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Old 01-19-2021, 04:54 PM   #1
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Autocross tire fitting assistance

I'm thinking trying to go big with tires sizes this autocross season and am looking for fitment confirmation. I'd like to run Nankang AR-1s but the rear size may be a bit problematic.

My Boxster is a stock setup with

front:
-2.2deg camber,
8.5" OZ's, ET53 (may push out with 3 or 5mm spacers)
255/35/18

rear:
-2.5deg camber,
10" OZ's ET40
295/30/18

I'm not worried about the fronts but am a bit with 295s.

Anyone had luck with something similar?

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Old 01-19-2021, 05:24 PM   #2
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Uh, how do you get -2.2 deg front camber with a stock setup????

Adjustable LCAs and /or camber plates are needed and neither of them are part of a stock setup
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Last edited by JayG; 01-19-2021 at 05:27 PM.
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Old 01-20-2021, 10:57 AM   #3
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Go 275 with an actual 200 rated tire of your choice. RT660 is doing well from what I’ve seen or go re71. I think the grip of the tires will pay off vs trying to get a 295 back there.
Two cents
Shawn
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Old 01-20-2021, 07:12 PM   #4
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Quote:
Originally Posted by JayG View Post
Uh, how do you get -2.2 deg front camber with a stock setup????

Adjustable LCAs and /or camber plates are needed and neither of them are part of a stock setup
GT3 adjustable LCAs in the front. Springs, shocks, & sways are stock
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Last edited by BrantyB; 01-20-2021 at 07:16 PM.
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Old 01-20-2021, 07:14 PM   #5
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Quote:
Originally Posted by Sveach756 View Post
Go 275 with an actual 200 rated tire of your choice. RT660 is doing well from what I’ve seen or go re71. I think the grip of the tires will pay off vs trying to get a 295 back there.
Two cents
Shawn
I've been using RE71s. I'd like to up the ante to Nankang AR-1s (100tw) - big grip. Not available in 285, and I'd like a bit more stagger with 255s in the front than 275s.
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Last edited by BrantyB; 01-20-2021 at 07:17 PM.
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Old 01-21-2021, 07:10 AM   #6
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I've found that 225/45 front & 255/40 rear Bridgestone RE71Rs on stock 17"x 7" fronts and 17"x 8.5" rear wheels is the fastest. I've also run Toyo R888R's on wider 18" OZ wheels but that resulted in slower track and autocross times (and a little fender rub). My '98 Boxster is stock with the exception of font adjustable LCA's. I think the lower HP car just doesn't like turning the larger/fatter wheels and tires.
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Old 01-22-2021, 03:56 PM   #7
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Interesting. I've never found to have "too much tire". I've autocrossed an NB Miata on 245s and still wanted more!

Quote:
Originally Posted by lawren View Post
I've found that 225/45 front & 255/40 rear Bridgestone RE71Rs on stock 17"x 7" fronts and 17"x 8.5" rear wheels is the fastest. I've also run Toyo R888R's on wider 18" OZ wheels but that resulted in slower track and autocross times (and a little fender rub). My '98 Boxster is stock with the exception of font adjustable LCA's. I think the lower HP car just doesn't like turning the larger/fatter wheels and tires.
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- PCA Zone 7: 2018, 2019 P14, & 2020 P02 Champion; 2020 1st Overall PAX
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Old 01-23-2021, 05:11 PM   #8
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Be careful with the stagger, this is the primary source of understeer in our cars. When I ditched the stock continental 205s for 225s it made all the difference in the world.

What is your ride height? If you're lower than usa stock specs i don't know how you'd get all that tire back there without going ultra low profile.

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Old 01-24-2021, 07:26 AM   #9
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I've been using stock size Re71 on 8" front & 9" rear OZs for the last couple years - 225 front 265 rear. That stagger is about 85% front to rear; 255/295 is 86%. That's why I like those proportions as it shouldn't change the understeer/oversteer characteristics. 255/35/18 front is 0.24% smaller circumference that stock and 295/30/18 is 1.3% less - shouldn't interfere height-wise.

The issue is more clearance from suspension components - particularly spring perches.




Quote:
Originally Posted by ike84 View Post
Be careful with the stagger, this is the primary source of understeer in our cars. When I ditched the stock continental 205s for 225s it made all the difference in the world.

What is your ride height? If you're lower than usa stock specs i don't know how you'd get all that tire back there without going ultra low profile.

Sent from my POCOPHONE F1 using Tapatalk

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- PCA Zone 7: 2018, 2019 P14, & 2020 P02 Champion; 2020 1st Overall PAX
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