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Thread: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

  1. #1
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    ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    Can anyone help?

    If I fit (on 18" wheels) 265/40 on the front, and 275/35 on the rear, I'm not sure what the rolling circumference figures are, but I calculate such a set up will mean the front wheels are 0.77 inches greater diameter than the rear. Will this cause the ABS/ASR to play jup?

    Is there an actual maximum % circumference difference figure available that the ABS/ASR will tolerate?

    Thanks in advance.

  2. #2
    E500E Guru TerryA's Avatar
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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    Raven,

    You can do the math all you want but it does not match real world tire sizes. The +size tires you choose must have diameters within I believe it’s 2% of the stock tire size. This is to prevent the ABS from malfunctioning. Go on line to the Tire Rack. There you can find comparisons of all tires they sell.

    Find the rolling diameter of the E500E’s stock 225/55R-16. Then compare the diameter of the tire sizes you are looking at.
    I am running Michelin Super Sports 245/40-18 on front and 275/35-18 rear with no problems.
    This is the suggested 18” tire size ((By Most Here I think?) >Dave may correct me on this<
    My first set was 255s front and 285s and were about 2 to 3 pounds heavier but they were still within the 2% diameter size.

    Anyway I hope this helps and didn’t just confuse you.

    Take Care
    Terry

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  4. #3
    E500E Guru maw1124's Avatar
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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    Don’t calculate, check tirerack.com specs for rolling diameters. +/- 3% was always what I have heard, read, and used. I think 265/40 is too big. 245/45 works, as does 255/40 (borderline). I’m not sure it throws the ASR/ABS computers out of wack, but speedo, gas mileage, etc. (which may or may not matter for you).

    GL

    maw

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  6. #4
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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    https://www.google.com/search?q=tire+size+calculator

    https://www.tacomaworld.com/tirecalc...0r18-275-35r18


    Given the sizes you posted: the rears are 2.9% smaller than the front... which is borderline. Under hard acceleration, the ASR *may* engage even without any loss of traction, as the computer sees the rears turning more revolutions than the fronts.

    Also, you may find the cruise control does not work at higher speeds, say above 80-100kph (50-60mph).

    I'd select different tire sizes that are better matched. Ideally you like to stay within 1% or so. I know from experience that with ~4% difference, cruise control would not work above 40mph or so.

    Dave M.
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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    Thanks for all your responses! I'm still a little confused! TerryA appears to say that any alternative setup should be within 2% of the original fitment (225/55 16). Or have I read him wrong?

    I understood that as long as all the fitted tyre/wheel sizes were (within a certain circumference tolerance) the same, then any size tyre and wheel combination could be used - which might not necessarily be the same as OE.

  9. #6
    E500E Guru maw1124's Avatar
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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    You want to be +/- 3% of the original fitment. Keep in mind: (1) there was an original 17” fitment, from which you can measure the 3%; and (2) on the OEM fitment, front and rear were the same. This means front and rear must be within +/- 3%, which is what GSXR indicated, and is consistent with what TerryA said.

    But as a shortcut, I’ve already done this exercise on my 18’s. 265/40 doesn’t work. 255/40 and 245/45 both work. The 275/35 I think is fine, so that’s not the problem. Your proposed front size is the problem.

    Make sense?

    maw

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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    Quote Originally Posted by r44raven View Post
    Thanks for all your responses! I'm still a little confused! TerryA appears to say that any alternative setup should be within 2% of the original fitment (225/55 16). Or have I read him wrong?

    I understood that as long as all the fitted tyre/wheel sizes were (within a certain circumference tolerance) the same, then any size tyre and wheel combination could be used - which might not necessarily be the same as OE.
    The difference is with respect to each axle, meaning the difference between the front and rear tires shouldn't be vary by more than roughly 3%. Changing diameters from stock will throw your speedometer reading off only...which is what Terry may have been referring.
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  13. #8
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    Re: ROLLING CIRCUMFERENCE DIFFERENCES/EFFECT ON ABS/ASR

    ^^^ All correct.

    The front and rear need to be as close as possible... ideally within 1-2%. You can go larger or smaller if desired (i.e., 5% smaller diameter is fine), with speedo correction as Glen stated. But the front + rear MUST be similar diameters/circumference or you'll have ASR/ABS issues, and also cruise control issues (which will vary based on the percentage difference). My experience was with 275/35 (0.5% smaller than my 245/45 fronts) compared with 275/40 (4% larger than fronts), and cruise refused to work at higher speeds.

    Remember, ABS/ASR computers do not know tire size, and also do not know actual vehicle speed. They determine vehicle speed from rotations of each wheel, and assume stock tire size, and stock gearing.


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