Geo question for those ever running Hoosiers or slicks on ACR

[stradman]

Hi guys, I've decided that I will run slicks on the circuit and have purchased some Forgelines for this. A question I have is with respect to the geometry settings and wonder if you have changed your settings for the slicks on track compared to the settings we were told to use on the Kumhos by SRT?

[Arizona Vipers]

Hi guys, I've decided that I will run slicks on the circuit and have purchased some Forgelines for this. A question I have is with respect to the geometry settings and wonder if you have changed your settings for the slicks on track compared to the settings we were told to use on the Kumhos by SRT?

What do you mean by "settings"? Alignment?

[FrankBarba]

Are you talking real slicks or hoosier type tires that have an R rating? Goodyear makes slicks, Hoosier might be not make slicks for our sizes, you can check Michelins they Make Slicks also.

[stradman]

I'm talking about going to slicks. Do you find you need to run different camber toe rake etc than the srt track settings for the Kumhos?

[GTS Dean]

Every tire has it's own cord, belt and shoulder/sidewall construction that give them their own personality. This is especially true of race tires. The compound of the tire and the inflation pressure/temperature will have a major impact on the loads input to the chassis. This will in turn put the suspension into different parts of the camber and toe curves. Copious notes and lots of track time will be your best guide.

[Arizona Vipers]

I'm talking about going to slicks. Do you find you need to run different camber toe rake etc than the srt track settings for the Kumhos?

You are going to have to play around to find out what you like, but can't go wrong with the ACR factory suggestions. The widths vary so much from the Hoosiers to the Pirelli's to the Michelin's (for example the Michelin is only a 310 rear) so you might want to play around with camber etc. Tire temps tell the tale. It's taken me years to finally figure out what I like.

[RedTanRT/10]

Stradman, beyond alignment specs you are (might) be changing ride height. A Hoosier 345/35/18 is 26.8" tall. The factory Kumho's are 27.5"

[stradman]

Stradman, beyond alignment specs you are (might) be changing ride height. A Hoosier 345/35/18 is 26.8" tall. The factory Kumho's are 27.5"

Thanks. But I am keeping 19's at the back

[Arizona Vipers]

Thanks. But I am keeping 19's at the back

Does Pirelli make a 705-19? Does Michelin make a 71-19? If not you are stuck with Hoosiers R7 or A7's as Hoosier slicks sizes won't work.

[13COBRA]

+1

Arizona knows what he's talking about.

[XSnake]

Does Pirelli make a 705-19? Does Michelin make a 71-19? If not you are stuck with Hoosiers R7 or A7's as Hoosier slicks sizes won't work.

Yes to both. 705/305/19 and 31/71/19. Hoosier also make R80's and R100's in 19s last I knew but I have not run them in a long time.

[stradman]

Yes to both. 705/305/19 and 31/71/19. Hoosier also make R80's and R100's in 19s last I knew but I have not run them in a long time.

Yes. Both Michelin and Pirelli make 19s as mentioned

[IHOP]

+1

Arizona knows what he's talking about.

+2 his help with tires and tire pressures has been priceless!

[Arizona Vipers]

Yes. Both Michelin and Pirelli make 19s as mentioned

The one advantage I see running a 19" rear is they will warm up faster. The 18's (which I run) have a HUGE sidewall and hold a LOT of air so they warm up slower than the fronts. I always give a quick burnout in first gear right when i pit out so that the front and rears get to temps at the same time. What have you been running so far, just the Kumhos?

[stradman]

The one advantage I see running a 19" rear is they will warm up faster. The 18's (which I run) have a HUGE sidewall and hold a LOT of air so they warm up slower than the fronts. I always give a quick burnout in first gear right when i pit out so that the front and rears get to temps at the same time. What have you been running so far, just the Kumhos?

Understood. Yeah just been running Kumhos up to now but time to step up onto slicks what with the 9.0 and other mods on car. So what camber are you running with the Michelin 's?

[Arizona Vipers]

Understood. Yeah just been running Kumhos up to now but time to step up onto slicks what with the 9.0 and other mods on car. So what camber are you running with the Michelin 's?

For me nothing is faster than an A7. Even after it starts to drop off at the end of a session, it's still as fast as a Michelin or Pirelli, but it lasts nowhere as long. I've got 7 track records with NasaProRacing.com and most were set on A7's and I haven't been able to beat those times trying many times with Pirelli's and Michelin's. The Pirelli's are extremely expensive so I switched to the Michelin's. Hard to say which is faster but the Pirelli's are extremely light. 44 lbs a set lighter than Hoosiers. Michelins are 16 lbs heavier than the Pirelli's.

[Arizona Vipers]

Understood. Yeah just been running Kumhos up to now but time to step up onto slicks what with the 9.0 and other mods on car. So what camber are you running with the Michelin 's?

For me nothing is faster than an A7. Even after it starts to drop off at the end of a session, it's still as fast as a Michelin or Pirelli, (and much faster first 1-3 laps) but it lasts nowhere as long. I've got 7 track records with NasaProRacing.com and most were set on A7's and I haven't been able to beat those times trying many times with Pirelli's and Michelin's. The Pirelli's are extremely expensive so I switched to the Michelin's. Hard to say which is faster but the Pirelli's are extremely light. 44 lbs a set lighter than Hoosiers. Michelins are 16 lbs heavier than the Pirelli's.

[stradman]

For me nothing is faster than an A7. Even after it starts to drop off at the end of a session, it's still as fast as a Michelin or Pirelli, but it lasts nowhere as long. I've got 7 track records with NasaProRacing.com and most were set on A7's and I haven't been able to beat those times trying many times with Pirelli's and Michelin's. The Pirelli's are extremely expensive so I switched to the Michelin's. Hard to say which is faster but the Pirelli's are extremely light. 44 lbs a set lighter than Hoosiers. Michelins are 16 lbs heavier than the Pirelli's.

Big difference in times between A7 and michelin/pirellis?

[Arizona Vipers]

Big difference in times between A7 and michelin/pirellis?

first few laps yeah big difference, then the slicks will start to catch up, maybe even pull ahead at the end of a 15/20 minute session

[FrankBarba]

i must be half retarded. To me when someone asks about slicks I think no DOT tire such as the Hoosiers A7, or R's
I think more on the lines of the Goodyear G 19 Eagle or the Michelin 27/65-R18 S9L, or the Hoosier (43678) 25.5X14.0R16 TA RC
These are slicks.

[stradman]

i must be half retarded. To me when someone asks about slicks I think no DOT tire such as the Hoosiers A7, or R's
I think more on the lines of the Goodyear G 19 Eagle or the Michelin 27/65-R18 S9L, or the Hoosier (43678) 25.5X14.0R16 TA RC
These are slicks.

That's true I guess. And over here in Europe Hoosiers are not as easy to get so I was always going to go down the route of slicks ie Michelin or Pirellis DH

[Darius]

For me nothing is faster than an A7. Even after it starts to drop off at the end of a session, it's still as fast as a Michelin or Pirelli, (and much faster first 1-3 laps) but it lasts nowhere as long. I've got 7 track records with NasaProRacing.com and most were set on A7's and I haven't been able to beat those times trying many times with Pirelli's and Michelin's. The Pirelli's are extremely expensive so I switched to the Michelin's. Hard to say which is faster but the Pirelli's are extremely light. 44 lbs a set lighter than Hoosiers. Michelins are 16 lbs heavier than the Pirelli's.

I thought the A7's were pretty damn good also. You think they are just as fast? That's pretty crazy to think knowing the Michelins were that much lighter.

[ek1]

Guys,

Somewhat unrelated, but I have been considering switching to 18" rims for the past year. During my last outing at VIR I smacked a curb so hard with the inside of my front wheel, that the rim flexed enough to allow the caliper hit the rim and leave an imprint (see pic). Strangely both the rim and tire are fine (I was running stock rims, 295/30/19 Hoosier R7 in the front) except some curb rash. I am trying to guess what would happen if I was running 18" wheels with super small clearances between the rim and the caliper, and I don't think it would have been good.

I think I'll just keep running 19" stock rims for now. Just ordered a pair of 345/30/19 Hoosier R7s for the rear. Because I mostly use the car for the track, I think I'll realign and corner balance the car for Hoosiers and will just run PSC2s for the street driving. Yes, my camber will be off but who cares, I drive around the speed limit outside of the racetrack anyway.34979

[Arizona Vipers]

I thought the A7's were pretty damn good also. You think they are just as fast? That's pretty crazy to think knowing the Michelins were that much lighter.

Yeah. Follow me back on Facebook so I can message you!

[ACR Steve]

So theoretically nothing should be faster then a real slick once its warmed up. I think the A7 is faster out of the box but after 2 laps a New Slick of medium compound should be considerably faster then an A7 . Key with a slick is to never let them heat up over 30psi. I start the race with 18lbs pressure and try and scrub them in on the warm up lap. It usually takes another 2 race laps to get them up to temp. Cost basis A7 are great though.

The issue is heat cycles as well. Slicks are only fast the first cycle maybe 2nd. After that they fall off considerably. A-7 seem to not fall off as fast . I run Pirelli med/hard on the race car because the class requires it but used to run the Michelin's when they were the sponsor. I hated those tires . After each heat cycle they would loose almost a second and then become almost not drivable

All around good tire for the money and doing HPDE its hard to beat an A7 - If you were racing however the slick would walk an A7

[stradman]

So theoretically nothing should be faster then a real slick once its warmed up. I think the A7 is faster out of the box but after 2 laps a New Slick of medium compound should be considerably faster then an A7 . Key with a slick is to never let them heat up over 30psi. I start the race with 18lbs pressure and try and scrub them in on the warm up lap. It usually takes another 2 race laps to get them up to temp. Cost basis A7 are great though.

The issue is heat cycles as well. Slicks are only fast the first cycle maybe 2nd. After that they fall off considerably. A-7 seem to not fall off as fast . I run Pirelli med/hard on the race car because the class requires it but used to run the Michelin's when they were the sponsor. I hated those tires . After each heat cycle they would loose almost a second and then become almost not drivable

All around good tire for the money and doing HPDE its hard to beat an A7 - If you were racing however the slick would walk an A7
Thanks for input Steve. I see with the Hoosier you guys are talking about the A7 and not the R7. I was under the impression the R7 was the better one for track purpose but I don't have any personal experience so maybe I'm wrong.

[ek1]

So theoretically nothing should be faster then a real slick once its warmed up. I think the A7 is faster out of the box but after 2 laps a New Slick of medium compound should be considerably faster then an A7 . Key with a slick is to never let them heat up over 30psi. I start the race with 18lbs pressure and try and scrub them in on the warm up lap. It usually takes another 2 race laps to get them up to temp. Cost basis A7 are great though.

The issue is heat cycles as well. Slicks are only fast the first cycle maybe 2nd. After that they fall off considerably. A-7 seem to not fall off as fast . I run Pirelli med/hard on the race car because the class requires it but used to run the Michelin's when they were the sponsor. I hated those tires . After each heat cycle they would loose almost a second and then become almost not drivable

All around good tire for the money and doing HPDE its hard to beat an A7 - If you were racing however the slick would walk an A7

Steve, what's your take on R7 vs A7? Most people I spoke to tend to like R7 for HPDE more - it performs more consistently over it's lifespan and lasts a bit longer.

[ACR Steve]

Hey guys - so hears the deal both tires are great ,both work so much better then a "R" compound street tire in that they have better grip and hold up on track. (yes they to are considered a street tire)
How ever they are not a real slick. They are an in-between tire and a great solution and a lot cheaper then a slick

So with that said -
R7- think endurance. Holds up for the longer track session. Wont fall off performance wise as fast when doing longer then 15-20 min sessions
I endurance raced with this tire . For HPDE you can get lots of heat cycles out of this tire. Another words you cant go wrong. 1-2 seconds faster then a typical "r" compound OEM street tire at a standard length track

A7- Think out of the box qualifying tire- originally for AutoX- Works great with just a little heat holds up great for 15 min stints- I have run 25-35 min Sprint races on this tire and they worked great . Maybe a little greasy towards the end of the race but very manageable. Will work great for HPDE 15-20 min on track just wont get as many heat cycles out of the tire. Maybe 25% less cycles before they are just heat cycled out. This tire as a sticker(brand new no heat cycle) is maybe half a second faster then a R7

Just remember these are Not slicks - a real Pirelli or Michelin slick will be about 1.5- 2 seconds a lap faster at most tracks then an R7 or A-7

[Racingswh]

One thing I will add is that I happen to like the gearing that comes along with a taller tire. The Hoosier's 345/35/18 I used in the past required a shift into 5th gear in the high 130's. Once in 5th it just does not have much more acceleration left. Common for me to see a 2-3 mph drop after the gear change and then slowly start to accelerate. The Michelin is a 31/71 so nearly 28" tall. I saw 146 mph in 4th gear with that tire. Makes a big difference to me anyway not having to shift to 5th in some places because the car pulls so much harder in 4th and shifting also wastes time.

Now I use a 31/71/18 Michelin or a 325/705/18 Pirelli (Both available in 19"s) in the rear and a 30/65/18 Michelin or a 305/645/18 Pirelli in the front. I don't think I will ever go back to Hoosiers on the Viper.

[ViperGeorge]

One thing I will add is that I happen to like the gearing that comes along with a taller tire. The Hoosier's 345/35/18 I used in the past required a shift into 5th gear in the high 130's. Once in 5th it just does not have much more acceleration left. Common for me to see a 2-3 mph drop after the gear change and then slowly start to accelerate. The Michelin is a 31/71 so nearly 28" tall. I saw 146 mph in 4th gear with that tire. Makes a big difference to me anyway not having to shift to 5th in some places because the car pulls so much harder in 4th and shifting also wastes time.

Now I use a 31/71/18 Michelin or a 325/705/18 Pirelli (Both available in 19"s) in the rear and a 30/65/18 Michelin or a 305/645/18 Pirelli in the front. I don't think I will ever go back to Hoosiers on the Viper.

Is there a speedometer error introduced by the taller tire? I would think it might underestimate your speed if I'm thinking about it correctly (1 rev of a bigger tire goes further).

[Arizona Vipers]

One thing I will add is that I happen to like the gearing that comes along with a taller tire. The Hoosier's 345/35/18 I used in the past required a shift into 5th gear in the high 130's. Once in 5th it just does not have much more acceleration left. Common for me to see a 2-3 mph drop after the gear change and then slowly start to accelerate. The Michelin is a 31/71 so nearly 28" tall. I saw 146 mph in 4th gear with that tire. Makes a big difference to me anyway not having to shift to 5th in some places because the car pulls so much harder in 4th and shifting also wastes time.

Now I use a 31/71/18 Michelin or a 325/705/18 Pirelli (Both available in 19"s) in the rear and a 30/65/18 Michelin or a 305/645/18 Pirelli in the front. I don't think I will ever go back to Hoosiers on the Viper.

Yeah the difference is pretty huge when you go to the tall tire. When I was at COTA for nationals and had to switch from slicks to A7's to stay in my class I couldn't believe how much everything changed. With the tall slicks I was in 2nd most of the track, with the Hoosiers I kept getting into third through the S's etc. With the slicks I can go 99mph on 2nd, with the Hoosiers it was like 92.

[Racingswh]

Is there a speedometer error introduced by the taller tire? I would think it might underestimate your speed if I'm thinking about it correctly (1 rev of a bigger tire goes further).

That's correct. The speedometer will read faster than you're actually traveling using a shorter tire and of course the opposite when using a taller tire than stock. I use the captured data to see my speeds. I am not sure I have ever looked at the speedometer.


Yeah the difference is pretty huge when you go to the tall tire. When I was at COTA for nationals and had to switch from slicks to A7's to stay in my class I couldn't believe how much everything changed. With the tall slicks I was in 2nd most of the track, with the Hoosiers I kept getting into third through the S's etc. With the slicks I can go 99mph on 2nd, with the Hoosiers it was like 92.

It's a big deal. I brushed it off when you told me how significant it was but when I went out and ran them back to back I know now an 18" Hoosier will never go back on the car unless I have some I am using up. Not tall enough with stock gearing for my liking.

[ek1]

One thing I will add is that I happen to like the gearing that comes along with a taller tire. The Hoosier's 345/35/18 I used in the past required a shift into 5th gear in the high 130's. Once in 5th it just does not have much more acceleration left. Common for me to see a 2-3 mph drop after the gear change and then slowly start to accelerate. The Michelin is a 31/71 so nearly 28" tall. I saw 146 mph in 4th gear with that tire. Makes a big difference to me anyway not having to shift to 5th in some places because the car pulls so much harder in 4th and shifting also wastes time.

Now I use a 31/71/18 Michelin or a 325/705/18 Pirelli (Both available in 19"s) in the rear and a 30/65/18 Michelin or a 305/645/18 Pirelli in the front. I don't think I will ever go back to Hoosiers on the Viper.

Would you say there is a tangible decrease in speeds produced by going to a 0.3" smaller tire? I switched from a stock Kumho (27.5" diameter) to a Michelin PSC2 (27.2" diameter) tire a while ago. I sort of had a feeling that my speeds were just a tad lower in the same gears, but could not put my finger on it.

[Racingswh]

Would you say there is a tangible decrease in speeds produced by going to a 0.3" smaller tire? I switched from a stock Kumho (27.5" diameter) to a Michelin PSC2 (27.2" diameter) tire a while ago. I sort of had a feeling that my speeds were just a tad lower in the same gears, but could not put my finger on it.

1.5 mph in 4th difference at 5000 rpm between those two diameters. Not enough to move the meter much at face value but it's certainly possible that you notice it. Many shift from engine tone and its possible since the engine reaches the same pitch at a marginally slower road speed you could perceive it to be slower in same gear definitely. There's also the possibility that advertised and actual height are farther apart than they they are on paper. That would result in a more noticeable change if the actual diameter spread is larger than advertised.