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Last Post 26 Jul 2015 04:38 PM by  drdisque
Wheel & Tire Selection
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onray.donpaul
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13 Jun 2015 02:05 PM

    Hi,

    I need help on deciding my wheel & tire size for autocross. I am currently looking at getting Enkei RPF1s +35 offset, 5x100PCD & 18 inch in diameter but I am undecided on how wide I should go. I was suggested 8 wide to keep the weight down but this gives a smaller contact patch than the 9 or 9.5 inch wide that others have been suggesting but this I fear will increase the weight over stock. The current specs on my car are below:

    Toyota GT86

    K&N panel filter

    Cusco strut bar with brake brace

    OFT ECU stage 1

    mFactory 4.67 ratio final drive

    aFe Takeda catback exhaust

    Any help or advice is greatly appreciated !!

     

    drdisque
    Basic Member
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    Posts:317


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    13 Jun 2015 05:10 PM
    I'm guessing that you will be autocrossing this car in STX?

    In that case you can't go wider than 9".

    Although, however, your changed rear end gear ratio sends you into street prepared I believe (C Street Prepared to be specific). In that class wide wheels and big R-Comps are de-facto required. I also think you should really consider going with 17x9's rather than 18x9's, whether you de-mod to run in STX or run in CSP.

     

    Am I correct that in Street Prepared that you can change the rear end gear as long as it fits in the original housing?

    EDIT: Upon re-reading the changed final drive ratio throws you into Street Modified. However, wheel and tire rules for Street Mod are the same as Steet Prepared. I recommend 17x9's with a nice set of R-Comps.

    onray.donpaul
    New Member
    New Member
    Posts:2


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    14 Jun 2015 02:06 AM
    Hi drdisque,

    Thank you for your reply. Actually I forgot to mention that I am running in the autocross out in the Middle East, Dubai to be specific and I don't think the rules are as stringent as you have described. I am plainly looking for a set of wheels that's gonna free up the car to accelerate harder.

    Correct me if I am wrong, but I always felt that having a bigger diameter wheel meant you covered more ground in a single rotation than a smaller diameter. Also wont an 18 inch wheel be need to clear a big brake kit (which I am planning for down the line)?


    That said, given that I'm still running on stock suspension, what is your recommended package wheels and tires that way I can see if it is feasible and available out here. Thank you again for your input it is much appreciated
    drdisque
    Basic Member
    Basic Member
    Posts:317


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    14 Jun 2015 11:09 AM
    Wheels don't make you faster. By increasing the total diameter of the wheel and tire combination, you can effectively alter your gearing, so with a taller tire you could top out higher in second gear for example. A shorter tire and wheel combination will allow faster acceleration but you will run out of each ear sooner. However you can change the profile of the tire, so you can in theory, achieve the same total tire diameter on a wheel of any size.

    You may need an 18" wheel to clear a big brake kit. But the brakes on your car are honestly pretty good, and at autocross speeds I don't think a big brake kit would help you all that much. If you decided you wanted to start racing the car on a track that would be another story. I recommend a set of 17x9's with the stickiest tires you can get. That would be indicated by a low treadwear number. If you have Hankooks (which I'm pretty sure will be available there), their RS3 V2 would be a great tire for you to use since they love the heat and it will obviously be very hot autocrossing in Dubai. You could also get a race tire like the Toyo Proxes R888 or RA1. You could go with an 18x9 if you prefer though.

    However, you did say you were concerned about weight. Going from 17" to 18" diameter will add far more weight than adding an inch of width to the wheel.

    Since upgrades are pretty "open" where you are. I would also recommend a set of aftermarket sway bars. The TRD ones are pretty good and should be available worldwide.
    onray.donpaul
    New Member
    New Member
    Posts:2


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    26 Jul 2015 03:58 PM

    Hi drdisque,

    Finally got my set of RPF1s shipped size is 17x9 +35... However, I have a problems with the tires I will have access to. None of the nice r compound tires seem to be available in Dubai. My choices are now narrowed to the offerings from Nitto. Any verdict on the performance of the NT05 as a street tire and as a competition tire? ADO8R, RS3, V12 Ventus, Z2 Star SPec none are available out here.

    drdisque
    Basic Member
    Basic Member
    Posts:317


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    26 Jul 2015 04:38 PM
    Nitto NT05's will work for you where you live, since it almost never rains there, and they are driveable in the rain, you just have to slow down, a lot. Don't expect to get more than 7 or 8000 km out of a set though.
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