For all considering 305-wide tires w/ stock suspension

Discussion in 'Brakes, Wheels and Tires' started by domesticpower, Jun 12, 2019.

  1. KRyn

    KRyn TMO Intermediate

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    @domesticpower do you use your car for auto-x events? If so, how are you finding second gear? Do you notice your self ever having to use 3rd? I was about to pull the trigger on a set of 18x10 rims I found locally for a steal of deal but decided against it last minute. Running a 285/30/18 RE71R would cost me around 6-7 mph in 2nd which I decided was too much.
     
  2. domesticpower

    domesticpower Track Addict

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    I don't do autox, sorry. What tires are you running now? The change in gearing did help me, but I went taller compared to 285/35/18 and 275/35/18's I had before. I had to coast for maybe 0.5-1 s in the back straight on our track before the change to avoid hitting the limiter. It wasn't worth it to shift to 5th and back. I don't have that problem anymore, with enough revs left in 4th to carry me to braking point. Otherwise, I just had slightly more speed per rpm but I'm carrying more speed in turns as well so shift points were basically unchanged.
     
  3. Red5OH

    Red5OH TMO Beginner

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    Hey KRyn, I actually do both track (Time Attack) and Regional Autoslalom. To answer your question, would also depend on the course you're on (lot or airfield), but also your final drive. I experience the same thing, and I found that with my 3.73 final drive, and keeping a 27" diameter wheel/tire combo, I tend to NOT hit 3rd on large airfield courses (unless the open up the course design), and in fact, spend quite a bit in 1st in tight parking lot courses, keeping within a 4000-6500 rpm powerband. I used to run a 26" diameter wheel/tire combo, often reached with 18" wheels and this often got me into 3rd or high 2nd in tight autoslaloms.

    On track, keeping the 27" diameter was more ideal with my 3.73 final drive, so I needed to adjust my driving style for autoslaloms vs track. I used a gear calculator to arrive at my final wheel and tire choice 285/35/19 RE-71Rs. It gave me the largest selection of tires for a street-class vehicle and be competitive in both disciplines.

    I was originally looking at 11" wide to accomodate 305 to 315, but wasn't getting the 27" overall diameter I was looking for, without only having one tire manufacturer as my sole choice of tires.
     
  4. KRyn

    KRyn TMO Intermediate

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    @Red5OH thanks for your input. I have a 2013 Boss 302 so I also have a 3.73 final drive ratio.

    Currently, 2 out of the 3 venues my auto-x club runs at are airfields, as such the average speed tends to be higher due to space constraints. For this reason, I believe going with 19" rims is the smarter decision. The only downside is going to be the increased price of tires. Currently I am leaning towards going with 19x11" rims and running 305/30/19s. I know they will fit, provide me the most lateral grip and I will only have to give up 2-3 mph in 2nd gear.
     
  5. domesticpower

    domesticpower Track Addict

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    @Red5OH do you have a GT or a Boss 302? Boss 302 has much shorter gears, just something to keep in mind for @KRyn if yours is a GT.
     
  6. JAJ

    JAJ TMO Addict

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    I just found this thread, and I'm not sure it's relevant because of the 60 TW rating, but the (frightfully expensive) Pirelli Trofeo R 285/35x19 actually measures as a 305/32.7x19. Tread face rubber touching the ground and section width on 10.5" rim is the same as an MPSC2 305/30. The helpful difference is that the 285 is 26.9" tall.

    I ran these on 9.5" rims on the back of my 2014 GT500 paired with 265/40x18 fronts and had no problem getting over 1 lateral g.
     
    Last edited: Jul 13, 2019 at 1:32 PM
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  7. Daegoba

    Daegoba TMO Intermediate

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    Do you happen to have a pic of that setup on the car?
     
  8. JAJ

    JAJ TMO Addict

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    Sadly, no I don't. The OEM tires on the 13/14 GT500 were 265/40x19 front and 285/35x20 rear, so I dropped the rims by 1" and ran the same widths. If you want to know how it all fit, just look at a picture of a 14 GT500 and imagine the tires a bit smaller. The suspension was Track Pack stock except for slotted front shocks and camber plates to get 3.5 degrees camber up front. It had the Bilstein switchable suspension.
     
  9. c2fx

    c2fx TMO Intermediate

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    How much street time have you logged with this setup (305s)? If so, is it livable as a daily? I am debating between 10" (285s) and 11" (305s) wide Apex wheel, but will be soon daily driving the boss for a few years while I live overseas. I know i wouldn't regret 305s on a track, just not sure for sustained street use.
     
  10. Bill Pemberton

    Bill Pemberton TMO Addict

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    You will not regret for street use either, just think of the sizes used for the GT350R and no concerns there. Ford is just more timid than GM and they undersize the rubber they put on the Stang, yet just think of the PP2 rubber, regular GT 350 and the R and you can see the rationale is there? Every test with the Camaro and the Mustang , GM has monster rubber and yet the Mustang is close on cornering with baby donuts. Put some actual meat on the car and , bingo, we get super grip!!
     
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  11. rwleonard

    rwleonard TMO Intermediate

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    I run 305 square on the street. I noticed maybe a small increase in tramlining, but other than that it's fine. I have not driven in heavy rain yet, though.
     
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  12. Bill Pemberton

    Bill Pemberton TMO Addict

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    Please keep in mind there may be some increase in tramlining ( say on rutted roads ), but that is not a given , as a lot of that occurrence can be traced to tire design, DOT Competition rubber, etc. Not all wider tires will always exhibit much difference in this situation.
     
  13. rwleonard

    rwleonard TMO Intermediate

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    Yeah, my experience is limited to RE71R's. The tramlining is nowhere near significant enough for me to abandon the 305's for what they provide on the track.
     
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  14. Bill Pemberton

    Bill Pemberton TMO Addict

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    ...... and that is the rest of the story, ha! Move on up to some fatter tubes , my friend.
     
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  15. rwleonard

    rwleonard TMO Intermediate

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  16. Red5OH

    Red5OH TMO Beginner

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    Yes...true. I have a GT MT-82.
     
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  17. c2fx

    c2fx TMO Intermediate

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    Haha. Thanks for the input. It's looking like I'm going 305s on 11 inch rims then! Tramlining should be much less of an issue in Germany...where they roads are waaay better than the US...especially here in Colorado.

    @domesticpower A very timely thread for me. Thanks for the specifics and the pictures! She's a bad looking Boss!
     
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  18. Stangra

    Stangra TMO Intermediate

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    I thought I heard that tire specs in Europe are different. If you daily drive much while you're there you may have difficulty buying replacements? 305s are soft & sticky but not a lot of treadwear.
     
  19. Bill Pemberton

    Bill Pemberton TMO Addict

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    Just got back from Germany ( on vacation) and the statement that the roads are waaay better than in the US is not only true I think you missed at least 5 more "a's" in your exclamation ----waaaaaaaay better!!!!!
     
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  20. c2fx

    c2fx TMO Intermediate

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    I'll have the OEM wheels for my winter tires and bring over a set of pilot sport 4s in 305 on the Apex wheels. Prob the best i can do while i'm there.
     
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