RS-4 on 18x10 - do I want 285/35 or 295/40

Discussion in 'Brakes, Wheels and Tires' started by Duane Black, Jan 27, 2019.

  1. Duane Black

    Duane Black TMO Advanced

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    It is tire time for me! I mainly just run HPDE4 and autocross with friends when I can. I’ve deduced I want some RS-4, but now the question is which tire size?

    My gearing means my car is out of ideas at 123 mph on 285/30/18 but data at roebling shows power band was tapped out earlier and i was at 129 on a taller tire (275/40/19). The correct answer obviously is switch back to 3:27 gear, but I digress.

    So I’m also concerned about width and sidewall height. Shorter sidewalls generally mean stiffer, correct? So should I go 285/35/18 or go 295/40/18 for better sidewall height that should save 4th gear to 130 mph? In my v6 auto, it’s out if ideas at 5th gear when it goes to 4200 rpm.

    So my pros of each right now are...

    285/35
    -$50 a corner cheaper
    -maybe a stiffer sidewall?
    -less risk of fender rub (my v6 leans a lot)

    295/40/18
    -better top speed on straights at Road Atlanta, VIR, etc
    -and thats it...


    I’d appreciate feedback!
     
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  2. Bill Pemberton

    Bill Pemberton TMO Addict

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    295s way too tall ---you need the tire to be in the 25 inch diameter range.

    Not a big fan of the Hankooks, the need a warm day to work. Dropped you a PM.
     
  3. Duane Black

    Duane Black TMO Advanced

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    I do live in the south so a warm day isnt usually an issue. I’ll keep an eye on my inbox
     
  4. Bill Pemberton

    Bill Pemberton TMO Addict

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    Oh, I do understand, but by cool I mean in the 60s. PMs here are under the heading conversation --click on your name and they are listed below.
     
  5. VoodooBoss

    VoodooBoss Rick Moderator

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  6. Grant 302

    Grant 302 OPM Spent: $665,833 Moderator

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    I'd have the tendency to prefer the shorter 285. And to change to a taller gear.
     
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  7. Norm Peterson

    Norm Peterson Corner Barstool Sitter

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    Your sixxer probably makes about the same power as my 4.6L, so I think high 120's, possibly as much as 130 or 131 on a really long straight or downhill, is about the most you can expect no matter what you do with axle gears and tire sizes. And 285/35-18's will give that to you with 3.55's in the axle and a 6R80's 5th gear. Unless the torque converter is allowed to unlock, rpms should be very close to what they are now with the 285/30-18 tires at 123 mph.

    That's separate from the 285/35 being a much better choice for 10" wide wheels than any 295/40.


    Norm
     
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  8. Duane Black

    Duane Black TMO Advanced

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    I did get to 145 at daytona with 3:27 gears and 275/40/19 tires. Of course, the right way to fix this is gearing. Its above ideal rpm by 110 so acceleration data shows it was actually better with 3:55 and the 19’s just because it was in the power band from 100-125. At the time I anticipated that I’d track on 19 inch tires and save my 18’s for autocross. But, no need to argue about how I got here, this is where I am. Either fix it with tires, fix it with gear, or live with it. Thanks for the input!
     
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  9. APEXRaceParts

    APEXRaceParts Race Proven, Street Approved

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    285/35-18 is a much better fit for 10" wide wheels compared to the 295/40-18. A local friend of mine ran the 295/40 RS4s on his 18x10" and they bulge considerably.

    [​IMG]
    [​IMG]
    [​IMG]

    Here is a snapshot of the actual measurements between the tires. If you need the extra gearing, no issue achieving that through taller tires. The 295/40-18 is a perfect fit on an 18x11" wheel, you could join the Group Buy, save a bunch of money, and get the tire you want. Just a thought :)

    upload_2019-1-28_14-46-18.png

    - Cory
     
  10. Duane Black

    Duane Black TMO Advanced

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    Wow, that’s more bulge than I thought.

    On recommendation, I called tirerack. The tipping point was both cost and availability. The 295/40 is “special order”. The guy told me it was basically a matter of whenever Hankook fills the container, they’ll ship it. Hevsaid that could even be May. I got a corded re71r and need tires in march. 285/35 are on the way!
     
  11. Grant 302

    Grant 302 OPM Spent: $665,833 Moderator

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    Yeah, forget waiting for backorder/special order items.

    Oh, don't bait me like that! ;) :D
     

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