245/45-17 VS 275/40-17 on 9" for Open Track - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 14 Old 07-07-2017, 07:35 PM Thread Starter
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245/45-17 VS 275/40-17 on 9" for Open Track

I am setting up a 2003 GT that will be for HPDE (only real street time it will see is to and from the track). I am looking at tires and in my search I see that there are some drivers that are using 275/40 on 9" rims for open track. I am curious about this. With the added section width, isn't there a substantial amount of side wall roll introduced?
The 245/45 section width is 9.65
The 275/40 section width is 10.83

That is a lot of cushion for the rim to roll on.

I will be running a 9" square set up.

Hopefully, one of you experienced open track guys can educate me a little.

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post #2 of 14 Old 07-07-2017, 07:54 PM
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Look at the tires recommended wheel width. That will tell you all you need to know.

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post #3 of 14 Old 07-07-2017, 08:40 PM Thread Starter
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How so?
For example, Nitto NT01
245/45ZR17 7.5 (8.0) 9.0
275/40ZR17 9.0 (9.5) 11.0

All this tells me is that they will fit. It does not tell me anything about how they will perform. My question is regarding the fact that you are mounting a tire with a very wide section width on the low end of the recommend rim size. I see that people are doing this for track applications. Doesn't the extra width over the side wall make the tire feel a little rollie pollie?

Like I said in my first post, maybe someone with experience can educate me on this.
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post #4 of 14 Old 07-07-2017, 10:07 PM
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Fraser (MFE) can probably be the best example of how 255/40/17's on a 9" wheel front & back can perform. He runs Maxxis RC1's on his car, and 275 RWHP with him behind the wheel seems to be all he needs.

Last edited by xps2; 07-07-2017 at 10:08 PM. Reason: Tire size
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post #5 of 14 Old 07-07-2017, 11:06 PM Thread Starter
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That size would make a lot more sense. It brings the sidewall down about 0.3" and adds just about 0.5" width. I would expect that to be a little firmer in cornering. The RC1 are really something. Price is decent too.
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post #6 of 14 Old 07-08-2017, 12:54 AM
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Not to overcomplicate things but it does depend a little on the brand of tire or the actual width. A Hoosier is wider than most other tires so it probably doesn't make much sense to use a 275 Hoosier on a 9" rim.
I've heard several people at the track say they've tried 255 and 275's on a 9" rim and their times were nearly identical.
I race in a class where 255 is the max so I use a 9.5" rim and I'm pleased with the performance but that's just an opinion I know.
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post #7 of 14 Old 07-08-2017, 08:19 AM
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As a general rule, mounting any given size tire on rims at the narrow end of the range results in turn-in response that's slightly 'softer', and steering precision that isn't quite as good as with widths out toward the wide end of the rim width range. Some people will notice this more than others, and I'm sure that there are some who'd never notice it at all.

Not trying to spend too much of your money, but I do have to wonder why you'd start out picking wheels as narrow as 9" for a dedicated track toy where there are no class rules limiting this dimension like there is in autocrossing. Unless 17" tires are easier to find than 18's, why not something like 18x10's instead, which would take 275/35's (or possibly 285/35's) still keeping to about the same OD as the 245/45-17 OE tires but with less sidewall height and cornering flexibility?


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Mine: '08 GT, 5MT, black/light graphite, un-Fstock (DD, occasional track day)
Wife's: '10 Legacy 2.5GT (DD, six-speed manual)
Spare:'01 20AE Maxima, 5MT (also my bad weather alternate)
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post #8 of 14 Old 07-08-2017, 09:21 AM
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255's if possible

-Mitch
68 Firebird, 428 Pontiac, CNC'd KRE Al d-ports, hyd roller, Mass-Flo EFI with EEC IV, 100mm MAF, 42#, TKO600 5-speed, TCI Eng subframe and Torque arm rear susp, Ridetech coil overs, Kore3 C6 Z06 brake kit, C6 dual mode mufflers
Roebling Road Raceway, NASA HPDE https://youtu.be/DPp1l9-FuNE
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post #9 of 14 Old 07-08-2017, 10:51 AM Thread Starter
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Quote:
Originally Posted by Norm Peterson View Post
I do have to wonder why you'd start out picking wheels as narrow as 9" for a dedicated track toy where there are no class rules limiting this dimension like there is in autocrossing.
Good question! I bought two cars. One had been stuffed into a wall at Laguna Seca. The owner had just spent a small fortune on suspension, gearing, seats, harnesses etc. It has new 9x17 95 cobra replicas. The second car I bought came with 9x17 Saleen replicas. I would like to use what I have to save a little money. Although I have been eyeballing the 9.5x18 2000 Cobra R wheels from AM. But those along with tires will put me out about $1500. I can just get the tires for about $800'ish.
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post #10 of 14 Old 07-09-2017, 07:10 AM
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That does change the game plan a bit . . . sorry to hear it involved somebody else's misfortune.


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Mine: '08 GT, 5MT, black/light graphite, un-Fstock (DD, occasional track day)
Wife's: '10 Legacy 2.5GT (DD, six-speed manual)
Spare:'01 20AE Maxima, 5MT (also my bad weather alternate)
Various Loose Parts: '79 Malibu
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post #11 of 14 Old 07-09-2017, 02:45 PM Thread Starter
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The driver is fine. He was wearing a full harness and HANS. He is going to move on to a spec Miata.
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post #12 of 14 Old 07-11-2017, 03:25 PM
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Quote:
Originally Posted by SilverGT1 View Post
Good question! I bought two cars. One had been stuffed into a wall at Laguna Seca. The owner had just spent a small fortune on suspension, gearing, seats, harnesses etc. It has new 9x17 95 cobra replicas. The second car I bought came with 9x17 Saleen replicas. I would like to use what I have to save a little money. Although I have been eyeballing the 9.5x18 2000 Cobra R wheels from AM. But those along with tires will put me out about $1500. I can just get the tires for about $800'ish.
I would encourage you to stay away from cheap Chinese wheels as I have cracked 7 and had one completely brake off the car causing lots of damage and I was on street tires and not R comps.The stuff from AM and most replicas is that junk I am referring to.

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post #13 of 14 Old 07-11-2017, 04:33 PM Thread Starter
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HOLY SMOKES! What brands are still made in the good ol' USA or are ones that can be depended on?
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post #14 of 14 Old 07-12-2017, 07:53 AM
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I got some Enkei RP-F1s in 17x9.5. Good price, strong and lost 9 lbs of rotational weight off of each corner.

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