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Thoughts on tire size for autocross.

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Old 3/11/18, 06:13 PM   #1  
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Talking Thoughts on tire size for autocross.

Iíve been running my 2016 V6 convertible in FStreet with 245/40-17 Hankook RS 3ís for the past few years (before you laugh too much, I finished 4th overall in our club series out of 80 competitors).

So, 245 isnít quite enough tire for such a heavy car on turns requiring sharper steering input but being restricted to the stock wheel width (7 1/2Ē on the 17ís), will going to a 255 be too wide for the rim? The reason for the 17ís is to improve acceleration. The lower profile works better on tighter courses and lowers the car by about an inch 1/2 over the 18íS.

Any thoughts on how a 255/40-17 would fit the wheel? Will there be too much rollover? Are Koni yellows worth the money?
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Old 3/11/18, 06:39 PM   #2  
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Recommended rim width for 255 40 17 Hankook's is 8.5 to 10". I wouldn't try them on a 7.7" wide wheel.
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Old 3/11/18, 06:54 PM   #3  
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They'll 'fit', but they'll not work worth a dang. Charts show a minimum rim width is 8" straight up. Which means they're likely to pop off the rim in a hard turn because they're too narrow at the beads (hence their minimum of 8" for 255), but even if they don't, that rollover is going to be hell. You're going to want 18x8 or 18x9 to get the wider treads to work. You might even consider having a race set and a show/go set of wheels/tires. Unless you can find some 17x8 or x9 rims to fit your budget, of course, with the right offset, then you'd be golden.

Have you considered maybe using a different tire? I mean, I'm no expert in compounds and tires and all that, just sizing issues (and even then, I'm just a postulator) but certainly different compounds/treads/sidewalls can make a difference. I'm sure you're all in on the Hankooks, but... all I know is the Cooper RS3-As were better tires on my old 17x8 rims than any of the tires I've tried on the 18x9.5s I run now.

I miss those Coopers...

Anyway, perhaps the Cooper RS3-S or the Michelin Super Sports or... well, I don't know, just maybe it's the tire makeup.

I can't say about the Koni yellows. Heard the oranges are iffy because of the change in manufacturing venue. That said I have oranges and I think they're ok, but I don't need adjustin', just stop the bouncin'.

For what any of that there is worth.
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Old 3/11/18, 08:06 PM   #4  
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As mentioned, I’m kind of stuck on the wheel size by running in Street. The decision to go to Hankook was originally made due to wear considerations. Bridgestone are probably stickier but wear faster. I’m thinking the way to go is stay with the 245’s and add the Konis hoping for better turn in. Hankooks are so much cheaper it’s hard to pony up for Rivals or RE71’s.
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Old 3/11/18, 08:11 PM   #5  
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You are already pushing it on a 7.5" wide wheel with the 245's. If they are working for you I would stay with them and look elsewhere to gain an advantage within the class rules.
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Old 3/12/18, 10:25 AM   #6  
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I wold keep the size but switch compound. 255 is waaay too much for 7.5 rims. Roll over will definitely be a problem.

If you can go with difference compound it will give you much more grip than extra 10mm or rubber.

And yes, Koni Yellows are worth the money. Along with a adjustable front sway bar and camber plates made a huge difference. I can sustain 1.1g
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Old 4/9/18, 10:15 AM   #7  
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Dear London,


Heh, figure since I have a lot of DNA from the British Isles in me I should step forward and give you the easiest answer......get a set of Bridgestone RE71Rs or a set of BFG G Force Rivals 1.5. Have been Autocrossing on and off for 37 years ( helped start the Salina Region of the SCCA here in the US ) and just happen to live about 60 miles from where the Solo Nationals are held in Lincoln , Nebraska. Almost to a fault, if you did not have one of the two tires listed above , at Nationals , you were just a participant. The Hankooks are notorious for not warming up quickly when cool ( hmm, sounds like normal weather in Jolly Olde England) and I can vouch for that, as I ran them for one Season. Great when it was super warm , but not on par the rest of the time, whereas the Bridgestone is the acknowledged King of Street Autocross Tires over the past few years -- and looks like it will stay that way. Good luck and both tires come in the size you are currently using. BFG seems to be a bit more durable for the folks who Autocross but also do some circuit time trials or High Performance Driving Events.

Last edited by Fastoldman; 4/9/18 at 10:41 AM.
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