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c5 and c6, 18" front wheel 17" rear wheel for autox/track?

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Old 03-19-2018, 03:12 PM
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froggy47
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Default c5 and c6, 18" front wheel 17" rear wheel for autox/track?
A guy has some ccw rims that are 18 front 17 rear. Tire fitment (side wall ratio) makes the stagger right . For sale.

1) Why do this?

2)Will 17" rear rim fit over oem c6z06 rear brakes. I don't know the offset. He has them on a c5 now.

I am getting c6z.

Thanks.

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Old 03-19-2018, 03:45 PM
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jaredtxrx
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Sounds like a drag racing set-up to me. 18" to fit he brakes, 17" in the rear for sidewall give and grip.
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Old 03-19-2018, 05:01 PM
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Originally Posted by jaredtxrx
Sounds like a drag racing set-up to me. 18" to fit he brakes, 17" in the rear for sidewall give and grip.
He is autox/track.

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Old 03-19-2018, 05:01 PM
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What size tire is he running out back?
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Old 03-19-2018, 05:08 PM
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Originally Posted by tlrskunk
What size tire is he running out back?
Not sure but it's like an xxx-35-17 and front is xxx-30-18 so it works, I know that. Just wondering WHY do that?
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Old 03-19-2018, 05:19 PM
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Originally Posted by froggy47
He is autox/track.


That's strange.

My only other guess is weight savings? A 17" wheel and tire will usually be lighter than an 18" wheel and tire of the same outside diameter and width.
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Old 03-19-2018, 08:09 PM
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Originally Posted by froggy47
A guy has some ccw rims that are 18 front 17 rear. Tire fitment (side wall ratio) makes the stagger right . For sale.

1) Why do this?
An old article in Grassroots Motorsports has an article which discusses Danny Popp's ASP C5Z06. In the article, titled Simply Stock by Scott Lear, Danny says he ran 18x11's in the front and 17x12's in the rear. Tires were Hoosier A3S04 (yes, old article) 305/30R18's front and 315/35R17's rear.

"You have a little crisper turn-in," Popp says in defending his unconventional wheel setup, "and because of the geometry we have to keep, the 18's allow me to be further inboard. They're less abusive to the fenders and the 402 horsepower is soaked up better by the larger sidewalls in the rear.
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Old 03-19-2018, 08:36 PM
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1st you would need to re balance the car to run such a set up. The 17’ are gonna decrease your rake. Next, C5 offsets will not clear the brake calipers of the C6Z.
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Old 03-20-2018, 02:05 AM
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Originally Posted by l98tpi
1st you would need to re balance the car to run such a set up. The 17’ are gonna decrease your rake. Next, C5 offsets will not clear the brake calipers of the C6Z.
Hi,

I don't agree that the rake changes, what matters of course is the TIRE DIAMETER, not the wheel.



I do not know the offsets on the 17" rear so may or may not clear. Probably something a spacer would fix, yes?

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Old 03-20-2018, 02:07 AM
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Originally Posted by MySR71
An old article in Grassroots Motorsports has an article which discusses Danny Popp's ASP C5Z06. In the article, titled Simply Stock by Scott Lear, Danny says he ran 18x11's in the front and 17x12's in the rear. Tires were Hoosier A3S04 (yes, old article) 305/30R18's front and 315/35R17's rear.
I knew there was something about smaller rear wheels, I guess that was it. Thanks. So we call this a Danny Popp setup? Maybe would dig off the line better like drag setup.

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Old 03-20-2018, 08:06 AM
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Originally Posted by froggy47
Hi,

I don't agree that the rake changes, what matters of course is the TIRE DIAMETER, not the wheel.



I do not know the offsets on the 17" rear so may or may not clear. Probably something a spacer would fix, yes?

You’re right on the diameter. I really didn’t check to see what the diameters were, just assumed the 17’s were smaller. The 315 would be wider so more tire on the ground for grip. 👍

probably need to test fit the wheels.
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Old 03-20-2018, 11:03 AM
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Originally Posted by froggy47
A guy has some ccw rims that are 18 front 17 rear. Tire fitment (side wall ratio) makes the stagger right . For sale.

1) Why do this?

2)Will 17" rear rim fit over oem c6z06 rear brakes. I don't know the offset. He has them on a c5 now.

I am getting c6z.

Thanks.

I did this both on my C5 and initially on my C6Z. The 17" rear wheel allows more sidewall in the rear to flex for power down and provide camber loss insensitivity when using the small diameter 315 or 335 rear tire. My 17" CCW wheels did fit over the stock C6Z rear brakes. The 18" front wheel has better steering feel/response and camber loss is not a concern.

If you're running a C6Z I'd recommend the taller 18" 345 tire in the rear for better power down.
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