Swapping from 17/18 OEM Street to 18/18 Autocross - CorvetteForum - Chevrolet Corvette Forum Discussion

Notices
Autocrossing & Roadracing Suspension Setup for Track Corvettes, Camber/Caster Adjustments, R-Compound Tires, Race Slicks, Tips on Driving Technique, Events, Results
Sponsored by:
Sponsored by:

Swapping from 17/18 OEM Street to 18/18 Autocross

Old 09-14-2018, 03:31 AM
  #1  
907Y02Z
Junior Member
Thread Starter
 
Member Since: Sep 2018
Location: Alaska
Posts: 4
Thanked 0 Times in 0 Posts
Default Swapping from 17/18 OEM Street to 18/18 Autocross

I'm looking to run my OEM 17/18 wheels with street tires (265/295) in my stock '02Z for street use, and then swapping to a 18x9.5/18x10.5 setup with Rival-S (275/315) or RE-71r (265/285) for A-street autocross. Car isn't lowered. Is there anything wrong with this that I'm missing? Does the suspension need to be altered? Is there a better way to go about running a good set of 190+TW autocross tires within the A-street rules (+/- 1" diameter rim, 9.5" rim up front, 10.5" rim rear)?
907Y02Z is offline  
Old 09-14-2018, 08:29 AM
  #2  
mattastick
CF Senior Member
 
Member Since: Feb 2016
Posts: 294
Thanked 40 Times in 37 Posts
Default

The only thing you're missing is a 19x10.5" rear wheel to run the 305 RE-71R. The current AS setups are either the 275/315 Rival S or 275/305 RE-71R. So you're close, but go with the extra tire.
mattastick is offline  
Old 09-14-2018, 02:11 PM
  #3  
froggy47
CF Senior Member
 
froggy47's Avatar
 
Member Since: Oct 2002
Location: Southern CA
Posts: 9,944
Thanked 107 Times in 93 Posts
Default

Originally Posted by 907Y02Z View Post
I'm looking to run my OEM 17/18 wheels with street tires (265/295) in my stock '02Z for street use, and then swapping to a 18x9.5/18x10.5 setup with Rival-S (275/315) or RE-71r (265/285) for A-street autocross. Car isn't lowered. Is there anything wrong with this that I'm missing? Does the suspension need to be altered? Is there a better way to go about running a good set of 190+TW autocross tires within the A-street rules (+/- 1" diameter rim, 9.5" rim up front, 10.5" rim rear)?

OT they have autox in Alaska? My daughter & son-in-law lived/worked there a while. I have visited, great place (in the summer).



froggy47 is online now  
Old 09-14-2018, 04:38 PM
  #4  
mattastick
CF Senior Member
 
Member Since: Feb 2016
Posts: 294
Thanked 40 Times in 37 Posts
Default

Originally Posted by 907Y02Z View Post

mattastick, thanks for your response.
The reason I was thinking 18/18 for autocross was that I'd read posts from members that said the car was better balanced, and that it helped cure the front end understeer 'plowing'. I've been digging up posts on 18/18 vs 18/19 for a bit, some members say the best reason to go 18/18 is for true square setups so you can rotate all four tires (which I obviously can't do for A-street). Has anyone tried 18/19 in Autocross that can compare it to the handling of a square setup? If I go 18/18, do I need to tune the chassis in any way to adjust for the difference in rake?

However, looking at tire prices makes me think I should just run a true 18/18 square setup for rotation purposes and forget A-Street... So many options.
The fast AS guys all run a 275 front tire, regardless of their chosen brand. This helps add front grip. The rear tire is a choice between the shorter BFG, which some people like, or the extra gearing and steering precision of the RE-71R. If you're running AS, these are your best options to be competitive. Anything else will be leaving performance on the table, IMO. Ignore what most people do here, and look at/talk to the folks that are competitive at National events. Most people here are either slow, or never leave their local lots (or both), though looking at my **** poor Nationals experience, I definitely fit in the former group.

If you want to forget about AS, get an extra pair of 18x10.5 rears, run 315 square Rival S' and run in CAM-S. The plus side here is that you can mod your car in whatever way you desire, and there are basically no limits.
mattastick is offline  
The Following User Says Thank You to mattastick For This Useful Post:
907Y02Z (09-14-2018)
Old 09-14-2018, 04:54 PM
  #5  
907Y02Z
Junior Member
Thread Starter
 
Member Since: Sep 2018
Location: Alaska
Posts: 4
Thanked 0 Times in 0 Posts
Default

Originally Posted by mattastick View Post
The fast AS guys all run a 275 front tire, regardless of their chosen brand. This helps add front grip. The rear tire is a choice between the shorter BFG, which some people like, or the extra gearing and steering precision of the RE-71R. If you're running AS, these are your best options to be competitive. Anything else will be leaving performance on the table, IMO. Ignore what most people do here, and look at/talk to the folks that are competitive at National events. Most people here are either slow, or never leave their local lots (or both), though looking at my **** poor Nationals experience, I definitely fit in the former group.

If you want to forget about AS, get an extra pair of 18x10.5 rears, run 315 square Rival S' and run in CAM-S. The plus side here is that you can mod your car in whatever way you desire, and there are basically no limits.
Sorry, I deleted my post because it was a double post, but a mod got it, so now both posts are gone (I'm new here) . Thanks for the advice.

Froggy: Yeah they do have AutoX in the summer! SCCA runs 14 events, PCA runs 8. They're generally low speed/technical courses. Not looking forward to having to put the car away for the winter...
907Y02Z is offline  
Old 09-17-2018, 10:24 PM
  #6  
MatthewMiller
CF Senior Member
 
MatthewMiller's Avatar
 
Member Since: Aug 2015
Location: St. Charles MO
Posts: 1,582
Thanked 221 Times in 187 Posts
Default

Originally Posted by mattastick View Post
The only thing you're missing is a 19x10.5" rear wheel to run the 305 RE-71R. The current AS setups are either the 275/315 Rival S or 275/305 RE-71R. So you're close, but go with the extra tire.
Just as a reinforcing opinion, I agree with mattastick's recommendations: use the bigger rear tires whether you go with the Rival S or RE71R. I'll add that the two tires drive quite differently, although I believe that they have pretty equal speed potential. If you can possibly do it, try to get a drive in cars with each tire to see which one you like better.
MatthewMiller is offline  
Old 09-18-2018, 08:29 PM
  #7  
DudeWithAVette
Junior Member
 
Member Since: Jan 2018
Posts: 15
Thanked 1 Time in 1 Post
Default

I ran 285/305 re-71 in A street with 18/19 front/rear aftermarket wheels...rules legal.

Why 275 up front? With max camber (I think -2.7ish) and lowish pressure (26-28 hot typically) I used every bit of the front 285s.

They fit just fine up front. If anything the 305s look more oversized to the wheel than the fronts as I struggle to get to the wear marker.

Still running this in cam until I wear out the fronts and switch to the cam rival setup.
DudeWithAVette is online now  
Old 09-18-2018, 08:50 PM
  #8  
MatthewMiller
CF Senior Member
 
MatthewMiller's Avatar
 
Member Since: Aug 2015
Location: St. Charles MO
Posts: 1,582
Thanked 221 Times in 187 Posts
Default

Originally Posted by DudeWithAVette View Post
I ran 285/305 re-71 in A street with 18/19 front/rear aftermarket wheels...rules legal.

Why 275 up front? With max camber (I think -2.7ish) and lowish pressure (26-28 hot typically) I used every bit of the front 285s.

They fit just fine up front. If anything the 305s look more oversized to the wheel than the fronts as I struggle to get to the wear marker.

Still running this in cam until I wear out the fronts and switch to the cam rival setup.
Good question. The 285/30/18 RE71R is almost an inch shorter than the 275/35/18, and that makes it 1.4" shorter than the 305/30/19 rear. That would be my main concern with that 285.
MatthewMiller is offline  
Old 09-18-2018, 08:54 PM
  #9  
DudeWithAVette
Junior Member
 
Member Since: Jan 2018
Posts: 15
Thanked 1 Time in 1 Post
Default

Great call-out.

I think I reset my ride height and rake with the new wheels/tires on but now you've got me doubting myself.

​​​​​​I've never had a problem with active handling or abs using this setup for autox and hpde for anyone who is curious.
DudeWithAVette is online now  
Old 09-18-2018, 09:04 PM
  #10  
MatthewMiller
CF Senior Member
 
MatthewMiller's Avatar
 
Member Since: Aug 2015
Location: St. Charles MO
Posts: 1,582
Thanked 221 Times in 187 Posts
Default

Originally Posted by DudeWithAVette View Post
Great call-out.

I think I reset my ride height and rake with the new wheels/tires on but now you've got me doubting myself.
To be fair, I'm not sure exactly how all the effects of this add up. It might even be a good thing. And the fact that the C5 is fully adjustable for ride height in Street/Stock class may mean isn't all that important. It will still change the roll geometry even if you keep ride height the same, but that could be good or bad depending on a lot of other things.
MatthewMiller is offline  
The Following User Says Thank You to MatthewMiller For This Useful Post:
DudeWithAVette (09-18-2018)
Old 09-21-2018, 09:34 PM
  #11  
smitty2919
CF Member
 
Member Since: Jun 2016
Posts: 62
Thanked 2 Times in 2 Posts
Default

18x10.5 square
smitty2919 is online now  
Old 09-21-2018, 09:39 PM
  #12  
MatthewMiller
CF Senior Member
 
MatthewMiller's Avatar
 
Member Since: Aug 2015
Location: St. Charles MO
Posts: 1,582
Thanked 221 Times in 187 Posts
Default

Originally Posted by smitty2919 View Post
18x10.5 square
Not for A Street solo competition - can't go wider than stock.
MatthewMiller is offline  
Old 09-24-2018, 03:37 PM
  #13  
smitty2919
CF Member
 
Member Since: Jun 2016
Posts: 62
Thanked 2 Times in 2 Posts
Default

Can't do a lot of good/typical stuff in A Street....no CAI, no LT's, no dyno tune, no smaller steering wheel.

A-Street won't be the class for me. CAM-S HERE I COME!
smitty2919 is online now  
Old 09-24-2018, 05:22 PM
  #14  
MatthewMiller
CF Senior Member
 
MatthewMiller's Avatar
 
Member Since: Aug 2015
Location: St. Charles MO
Posts: 1,582
Thanked 221 Times in 187 Posts
Default

Originally Posted by smitty2919 View Post
Can't do a lot of good/typical stuff in A Street....no CAI, no LT's, no dyno tune, no smaller steering wheel.

A-Street won't be the class for me. CAM-S HERE I COME!
I'm there now. But be warned, if you run 10.5" square in CAM-S, you'll be in the narrow-wheels club!
MatthewMiller is offline  
Old 09-24-2018, 05:33 PM
  #15  
smitty2919
CF Member
 
Member Since: Jun 2016
Posts: 62
Thanked 2 Times in 2 Posts
Default

Originally Posted by MatthewMiller View Post
I'm there now. But be warned, if you run 10.5" square in CAM-S, you'll be in the narrow-wheels club!
True, BUT 315/30/18 Rival-S are getting plentiful and cheap at the end of each season. The most common 18" tire. Or the 335/30/18
smitty2919 is online now  
Old 09-24-2018, 05:44 PM
  #16  
MatthewMiller
CF Senior Member
 
MatthewMiller's Avatar
 
Member Since: Aug 2015
Location: St. Charles MO
Posts: 1,582
Thanked 221 Times in 187 Posts
Default

Originally Posted by smitty2919 View Post
True, BUT 315/30/18 Rival-S are getting plentiful and cheap at the end of each season. The most common 18" tire. Or the 335/30/18
Definitely. It's just that most people run the 315 on an 11" wheel. The 10.5 will work - it's just not optimal. How much of a difference it really makes, I don't know. The 335s are mo' bettah, but on my C4 they would require flares to tuck properly with a lowish ride height. They are also taller tires, so there are tradeoffs.
MatthewMiller is offline  
Old 09-24-2018, 07:23 PM
  #17  
smitty2919
CF Member
 
Member Since: Jun 2016
Posts: 62
Thanked 2 Times in 2 Posts
Default

Yep. It's super easy and cheap to go 18x10.5 C5Z rear wheels all around and 315/30/18.

Outside of that you are buying Forgestar wheels with capability of custom offsets for 18x11 or 18x12. And beyond that is Forgeline....

So yea, I'll stick with the easy button I don't have the wallet to play THAT hard.
smitty2919 is online now  
Old 09-26-2018, 02:33 PM
  #18  
ztnedman1
Junior Member
 
Member Since: Jun 2014
Posts: 6
Thanked 0 Times in 0 Posts
Default

Originally Posted by 907Y02Z View Post
I'm looking to run my OEM 17/18 wheels with street tires (265/295) in my stock '02Z for street use, and then swapping to a 18x9.5/18x10.5 setup with Rival-S (275/315) or RE-71r (265/285) for A-street autocross. Car isn't lowered. Is there anything wrong with this that I'm missing? Does the suspension need to be altered? Is there a better way to go about running a good set of 190+TW autocross tires within the A-street rules (+/- 1" diameter rim, 9.5" rim up front, 10.5" rim rear)?
275/18 305/19 RE71 is damn near the exact same tire diameters as the OEM 265/295. Your car will be exactly the same height and have the same wheel gaps. No changes needed.
ztnedman1 is offline  


Thread Tools
Search this Thread
Sponsored Ads
Vendor Directory

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: