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Occasional use off-road wheels on a budget???

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    #31
    A lot of the question about using push-rims with different size wheel rims probably depends on the exact style of rim and how they mount - but there isn't anything that would stop you from making some kind of adapter plates, or bending / re-drilling any metal mounting tabs... It's just metal, easy enough to cut and bend.

    As a first guess, there is a 33mm difference in the bead seat diameters, and assuming similar construction, I'd expect about the same difference at the pushrim mounting points. Divide 33 by 2, and that's 16.5mm on each side, or for us Americans, 3mm is about 1/8" so you'd need about a 5/8" offset.

    Slightly more of a challenge is if using bicycle rims, is making the mounting points to start with, but I don't see that as all that big of a problem - again it's just metal...

    ex-Gooserider
    T-5 ASIA-B para, currently working on building own power chair, as being in a manual is an EXTRA handicap.

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      #32
      Originally posted by ex-Gooserider View Post
      ...clip... but there isn't anything that would stop you from making some kind of adapter plates, or bending / re-drilling any metal mounting tabs... It's just metal, easy enough to cut and bend....clip...
      It sounds simple enough. The problem I had was keeping the rim circle to be perfectly parallel to the tire circle. At slow speed, such as climbing it might not matter, but mine turned out so waperjawed, I did not even try it out.
      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.

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        #33
        Originally posted by nonoise View Post
        It sounds simple enough. The problem I had was keeping the rim circle to be perfectly parallel to the tire circle. At slow speed, such as climbing it might not matter, but mine turned out so waperjawed, I did not even try it out.
        What do you mean by this? You tried drilling holes in a bike rim for handrims and it messed it up? Did you have the spokes in to help hold the shape while you were doing it?
        Board Member of Assistance Dog Advocacy Project working in Education. Feel free to ask me any service dog questions!

        I am not paralyzed. I have a genetic connective tissue disorder with neuro complications and a movement disorder.

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          #34
          Originally posted by ~Lin View Post
          What do you mean by this? You tried drilling holes in a bike rim for handrims and it messed it up? Did you have the spokes in to help hold the shape while you were doing it?
          Not drilling the rims, when I go the wide tire route it will be for beach sand and no push rim will be needed.

          I wanted, (still do) to put 24 inch vinyl post rims from sun wheels on 24 inch Spinergy LX tab mounts. I made "L" shaped conversion brackets and the whole deal, it just did not true up. If I had done the work in a machine shop using better tolerance control, I may have had better luck. It should be doable.
          Last edited by nonoise; 26 Oct 2014, 4:56 AM.
          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.

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            #35
            I tend to be a go-for-it type of person, but I think when it comes to wheels, the right equipment and a lot of experience are really needed. Although many things are possible, the results may not be that workable, as Nonoise pointed out with trying to modify hand rims.

            It does not take much for a wheel not to be true, and in our situation I don't think it's worth the investment in materials and time to have a bad result. That’s why our project discussed in this post Advice for best shock absorbing outdoor rear tires is taking so long.

            Even my brother who is an experienced mechanical engineer with a major bike component manufacturer with a full workshop says it's not worth it to do his own wheel stuff. See Sheldon Brown's and Roland Cook's wheel building sites if you want to know more.

            Partner of an incredible stroke survivor. Limitations: hemiparesis and neglect (functional paralysis and complete lack of awareness on one side). Equipment: TiLite ZRA 2 and 2GX, Spinergy ZX-1, RioMobility Firefly. Knowledge: relative newbie for high-level equipment (2012), but willing to try to help others who are new with similar limitations (definitely not a guru, but inquisitive).

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              #36
              Adapting the pushrims to a different diameter rim may also be easier or harder depending on the style of rim and it's mounting. I'm sure there are lots of variants, but on my two sets of wheels, one would probably be easier to modify than the other. Ironically it is the set that would be harder to modify that I'm looking to change.

              Both are "Natural Fit" rims, but one is the regular, and one is the "LT" smaller style. (I like the larger cross section regular style much better)

              (Note - the following is eyeball sketching, I haven't bothered taking measurements and making drawings, and won't be since I don't plan to put pushrims on the modified wheels)

              The LT style rim's wheels have tabs that stick out of the rims, with holes in the tabs. Screws go straight through the tabs, some spacers, and into threaded holes in the pushrim. To modify those would require bending some brackets, with at least two bends, and a hole in each end - a bit tricky to get consistently made w/o building some jig fixturing and precision work.

              The regular rims have tabs on them that stick out and are bolted directly to the rims through holes that are drilled in the spaces between the spokes. While it might be possible to just bend the tabs to a new position, I suspect that it would also be necessary to also add a short extension to each tab. However that should be easier to do as the needed part would be easier to make.

              ex-Gooserider
              T-5 ASIA-B para, currently working on building own power chair, as being in a manual is an EXTRA handicap.

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                #37
                My thought is to try and get a pair of 25/559 size natural fit (lt, the smaller size works better for me) tab mount (bolt directly to the rim) and drill the holes in 559 bicycle wheels to attach them. Much simpler than modifying the natural fit attachments I think.

                I have a pair of NFs that are I believe whats called post mount, with the bend in them. I definitely wouldn't want to mess around with modifying those or modifying wheels to work with those!
                Board Member of Assistance Dog Advocacy Project working in Education. Feel free to ask me any service dog questions!

                I am not paralyzed. I have a genetic connective tissue disorder with neuro complications and a movement disorder.

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                  #38
                  Originally posted by nonoise View Post
                  Well that is a surprise. I copy pasted Melrose X-Wheels and got the picture instead, cool. So looking at that picture, a year ago I tried to build something like that out of composite (the cheap plastic) wheels hooking them up side by side. Some things don't work out. Ah, many things don't work out.
                  Pity the composite ones didn't work out, the melrose ones are welded together, best not to do three in a row though as it takes quite a while and a bit of effort to pull the centre tyre/tube on.

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                    #39
                    Originally posted by Tajio View Post
                    Pity the composite ones didn't work out, the melrose ones are welded together, best not to do three in a row though as it takes quite a while and a bit of effort to pull the centre tyre/tube on.
                    We could strap them together using the tab mount holes in the rims.
                    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.

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                      #40
                      It has been a while, but I thought I should post an update... I have made a set of off-road wheels and they seriously kick butt...

                      First off - a lot of this info comes from the 'Sheldon Brown' website, which is one of the most authoritative sites around for all things bicycle, which has relevance for our chairs in terms of wheel sizing...

                      To summarize the most relevant bits for most of us....

                      The best, most consistent sizing information on tire and wheel sizing is the ISO or ERTO metric standards, which ALL the other sizes can be translated into... The main number is the 'bead seat diameter' which is the diameter of the part of the rim where the tire bead sits, and is primarily what determines if a given tire will fit on the rim.

                      There are TWO different US "24 inch" tire size standards, and a tire made for one size will NOT fit on a rim from the other size. They are the FRACTIONAL size system that will be sized 24 X <number and a fraction> - i.e. 24 X 1, 24 X 1 3/8, 24 X 1 1/2, etc; and the DECIMAL size system that will be sized 24 X <number and a DECIMAL> i.e. 24 X 1.00, 24 X 1.325, 24 X 1.5, etc... The Fraction sizes all use an ISO '540' mm rim diameter, and the Decimal sizes use an ISO '507'mm rim diameter. In both cases, the number after the X is the 'section width' of the tire, which is approximately the diameter - both height and width of the inflated tire. In the ISO system, the section width is given in mm before the rim diameter, so for instance the 24 x 1 3/8 tires on my old wheels would be a 37-540 ISO size.

                      MOST wheelchair tires (especially the 'hospital grey' ones) use the 24-FRACTION size system, or a 540mm diameter rim. Typically the tires used are fairly narrow, around 1 to 1 3/8" either solids or pneumatics - with the pneumatics using a high pressure tire for claimed extra low rolling resistance.

                      Per Sheldon's website, if one ignores wind resistance, which is not really a factor for most wheelers, the rolling resistance of a fat tire at a low pressure is the same as a skinny tire at higher pressure, but the low pressure tire will be MUCH better at soaking up bumps

                      Since the tire wraps around the wheel, one can estimate the approximate wheel diameter by twice the ISO section size, plus the rim size, so my 37-540 wheels should be (37 x 2) + 540 = 614mm. I measured them as about 610mm, which is pretty close - between possible measuring error, and that tire sizes are approximate anyway, spot on...

                      So if one can switch the rim to a 507, your rim is 33mm smaller, divided in half since it's a diameter, says a 12mm larger section size tire would be about the same diameter (49-540 would be about a 24 x 2.00 tire)

                      As has been mentioned, one of the challenges is that most chair hubs seem to be 30 spokes or other strange numbers, and most bicycle rims are 36 hole. The biggest challenge I found was finding suitable hubs.

                      Sport-Aid lists some hubs made by SUN in their catalog at US$60-70 pair, but I ended up getting a pair of 'new-old stock' hubs from Melrose at less than that, but I don't know if they have any more of them. I suspect they are the Sun hubs with Melrose stickers on them, as they look the same.

                      I got the widest aluminum rims I could find, and decided that I wanted to go 'whole hog' and get 3.00 inch tires, which gave me wheels about 2" bigger in diameter than the old ones but see more on this later... This is about a 75-507 ISO size tire.

                      Another challenge is getting the right spokes, as you need to get just the right length. One can spend a lot of money on very fancy spokes, or cheap out on the minimal ones. I opted to take the middle ground as there is a strong case that the best blend of strength, durability and reliability is to go with a 'double butted stainless steel' spoke with brass nipples. There is a company called "Dan's Comp' which I am told by many friends in the custom bicycle world is the best place to get spokes... I think I ended up paying 25 cents each, for 80 spokes or $20... (get extras, you will want them)

                      One also has to determine the spoke pattern. Most chair wheels are 'radial spoked' which is slightly lighter, but technically weaker (one is strongly advised never to do radial spoking on a bicycle wheel). Since I am going to be using these wheels off road, I opted to use a 'three cross' pattern, which is the most common bicycle spoking, where each spoke crosses three others - in theory this is one of the strongest and stiffest patterns.

                      The sizing is tricky as you need to precisely measure the diameter of the spoke hole circles in the wheel flanges on the hubs, the distance between the flanges, and the actual diameter of the spoke circle on the rims... These numbers are fed into formulas that determine just how long the spokes need to be... Fortunately there are many online calculators for determining spoke length. Use several as they don't all give quite the same answer...

                      I built the wheels myself, with some help and advice from friends that do custom bike building, but mostly using information online. The process is a bit slow and tedious, especially the first time, but it is NOT all that complex or mysterious if you can read and follow the step by step instructions they give you...

                      I did NOT use push-rims on these wheels, as the three-inch wide tires make the overall chair width about the same or a little wider than it is with the regular wheels and push rims, and I didn't want to make it any wider... I was also wanting to not have more things to get bashed while getting the chair over rocks and the like. I can push on the tires instead (wear gloves)....

                      I had to build the wheels with a considerable 'off-set' to push the rims as far to the outside as I could (this complicates truing the wheels slightly, and does weaken them (one reason I used the stronger spoking pattern to compensate)) in order to get clearance on the frame. Even so, I still needed to use over-length axles and add a spacer in between the wheel and the chair frame in order to keep the tire from rubbing. It wouldn't be a problem with skinnier tires, and details on this will vary somewhat depending on the chair.

                      As mentioned above, the fat tires do make the total wheel diameter larger than the old wheels. So if I changed just the wheels, it would upset the seating angles and general balance of the chair. So I also was able to replace the front caster forks with ones that allow me to mount either 4 or 6" casters. I normally use 4" casters, but when I go to the off road wheels, I also swap the front casters for the 6" size. The bigger front casters are better on rough ground, and raise the front of the chair about the same as the rear wheels raise the back of the chair, so everything stays the same, except the seat-ground height goes up...

                      Obviously this also changes the settings I need on my brakes, but I found a neat trick that works for my chair, but might not work for others... I can adjust where the clamps that hold the brakes are on the frame, so I pushed the brakes all the way into the clamps, and then positioned the clamps so the brakes work on the smaller wheels. When I put on the bigger wheels, I leave the clamp in place, but slide the brake out in the clamp till the end of it is flush with the end of the clamp, which works perfectly with the big wheels...

                      So I can go from indoor to off-road configuration in about 20 minutes by swapping the wheels, casters and resetting the brakes. With lots of practice I could probably do it even faster, but....

                      ex-Gooserider
                      T-5 ASIA-B para, currently working on building own power chair, as being in a manual is an EXTRA handicap.

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                        #41
                        Wow ! great job obviously !
                        Some picts could be an help, especially for the brake mods (I didn't understand well
                        C6-7 since mid 2002, no hand control nor triceps.
                        my website & my job (in France): Accessibility advisor www.acceslibre.eu
                        Also working on a French research about Peer counseling and Empowerment.

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                          #42
                          Sorry, don't really have any photos...

                          I agree the brake description wasn't very clear, so I will try a bit more... I use side-swinging 'snap' brakes, but it really doesn't make a lot of difference, as most brakes I've seen, particularly the ones intended for use on a lot of different chair models, are based on the same construction idea. The moving parts of the brake are mounted on a round shaft or bar that slides in and out of a clamp to adjust the amount of pressure the brake applies to the tire when engaged.... This design allows a lot of flexibility as it allows an easy choice among the many different styles and operating methods of brakes without needing any other modification to the chair.... Since both personal tastes and the ability to operate a given mechanism varies this is an important feature...

                          The exact design of the clamp varies from chair to chair, so my approach won't work for a lot of folks, but on my chair (a Quickie Q-7) the clamp has two sets of bolts, one that secures the clamp in position on the chair frame, and the other that secures the brake bar... Normally one would leave the frame half of the clamp in place and just make adjustments by sliding the brake bar back and forth...

                          Since I needed to fit a wide range of tire diameters, from the 'Mako Kik' solid tires (estimated 25-540 size, measured diameter 588mm) to the off road wheels (78-507, estimated diameter 697mm) I found that if I pushed the brake bar all the way into the clamp, and then set the clamp to the right place on the frame to work with the Mako tires, which were the smallest diameter I ever expect to use, then I could simply leave the clamp in place, and slide the bar out as far as it should go and it would be in the right position to work on the large tires.... This means that I can reset the brake position without needing to do a lot of fiddling to get the adjustment right....

                          Hope this helps...
                          T-5 ASIA-B para, currently working on building own power chair, as being in a manual is an EXTRA handicap.

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