Noel

As many of you know, I am a huge proponent of using street tires for my DE endeavors for numerous reasons. Last weekend I was at Mid-Ohio driving a friend's '81 SC with a 3.6L engine and street brake pads and street tires.

This got me thinking about how much time I could actually cut by switching to a set of R compound tires. I've heard people say that they are good for 3-6 seconds a lap. Since the last time I used R compound tires was about 6 years ago, I have lost touch with the comparison.

Using my fastest lap time as an example of 1:48.3 using the above car (Dry track sunny and 65 degrees), anyone have any idea how much time I could theoretically expect cut simply by switching to R compound tires?

chrisp

Not to highjack this but I would be interested if people could share comparisons between different DOT-R tires (Hoosier vs. MPSC vs. RA-1). At tracks that size I have heard that within the class of DOT-R's there could be a 2-3 sec spread.

Veloce Raptor

Too much else here is variable to quantify differences in seconds:

-suspension type & set-up
-driving style
-weather
-track conditions
-etc.

Van

Running Hoosier R6s give me over a 1 second improvement at Lime Rock, over the Michelin PSCs -- that's about a 2% improvement.

tdf360

All things being equal, R-comps should be about 1.5-2 sec/min quicker than a good street tire, with race slicks having about the same gap over R-comps. That will vary of course depending on the track.

Gary

Bryan Watts

Too many variables...what kind of street tires? what kind of R-comps? "FAST" street tires are almost as fast if not faster than some of the slow R-comps these days. There are seconds of difference between a slow R-comp and a fast R-comp on some cars and some tracks. Alignment, spring rates, etc, etc all play into it as well. Some race tires require that you refine the setup to really get the most out of them, and a car setup to be fast on street tires might not necessarily see the full benefits of simply bolting on R-comps.

Need more details before anyone could even start to compare.

Noel

Good points guys. I should have mentioned that the tires I used were Potenza S-03s, which I suppose are considered to be on the sticky side of a street tire, but hard enough that they scream the entire way around the track.

Bryan Watts

The screaming is a result of the tread...R-comps like the older Victoracers and Toyo's with full tread make noise too.

joseph mitro

in my experience, i didn't measure lap times on street tires, but i can say that switching from Hankook Z211s to Hoosier R3S05s dropped my lap times about 1.5 seconds on a 1.8 mile track. same suspension setup and roughly the same track conditions. i was carrying a little more weight (50+ lbs) with the hoosiers too

sjanes

it also depends on driving ability. If you can't drive your existing tire to it's limits, then a "faster" tire may not be faster. If all of your tires are "screaming" around the track (not just the fronts), then you will see a difference by moving to an R, but how much of a difference depends on how close to the limit of the new tire you can get.

Vampire

Another variable: New Hoosiers are 1-2 seconds faster than old (many heat cycles) Hoosiers.

Chris M.

How would you define driving a tire to it's limits?

RonCT

Not sure how to define a feeling... When the streets start making noise, they still are quite a distance from maxing out - the tread blocks are vibrating letting you know they are working hard. When you are right on the verge of all 4 tires slipping at the same rate - on the knife's edge - then I'd say you are at their limit. Any less and you are leaving grip on the table. Any more and you are losing grip to slip...

The PS2s are capable of 1.51 g cornering and 1.42 braking in my otherwise bone stock 997s. That was just my 3rd day with a Porsche, but I sense that I was either at or very near their limits. A fellow 997s driver with PSCs and suspension work (control arms for more camber, full race pads) showed 1.82 g lateral but only 1.38 g braking (curious that). So that gives you an idea of lateral grip differences between PS2 and PSC (1.51 vs. 1.82), though some of that might be camber...

JackOlsen

Other people have said it, but I'll repeat: Tires are made with different rubber compounds. Some are harder, some are softer. There is no mysterious "R" molecule in the R-compound rubber. It just means that it's a softer rubber compound. Good "street" tires can be quicker than some R-compounds. A lot depends on the characteristics of the car, but I'm quicker on BFGoodrich g-force T/A KDs (a street tire) than I am on Yokohama A032Rs (a now-discontinued R-compound).

There might be a 6-second difference between a crummy performance street tire and Hoosiers, even with proper suspension settings for both. But it's a stretch. S03s to RA1s would probably be a 1-3 second gap, tops. Both scream, under the right circumstances.

Forgiveness, feedback and finances are the three good reasons to use street tires for as much driving as you can. I've only recently (after 7 years of tracking my car) switched over to more-or-less full time use of RA1s.

If you're racing, it's a different game.

sjanes

I would define a tire being at it's limit when there is a slight (4-5 degrees) slip during cornering, with the tires mildly squealing, but not howling. If the driver had the tires "howling" and is sliding wide of apexes, that is not being at the limit, but over it and is not a sign you need R tires, but instead an indicator the driver needs to learn how to read the feedback the car/tire is giving them.