Street tires vs R888, 5PIPs?

[bsclywilly]

There has been alot of debate as to whether the current crop of street tires is nearing the performance of R-compounds, specifically the Toyo's which seem to be the tire of choice for most Solosprint competitors. Wes was greatful enough to lend his R888 for me to try during the last timed session. The idea of this comparison is to determine whether the 5 pip difference between street tires and non-premium R's is justified. Originally I wanted Wes to put some comparison laps using my streets since he has been the most vocal on the issue but he declined so instead I used my last timed session to put a few laps on his R888.

The comparison test was during event #8 on SMP Long. I'll layout the data that I collected and then add my comments after. As you may know I've competed this whole season on Bridgestone RE-11. Prior to this tire, I have done about 10 lapping days using the Bridgestone RE-01R street tire since 2007. Prior to that tire, I've also done a couple lapping days on Falken Azenis 615. My experience with r-compounds has been limited to Hoosiers and Hankooks during autocross only and a handful of laps in the ATR 4 door with R888 last year on SMP Long. I've attended 3 lapping events on SMP Long prior to our competition last Sunday.

My car is the black Honda Civic hatchback in GT2 class. My camber is set to -1.8f/-2.0r and toe is zero all around. With the RE-11 they typically lose grip past 180F. Pressures, camber and toe are set with the aid of a pyrometer. The alignment was set just minutes before the morning lapping session because I had to swap out a steering knuckle and hub from the day before.

Currently the tire pips are separated by 5PIPs or one class. Our linear classification system seperates each class by about 1.2% in lap time. Between GT2 and GT1 that should result in a 0.77s difference in lap time per 60 second lap. On SMP Long where I was lapping at 123.20s, ideally 5 pips would reduce my lap times by 1.55s.
Data is collected with an AIM XG Log data acquisition unit. Wheel speed was calibrated with GPS on RE-11 and the unit has internal accellerometers. The change in diameter of the R888 was accounted for by normalizing the lap distance.

To calculate theoretical best lap, 6 sectors were used. The sectors were chosen to minimize the interactions between corners and placed at the beginning of braking zones.


...Street Tires RE-11... 205/50-15 on 8" wide rim +35
Tire Condition - Evenly worn with 4-5/32nds measured anywhere

Morning Lapping, 3 hot laps
Morning Timed sessions, 6 hot laps

20C Ambient temp at 11am

Hot Pressures
Front 38 38
Rear 34 34

Tire Temps - as viewed from above
Left Front (153 166 174) (158 154 131) Right Front
Left Rear (123 131 131) (125 123 112) Right Rear

Laptimes from best session (s):
1. 123.204
2. 123.349
3. 123.985
Average 123.513
Best Rolling Lap: 122.888
Theoretical Best: 122.372

Peak lateral acceleration (g):
1. 1.64
2. 1.55
3. 1.74

Top Speed (kph):
1. 163.0
2. 161.7
3. 163.0

...R888...225/50-15 on 7" wide rim

Tire condition - Fronts (LF in particular) worn heavily in centre, eyeballed tread depth of 0-2/32nds. Rear evenly worn eyeball 3/32nds.

Skipped 3rd session
Total laps, 3 hot laps

24C Ambient temp at 3:45pm

Cold pressures set 25f/30r

Hot Pressures
Front 34 32
Rear 35 33

Tire Temps
Front (170 164 194) (177 171 159)
Rear (140 138 142) (135 134 135)

Laptimes (s):
1. 122.203
2. 122.244
3. 122.505
Average 122.317s
Best Rolling Lap: 121.841
Theoretical Best: 120.845

Peak lateral acceleration (g):
1. 1.70
2. 1.81
3. 1.77

Top Speed (kph):
1. 162.1
2. 161.7
3. 162.7

Impressions on my BS RE-11 tires are that it usually takes about 1/2 lap to bring them up to temperature. This is judged by how much tendency the car has to oversteer since the rears on the FWD car take longer to heat up. It's quite tail happy on the first few turns. Overheating the front tires is an issue and it's been made more apparent when looking at lap times. Since Mosport, Jon and I have consistently set our fastest laps on the first hot lap and generally got slower and slower. I did not notice this in events earlier in the year. Feedback is generally good and audible when you've gone beyond it's limits but grip doesnt drop off too sharply with increased steering angle. The Toyos were noticable grippier as I cautiously began my warmup lap since I didn't know what to expect. They seemed very easy to get used to and sliding the car was not a problem and I was confortable pushing my braking points further. Steering feedback seemed more sensitive where you knew what the right steering angle for peak grip was rather than the vague sensation that you might just be scrubbing the tires sideways. The balance of the car was the main thing I took notice to since Miles had mentioned to me to keep in mind just before I went out. It was essentially the same with generally less understeer but a lot of oversteer in a few specific corners. In T2 and the carousel, there was noticably more oversteer. In T2 it was nice to get the car rotated and on the throttle early but through the carousel, not as comfortable as you're trying to lineup the exit onto the straight before the fast left in the middle of the track. From my few laps, i'd say the R888 can handle the temperatures on a FWD car much better resulting in a more balanced ride for longer. Ideally, I would have wanted to go out and set a few laps on the R888, come in and check temperatures and adjust pressures accordingly, then go and set some hot laps. Unfortunately that wasn't going to happen since we were doing this during the timed sessions. Wes chose which corner each tire would go on, I think based on the treadwear. Unfortunately the cold pressures were all over the place now since the front and rears got swapped. Wes suggested 31psi all around and I guessed that 25f/30r semi-cold pressures would do. Looking at the tire temps and pressures after coming in hot was a bit confusing because the centres were cold on the left tires (most important temps, since CW track) even though the pressures were up. I suspect this was due to the uneven wear of the tires, since the centres were cupped they weren't generating as much heat. It's hard to say what hot pressures to run since the tire wear was irregular but I would have guessed that 35psi alla round would have done the trick. Instead, i was lapping on tires with pressures up and down a few psi. So in the end if you compare my fastest laps on each tire the difference ended up being only 1.00s. If that is the best possible time using the R888, the difference would equate to about 3.2PIPs not the 5PIPs as current. But, if you consider that my car's setup and alignment has been fine tuned for the street tires and the limited number of laps I had on the R888, then you must ask, if I had time to setup the car with a good set of Toyos and equal number of laps would I have gained another 0.55s? I think it'd be pretty close. Track temps were higher in the afternoon with the R888 and when the lap times are published you can see whether people were running faster or slower, generally. If you look at my theoretical best lap, the difference becomes 1.53s, not too bad, eh? Then consider that the theoretical best for street tires was based on 9 laps and only 3 laps on the R888.

Peak lateral g's occured in the two right turns following the Fabi straight. R888 had on average 7% higher peak lateral g's but that's probably not a very good indicator compared to average g's in a specific corner. Those of you with GPS loggers may look at those peaks and say they're awfully high. They're actual g's not GPS derived garbage.

Another point to make. The top speeds on the straights are still very similar. Before this year I hadn't heard people talking about the difference in rolling drag between r-compounds and street tires. I always thought that if there was a difference it'd be very small or negligible. It could be argued that the corner exit speeds were higher with the r-comps (and they were by about 4.5kph through the hairpin) but even so, if the exit speeds were the same, the difference in trap speed would be much less than the initial speed difference. So, small difference but not negligible.

[wrxr176]

Wow very informative great job Will

[nissannx]

Incredible information.
Something else to throw into the equation - how many heat cycles have the R888s been through. You indicated that one was very worn and other's evenly worn. My experience with the R888s last year was that they were faster when new versus at the end of the season. Just another twist to consider in the debate.
Keep up the great analysis. Thanks Will. Thanks for donating the tires, Wes.

[MazdaMatt]

Just to toss another little tidbit in here... sorry if this is a wrench to your agenda... The solosprint pip schedule is based on optimisation. R888's, although popular are not optimal. The R888s are comparible to RA1's (opinions vary to the better and worse) and I have used both RA1 and Kumho Ecsta V70A's (also a non-uber). The V70A's were literally scary the first time i used them because they were so incredibly grippy over RA1's.

I appreciate your incredible review of the tires, but you must remember you were using a non-optimized setup to make a case regarding a point system that expects optimization.

That aside, when I'm back in the game, i'll likely be using toyos.

[bsclywilly]

I am biased towards street tires so that helps my argument, Matt. Thanks! Maybe my unbiased tone threw you off?

I think more people should run on streets. They are safer since cornering speeds are reduced, they can help drivers improve because the limits are easier to reach, there are so many more choices, and they can handle many many heat cycles. Cheaper in the long run.

I've recommended that the CCC (of which I'm also a member) also include tires of treadwear 140 and up to give us more choices. That treadwear cutoff limit is also used by the SCCA, NASA and the most popular TA series.

[ShaneG]

Will, with both you and Jon using your car/ tires, can you estimate how much life is left in them? both in terms of treadwear and competitive life.

I noticed Riaan's tires *appeared* to be toast ( I don't know how manu events he has done)

I love the RA-1s, I can run big slip angles and still feel completely in control, but not knowing if they'll be available in the future and the questions around the 888s maks eme wonder what else is available.

if I can get more events on streets at a decent (cheaper overall) price....I'll run the cheaper option. so we may get the trailer queen on streets

[bsclywilly]

Tread depth was between 4-5/32nds. New, they're listed as 9/32nds. So about 50% tread left. That's for 2 drivers in the solosprint series and about 6 other lapping events this year. Oh and daily driving, but that's only about 5000kms.

Performance is pretty steady, and even improving with more wear. I think with street rubber the compounds are more stable so heat cycles don't affect them as much. But as the tread wears more, the tire temps go down since the tread is squirming less and that can benefit heavy axles like on FWD. I don't think i'm ready to show up with shaved street tires just yet but there could be some improvement there.

The first event at DDT I ran my RE-01R that were 3 years old and about 50% tread left. Cornering g's were the same as previous year.

With Riaans tires, I think because there is so little void (grooves) that with wear, they get filled in and it appears the tire has worn alot when it hasn't really.

[thgear]

Excellent Will.

[ShaneG]

Thanks Will.

[Cap'n Pete]

Wow, that took a lot of time to put together in such an easy to read and understand explanation ... good work!! Thanks!

Interesting to see "proof" that the R-comp's do in fact warrant the 5 PIPs. Now you need to do the same with a set of ubers .

[bsclywilly]

After one season.

[RRRex]

Great info Will! Thanks for sharing. Your car was setup to run the street tires and so is the bulk of your experience this season is on street tires. I believe your lap times are pretty close to being maximized with your street tires since your theoretical times are pretty close to your actual. But when you put the R-comps on the theoretical time is further apart from your actual. I'm thinking there's still likely some time to be made up by optimizing your alignment and tire pressures. Also with seat time comes confidence so some more time to be gained in the corners. I also think there's a good amount of time to be saved in the braking zones. Would've been nice to see what Wes could've done on streets. Awesome data.

[RRRex]

Oh, and I think R comps are safer than streets since they brake better, corner more consistently and respond better than a street tire does. Ubbers however are a different story. I find them greasy cold, don't communicate well in the braking zones but carry more grip through a corner. But when they go off they're done. I've gone from going hot and grippy to greasy in 2 laps. Unless you've got the seat time to know what's happening, a less experienced driver could easily find themselves in a hairy situation. IMO a low hp car with R-comps is the safest solo setup.

[Cap'n Pete]

Has anyone heard anymore word about whether Toyo is going to bring back the RA1 abroad, or just to some of the Spec series in the States?? If they bring them back and make them widely available, I can see MANY people running them again. Heck, I might even run them! (and yet I love my sticky-for-awhile Hoosiers ).

[nissannx]

Originally Posted by bsclywilly

After one season.

Hmmmm! I'll have to post up some pictures of my Hankook and Hoosier ubers - I've gone through a set of each this season (obviously both Katie and myself driving). One set of street tires is absolutely cheaper.

My goal this season was to push the car and driver to the limit. I think we've done that so it was worth the expense.