Track Wheel & Tire Advise needed

[devildog1679]

I decided on NT05's for $204 in 275/35 18 or GY F1 SC for $158 in 285/40 18. Which should I go with?

 

[Napoleon85]

Those Nitto 275/35r18 will be very short. I'm running the 275/40R18 and they're still almost and inch shorter than stock.

 

[devildog1679]

Those Nitto 275/35r18 will be very short. I'm running the 275/40R18 and they're still almost and inch shorter than stock.

Yea, they'll be 25.63" vs. the stock 27". Other than changing my gearing what issues are there?

 

[Norm Peterson]

Depends a bit on your usage.

At autocross you'll very likely need to be shifting between 2nd and 3rd (where you'd really rather not have to make more than the one shift into 2nd). Out on a road course, you'll definitely be needing at least 5th. On a track with a longer straight, maybe even 6th.

That does assume that you still have 3.73's in the axle.


Norm

 

[Gray Ghost GT]

+1 for the 275/35-18 tires on OEM 18x9.5 GT500 wheels (front and rear)

 

[Vorshlag-Fair]

Yea, the 27" tall OEM tire heights really screw with your choices for "bigger" tires for track or autocross use. We played with this a LOT in STX/STU autocrossing, track events on street tires, and still fight with tire heights with 315mm+ R-compound race tires. The choices pretty much suck for 27" tall "race" or track worthy tires.

When we were limited to a 9" wide wheel we went with a 265/35/18 Hankook RS-3 but found the that 265/40/18 version of the same tire was a LOT more driveable... because it was taller, it had better overall gearing (a tick less torque to the tires) and stretched 2nd gear out a good bit more.

Stock Mustang GT Brembo car's 255/40/19 (left, 27" tall) next to a 285/30/18 Hoosier (right, 24.8" tall!)

When we left the class that had that tire/wheel limitation I went to a Kumho V710 R-comp in 315/35/18. It is a FREAK tire (literally nobody else makes race tires in this size!) and it works SO WELL on an 11-12" wheel for an S197. It is 26.7'' tall and the only thing remotely close to OEM tire heights.

Tire calculator: http://www.rimsntires.com/specs.jsp

Then we went to a Hoosier and the only thing they had was a 315/30/18 Hoosier A6, and it is a LOT shorter. This thing is 25.5" tall and looks silly on the car, and it lowers the speed limits ion 4th and 5th gear. At a track event this past weekend (NASA TT3 at TWS) I topped out 5th gear with my 3.31 rear ratio car, so the 3.55 or 3.73 gear would have been a MESS.

Running on 25.5" tall Hoosier A6 in 315/30/18 = short!

Gearing calculator: http://users.erols.com/dmapes/GEARCLC.HTM

5th gear is 1:1, I was running a 25.5" tall tire, 3.31 rear, and at 7000 rpm it tops out at only 160 mph! Weak. The .65 ratio 6th is too tall to use on any road course with anything like 600 whp or less. Mega-Over-Drive.

Running on 25.5" tall Hoosier A6 in 315/30/18 = short!

Change that to the 26.7" Tall 315/35/18 and it tops out at 168mph.

You know, that still sucks... for a faster track like VIR it would top out long before you ran out of track. I've gotta get rid of this PoS Getrag and get a real T56 Magnum into this car, which was a more usable 0.74:1 ratio in 5th gear (and an even better, optional .80 5th). After we blew up 3rd gear on the stock MT-82 Getrag 2 weeks ago, and with these weird speed limitations, I think we've exceeded the limits of this transmission... we are already working with Tremec to install a T56 Magnum retrofit kit into a 2011+ 5.0 car.

Cheers,

 

[zquez]

Probably overkill, but you should look into the T-56 out of the Boss 302R. Its got some nice gear ratios. I doubt the price difference is worth it though...


http://rehagenracingproducts.com/2010-Ford-Mustang-Boss302R1-Transmission-T56-6-Speed-M-7003-BOSSR1.htm

 

[HushH]

I decided on NT05's for $204 in 275/35 18 or GY F1 SC for $158 in 285/40 18. Which should I go with?

Wow, wish I'd known those Goodyears were at that price a few weeks ago.

 

[devildog1679]

Depends a bit on your usage.

At autocross you'll very likely need to be shifting between 2nd and 3rd (where you'd really rather not have to make more than the one shift into 2nd). Out on a road course, you'll definitely be needing at least 5th. On a track with a longer straight, maybe even 6th.

That does assume that you still have 3.73's in the axle.


Norm

At Road America my current skill level wont see 6th.

 

[devildog1679]

Yea, the 27" tall OEM tire heights really screw with your choices for "bigger" tires for track or autocross use. We played with this a LOT in STX/STU autocrossing, track events on street tires, and still fight with tire heights with 315mm+ R-compound race tires. The choices pretty much suck for 27" tall "race" or track worthy tires.

When we were limited to a 9" wide wheel we went with a 265/35/18 Hankook RS-3 but found the that 265/40/18 version of the same tire was a LOT more driveable... because it was taller, it had better overall gearing (a tick less torque to the tires) and stretched 2nd gear out a good bit more.

Stock Mustang GT Brembo car's 255/40/19 (left, 27" tall) next to a 285/30/18 Hoosier (right, 24.8" tall!)

When we left the class that had that tire/wheel limitation I went to a Kumho V710 R-comp in 315/35/18. It is a FREAK tire (literally nobody else makes race tires in this size!) and it works SO WELL on an 11-12" wheel for an S197. It is 26.7'' tall and the only thing remotely close to OEM tire heights.

Tire calculator: http://www.rimsntires.com/specs.jsp

Then we went to a Hoosier and the only thing they had was a 315/30/18 Hoosier A6, and it is a LOT shorter. This thing is 25.5" tall and looks silly on the car, and it lowers the speed limits ion 4th and 5th gear. At a track event this past weekend (NASA TT3 at TWS) I topped out 5th gear with my 3.31 rear ratio car, so the 3.55 or 3.73 gear would have been a MESS.

Running on 25.5" tall Hoosier A6 in 315/30/18 = short!

Gearing calculator: http://users.erols.com/dmapes/GEARCLC.HTM

5th gear is 1:1, I was running a 25.5" tall tire, 3.31 rear, and at 7000 rpm it tops out at only 160 mph! Weak. The .65 ratio 6th is too tall to use on any road course with anything like 600 whp or less. Mega-Over-Drive.

Running on 25.5" tall Hoosier A6 in 315/30/18 = short!

Change that to the 26.7" Tall 315/35/18 and it tops out at 168mph.

You know, that still sucks... for a faster track like VIR it would top out long before you ran out of track. I've gotta get rid of this PoS Getrag and get a real T56 Magnum into this car, which was a more usable 0.74:1 ratio in 5th gear (and an even better, optional .80 5th). After we blew up 3rd gear on the stock MT-82 Getrag 2 weeks ago, and with these weird speed limitations, I think we've exceeded the limits of this transmission... we are already working with Tremec to install a T56 Magnum retrofit kit into a 2011+ 5.0 car.

Cheers,

Awsome info. What's the widest I can fit on 9.5" wheels still staying safe for track use?

 

[Napoleon85]

Awsome info. What's the widest I can fit on 9.5" wheels still staying safe for track use?

That's going to vary a bit from tire to tire. If you go look at the manufacturer specs they should list approved sizes for each tire they sell, I usually try to be in the middle of that range if possible. Being at the low end will have a tire that bulges and the high end will have a tire that's stretched at the sidewall.

 

[zquez]

That's going to vary a bit from tire to tire. If you go look at the manufacturer specs they should list approved sizes for each tire they sell, I usually try to be in the middle of that range if possible. Being at the low end will have a tire that bulges and the high end will have a tire that's stretched at the sidewall.

I think you have that backwards, but good gouge nonetheless. Tire manufacturer recommendations are the best and easiest way to determine what size tire you should get for your rim. I would venture to say though that a 285 will be the biggest you should go on a 9.5" wheel.

Sent from my DROID RAZR using Tapatalk 2

 

[Napoleon85]

I think you have that backwards, but good gouge nonetheless. Tire manufacturer recommendations are the best and easiest way to determine what size tire you should get for your rim. I would venture to say though that a 285 will be the biggest you should go on a 9.5" wheel.

Sent from my DROID RAZR using Tapatalk 2

I don't think so ... a narrow wheel will make the tire bulge where a wider wheel will make the tire stretch. Maybe I haven't had enough coffee, but I'm pretty sure that's right.

 

[zquez]

I don't think so ... a narrow wheel will make the tire bulge where a wider wheel will make the tire stretch. Maybe I haven't had enough coffee, but I'm pretty sure that's right.

I thought you were talking about tire sizes, not wheel sizes. Wheel sizes yes, but it would be opposite for tires. A narrow tire on a wide wheel will stretch, etc.

Sent from my DROID RAZR using Tapatalk 2

 

[Norm Peterson]

If crisp handling is part of what you're after, you want to be more toward the wide end of the range of recommended widths. IOW, a mild stretch relative to the "measuring width".

If you're more into the straight line stuff and don't care about handling feel, more toward the narrow end.

Stock category autocross tire vs wheel widths is an anomaly that's forced by restrictive rules.


Norm

 

[06underme]

I'm assuming that you meant 18 x 9.5. That's as narrow as I'd ever run 275-wide tires on and narrower than I'd run 285's on barring any wheel width limitations per class rule restriction or points penalty. But quite a few people have been running on 275-wide sizes. I'm on 18 x 9.5's with 255/45's that's a really good combination for general "3-season" street use although it gives away a bit in the occasional harder use.

An all-out effort would want still more wheel and more tire - see Terry Fair's "Vorshlag Mustang" thread and look toward the end where the car was refitted to ESP where the wheel width was not so limited.

FWIW, I'm starting to look at 18 x 10's and a little more tire for autocross and track time, just having a little trouble finding available tires in the 200 treadwear required by the organizers of certain events.


Norm

My last autox, this guy was in fstock with a highly moded 05-09 gt, said it was modded to a gt500 so he could be in f stock...yeah, whatever man....anyways, he had 8.5" rims running 295 slicks all the way around....that seemed pushing it to me.

 

[dontlifttoshift]

That is quite common for SCCA stock class racing. You are limited to a stock wheel width but are allowed to put any size tire on it you want. Hoosiers are more forgiving to the practice of "too wide a tire on too narrow of a rim".

It is also entirely possible that the car was upgraded to GT500 specs. There is a car up here that is upgraded to shelby specs to get all the good stuff on an otherwise mundane car.

 

[Whiskey11]

That is quite common for SCCA stock class racing. You are limited to a stock wheel width but are allowed to put any size tire on it you want. Hoosiers are more forgiving to the practice of "too wide a tire on too narrow of a rim".

It is also entirely possible that the car was upgraded to GT500 specs. There is a car up here that is upgraded to shelby specs to get all the good stuff on an otherwise mundane car.

I'm not sure he meant "Shelby" as in GT500 since the GT500 is an A-Stock car. I'm assuming he upgraded to the Shelby GT which is nothing more than a glorified California Special with the Ford Racing CAI, Ford Racing handling Pack and Shelby's signature.

Ok, that's an oversimplification... close enough!

 

[Norm Peterson]

My last autox, this guy was in fstock with a highly moded 05-09 gt, said it was modded to a gt500 so he could be in f stock...yeah, whatever man....anyways, he had 8.5" rims running 295 slicks all the way around....that seemed pushing it to me.

You'll see truly nutty combinations like that at autocross for the reason dontlift gave.

People can get away with it because you're only driving about half a mile at a time before giving the tires a chance to cool down a bit, under 5 miles total in a day, and you'll either heat-cycle the tires to the point of uselessness or cord them inside of 100 miles. IOW, long term cumulative effects of excessive sidewall flexing are virtually nonexistent.

Neither street nor big track driving should run on combinations anywhere that. Cantilever race slicks are a different story.


Norm

 

[devildog1679]

I went with Nitto NT05's in 275/35/18. I was really impressed, after 1 hour of track time tread depth is just shy of 6/32. They held up nicely and performed incredibly. Due to shorter OD, I was in 4th most of the time. Here is a video

http://www.youtube.com/watch?v=Jpgf-50RTEk