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Thread: Value performance analysis of 15x8 vs 15x9

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    RaceTape Ninja Force McCocken's Avatar
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    Default Value performance analysis of 15x8 vs 15x9

    I'm looking to move into a different set of wheels for my dual-use '92. I understand 205s square up on a 15x8, but I am wondering if a 15x9 would offer a better value in terms of optional sizing and performance? 205s on a 9" wide wheel would be a little stretch of the sidewalls, but is it a detriment to performance? If I wanted to try 225 or "plus" sized 205 tires, the 8" wheels introduce slip. Seeking some feedback or advice, thanks!
    Yer pal,
    Force

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    Senior Member fatbillybob's Avatar
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    look at the Hoosier tire chart for the A7/R7. You can run up to a 275x15 on 8" wheel. On the Hoosier chart there does not seem to be an advantage to a 9 x15 and a 205 on a 9 sounds wrong. You want the tire to be well supported on the wheel. If you run a spec tire for example see what the manufacturer recommends as a starting point. And a 8" should be lighter unsprung weight than a 9. Sometimes you cheat a little like in the old days of SCCA T1 we ran 315 square on 11" rears and 10" fronts because we did not see a fall off in laptimes despite the wrong sized front and it was easier to have 4 tires the same logistically. RyanC who used to be around here (held T1 track records in the day) was the lone T1 racer who ran smaller correct front tires at ACS because he found a slight advantage to doing so but no one else did.

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif emilio700's Avatar
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    One additional factor you may not have considered is NVH and utility. The wider tire/wheel option on the NA chassis will tramline, be harder to steer at low speeds as well as add NVH properties. This is the trade off for the significantly higher grip they provide.
    Our dailies at 949 tend to run 205's on 15x8 for that reason. Still plenty of grip but a better street solution. Also, the 225/45's are all 200tw so focused on grip at the expense of civility. In 205/50/15 you can fine some medium grip tires with much quieter treads, lower rolling resistance, longer life, etc.

    If grip is job one however, the choice is simple: 225/45/15 on 15x9.
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    RaceTape Ninja Force McCocken's Avatar
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    Excellent. Appreciate the feedback gentlemen!
    Yer pal,
    Force

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