How tall/short tire options

Discussion in 'The Hides' started by Nailhead Ronnie, Jan 12, 2018 at 4:12 AM.

  1. Nailhead Ronnie

    Nailhead Ronnie Well-Known Member

    When looking at this equation

    RPM = MPH x GEAR RATIO ×336 ÷ TIRE DIAMETER
    What the tallest and shortest tire that can be fit in a Buick 1964 and 1965 A Body like Skylarks and Specials.

    When does width start to play a factor in the tire and how wide can you go, what then starts to become disadvantages if any of trying to go too wide for traction sake. Will that also affect this formula?



    Thanks,
    Ronnie
     
  2. Nailhead Ronnie

    Nailhead Ronnie Well-Known Member

    I pulled this formula off a Hot Rod magazine YouTube video. But why is the transmissions gear not in the formula above?
    I was thinking the transmission gear would be of importance since its all in the mix.
    Thanks in advance. I can post the video if need be
     
  3. Bigpig455

    Bigpig455 Fastest of the slow....

    One of the tallest tires I've used that fit easily is a 235-75-R15 at 29 inches - all those fancy 17 and 18 inch wheel /rim combos dont ever seem to get much taller than that due to wider aspect ratios.. Even a 275-60-15 is only like 28 inches.....as far as the short side, look at all those lowriders running vogues that arent much bigger than the brake drum, right? A short 215-75-R14 tire 60 foots unusually well in my 65 GS, by making a 3.42 gear feel more like a 3.73..that same 3.42 with a 29 inch tire would probably react more like a 3.08 or something.

    This thread talks about the absolute size of tires that people are able to fit on an A body and modifications required, but the conversations always seems to be more about width limitations..
    http://v8buick.com/index.php?threads/how-to-fit-a-275-315-on-the-front.328921/#post-2757284

    From a width and traction perspective, for street/strip cars people seem to find all the traction they need from a 9-10 inch drag radial or slick, I can run a 1.80 60 foot on a 275-60 15 street radial which is about 10 inches wide, Ive seen guys run 1.7x 60's on F-70-14's.... its more about how the car and suspension are set up. Go too wide on the tire, like a big 515-45-15 and that tire takes so much horsepower to turn I dont know if its worth it....and it'd never fit in the wheelwell. Others may have different experiences

    As far as transimission ratio, that does have an effect if you wanted to understand the absulute torque output of a drivetrain on a chassis dyno or something, but the formula you are using strictly measures RPM/MPH of a combo, not power....you could draw some conclusion from that, like you are keeping a car in the powerband, etc..
     
    Last edited: Jan 12, 2018 at 4:48 AM
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Top gear in any non OD transmission is 1:1. Tire height and width are related by the aspect ratio. Take for instance the P245/60R-15. The aspect ratio is 60. What that means is the height of the sidewall is 60% of section width. The section width is 245, that is 245mm. The tire height is 2 times the sidewall height + the rim height. It is easier to convert everything to mm, then figure the result in inches. There are 25.4mm/inch. 15" is 381mm. The sidewalls for the above tire are .60 X 245 = 147mm. 2(147) +381 = 675mm. 675/25.4 = 26.57". So as the section width of a tire increases, so does the sidewall height if the aspect ratio remains the same.
     
  5. Nailhead Ronnie

    Nailhead Ronnie Well-Known Member

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