Widening Speedline 18x10.5 to 18x11.5 for front of C5Z
11-21-2009, 09:49 PM
#1
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Widening Speedline 18x10.5 to 18x11.5 for front of C5Z
Has anyone tried this for autocross to optimize the wheel for Hoosier 315-30/18?
Wheel widening is usually done at the expense of increased backspace. I plan to use a 1/2" spacer to maintain the same offset. In any case I am concerned about the rim rubbing the upper conrol arm at close to full lock in this configuration.
An alternative would be to widen the wheel by only 1/2 inch which would be acceptable for that tire size but not ideal. Using the same 1/2" spacer would pull the wheel out and not have the rim interfere with the upper control arm. What will this do to the Ackerman steering?
No widening is considered below the requirement of Hoosier 315-30/18. Is this safe? What will it do to the performance of the tire?
I would appreciate some input.
Thanks
Wheel widening is usually done at the expense of increased backspace. I plan to use a 1/2" spacer to maintain the same offset. In any case I am concerned about the rim rubbing the upper conrol arm at close to full lock in this configuration.
An alternative would be to widen the wheel by only 1/2 inch which would be acceptable for that tire size but not ideal. Using the same 1/2" spacer would pull the wheel out and not have the rim interfere with the upper control arm. What will this do to the Ackerman steering?
No widening is considered below the requirement of Hoosier 315-30/18. Is this safe? What will it do to the performance of the tire?
I would appreciate some input.
Thanks
11-21-2009, 11:26 PM
#2
Le Mans Master
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I ran a Hoosier R6 315/18 on a 10.5 wheel all last season with no issues at all. There are a bunch of guys that run a 315 square set up on 10.5 speedlines as well. I would just mount it...set agressive camber and run it.
11-22-2009, 02:13 AM
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I also seem to remember reading that some autocrossers use 315 x 4 on Speedline 18 x 10.5 but never actually saw it done.
Other tire manufacturers than Hoosier accept 10.5 rims for their 315 tires (Toyo, Kumho, Pyreli, Michelin etc). I think that Hoosier mainly want to protect their performance reputation by insisting on optimal rim size but their reps don't openly say so ... I talked to customer support at Hoosier and they go by the book.
Thanks for your encouragement.
M
Other tire manufacturers than Hoosier accept 10.5 rims for their 315 tires (Toyo, Kumho, Pyreli, Michelin etc). I think that Hoosier mainly want to protect their performance reputation by insisting on optimal rim size but their reps don't openly say so ... I talked to customer support at Hoosier and they go by the book.
Thanks for your encouragement.
M
11-22-2009, 04:42 PM
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11-23-2009, 05:19 AM
#6
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I only ran the 9.5" for one weekend. I couldn't tell a difference, but I got the 10.5" so it wasn't an issue. No problems with 10.5" and A6's or V710's. I usually run tire pessure 32-36lbs.
11-23-2009, 12:32 PM
#7
Burning Brakes
I run 11" rims on the front. If your car is lowered you will rub on the lower control arm at lock. I thought I had allowed enough room when I ordered my rims but I still had to use a 1/4" spacer. This put my tire outside of the wheel well. Fender flares are next since I will be running SCCA Solo this coming season.
I also had MSI install their drop spindle uprights to bring the control arms back to close to level. No rubbing now.
I also had MSI install their drop spindle uprights to bring the control arms back to close to level. No rubbing now.
11-23-2009, 10:48 PM
#8
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Spacers and wider wheels do not effect Ackerman. Ackerman is "Toe out in turns".
Spacers will effect scrub radius. I'd probably save my money and run the 305s on 10.5 rims on the front. IMO alot of your underssteer is caused by suspension geometry and spring rate not tire width.
Steve (steponc) has seen a huge leap in handling with our drop spindle uprights and coil overs, which do correct alot of the suspension geometry issues..
Spacers will effect scrub radius. I'd probably save my money and run the 305s on 10.5 rims on the front. IMO alot of your underssteer is caused by suspension geometry and spring rate not tire width.
Steve (steponc) has seen a huge leap in handling with our drop spindle uprights and coil overs, which do correct alot of the suspension geometry issues..