Coef of friction vs. contact patch
04-05-02, 11:55 AM
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Coef of friction vs. contact patch
Been thinking about new rims and tire combinations for track events. Can anyone opine on whether, for example, an FD with stock rims and say Toyo RA-1s (R-compound) would have better overall dry grip and performance on a track course (not autocross) than an FD with 17x8.5 (245s) & 17X10 (275s) with say SO3's or Michelin Pilots. Please assume all other car modifications (suspension and power) are the same. Would your answer change after the cars did 20 minutes of a lapping session?
Thanks for any input.
Thanks for any input.
04-05-02, 12:57 PM
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Ramon,
I've been down this path before...
Assuming the use of competition brake pads, and above average driving skills (A/B group driver ed student), the wider road tires would hang with the stock width Toyo RA-1 race compound tires, but the wider road tires would eventually exceed their optimum heat temp range, and you'll begin sliding the car...which does nothing but INCREASE your laptimes. Meanwhile the stock sized Toyo RA-1s will be operating within its optimum temp range since the tire was designed for competition use...
IME (In my experience) high performance road rubber, and track pads will be good for about 12 to 15 minutes of hotlapping, as fast as you can drive. After midway through the session, you'll notice the road tires will begin to go away, and width won't matter anymore, as traction has decreased. It's like losing traction in the wet, or snow...width doesn't matter when you've lost available traction! Tire width only matters when you're operating within the rubber compounds intended heat range.
Since you've been to Putnam Park before, I'll give you laptime comparisons in my lightly modded Rx7 R1. These laptimes were generated with no changes to my R1's horsepower.
8 x 16, 38-mm offset SSR Integral A2s and Brdgetone Expedia S-07 OR Pirelli P-Zero Asimmetric road tires, Hawk HP Plus or Carbotech Panthers--1:25 to 1:26
8.5 x 16, 37-mm offset Kosei K1 Racing wheel with 245/45-16 Hoosier Motorola Cup compound, Carbotech Panther Plus OR Porterfield R4 fronts and Carbotech Panther rears--1:23 to 1:24
8.5 x 17 front and 9.5 x 17, 42-mm offset, SSR Competitions with 245/45-17 and 275/40-17 Hoosier R3S03--Hawk Black fronts and Carbotech Panthers rear--1:20 to 1:22
I'm currently trying break into the 1:19s...I believe I can with larger '99 FD Rx7 Type RS brakes (fr/rr) and serious motorsports competition brake pads--Porterfield R4E, front and rear...
I'll know this during the 26/27/28 April, Central Indiana Region Porsche Club drivers education weekend at Putnam Park!
Anyhow, you can see that I'm up to 5 seconds faster with wider rubber AND sticky Hoosier tires!
SSR Integral A2s 8 x 16, 38-mm were 16 lbs. SSR Comps, 42-mm--8.5 x 17s are 15 lbs, and the 9.5 x 17s are 16 lbs. The Kosei K1 Racings in 8.5 x 16, 37-mm were 16 lbs each.
Tire weights? Both OE road tires were 23 lbs each. The Hoosier 245/45-16 were 18 lbs each. The Hoosier 245/45-17 and 275/40-17s were 20 and 21 lbs each, respectively.
If you do the math, the racing compound tires on track-only wheels were between 34 and 37 lbs, while the road tire/wheels were 39 lbs.
For comparison, my current road setup are 9 x 17, 45-mm SSR Integral A2s with 255/40-17 Yokohama AVS Intermediates. Wheel/tire weight is 45 lbs.
As an experiment to truly answer your post, I may run my road setup at the PCA event, with my current EBC Green Stuff pads to see if I can better 1:25/1:26 with wider contact patches of road rubber. Of course I'll have the larger '99 Type RS brakes, so that might be the factor if I end up turning faster laptimes...
Hope to see you sometime at the track, Ramon!
I've been down this path before...
Assuming the use of competition brake pads, and above average driving skills (A/B group driver ed student), the wider road tires would hang with the stock width Toyo RA-1 race compound tires, but the wider road tires would eventually exceed their optimum heat temp range, and you'll begin sliding the car...which does nothing but INCREASE your laptimes. Meanwhile the stock sized Toyo RA-1s will be operating within its optimum temp range since the tire was designed for competition use...
IME (In my experience) high performance road rubber, and track pads will be good for about 12 to 15 minutes of hotlapping, as fast as you can drive. After midway through the session, you'll notice the road tires will begin to go away, and width won't matter anymore, as traction has decreased. It's like losing traction in the wet, or snow...width doesn't matter when you've lost available traction! Tire width only matters when you're operating within the rubber compounds intended heat range.
Since you've been to Putnam Park before, I'll give you laptime comparisons in my lightly modded Rx7 R1. These laptimes were generated with no changes to my R1's horsepower.
8 x 16, 38-mm offset SSR Integral A2s and Brdgetone Expedia S-07 OR Pirelli P-Zero Asimmetric road tires, Hawk HP Plus or Carbotech Panthers--1:25 to 1:26
8.5 x 16, 37-mm offset Kosei K1 Racing wheel with 245/45-16 Hoosier Motorola Cup compound, Carbotech Panther Plus OR Porterfield R4 fronts and Carbotech Panther rears--1:23 to 1:24
8.5 x 17 front and 9.5 x 17, 42-mm offset, SSR Competitions with 245/45-17 and 275/40-17 Hoosier R3S03--Hawk Black fronts and Carbotech Panthers rear--1:20 to 1:22
I'm currently trying break into the 1:19s...I believe I can with larger '99 FD Rx7 Type RS brakes (fr/rr) and serious motorsports competition brake pads--Porterfield R4E, front and rear...
I'll know this during the 26/27/28 April, Central Indiana Region Porsche Club drivers education weekend at Putnam Park!
Anyhow, you can see that I'm up to 5 seconds faster with wider rubber AND sticky Hoosier tires!
SSR Integral A2s 8 x 16, 38-mm were 16 lbs. SSR Comps, 42-mm--8.5 x 17s are 15 lbs, and the 9.5 x 17s are 16 lbs. The Kosei K1 Racings in 8.5 x 16, 37-mm were 16 lbs each.
Tire weights? Both OE road tires were 23 lbs each. The Hoosier 245/45-16 were 18 lbs each. The Hoosier 245/45-17 and 275/40-17s were 20 and 21 lbs each, respectively.
If you do the math, the racing compound tires on track-only wheels were between 34 and 37 lbs, while the road tire/wheels were 39 lbs.
For comparison, my current road setup are 9 x 17, 45-mm SSR Integral A2s with 255/40-17 Yokohama AVS Intermediates. Wheel/tire weight is 45 lbs.
As an experiment to truly answer your post, I may run my road setup at the PCA event, with my current EBC Green Stuff pads to see if I can better 1:25/1:26 with wider contact patches of road rubber. Of course I'll have the larger '99 Type RS brakes, so that might be the factor if I end up turning faster laptimes...
Hope to see you sometime at the track, Ramon!
Last edited by SleepR1; 04-05-02 at 01:13 PM.
04-05-02, 03:55 PM
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FWIW, I'd go with the 9 x 17 SSR Integral A2 wheels in 45-mm offsets, and 255/40-17 Kumho V700 Victoracers (if on a budget), or the 255/40-17 Michelin Pilot Sport Cup Competition R-compound tires. I think both the Kumho and the Michelin R-compound tires are usable on the public roads. Hoosiers are NOT intended for public road use, as they're easily damaged by road debris due to the Hoosier's lightweight fiberglass/nylon/rayon construction.
The Pilot Sport Cup Comp race compound tires will be almost as much as the SSR IA2s ($289 each for each SSR, and $247 for each Michelin).
http://www.tirerack.com/tires/michel..._sport_cup.jsp
If I had to compromise (no trailer) that's what I'd do...BTW buy a set of 5 wheels/tires...the set of four to drive on, and the 5th to serve as a full-sized spare...this works very well if you happen to run over something and puncture one of your R-compound race tires...your whole weekend isn't blown then
Another tire to consider is the P-Zero C or the Corsas...Tire Rack will be carrying these in the near future...
The Pilot Sport Cup Comp race compound tires will be almost as much as the SSR IA2s ($289 each for each SSR, and $247 for each Michelin).
http://www.tirerack.com/tires/michel..._sport_cup.jsp
If I had to compromise (no trailer) that's what I'd do...BTW buy a set of 5 wheels/tires...the set of four to drive on, and the 5th to serve as a full-sized spare...this works very well if you happen to run over something and puncture one of your R-compound race tires...your whole weekend isn't blown then
Another tire to consider is the P-Zero C or the Corsas...Tire Rack will be carrying these in the near future...
Last edited by SleepR1; 04-05-02 at 08:22 PM.
04-05-02, 07:33 PM
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Manny thanks for the edifying response. I knew I could count on you.
So essentially you are saying that a wide DOT tire will keep up with the smaller R-compound tire for a few laps, but the performance of the DOT/street tire will fall off dramatically and the R-tire will last a bit longer. I guess that's what I experienced with my old SO2s. They would become "greasy" after a few laps. I wonder how is it that Rick Potter at MADS last fall was able to easily keep up and even surpass others in his driving section (I believe he was an instructor) with street tires. I asked him this particular question and he merely stated that he had been doing track events for 20 years. At the time I thought it was a good enough answer.
Right now I have no problem running my RA-1s on the street but I always get real nervous when it rains. So, I've been thinking about going back to the SO2/SO3s. Another option for me would be to keep my rims and change my tires (Belle Tire or something) right before the track event.
I guess I need to decide whether 2-3 seconds is really worth it. At Putnam park how many car lengths is 2-3 seconds? My goal is to put Fikse 17x10s all around--I think I have room b/c of the coilovers.
Incidentally, I hope to be back at Putnam this year. I was hoping you were going to have a "Friday night at the track" event on May 3, which is the day before One Lap of America begins their journey at Indianapolis. Last year I got to see them at MIS. It was awesome to see all the different cars.
Ramon
So essentially you are saying that a wide DOT tire will keep up with the smaller R-compound tire for a few laps, but the performance of the DOT/street tire will fall off dramatically and the R-tire will last a bit longer. I guess that's what I experienced with my old SO2s. They would become "greasy" after a few laps. I wonder how is it that Rick Potter at MADS last fall was able to easily keep up and even surpass others in his driving section (I believe he was an instructor) with street tires. I asked him this particular question and he merely stated that he had been doing track events for 20 years. At the time I thought it was a good enough answer.
Right now I have no problem running my RA-1s on the street but I always get real nervous when it rains. So, I've been thinking about going back to the SO2/SO3s. Another option for me would be to keep my rims and change my tires (Belle Tire or something) right before the track event.
I guess I need to decide whether 2-3 seconds is really worth it. At Putnam park how many car lengths is 2-3 seconds? My goal is to put Fikse 17x10s all around--I think I have room b/c of the coilovers.
Incidentally, I hope to be back at Putnam this year. I was hoping you were going to have a "Friday night at the track" event on May 3, which is the day before One Lap of America begins their journey at Indianapolis. Last year I got to see them at MIS. It was awesome to see all the different cars.
Ramon
04-05-02, 08:54 PM
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Yeah, Rick was turning 1:20s on Michelin Pilot SXes at the 1999 PSD Putnam Park school, so I truly believe driving skill weighs heavily into that equation!
Well two to three seconds per lap is quite a bit faster. Over a 25-minute session the guy your chasing that's turning 2 to 3 seconds faster would disappear from your view by the end of the session.
FWIW, the Toyo RA-1s were designed as rain tires. That's why they come 8/32nds tread depth. Toyo recommends you shave their RA-1s down to 4/32nds for dry track performance. Incidentally, Rick Potter probably has his Michelins shaved for track events...(I don't know though...are they allowed to shave tires for the One Lap?).
Speaking of skill Greg Stasiowski has the same kind of driving skills. I watch him run with A group and instructor cars shod with Hoosiers, while he's tearing things up with nearly bald Michelin Pilots at Mid Ohio!!!
BTW, I would run 9.5 x 17 with 50.4-mm offset all the way around for the Fikses. The 10 x 17 with 44-mm offsets will rub on the front fender lips (guaranteed!), especially if you planned to run 275/40-17s (which I wouldn't recommend as they're too tall in DOT road rubber guise). If you're planning to stay with road rubber, go with 255/40-17s on the 9.5 x 17 Fikses (preferably the Mach Vs because they're SO SWEET!). The 255/40-17 tire size is ~25-inches on overall diameter, and shouldn't pose a rubbing problem up front. If I had the money to do Fikses, that's what I'd do! Tire choice would be simple--BFG G-Force KD. They're the stickiest dry performance road tires available. Yeah they're pricey ($249 each), but with a 200 UTQG, they're bound to last at least an entire season!
For comparison's sake, I had brand new sticker Hoosiers during my Dec 15 '01 Putnam Park test session. After my MDC Putnam event 2 weekends ago, I'll get through the CIR PCA Putnam Park DE in 2 weeks. By my MOR PCA Mid Ohio DE (May 9/10), and I'll need to flip the Hoosiers on the wheels to maximize tire wear. The flipped Hoosiers should get me through my Mid Ohio DE event, the June Gingerman PCA DE. By August I'll need new Hoosiers ($850 for the set!) to finish my MDC events at Putnam Park through August and September, and to do Road America with the Badger Bimmers in October!
With that schedule you could do an entire season on ONE set of BFG G-Force KDs!
Well two to three seconds per lap is quite a bit faster. Over a 25-minute session the guy your chasing that's turning 2 to 3 seconds faster would disappear from your view by the end of the session.
FWIW, the Toyo RA-1s were designed as rain tires. That's why they come 8/32nds tread depth. Toyo recommends you shave their RA-1s down to 4/32nds for dry track performance. Incidentally, Rick Potter probably has his Michelins shaved for track events...(I don't know though...are they allowed to shave tires for the One Lap?).
Speaking of skill Greg Stasiowski has the same kind of driving skills. I watch him run with A group and instructor cars shod with Hoosiers, while he's tearing things up with nearly bald Michelin Pilots at Mid Ohio!!!
BTW, I would run 9.5 x 17 with 50.4-mm offset all the way around for the Fikses. The 10 x 17 with 44-mm offsets will rub on the front fender lips (guaranteed!), especially if you planned to run 275/40-17s (which I wouldn't recommend as they're too tall in DOT road rubber guise). If you're planning to stay with road rubber, go with 255/40-17s on the 9.5 x 17 Fikses (preferably the Mach Vs because they're SO SWEET!). The 255/40-17 tire size is ~25-inches on overall diameter, and shouldn't pose a rubbing problem up front. If I had the money to do Fikses, that's what I'd do! Tire choice would be simple--BFG G-Force KD. They're the stickiest dry performance road tires available. Yeah they're pricey ($249 each), but with a 200 UTQG, they're bound to last at least an entire season!
For comparison's sake, I had brand new sticker Hoosiers during my Dec 15 '01 Putnam Park test session. After my MDC Putnam event 2 weekends ago, I'll get through the CIR PCA Putnam Park DE in 2 weeks. By my MOR PCA Mid Ohio DE (May 9/10), and I'll need to flip the Hoosiers on the wheels to maximize tire wear. The flipped Hoosiers should get me through my Mid Ohio DE event, the June Gingerman PCA DE. By August I'll need new Hoosiers ($850 for the set!) to finish my MDC events at Putnam Park through August and September, and to do Road America with the Badger Bimmers in October!
With that schedule you could do an entire season on ONE set of BFG G-Force KDs!
Last edited by SleepR1; 04-05-02 at 08:59 PM.
04-06-02, 04:37 AM
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OR...if you like the Toyo RA-1s, you can get them in 255/40-17 from Vilven Tire, Royal IL. The 255/40-17 sells for $180 each. This includes shaving AND shipping! Give Vilven Tire a call at 1-888-775-8646
04-06-02, 05:13 AM
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Of course there's nothing wrong with using DOT road tires for track lapping events. I did that for four years...from 1997 to 2000. In a sense, it's actually better that I did that, since I learned car-control skills by figuring out how to drive the car sliding through all the turns...it was alot of fun too!
When you see Rick Potter or Greg Stasiowski turning laps that Hoosier tire-shod racers are turning, I tend to think that I'm not driving to the DOT road tire's absolute limits either...
I'm looking forward to trying out my 255/40-17 Yokohama AVS Intermediates-shod on my 9 x 17 SSR Integral A2 wheels in a couple of weeks at Putnam Park. Who knows...I might like the feel, and the setup might be "fast enough". If that's the case I'd convert my SSR Comps to road wheel/tire status, and run my SSR Integral A2s with Yokohamas for track lapping events during the motorsports season...wouldn't need a trailer THEN
On a sheer cost basis...replacing a set of 255/40-17 AVS Intermediates once per year is a hell of lot cheaper than getting two sets of Hoosier R3S03s per season.
Let's do the math. $515 per set of FIVE Yokohama AVS I's (currently $103 each at the Tire Rack)--I run a full size spare plus the four I drive on, and I rotate IN the spare during the course of the season--OR--$1700 for two sets of 245/45-17 and 275/40-17 Hoosier R3S03s.
I begin to wonder myself, whether the 5-seconds (or maybe just 3 seconds with the new road setup) is worth the nearly $1200-premium to run DOT "cheater slicks"!!
When you see Rick Potter or Greg Stasiowski turning laps that Hoosier tire-shod racers are turning, I tend to think that I'm not driving to the DOT road tire's absolute limits either...
I'm looking forward to trying out my 255/40-17 Yokohama AVS Intermediates-shod on my 9 x 17 SSR Integral A2 wheels in a couple of weeks at Putnam Park. Who knows...I might like the feel, and the setup might be "fast enough". If that's the case I'd convert my SSR Comps to road wheel/tire status, and run my SSR Integral A2s with Yokohamas for track lapping events during the motorsports season...wouldn't need a trailer THEN
On a sheer cost basis...replacing a set of 255/40-17 AVS Intermediates once per year is a hell of lot cheaper than getting two sets of Hoosier R3S03s per season.
Let's do the math. $515 per set of FIVE Yokohama AVS I's (currently $103 each at the Tire Rack)--I run a full size spare plus the four I drive on, and I rotate IN the spare during the course of the season--OR--$1700 for two sets of 245/45-17 and 275/40-17 Hoosier R3S03s.
I begin to wonder myself, whether the 5-seconds (or maybe just 3 seconds with the new road setup) is worth the nearly $1200-premium to run DOT "cheater slicks"!!
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