle position with the right steering angle where PSM aka SC / TC will not intervene. The SC assumes that if the suspension is loaded and the throttle is not about 50% or more, the driver is making a mistake (it's probably right) and if the throttle is more than about 50-75% and the steering angle is more than a hand-width off straight-ahead, the driver is making a mistake (again, it's probably right.) If you feel the steering loading up, it's incipient oversteer and the SC will intervene earlier, especially if there's too much throttle. If the weight is forward, SC will complain. When in doubt, have the steering straight-ahead and the throttle at 50-75% -- just like any 911. If the weight is rearward and the steering input is straight or tad oversteer slip angle, SC will allow ample power down and it permits glorious power oversteer, but if you blink (tighten the steering angle at all) it will call foul and you're in the dog house with the inside rear brake pulling you back in line. Once you find the "envelope" you can flog the car on numerous tire combinations without SC tapping you on the shoulder. I went through a set of rear brake pads "practicing" these limits. I subsequently did two days at Sears and a day at Thunderhill and a day at Laguna and wore out the fronts, not the rears. It was rewarding to find the car so well balanced (aside from 1.8 front and 2.2 rear camber, I run the stock front and rear sways with 265 and 345 R6's) and it showed me how much more it has in reserve if I can learn to tap into those reserves.

Bob Rouleau

The OP said SC off. On my car I have found that traction control is VERY intrusive. It works the rear brake pads hard and on my home track destabilizes the car. I am fairly sure your smoking rear brakes are the result of TC. If you are smooth on throttle application you should not need TC. Sadly there is no way to leave SC on and have TC off that I know of so I turn everything off. My rear pads wear at the same rate as the fronts . Pagid RS 29.

TRAKCAR

I have to agree. I am on my second set of Toyo's. Yes the rear breakes get very hot, more so then in MKI, I think due to more rubber and more downforce. A better LSD will help I think, getting one this week, we will see.

I run the same sizes as OP, not problem at all. I run with SC and TC off and the rear bads wear maybe 10% then the front, but almost the same.

911SLOW

Bob maybe it's time to put back the ceramics..

997gt3north

As everyone found out with the 997.1, it is extremely likely that the 997.2 also needs to have TC in the off position if you care about your rear pads. Theses cars are so balanced and the engine is perfectly linear so TC is not needed. In the off position your brain will pick up the rear moving and you will adjust your right big toe accordingly.

SC and TC may allow you to go faster at the beginning point of a learning curve but ultimately hide the feedback the car is trying to give you and this will prevent further progress.

To the OP, the tire specs are within tolerance.

Does the 997.2 RS have the rear braking cooling ducts?

carrering

question, with both SC and TC on will they every use the rear brakes without flashing the yellow triangle?

I only see the flash when the car is momentarily airborne (thanks larry) or in the karussell on the ring. otherwise it would take a an autocross for it to flash and feel it attempting to control the rear. i haven't autocrossed this car yet, just the .1 GT3. pad wear seems to be fairly moderate in rear although still higher rate than the fronts. much less so than the .1 GT3. i was concerned about my rear pads being worn down earlier, but now with 10 track days they are still above 50%. only turned TC/SC off for skid pad work and few laps at Leipzig.

oh, and i can still get the car about as sideways as i dare on empty roads when playing around and still not see the light come on or feel it trying to save itself. maybe my tc/sc is broken?

Carrera GT

Yes.

Carrera GT

I don't have the "algorithms" in printed form, but from observation, I'd say SC and TC intervene at very low levels without the blinking light. Perhaps it's not until it actually takes power out of the engine that the light blinks -- or the but of most drivers detects the intervention.

As you note, driven properly, SC/TC will permit significant slip angles without intervention. The "engine drag" feature will also match rpm on downshifts and when I've made a rough downshift, well, I'm not studying the blinking light, but the feel is as if the rear is also being "managed" by SC or TC to keep everything orderly.

I was recently at Sears through the Carousel doing lurid sideways slides across the exit and my passenger had his eyes glued to the blinking light and reported that it never blinked once, but I could feel SC intervention from time to time -- this is one case where I "learned" how it responds to tightening the steering angle just a degree too much and it would respond by gently dabbing the inside rear brake just a tad. After several days at Sears, it's also apparent that when the track surface changes to offer significantly diminished grip (as it does through the double-apexes of T7) the SC/TC systems cannot adapt and assume things have gone wrong (imposing stricter limits and requiring a much more conservative line ... it seems smart enough to figure out a single or double apex line, but it won't allow the same deep trail that it would allow at other turns regardless of the pitch and camber of the track surface.)

sasportas

Soften your rear sway bar. Lower the pressures in the rear for the RA-1s so that hot they are 34-36 max.

va122

No. The RA-1s are designed to run closer to 40 PSI. I run mine at 38 confirmed with a pyrometer. You're sacrificing grip at those pressures.

Bob Rouleau

According to the last bulletin from Toyo the R888 should be run 32-35 hot which is a change from the high 30's low 40's they originally suggested. The RA1 is still high 30's as far as I know.