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Old 11-18-2015, 08:37 PM   #1
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Default Another thread on tire selection - on my!

Over the months I've read dozens of threads with tire comparisons, racking-and-stacking of the old best vs the new best, etc.

What I can't find is data on the following:

1) Selecting 205 (on 9s) vs 225 (on 9s) vs 245 (on 10s) for "A, B, or C" tracks. I assume it's a function of the car's power/wt, or maybe just overall power, and the average speed of said road course (think tight Thunderwest vs Buttonwillow)

2) Selecting the above in Hoosier A vs Hoosier R compound based on ambient and track temperatures

For this exercise, one may assume I am 'stuck' with my current engine build of ~150whp, but have unlimited mobility in wheel and tire size as well as tire selection with a goal of simply the fastest lap time, a la time trial, as I try to compete with my buddies that have 'faster' cars.
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Old 11-18-2015, 08:58 PM   #2
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Have you read this?

https://www.miataturbo.net/race-prep...hy-chat-76811/

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Originally Posted by Dunning Kruger Affect View Post
Notes: A 225/45R15 will be -.75 to -1 second faster than a 205.
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Old 11-18-2015, 09:58 PM   #3
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Read through the suggested thread but I think the ROUGH rule of thumb generally is....

205 = 7.5" - 8"rim

225 = 9" rim

235-245 = 10"

245+ = 11" rim

changing tyre sizes for different tracks is not normally done as most cars have an optimum grip level to suit chassis and power rather than track specific.....tyre pressures, alignment settings can vary track to track.

But whatever floats your boat
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Old 11-18-2015, 10:16 PM   #4
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Originally Posted by aidandj View Post
I have - it doesn't answer my specific questions. . .

Quote:
Originally Posted by mx5-kiwi View Post
Read through the suggested thread but I think the ROUGH rule of thumb generally is....

205 = 7.5" - 8"rim

225 = 9" rim

235-245 = 10"

245+ = 11" rim

changing tyre sizes for different tracks is not normally done as most cars have an optimum grip level to suit chassis and power rather than track specific.....tyre pressures, alignment settings can vary track to track.

But whatever floats your boat
I have 8, 9, and 10" wheels with tires ranging in size from 205 - 245. I'm still looking for results based on experience, as I understand and follow the logic on tire sizing relative to wheel widths. Thanks!
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Old 11-19-2015, 03:27 AM   #5
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On small, tighter tracks tire width is king (yes, Buttonwillow fits into this category too). On faster road courses or ovals (Willow Springs, Auto Club Speedway) drag begins to be a factor that may limit the ideal tire width.
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Old 11-19-2015, 04:14 AM   #6
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Fastest single lap in a 150whp car with no regard for cost = 225/45 Hoosier A7. On some tighter tracks, the 245/40 might be faster.

Width is selected by the emphasis a track puts on aero vs. grip balance. Most tracks trend towards grip. The only way to know for sure is to A/B test the two tires.

As are virtually always faster in a single-lap format. They will overheat and go off in warm/hot weather after multiple laps, so for a long run (30min event), the R may be a superior choice. This is affected by chassis weight more than anything else, since a light car on 245s will keep an A7 under the car much longer than a heavy car on a 205 or a 225.
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Old 11-19-2015, 12:16 PM   #7
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Quote:
Originally Posted by ThePass View Post
On small, tighter tracks tire width is king (yes, Buttonwillow fits into this category too). On faster road courses or ovals (Willow Springs, Auto Club Speedway) drag begins to be a factor that may limit the ideal tire width.
I follow - thank you.

Quote:
Originally Posted by Savington View Post
Fastest single lap in a 150whp car with no regard for cost = 225/45 Hoosier A7. On some tighter tracks, the 245/40 might be faster.

Width is selected by the emphasis a track puts on aero vs. grip balance. Most tracks trend towards grip. The only way to know for sure is to A/B test the two tires.

As are virtually always faster in a single-lap format. They will overheat and go off in warm/hot weather after multiple laps, so for a long run (30min event), the R may be a superior choice. This is affected by chassis weight more than anything else, since a light car on 245s will keep an A7 under the car much longer than a heavy car on a 205 or a 225.
I am working on some A/B testing once I get the car all settled with new suspension. Is "170whp" (dynopack? dynojet?) still the approximate threshold for when the 245 is faster on 'all' tracks, in your experience/opinion? I've read anywhere from 170-200whp, but I don't know if that's on a dream dyno like the one in SoCal, a pack, or a jet. My car makes ~10% more power at T-hill's dyno than where I dyno here. And two 'exact' dynos here on the same day with the same inputs gave a 3% delta as well. FUN!
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