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Wheelchair physics -- need an explanation

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    #31
    My very untech version at times I'll need to push my sideguards in as the wheels will rub....
    Get involved in politics as if your life depended on it, because it does. -- Justin Dart

    I shall not tolerate ignorance or hate speech on this site.

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      #32
      Originally posted by tooley View Post
      Isn't that what I tried to say?

      I knew I should have added an OT to my screen name when I joined.
      OTooley?
      stephen@bike-on.com

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        #33
        Originally posted by stephen212 View Post
        OTooley?
        sounds Irish.

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          #34
          The wheel spacing for my ZR2 was spec'd at 1" with TiLite's standard wire wheels. I never used those wheels, having always intended to use the Round Betty Dinos that I ordered at the same time. I just measured the wheel spacing and the distance is < .75", which probably explains the wheel rubbing into the side guards.

          I'm not sure if the discrepancy in the wheel spacing is an error on TiLite's part (a too narrow camber tube) or just a difference between the geometries in the different wheelsets. (I no longer have the original wheels to check and see.) I've long wished that TiLite would offer a camber tube that can accommodate adjustments to rear wheel spacing without having to futz around with adding spacers between the axle receiver and camber plug. Top End's camber tubes have receivers that allow for "infinite" adjustments. They're not pretty, but they alleviate headaches like this. (I bought a set for my Halls chair.)

          stephen@bike-on.com

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            #35
            I'm wondering if a higher spoke tension would help with this case. Though it also depends on how much tension the dino spokes can handle. I understrand they are tube type spokes.

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              #36
              Originally posted by clem View Post
              I'm wondering if a higher spoke tension would help with this case. Though it also depends on how much tension the dino spokes can handle. I understrand they are tube type spokes.
              Must of been the improper spelling of the word "understand" that led to being banned the same day as joining CareCure after a single post.

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                #37
                Any chance you had damage to the chair while on a flight?
                Every day I wake up is a good one

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                  #38
                  Originally posted by cheesecake View Post
                  Any chance you had damage to the chair while on a flight?
                  I've never flown with this chair.

                  I think the leaning in tendency of the wheels when turning was well explained above. I removed the rubber washers that I had added to the inside of the side guards and now there is no clearance issue. I'm still not sure, however, if the wheel spacing I spec'd is the wheel spacing I got.
                  stephen@bike-on.com

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                    #39
                    Originally posted by cheesecake View Post
                    Any chance you had damage to the chair while on a flight?
                    I've never flown with this chair.

                    I think the leaning in tendency of the wheels when turning was well explained above. I removed the rubber washers that I had added to the inside of the side guards and now there is no clearance issue. I'm still not sure, however, if the wheel spacing I spec'd is the wheel spacing I got. Anyone want to take a stab at answering my question in post #34?
                    stephen@bike-on.com

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                      #40
                      Originally posted by SCI_OTR View Post
                      Must of been the improper spelling of the word "understand" that led to being banned the same day as joining CareCure after a single post.
                      Ouch.

                      No soup for Clem!

                      (maybe it was an IP of an already banned member, re-registered?)
                      "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

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                        #41
                        Originally posted by stephen212 View Post
                        OTooley?
                        with the O being short for Obnoxious.

                        Originally posted by -scott- View Post
                        sounds Irish.
                        lol. you better believe it, look out when I've been drinking.


                        It really makes me wonder why people are still throwing out shots in the dark at the OP's post when I firmly believe we've explained it away. Might not be as evident for some with high spoke tension on their wheels, but is obviously present for folks using wheels with low spoke count.

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                          #42
                          There's no good way to get around the physics of the wheel "scrub." When turning in place, it generates forces that create deflection. Essentially, the only way to eliminate the aforementioned scrub would be to add a LOT of camber to the wheels. When wheels are straight up and down, they like to go in the direction in which they are pointed. Think about being on carpet and turning in place while using a basketball or tennis chair. How would it compare to making the same turn in your everyday? The cambered wheels on the ball chairs are sort of always in a "turn." So, you'll feel a lot less scrub when you're turning in place.

                          Of course, with a lot of camber, you can't get through doorways. Plus, if the camber isn't dialed in just right, it can induce rolling scrub (from toe-in or toe-out.) The best way I've found to get rid of sideguard rubbing is with a solid axle system. Wheel rigidity and integrity also plays into it, but a solid axle setup probably makes the biggest difference. The Schmicking axle system that was pictured is fantastic. I would love to have that on an everyday chair. My everyday rigid chair is set up with threaded axles (same as one might find on a racing chair or handcycle.) I rarely take the wheels off, and I wanted to see how much difference it makes. The difference between fixed and standard QR axles is considerable. My wheels don't deflect nearly as much, and the chair tracks a straight line MUCH better.

                          Unfortunately, crappy 1/2" quick-release axles are still the industry standard. At the Schmicking factory, I did see a set of QR axles that had an interesting mechanism that would sort of "expand" the end of the axle to make it more rigid. It seemed to work pretty well, but it wasn't anywhere near as nice as their 25mm setup. I've found that a solid axle system also makes pushing more efficient. There isn't as much energy lost to rolling wheel scrub, and there's a lot less deflection when pushing on the handrims.

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                            #43
                            Welcome "wheel scrub" to my wheelchair lexicon! Never heard the word scrub used this way before.

                            TWL, what's involved in converting a standard axle into a threaded axle setup? Are there axle receivers that can be easily swapped out into, say, a TiLite camber tube?

                            And of course you would like the photo of the Schmicking setup -- I got it from you!
                            stephen@bike-on.com

                            Comment


                              #44
                              Originally posted by ChrissyOT View Post

                              It is for the same reason that wheelchair wheels tend to squeak on hard surfaces while not squeaking when going straight.

                              Your tires will probably do this more on carpet (as the tires can't just slide about) and less on hard surfaces.
                              Your explanation was excellent, but I have to comment that most of my tire squeal is the result of underinflated or damp/wet tires. Although tire squeal is more likely to occur with more camber.

                              Comment


                                #45
                                Great discussion!

                                I learned a good one this weekend. I decided to make my chair a little narrower by switching from 2° to 0° so I might fit in a travel trailer my in-laws bought.

                                Got done and tried out my chair with 0° camber and was amazed how much harder it pushed AND how much harder it was to turn the chair. I went 2 days to see if I would get used to it, I didn't.

                                I switched back to 2° and could not believe how much nicer it turned and pushed. Wish I could try 4° but 1 door in my house is too narrow.

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