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Thread: difference in diameter better 24inch(25-540) and 26inch(25-590) wheels

  1. #1

    difference in diameter better 24inch(25-540) and 26inch(25-590) wheels

    if you calculate it based on the circumference and rounding the number it would be

    (26inch) 590 / 3.14 diameter = 187mm
    (24inch) 540 / 3.14 diameter = 171mm

    Or using the online calculator https://www.omnicalculator.com/math/circumference

    Anyway I need to know because I'm ordering a new chair and need to adjust my front frame and rear frame heights based on the difference in height of the wheels.

    A difference in height of 16mm seems too small from what I can remember when seeing both sizes together but I could be wrong.

    If anyone knows let me know?

    Thanks,
    Rob

  2. #2
    Senior Member tooley's Avatar
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    187mm = ~7.4 inches. Not sure what you're trying to work out there? Circumference is diameter multiplied by pi.

    it's my understanding that the 590, 559, 540, etc. is the diameter of the rim.

    25.4mm in an inch, so the difference in diameter is ~2 inches from a 24" to a 26" wheel. (which seems logical?)

  3. #3
    Keep in mind that difference in diameter number is only half when applied from the axle to the ground.

  4. #4
    I think 540/590 is the diameter of the rim, you then need to add the tyre height which is usually a % of the width. That isn't an easy number to find.

  5. #5
    Senior Member Oddity's Avatar
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    Not sure of the exact question, but for every 1" diameter difference you'll only get .5" of ride height difference. Important when trying to figure out ride height difference based on diameter differences,
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

    "If you only know your side of an issue, you know nothing." -John Stuart Mill, On Liberty

    "Even what those with the greatest reputation for knowing it all claim to understand and defend are but opinions..." -Heraclitus, Fragments

  6. #6
    Quote Originally Posted by mrb View Post
    I think 540/590 is the diameter of the rim, you then need to add the tyre height which is usually a % of the width. That isn't an easy number to find.
    Yes. Use inches. 590 is the rim. 590 mm = 23.2 inches.
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

  7. #7
    Senior Member tooley's Avatar
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    I will also add that if the intent is to change from a 24" wheel to a 26" wheel (assuming the same center-of-gravity setting) you will not be as nimble in tight spaces, ie. washrooms. That extra inch behind you doesn't sound like much but it's actually a lot when trying to back over a toilet to get the door shut or even in a smaller apartment-style kitchen trying to turn around between the 2 countertops/cabinets.

  8. #8
    Thanks for the replies.

    Jeez I just did those calculations without thinking haha! Yeah I had thought the 590 and 540 were the circumferences, when they are obviously the diameter!

    But the diameter from from the rim to rim because 590mm is only 23inches?

    Am I right in thinking the difference in wheel height between 26inch and 24inch is 50mm?
    This is what I had originally thought before doubting myself.

    I am moving from 26inch wheels to 24inch wheels, so it should be easier to manoeuvre.

    My front frame height in my current chair is 490mm and the rear frame height is 420mm, with 26inch wheels.

    For the new chair with 24inch wheels, I don't want to sit too much lower, but still have much the same pushing position.

    Between the 24inch and 26inch wheels there is a 50mm difference in height, yeah?

    I was thinking with the 24inch wheels a front frame height of 465mm and a rear frame height of 395mm. Both frame heights reduced by 25mm.

    So, for the new chair, by reducing my frame height by only 25mm for the new frame, instead of the 50mm difference in height between the wheel sizes, the distance between my shoulder height(sitting in chair) and the top of the wheel would be 25mm longer than the distance between my shoulder height and the wheel with my current set up.

    I know I have explained this badly, but if you get what I mean, is that correct?

    Thanks,
    Rob

  9. #9
    Quote Originally Posted by rob1 View Post
    ...For the new chair with 24inch wheels, I don't want to sit too much lower, but still have much the same pushing position.

    Between the 24inch and 26inch wheels there is a 50mm difference in height, yeah?...
    I may be a bit confused by your question, but here goes:
    1. You will sit 1 inch closer to the floor since the diameter of the wheel is one inch less.
    2. Your shoulder to axle distance will be the same since it is independent of the wheel size.
    3. Your shoulder to tire distance will be 1 inch more since the wheel is smaller, that is the top of the wheel is 2 inches closer to the floor but your shoulder is only 1 inch closer.

    But if you are ordering a chair, is any of this relevant? Don't you do this by FSH, RSH, dump, and wheel size? Just keep the first three the same as you have now.
    I have had periodic paralysis all my life. I lost my ability to walk in 2011 beginning with a spinal block, which was used for a hip fracture caused by periodic paralysis.

  10. #10
    To muddy it further??.
    AFAIK. 540, 559 etc relates to the bead set diameter, so not actually the rim diameter. I run Spinergy 559 and have some 540. If you wish I can supply you with the diameter of these wheels running Schwalbe Right Runs/Marathons.

    If you intend to use the same tyres; to determine the difference in ride height, just add or subtract half the difference between your existing wheel-set and what wheel-set you anticipate purchasing.
    I don't bother converting from ITRTO to inches; metric is far simpler to work with.

    Are you looking for increased ride height or gain distance per revolution?
    Ride height is easy enough to calculate; circumference will depend on your tyre choice.
    Last edited by slow_runner; 06-27-2019 at 08:27 PM.

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