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Thread: Wheel Diameter Question?

  1. #1

    Wheel Diameter Question?

    Hello All,
    Newbie here when it comes to wheelchairs. So, I am about to take possession of my first wheelchair which is a Tilite ZRA on June 6th....Finally. I am also a gear head so I have ordered some extra wheels. I bought a set of fat wheels to make it easier to get around in the yard, ball fields and trails. I also bought a set of Spinergy Carbon Blades. I have spent a lot of time around grand prix sailboats where carbon fiber is the material of choice and it just looks so cool....My wedding band happens to be titanium with carbon as well ;-). I just received the Carbon Blades and they look OK, the finish could be better but we are not talking about a half million dollar mast here.

    With that said I have a question on wheel diameters. I was told that my fat wheels would be a wee bit smaller in diameter then my regular wheel when I bought them and it should not be a problem.....and then I started doing some reading. So comparing my skinny wheels to my fat wheels they are approximately 25MM's smaller in diameter meaning that when installed the back of the chair will sit @ 12MM (1/2") lower. To me that does not seem like a huge issue but doing some reading makes me second guess my thoughts. I would imagine that being a bit lower in the back will make the chair a bit more tippy and the geometry of the casters will be off a bit. How much of an issue is this? The chair is being delivered with the CG set at 2.5" (I find the whole CG thing very strange because the biggest contributor to the CG, the person sitting in the chair, is always moving so the CG is pretty dynamic) and the chair is coming with 2" of dump. I am thinking that 75% of the time I am using the fat wheels I will have a freewheel attached to the front of the chair.

    Thoughts?

    Cheers,
    Jim

  2. #2
    Senior Member Oddity's Avatar
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    A properly setup Freewheel will add another 3/4-1" of front seat height, so that would be too much dump for me (including the smaller wheels). You can tune that down to ~1/2" but that isn't enough rise for the casters IMO. You'll just have to see how it works out for you. My axle position (better term than CoG) is set at 4" though, so my setup is far less forigiving in the rearward stability department. I can become unpushably unstable just by changing my backrest angle by a degree or 2. A Freewheel works best with some weight on the front end, part of its beauty is in how far it extends the wheelbase and spreads out the load. Too much dump causes the Freewheel to spend most of its time off the ground under hard pushing, and all of your weight sinking into the ground under the back wheels. Since your chair is adjustable you might want to tune 1/2" or dump out and add some squeeze with the backrest. That's what I would try, anyway, to try to find a CoG balance between the wheel sets plus the Freewheel.
    "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

  3. #3
    Quote Originally Posted by Oddity View Post
    A properly setup Freewheel will add another 3/4-1" of front seat height, so that would be too much dump for me (including the smaller wheels). You can tune that down to ~1/2" but that isn't enough rise for the casters IMO. You'll just have to see how it works out for you. My axle position (better term than CoG) is set at 4" though, so my setup is far less forigiving in the rearward stability department. I can become unpushably unstable just by changing my backrest angle by a degree or 2. A Freewheel works best with some weight on the front end, part of its beauty is in how far it extends the wheelbase and spreads out the load. Too much dump causes the Freewheel to spend most of its time off the ground under hard pushing, and all of your weight sinking into the ground under the back wheels. Since your chair is adjustable you might want to tune 1/2" or dump out and add some squeeze with the backrest. That's what I would try, anyway, to try to find a CoG balance between the wheel sets plus the Freewheel.
    Thanks for the Info Oddity. I had to talk to Ryan at Spinergy because one of the push rings was mounted backwards on my Carbon Blades so I wanted to make sure I was changing the correct one. Ryan has been great not only with answering my questions about Spinergy product but also offering help with anything related to my injury...pretty darn nice of him and he has 25+ years in a chair. He said pretty much what you said in that I should try it out first and see how it works and if need be I can raise the RSH one step if need be depending on just how much time I have the fat wheels on the chair and how it feels.

    Thanks again for the info....can't wait to get into the new hair and check out the different wheels and Freewheel.

    Cheers,
    Jim

  4. #4
    What is your level of injury? The ZRA is fully adjustable where you can change your COG (axle location), caster angle, rear seat angle, and Rear seat height pretty easily. If you're a gear head like I am, then you should be able to adjust the chair pretty easily. In regards to the fat wheels with the free wheel the increase of height for the freewheel in front and the 25mm increase in height for the fat wheels should be a negligible difference especially for offroading. The 2.5" COG will keep you pretty steady which means it's harder to do a wheelie or flip backwards (yes dependent on your body) and the 2" dump (depending on your level of injury). You can use the manual to learn how to properly adjust the chair for your needs. For example, I started off with a 2.5" COG on my first chair. On my current (third) chair I am at 3.5" with a T7 Complete injury. I also use off road wheels a set of 25" spinergy with 2.25" tires and with my freewheel if I really need it. I'm trying to be more simple and use less so I'm not using my freewheel as often, 1-2 times a year. I normally run my spinergy carbon blade with the schwalbe one tires for every day.
    http://www.adaptivesportsforums.com/

    I love sports! Wheelchair Basketball, Sled Hockey, Mono-Skiing, and Handcycling.

  5. #5
    Quote Originally Posted by outkastsl View Post
    What is your level of injury? The ZRA is fully adjustable where you can change your COG (axle location), caster angle, rear seat angle, and Rear seat height pretty easily. If you're a gear head like I am, then you should be able to adjust the chair pretty easily. In regards to the fat wheels with the free wheel the increase of height for the freewheel in front and the 25mm increase in height for the fat wheels should be a negligible difference especially for offroading. The 2.5" COG will keep you pretty steady which means it's harder to do a wheelie or flip backwards (yes dependent on your body) and the 2" dump (depending on your level of injury). You can use the manual to learn how to properly adjust the chair for your needs. For example, I started off with a 2.5" COG on my first chair. On my current (third) chair I am at 3.5" with a T7 Complete injury. I also use off road wheels a set of 25" spinergy with 2.25" tires and with my freewheel if I really need it. I'm trying to be more simple and use less so I'm not using my freewheel as often, 1-2 times a year. I normally run my spinergy carbon blade with the schwalbe one tires for every day.
    I am a T10 Complete (supposedly)....I have gotten pretty good strength back in my hip flexors and some action in my butt muscles as well as a bunch of sensation in my skin down to my knees. I am just back from a PT session after a two week lapse and my PT is shocked how strong my hip flexors have gotten and said there is no way I am actually "Complete", not sure what that gets me but I will take it.

    On the chair I will actually be loosing about 12MM on rear seat height with the fat wheels on and the the added 25MM+ front seat rise because of the Freewheel. I have been practicing leaning forward in the hospital chair I am still in but I am still not very good at doing that along with pushing. I have read the whole manual for the ZRA and yes adjusting things will not be an issue for me. One thing I was told is change one thing at a time and see the results...sounds like what you should do whenever you are "tuning" anything from car to a boat and now a wheelchair. On adjusting the RSH do you know what the increments are?

    Question on your Carbon Blades, are yours the spread tow version that Spinergy did for Tilite or the more twill like version from Spinergy. How is the finish on yours? I know I am being picky but mine are only so so. If I cared more I would think about taking the wheels apart and doing some more clear coats on them.

    Thanks.

    Cheers,
    Jim

  6. #6
    Rather than adjusting rear seat height when you swap out your wheels, you can get bigger off road tires. That way you'll have less dump to compensate for the freewheel.

  7. #7
    Quote Originally Posted by August West View Post
    Rather than adjusting rear seat height when you swap out your wheels, you can get bigger off road tires. That way you'll have less dump to compensate for the freewheel.
    Negative....Already have a wheel set with off road tires and there are not a lot of offerings in the 501 rim diameter to go bigger.

    At lunch I talked to a guy, who I have gotten friendly with, who is running the same wheels (both fat and skinny) and the geometry of our chairs is pretty similar. He says he can feel the difference a wee bit but it has not caused any issues at all. I am thinking I am going to be fine as most of the time the wheels are going to be used for to and from the wee mans base ball games, up in VT to get from the lodge to the where I strap on a sit ski, and in the back yard so not a lot of long distance stuff. If we do a longer "walk" and I do have an issue I can take the 10 minutes to adjust the RSH. I just found that the adjustment increments for the RSH is 3/8" (10MM) so that will be pretty darn close.

    Cheers,
    Jim

  8. #8
    Just an idea if dump is an issue for you as it is for Oddity. It's not an issue for me. But then again, my COG is 3.5" not 4". You'll find what works for you. Good luck.

  9. #9
    Quote Originally Posted by LJH View Post
    I am a T10 Complete (supposedly)....I have gotten pretty good strength back in my hip flexors and some action in my butt muscles as well as a bunch of sensation in my skin down to my knees. I am just back from a PT session after a two week lapse and my PT is shocked how strong my hip flexors have gotten and said there is no way I am actually "Complete", not sure what that gets me but I will take it.

    On the chair I will actually be loosing about 12MM on rear seat height with the fat wheels on and the the added 25MM+ front seat rise because of the Freewheel. I have been practicing leaning forward in the hospital chair I am still in but I am still not very good at doing that along with pushing. I have read the whole manual for the ZRA and yes adjusting things will not be an issue for me. One thing I was told is change one thing at a time and see the results...sounds like what you should do whenever you are "tuning" anything from car to a boat and now a wheelchair. On adjusting the RSH do you know what the increments are?

    Question on your Carbon Blades, are yours the spread tow version that Spinergy did for Tilite or the more twill like version from Spinergy. How is the finish on yours? I know I am being picky but mine are only so so. If I cared more I would think about taking the wheels apart and doing some more clear coats on them.

    Thanks.

    Cheers,
    Jim
    Hey Jim, not sure what you mean regarding my spinergy carbon blades when you stated "the spread tow version that Spinergy did for Tilite or the more twill like version from Spinergy." The finish looks good to me but I'm not an expert in carbon fiber.
    http://www.adaptivesportsforums.com/

    I love sports! Wheelchair Basketball, Sled Hockey, Mono-Skiing, and Handcycling.

  10. #10
    Senior Member Oddity's Avatar
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    Quote Originally Posted by August West View Post
    Just an idea if dump is an issue for you as it is for Oddity. It's not an issue for me. But then again, my COG is 3.5" not 4". You'll find what works for you. Good luck.
    Actually I'm at 4.5", just checked while cleaning. Has a lot to do with lower body counter weight too. I'm a lower motor neuron injury so my legs are just bones at this point, completely atrophied. I'm all upper body weight. And rising.
    "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

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