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

  1. #11
    hey, slow_runner yeah that would be useful if you could tell me the diameter of the 540 running Schwalbe Right Runs/Marathons?

    Can anyone confirm the difference in diameter between a 26inch(25-590) wheel and a 24inch(25-540) wheel both running Schwalbe Marathons is 50mm?

    I measured my 26inch(25-590) wheel running Schwalbe Marathons and from the floor to the top of the tyre it is 650mm. I would like to confirm what the measurement of a 24inch(25-540) wheel running Schwalbe Marathons is from the floor to the top of the tyre?

    I should probably make it a clear question. If your front seat height is 490mm and your rear seat height is 420mm and you have a 26inch wheel and you were getting a new chair with 24inch wheels and wanted to keep the same pushing position, how much would you have to lower your front and rear seat height?

    Thanks,
    Rob
    Last edited by rob1; 06-28-2019 at 11:20 AM.

  2. #12
    hey, slow_runner yeah that would be useful if you could tell me the diameter of the 540 running Schwalbe Right Runs/Marathons?

    Can anyone confirm the difference in diameter between a 26inch(25-590) wheel and a 24inch(25-540) wheel both running Schwalbe Marathons is 50mm?

    I measured my 26inch(25-590) wheel running Schwalbe Marathons and from the floor to the top of the tyre it is 650mm. I would like to confirm what the measurement of a 24inch(25-540) wheel running Schwalbe Marathons is from the floor to the top of the tyre?

    I should probably make it a clear question. If your front seat height is 490mm and your rear seat height is 420mm and you have a 26inch wheel and you were getting a new chair with 24inch wheels and wanted to keep the same pushing position, how much would you have to lower your front and rear seat height?

    Thanks,
    Rob
    Last edited by rob1; 06-28-2019 at 11:21 AM.

  3. #13
    Quote Originally Posted by rob1 View Post
    hey, slow_runner yeah that would be useful if you could tell me the diameter of the 540 running Schwalbe Right Runs/Marathons?

    Can anyone confirm the difference in diameter between a 26inch(25-590) wheel and a 24inch(25-540) wheel both running Schwalbe Marathons is 50mm?

    I measured my 26inch(25-590) wheel running Schwalbe Marathons and from the floor to the top of the tyre it is 650mm. I would like to confirm what the measurement of a 24inch(25-540) wheel running Schwalbe Marathons is from the floor to the top of the tyre?

    I should probably make it a clear question. If your front seat height is 490mm and your rear seat height is 420mm and you have a 26inch wheel and you were getting a new chair with 24inch wheels and wanted to keep the same pushing position, how much would you have to lower your front and rear seat height?

    Thanks,
    Rob
    This I have done in the past.
    If the rim width is 25mm and same for all rims. Unloaded. Not on chair. 130 psi or 9 bar. Not new tyre but not overly worn.
    540 with marathon equals diameter 598mm or 23.54 inch
    559 with marathon equals diameter 617mm or 24.30 inch
    590 with marathon equals diameter 648mm or 25.51 inch
    The marathon tyre adds 29mm of sidewall height from the clincher bead. Rim size is measured to bead not edge.
    3 ways to fix seat height. Seat height is set from floor.
    Relative to the world such as tables and counters. Don't change measures from existing rig.
    Relative to axle. Shoulder to axle. Used by most fitters. Lower seat height by 25mm or 0.98 inch. This is the difference in radii from 590 to 540.
    Relative to push rim. Shoulder to push rim. Changing this measure will alter your stroke mechanics. Difference in elbow crock angle is noticeable. To maintain from 590 to 540 add 25mm or 0.98 inch to seat height.
    Altering seat height relative to axle alters vertical center which can affect horizontal center of gravity for some depending on individual characteristics.
    Did these measures with old-style marathons. Current marathon material is a bit more squishy.
    Hope this helps. Went through all this years back with help from schwalbe and tilite. Back when you could email them for tech stuff...

  4. #14
    I thought that I would check in before heading outside to prep and paint the Shadow foot plates/brackets and sorting out the dimensions for Rob.
    You have saved me some time digging out the wheels from my shed; thanks Grunt .
    I am sure that Rob will be appreciative too. The information is an excellent reference - Top marks.
    Perhaps a sticky of such tech stuff is in order?

  5. #15
    Senior Member NW-Will's Avatar
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    I did a this wheel tire measuring a while back.. Running a 25" wheels with balloon tires that have the same diameter as 27" wheels with standard wheelchair tires etc.. so they swap out with no changes to brakes, CoG etc.

    Using standard wheel chair wheels and tires so approximately 1" wide rims (23mm-28mm) seems to be the range.

    Diameter of wheels plus tires, floor to max height of tires full inflated.

    24" 540mm bead diameter - actual diameter with tire 23 7/8"
    25" 559mm bead diameter - actual diameter with tire 24 7/8"
    26" 590mm bead diameter - actual diameter with tire 25 7/8"
    27" 622mm bead diameter - actual diameter with tire 26 7/8"

  6. #16
    Thanks for all the replies. So difference in height between 26inch and 24inch tyres is 50mm. So I think I have adjusted the frame heights by the right amount.

    @Grunt "Relative to push rim. Shoulder to push rim. Changing this measure will alter your stroke mechanics. Difference in elbow crock angle is noticeable. To maintain from 590 to 540 add 25mm or 0.98 inch to seat height."

    Is that right, seems weird that adding 25mm to seat height when moving from 590 to 540 wheels would maintain stroke mechanics because that would take you even further away from the wheels and pushrims?
    Last edited by rob1; 06-30-2019 at 09:55 AM.

  7. #17
    Quote Originally Posted by rob1 View Post
    Thanks for all the replies. So difference in height between 26inch and 24inch tyres is 50mm. So I think I have adjusted the frame heights by the right amount.

    @Grunt "Relative to push rim. Shoulder to push rim. Changing this measure will alter your stroke mechanics. Difference in elbow crock angle is noticeable. To maintain from 590 to 540 add 25mm or 0.98 inch to seat height."

    Your seat height is 420mm. Noted above.
    Assume shoulder height above seat is 580mm. Total shoulder height of 1000mm or 1m.
    Both are fixed from floor.
    Push rim diameter is typically same as rim not tyre. But for ease of figuring assume the same diameter. Note that sum pushers push on tyre.
    Top of pushrim is also fixed from floor. Actual height equals diameter of rim plus one tyre sidewall height.
    Formula.
    Shoulder height from floor minus top of pushrim from floor equals shoulder to pushrim distance.
    Case with 590 rim. 1000 minus 648 equals 352mm from shoulder to pushrim.
    Case with 540 rim. 1000 minus 598 equals 402mm from shoulder to pushrim.
    Note that distance from shoulder to pushrim increases with smaller diameter wheel. To keep the same distance with larger diameter you must raise the seat height from floor.

    Shoulder to pushrim distance is but one factor of your push mechanics. Wheel diameter alters effective push stroke. This is quite different for every individual. But in general.
    Larger diameter means less downward reach. Contact arc is flattened. Gravity assist is less. Stroke becomes more forward extension with less downward contact. Higher speed at same rpm. Less leverage. More energy to propel.
    Smaller diameter increases downward reach. Larger percent of the rotation is within reach. Why racers use really small pushrims. Shorter front to back reach distance per stroke. Less rim speed at same rpm. More gravity assist and more torque equals less energy to propel.
    Efficient stroke mechanics preserve shoulder and elbow function. Efficient stroke mechanics for you is what works easiest for you.


    Is that right, seems weird that adding 25mm to seat height when moving from 590 to 540 wheels would maintain stroke mechanics because that would take you even further away from the wheels and pushrims?
    I think I goofed up the quote function ...

  8. #18
    Thanks for the reply you really know your stuff!

    I do push on top of the wheel because I have no grip so mostly just touch the top central portion of the tyre and pushrim. So I think adjusting the seat height by the difference between 26 and 24 inch wheels works for me because my push mechanics are different because I'm not grabbing the rim and pulling it round in an arc in a large range of motion like most people can.

    Is that right, as you know how this works?

    Thanks,
    Rob

  9. #19
    Quote Originally Posted by rob1 View Post
    Thanks for the reply you really know your stuff!

    I do push on top of the wheel because I have no grip so mostly just touch the top central portion of the tyre and pushrim. So I think adjusting the seat height by the difference between 26 and 24 inch wheels works for me because my push mechanics are different because I'm not grabbing the rim and pulling it round in an arc in a large range of motion like most people can.

    Is that right, as you know how this works?

    Thanks,
    Rob
    I have better arm function than most but slight hand and compromised proprioception. I push via contact of my heels against the side of tyre and top of pushrim. Starting from a stop I use the small apex at the top of the wheel just as you describe. But once moving the rotational momentum helps pull the hand and arm farther forward along the arc before the disconnect lengthening the stroke. This element of push mechanics is noticeably altered between 540s and 590s. If you raise the seat the full 50mm difference there are two considerations. One. You may not be able to reach as much of the effective arc of the smaller pushrim. Depends of course on your core function. May result in much less push efficiency requiring more energy and typically increasing strain on shoulders and arms. Two. Raising your seat 50mm will also raise your vertical center. This may require altering your horizontal center as in relative axle position. Altering axle position will typically alter push mechanics to some degree. Even minor adjustments can decrease or increase push efficiency. Suggest you experiment to find what is best for you. Every pusher is different. Small changes can produce significant long term effects. Took about six months after switching to 590s for me to realize shoulder pain was related to push mechanics. Eventually compromised on 559s. Because they fit best for me.
    Efficient push mechanics save shoulders. Shoulders are the key to independence. Listen and learn from others but pay sharp attention to what your own body tells you.

  10. #20
    @Grunt so when moving from 26inch wheels to 24inch wheels, reducing my seat height by the difference in wheel height between 26inch and 24inch wheels (50mm), is how to keep my push mechanics the same with my method of pushing mostly on the apex of the wheel.

    Is that correct?

    Thanks,
    Rob
    Last edited by rob1; 07-09-2019 at 10:35 AM.

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