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Thread: Need wheel & tire advice. Looking for street setup with some autocross.

  1. #1
    wildswing
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    Need wheel & tire advice. Looking for street setup with some autocross.

    Hey fellas,

    Sorry for the long and complicated question. Tried a search but didn't find anything quite right.

    My '05 GT currently has stock 17" wheels with 235/55-17 BFG G-Force T/A tires. Suspension is Eibach pro system plus so it's lowered about 1 1/2". I'm old school. I like the look of more sidewall. So I like the existing look of the 17" tires, but was playing with the idea of new wheels anyway. The oem wheels are grey bullets (?) but, I've always preferred chrome, so have been looking at options. Advice I've received is to go no larger then 18" to keep the sidewall look. Besides, I'm not a fan of the harsher ride of 19 and larger wheels & tires. I really like the deep dish wheels like American Muscle bullets. If I'm going to go there, I might as well get the widest that will reasonably fit without re engineering things or adding spacers and such. One thing I DO NOT want is the stretched look. Sidewalls should be wider than the rims, not vice versa.

    I thought I had this figured out, until I went to my first autocross last weekend. What a blast. Now I'm wondering how to improve grip on top of the looks. The BGF tires were screaming like stuck pigs. The whipple can overpower these tires easily and it understeered a lot. Tire pressures started at 42 in all. Eventually going down to 40 in the front and 36 in the back. I know, a lot of that is me. I run out of talent long before I run out of car, so seat time is what I need most. My best times were when the tires were the quietest. Beyond that, all the guys I met said better tires would be a big help. Many were running Bridgestone Potenza RE-71R tires, but they all said tire wear doesn't make them a good street DD tire. I'm not ready to build a dedicated set quite yet either. My source recommended Mickey Thompson Street Comps.

    Can I do both? Can I improve the looks, with wider tires on deep dish wheels AND get a reasonable improvement in grip for the few autocrosses I hope to do each summer. I assume there must be some trade offs from either side. How much though? Are the deep dish wheels or staggered tire width an issue for autocross grip? I'm willing to stay equal width all around as a compromise. Is there a less expensive route to creating a dedicated set that could be driven, maybe an hour or so, to get the the event. Maybe then I'd look at the Potenzas. I definitely won't be changing tires at the site.

    Advice I've received from a reputable source said max equal tire size would be 255/45-18 on 18x9 wheels. Staggered max would be 275/45-18 out back.

    Your advice would be very much appreciated. Thanks in advance.

    YooperCup2018 - 14.jpg YooperCup2018 - 15.jpg

  2. #2
    Posting and liking.... Ponyryd's Avatar
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    I can’t comment on sizes, but on a Mustang you don’t want a wider rear tire for autocrossing, a square setup would be best and I’d bet fastEd would be very helpful with this as he had a similar car for a while and he’s an autocrosser.
    With regards to the “tire wider than wheel”, I’m no expert but I’m sure that would create unpredictable handling at the track as the tires would be more prone to fold and flex, I’m thinking the best option would be tire width equal to rim width or slightly smaller for sharper turn-in.

  3. #3
    wildswing
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    Thanks Ponyryd.

    When I say "tire wider than wheel" I mean the traditional look where there's some bulge to the sidewall. The sidewall is the widest part, like in the attached picture. What I do not want is the edge of the rim to be the furthest thing outboard. Seems to be a new thing, I see with lower profile tires, that this old fart just can't get his head around. Just does not look right to me, and besides, it's far easier to scrape your rims with that look.

    EDUplus-sizing_small.png

    **** Also, to clarify/add a point. I'm working on the assumption that lower profile tires handle better and will have less sidewall flex than my oem 17s. If I can get a decent improvement in grip and stay with 17s, then that's another option I'm willing to explore.

  4. #4
    Posting and liking.... Ponyryd's Avatar
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    That depends on the tire, if you get a 17” track tire it will have much better grip and less sidewall deflection than an 18” all season.

  5. #5
    wildswing
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    Quote Originally Posted by Ponyryd View Post
    That depends on the tire, if you get a 17” track tire it will have much better grip and less sidewall deflection than an 18” all season.
    I hear ya. I'd rather not go all out this early in my autocrossing career and get a dedicated set of track tires. I'm just looking for a reasonable compromise between streetable tire wear and ride quality and improved cornering ability. If I can do that with the staggered, deep dish look, then great. If not, then I'll have to decide which is more important.

    EDIT:
    Thinking out loud. Options?
    - instead of staggered get equal width deep dishes?
    - would the added offset of the DD wheels adversely effect autocross type handling, or what about max tire width? Overthinking? yes.
    - get the staggered DD wheels and decent street tires, then use the old oem 17x8 rims for autocross. I'd need 17" sticky tires.
    Last edited by wildswing; 06-27-2018 at 01:23 PM. Reason: added stuff

  6. #6
    Posting and liking.... Ponyryd's Avatar
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    If it was me I’d go for a square deep dish setup and be done, that’s the easiest and most economical, and of course you can keep your old wheels to use for dedicated track tires if you find yourself tracking enough to justify it.
    Really though, when it comes to autocross, a light wheel/tire combo is best, and an AM deep dish wheel isn’t exactly light, but it’s a good place to start and see if you want to get into it farther.

  7. #7
    Super Moderator Stephen06GT's Avatar
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    As someone who tracks a similar car, 2006 GT with a Roush M90, this it what I have done:

    Always a square set. First was the stock 17x8 Bullitts with 235/55/17s. Moved quickly to 18x8.5 Bullitts, first with 235/??/18s then 255/45/18s. Currently running a set of Roush 18x10s with 275/45/18s. The car has always been driven to and from the track. Because the car was a daily driver, yes even in the winter, the tires had to be some what streetable. The OEM BFGs on the 18s were decent enough while I was learning to track the car. Next was set of Nitto555s. They were an exceptional all around tire and more than enough for me to have loads of fun at the track. They are still on the 18 Bullitts today. Earlier this year while researching new tires, I was lucky enough to get the set of Roush wheels clad with Cooper tires. I've only had one track day with them, and they more than held their own. If I didn't get the 18x10s I was debating between the Nitto555 Gen IIs and the Firestone Firehawk Indy 500s. If money was no object, And I could trailer the car to the track Iwould have a dedicated set of track tires, read slicks, on light weight wheels. Will dedicated ultra sticky track improve your lap times, probably, but are they worth the extra money for just a few times a year, and will the increase the smiles/lap factor?

  8. #8
    wildswing
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    Quote Originally Posted by Ponyryd View Post
    If it was me I’d go for a square deep dish setup... Really though, when it comes to autocross, a light wheel/tire combo is best, and an AM deep dish wheel isn’t exactly light, but it’s a good place to start and see if you want to get into it farther.
    Good points. Thanks.

    Quote Originally Posted by Stephen06GT View Post
    As someone who tracks a similar car, 2006 GT with a Roush M90, this it what I have done: Always a square set...Currently running a set of Roush 18x10s with 275/45/18s...
    Please tell me more about the 18x10 wheels & 275 tire combo. On all 4 corners? Are you using spacers or any other mods? Is your car lowered? Mine is. No rubbing or interference with suspension articulation or steering? Do you know the offset or backspacing on those rims? A trusted source told me the the widest I could run on my '05, without spacers or other mods, is 255/45-18 up front and 275/45-18 out back. Can you post some pictures from different angles and close up please?

    Quote Originally Posted by Stephen06GT View Post
    Will dedicated ultra sticky track improve your lap times, probably, but are they worth the extra money for just a few times a year, and will the increase the smiles/lap factor?
    I hear ya. As you said, we're talking about something that's only going to happen a couple times a year. I just want less squealing, and a little better response & handling. Some of that will come from me getting more seat time, but the "extra" that lighter wheels or ultra sticky track tires would garner is not worth the extra expense and work.

    Thanks again fellas. Much appreciated.

  9. #9
    Admin ZR's Avatar
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    In the same breath, drive with dedicated ultra grippy tires just once.............ruined for life.
    BFG R1s on the Cobra, epic difference.



  10. #10
    Club Sponsor Parkway Ford Lincoln SVT's Avatar
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    There are very few choices in 275/45R18, that is an OEM size for Porsche and Mercedes SUVs so the selections are all expensive high-end tires.

    You should look at 275/40R18 if doing a square setup, or if you insist on staggered, then look at 255/45R18 and 285/40R18 so that the overall diameter matches front to rear.
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