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Getting a new ZRA (or ZR), would appreciate some advice!

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    Getting a new ZRA (or ZR), would appreciate some advice!

    Hi everyone! It's time for a new wheelchair, and I'm thinking of either getting another ZRA, or taking the plunge and going full ZR!

    Most of my configuration is staying the same, but I'm debating going up to 26" wheels from my 25", and wondering if folks here have experience with that, and recommend for it or against it?

    I'm pretty happy with my current 25"s (and they're a huge improvement over the 24"s I had before), but I know 26" is a bit more of a standard bike wheel size, which can make it a lot easier to find replacements/spares at a regular bike shop, but I'm wondering:
    • Will they be significantly harder to push, or more strenuous on my arms?
    • Do I need to adjust my RSH/FSH or any other dimensions to account for the increased wheel diameter? The current numbers are based off my existing 25" ZRA
    • If I change the wheel size I'm assuming my COG changes too, so would it be better to stick with a ZRA until I can actually dial in exact numbers?
    Rear Seat Width: 16"
    Front Seat Width: No Taper
    Seat Depth: 15" + 3" (I thought my previous chair was ordered at 17" + 1" but the actual seat upholstery only seems to be 15")
    Front Seat Height: 20"
    Rear Seat Height: 17"
    Front Angle: 85°

    Seat to Footrest: 14.5" (my current is 16" which was adjusted down to 15.5" but STILL too far)
    Footrest Type: Titanium Footrest w/ Flat ABS Cover
    Front End Type & Footrest Width: Standard Front End - 12" (1.5" Taper)
    Back Upholstery: Velcro Adjustable
    Seat Back Type: Folding Titanium Adjustable Height w/Precision Lock Back and Rounded Rigidizer Bar
    TiShaft Back Release Bars: Aluminum
    Seat Back Height: No Push Handles - Short - 12"
    Seat Back Options: Seat Back Fold Lock, Custom 45° Angled Rigidizer Bar
    Seat Back Angle: 92°

    Center of Gravity: 3.25"
    Rear Wheel Spacing: 0.75" with adjustable plugs and spacers
    Camber: 4°
    Camber Tube Type: Titanium Camber Tube

    Seat Upholstery: Tension Adjustable Bolt On
    Seat Cushion: ROHO High Profile Quadtro Select

    Front Casters: 5" x 1.5" LiteSpeed Aluminum Wheel w/ Soft Roll Tire
    Front Forks: TiLite Slipstream Single-Sided Fork w/ Titanium Fork Stems
    Rear Wheels: 26" Spinergy LX
    Axles: Titanium Quick Release
    Rear Wheel Tire: 26" Schwalbe Marathon Plus Evolutions
    Handrims: Surge LT - Short Tabs
    Wheel Locks: Composite Scissor Locks

    Side Guards: Carbon Fiber Rigid Removable - Standard, Custom Cut to Wheel Profile
    Calf Strap: Bodypoint Padded Velcro Adjustable - Medium

    Link to the previous ZRA order thread from almost a decade ago

    #2
    Since the chair is being built around the larger wheels, you would not need to compensate by changing any of the other measurements. That's really only necessary (or a very good idea, at least) when changing sizes in a chair originally built around another size wheel. What will be different is that they will come slightly higher up under your arms than the 25" did, and require a tiny bit more energy to get rotating. Upside of needing more energy on the input is they carry the momentum farther, so it's really about what matters to you most/how you use the chair. I prefer smaller wheels for lots of short trip and lots of turning indoor chair use (like an office or home or work shop etc) but larger wheels when "touring" in more open spaces. 25" is a decent compromise IMO, and using the ERTO sizing (540, 559, and 590 for 24, 25, and 26 inch) makes finding the right tire pretty easy. Our 25"/559 is actually a very common bike tire size, but the bike world typically calls that 26", so wheelchair folks often don't know it's actually our 25", and is easy to find. (That's why ERTO is what we should always use to avoid the confusion when shopping for tires!)

    CoG should be similar enough, IMO. Not much different really, maybe a tad more rear stable but not by much.

    Since you're getting an adjustable angle back, the only differences with the ZR will be no caster angle adjustment and very limited CoG adjustment. I'd probably only opt for the ZR if I were also getting a fixed back, but that's just me. The ZR represents a chair that can be fixed around exact measurements, and leaving it with an adjustable back lessens that
    (its main) attraction for me.

    "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

    Comment


      #3
      Originally posted by Oddity View Post
      Our 25"/559 is actually a very common bike tire size, but the bike world typically calls that 26", so wheelchair folks often don't know it's actually our 25", and is easy to find. (That's why ERTO is what we should always use to avoid the confusion when shopping for tires!)
      25/559 tires/tubes are MUCH easier to find than 26/590s.

      I had a ZRA with 26/590 rims and when I had a tire failure when I was out of town I had to pay $100 in shipping to next day a set of schwalbe marathons because no bicycle shop in the city (of one million people) carried 590s.

      Because of that incident I switched to 559s for my next wheelchair (a similarly spec'd TRA) and am much happier with them. I had a flat last weekend and went into a bicycle shop because I needed a set of tire levers to change the tires. I already had the tires, but the shop asked me if I wanted a set of tubes. I told them they probably didn't have it (never saw any appropriate 590 tubes with schrader valves in any bike shop), but she went into the back and got me a pair of 559 tubes with schrader valves no problem. Asked me how many pairs I wanted!


      I wore my old 590s to the bicycle shop, which is about a one mile trip. I've made the 1 mile back and forth with my current 559s and it was noticeably more difficult with the large wheels. I don't think this had anything to do with the size of the wheels. My old 590s are SPOX wheels with marathon tires. My new wheels are XLXs with lighter weight Schwalbe Ones and they way about 20% less (apx 1.6 kg vs 2 kg each). In my opinion the lighter weight wheel/tire combination makes more of a difference than the larger diameter, which in theory should make pushing long distances in a straight line easier.

      Indoors going short distances (where I do the vast majority of my pushing) the smaller, lighter wheels are much easier to whip around without much effort and that extra tire diameter means the turning radius gets longer too.

      The only real advantage I saw with 590s over a 559 is it is easier to hop up a curb. But to me that very marginal difference isn't worth the downsides and the lack of availability of 590 tires and tubes is the main reason I'll never go back to them as an everyday wheel.

      Comment


        #4
        To both of you, thanks! Tire sizing is a really rocky/messy area, and I definitely didn't know that 559s were equivalent to bike 26" tires, so that's super helpful.

        Originally posted by Oddity View Post
        Since you're getting an adjustable angle back, the only differences with the ZR will be no caster angle adjustment and very limited CoG adjustment. I'd probably only opt for the ZR if I were also getting a fixed back, but that's just me. The ZR represents a chair that can be fixed around exact measurements, and leaving it with an adjustable back lessens that
        (its main) attraction for me.
        Ah, that's a fair point! I actually don't need an adjustable back, but does not having one mean you can't fold it down either? The folding is pretty important to me for getting the chair in and out of the car.

        And how much COG adjustment would you get on a ZR? Are we talking +/- 1" from what it's set to, or even less?

        Originally posted by funklab View Post
        My new wheels are XLXs with lighter weight Schwalbe Ones and they way about 20% less (apx 1.6 kg vs 2 kg each). In my opinion the lighter weight wheel/tire combination makes more of a difference than the larger diameter, which in theory should make pushing long distances in a straight line easier.
        Oh huh, what do you see as the different between the XLX and Spox? Are the XLX just much lighter? And what performance differences do you see between the MPEs and Ones? I've been using MPEs cuz I live in a pretty urban area and used to get a LOT of flats before the MPEs

        Comment


          #5
          Originally posted by faji_tama View Post

          Oh huh, what do you see as the different between the XLX and Spox? Are the XLX just much lighter? And what performance differences do you see between the MPEs and Ones? I've been using MPEs cuz I live in a pretty urban area and used to get a LOT of flats before the MPEs
          Spot has more spokes. Mine are different sizes, but I suspect a similarly sized spox wheel weighs a tax more than XLX, which are really just X laced LX wheels, so I assume yours as spec’d out above would be similarly light.

          performance on the Schwalbe ones are definitely better than the marathons, except in loose dirt or mud. They weigh much less (website says 215 grams vs 520 grams each, which is nothing to sneeze at!). Unless I lived in a snowy place or spent a lot of time off of paved surfaces I’d go with the Ones every time for performance. They are also much easier to change that the stiff marathons. That being said I just had to repair my tire recently because of a tiny piece of metal that never would have defeated the marathons I used to run.

          I think for everyday I’ll continue to run the Schwalbe Ones, but if I’m traveling or doing anything outdoorsy I’ll probably switch back to the marathons for their reliability and better grip.

          Comment


            #6
            Yep! 559 is my best choice too. For all those reasons.

            Rotational mass is an interesting thing. In and of itself, it doesn't actually consume energy, rather, it stores energy! The additional energy needed to deflect a heavier mass into a rotation is stored and returned until it is dissipated by an external force (i.e. into heat by grabbing the push rim; friction between tire and ground, etc.)

            In the Spox vs LX example, all the weight savings is in the hub, which is actually the least important factor. The distance from center, of the mass, of a rotating object, is the biggest factor in how it stores and releases energy. That's mostly down to tire and rim weights. Making the hub lighter is almost irrelevant to how they push, since it is the center of the mass (makes lifting them easier though.) What you're feeling is almost entirely down to the new tire you chose being so much lighter, and smaller...because...

            ...depending on how far away from center, the differences in how mass changes the performance -energy storage and release- characteristics of a rotating mass. It changes by the square of the radius difference. Meaning doubling it would cause a 4x change in stored energy potential! So, little changes on the perimeter make the biggest difference!

            A lighter tire on a smaller rim is about the biggest change we can experience in this regard!

            The rate at which we accelerate is the key external factor, that we control, that affects how much additional "horsepower" we need to initially store into the rotating mass to begin acceleration. This affects our senses and can feel "heavier" to start, but we get most of that back if we just let it roll out. It's a trade off. Want to accelerate fast over a short distance? That will take (and store) more energy than a slower acceleration over a longer distance. So, how they "feel" also comes down to our push technique/goals (are we moving around a kitchen? Cruising the mall? In a race? Etc.)

            The biggest trade off is that WE are the ones who typically have to dissipate the stored energy of our wheels into heat in order to stop, or change directions! More stored energy = more effort on that side of the equation, too, by us.

            All this to say:

            - Lighter tires are WAY more important than lighter hubs and axles etc.

            - Larger wheels don't take "more" energy, they "store" more energy, BUT...

            - Since we typically have to dissipate that stored energy ourselves, we aren't often benefitting from the additional stored energy. Only folks who are pushing long distances, and relatively straight, tend to benefit from the "stored energy" characteristics of larger diameter wheels.

            Anyway, that's my take on 'rotational mass' and pushing a chair. I chose the middle size just to split all the differences. I use Marathon tires when I don't care, and Speed Runs when I do, since we're mostly experiencing/"feeling" the tire and tube weights, and tire pressure, anyway.

            👍😃




            Originally posted by funklab View Post

            25/559 tires/tubes are MUCH easier to find than 26/590s.

            I had a ZRA with 26/590 rims and when I had a tire failure when I was out of town I had to pay $100 in shipping to next day a set of schwalbe marathons because no bicycle shop in the city (of one million people) carried 590s.

            Because of that incident I switched to 559s for my next wheelchair (a similarly spec'd TRA) and am much happier with them. I had a flat last weekend and went into a bicycle shop because I needed a set of tire levers to change the tires. I already had the tires, but the shop asked me if I wanted a set of tubes. I told them they probably didn't have it (never saw any appropriate 590 tubes with schrader valves in any bike shop), but she went into the back and got me a pair of 559 tubes with schrader valves no problem. Asked me how many pairs I wanted!


            I wore my old 590s to the bicycle shop, which is about a one mile trip. I've made the 1 mile back and forth with my current 559s and it was noticeably more difficult with the large wheels. I don't think this had anything to do with the size of the wheels. My old 590s are SPOX wheels with marathon tires. My new wheels are XLXs with lighter weight Schwalbe Ones and they way about 20% less (apx 1.6 kg vs 2 kg each). In my opinion the lighter weight wheel/tire combination makes more of a difference than the larger diameter, which in theory should make pushing long distances in a straight line easier.

            Indoors going short distances (where I do the vast majority of my pushing) the smaller, lighter wheels are much easier to whip around without much effort and that extra tire diameter means the turning radius gets longer too.

            The only real advantage I saw with 590s over a 559 is it is easier to hop up a curb. But to me that very marginal difference isn't worth the downsides and the lack of availability of 590 tires and tubes is the main reason I'll never go back to them as an everyday wheel.
            Last edited by Oddity; 28 May 2021, 10:28 AM. Reason: Used the wrong Emojii! Definitely needed to be changed.
            "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

            Comment


              #7
              If you need folding, then you need the adjustable one.

              The CoG adjustment of a ZR is ~1" in total, so like ~1/2" either way off the center position. Maybe a little more. Not much though.

              re: LX/Spox/XLX;

              LX and XLX are lighter to lift when transferring. XLX are cross laced so quite a bit more rigid than either of the others.



              Originally posted by faji_tama View Post
              To both of you, thanks! Tire sizing is a really rocky/messy area, and I definitely didn't know that 559s were equivalent to bike 26" tires, so that's super helpful.



              Ah, that's a fair point! I actually don't need an adjustable back, but does not having one mean you can't fold it down either? The folding is pretty important to me for getting the chair in and out of the car.

              And how much COG adjustment would you get on a ZR? Are we talking +/- 1" from what it's set to, or even less?



              Oh huh, what do you see as the different between the XLX and Spox? Are the XLX just much lighter? And what performance differences do you see between the MPEs and Ones? I've been using MPEs cuz I live in a pretty urban area and used to get a LOT of flats before the MPEs
              "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

              Comment


                #8
                Originally posted by Oddity View Post
                LX and XLX are lighter to lift when transferring. XLX are cross laced so quite a bit more rigid than either of the others.
                and XLX has a lot more room for your fingers since the spokes cross right at the hub effectively making it only 3 spokes when you go to grab it. That’s the main reason I went with xlx instead of lx.


                Comment


                  #9
                  Originally posted by Oddity View Post
                  LX and XLX are lighter to lift when transferring. XLX are cross laced so quite a bit more rigid than either of the others.
                  So not much difference in weight between these two then? What does the additional rigidity give you? I'm assuming it means less energy lost to flex, so more energy goes towards actual pushing and forward motion?

                  Comment


                    #10
                    I don't think the stiffness differences are big enough to make much difference push efficiency wise, but maybe. They help with limiting spoke flex when using hub locks. That is why I chose them. And they look interesting. Expensive though, IMO.

                    Click image for larger version

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                    "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

                    Comment


                      #11
                      Those do look pretty rad! Spoke with my ATP though and it sounds like if I wanted the XLX I'd have to pay out of pocket for those, but they'd be willing to cover the LX, so, LX it is!

                      Comment


                        #12
                        Originally posted by Oddity View Post
                        I don't think the stiffness differences are big enough to make much difference push efficiency wise, but maybe. They help with limiting spoke flex when using hub locks. That is why I chose them. And they look interesting. Expensive though, IMO.
                        Hi Odd. I am no expert, however as far as I know cross laced bike wheels are for drive wheels and wheels that take larger toque and side load. I think that if Spinergy were serious about providing a truly rigid wheel the construct would follow convention rather than providing what I see as a compromise wheel and a marketing move for the more fashion focused. The standard LX is a good functioning long lasted wheel IMO and does go some way to providing a degree of 'suspension' that doesn't bother me.
                        Good, sensible choice faji-tama.
                        Last edited by slow_runner; 1 Jun 2021, 4:55 PM.

                        Comment


                          #13
                          I might start a new thread about this specific issue, but I'm curious if anyone with a ZRA has had issues with it being a little too forward-tippy? I can go over small rocky/pebbly ground and uneven pavement okay, but if I hit any obstacle that's a hard stop (like an elevated tile, curb, etc) that's half an inch or more higher than my current ground, my casters have a tendency to catch, which can sometimes threaten to throw (or has thrown) me out of my chair if I'm going fast enough.

                          My COG feels like it's set pretty well: it's far back enough that I'm not super backwards-tippy, but forward enough that I can still pop wheelies very easily. I think the bigger issue might be that the overall length of my current ZRA is shorter than my old Quickie Revolution? Having measured it though, the distance from the fork stem to center of my rear wheel (or the center of caster of center of rear) is the same on both, and if I ever lean my weight forward on the chair, my hand and weight placement still falls behind the stem on both chairs: see the diagram below for an idea of what I mean...

                          Click image for larger version  Name:	chair.png Views:	0 Size:	902.1 KB ID:	2909903

                          At first I thought the two distances were shorter between my chairs, but having measured it that doesn't seem to be the case, so I'm not sure what's increased the tippiness of the ZRA, and would appreciate some ideas around it that don't result in increasing the length of the chair.
                          Last edited by faji_tama; 1 Jun 2021, 10:39 PM.

                          Comment


                            #14
                            Originally posted by faji_tama View Post
                            I might start a new thread about this specific issue, but I'm curious if anyone with a ZRA has had issues with it being a little too forward-tippy? I.
                            A full side on flat perspective image would help faji.
                            I do know that those damn TiLite suspension units are rubbish as in they have too much trail in the static position and when the elastomar is under compression the trail becomes even more exaggerated. They are not my cup of tea. If you roll along sedate and require a softer ride they are probably ok.

                            Comment


                              #15
                              Originally posted by slow_runner View Post
                              A full side on flat perspective image would help faji.
                              I do know that those damn TiLite suspension units are rubbish as in they have too much trail in the static position and when the elastomar is under compression the trail becomes even more exaggerated. They are not my cup of tea. If you roll along sedate and require a softer ride they are probably ok.
                              Yup, just posted one with measurements! I have the titanium forks with the single-tine slipstreams, along with soft rolls, so no actual suspension in mine

                              Comment

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