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Old 10-21-05, 11:00 AM   #1
MMACH 5
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Plastic pellet-filled tires????

This is pretty well off topic, but I think y'all can help...

My eight year old daughter spends part of her day in a wheelchair, (she can walk, but a metabolic muscle disease leaves her exhausted if she overdoes it).

Insurance recently paid for a new wheelchair. It is titanium and super-nice. The only problem is that they outfitted it with tires that contain plastic pellets instead of standard pneumatic tires. My wife, basically relaying what the wheelchair rep had told her, said these tires would be just as comfortable as inflatables without the maintenance.

So I hopped in the chair and took it for a spin. What a crock! It feels like the chair is riding on the rims. You can feel every crack and pebble. I told my wife that we needed to pop those tires off, take out the pellets and put in tubes. She will have none of it. She likes the "no maintenance" part of it. I just really think it will make a huge difference in comfort. My daughter is seems to be fine with it either way, but I think she'll change her tune if she has to spend an extended time in the chair.

If anyone has any selling points, besides the comfort, (since my wife thinks these tires will be just as comfortable), please let me them pass them on.
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Old 10-21-05, 11:32 AM   #2
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I don't in any way mean to dissuade you from making your inquiry here ... and I wish you all the best of luck with your daughter (hard enough to raise a kid without obvious physical challenges....), but have you tried looking for forums specifically for wheelchair-bound people, too?

This sounds like the wheelchair-world's equivalent of "what chain lube should I use?"

Best of luck.
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Old 10-21-05, 12:06 PM   #3
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Did you factor in your weight when feeling the ride? I'm guessing your daughter is half your weight, so she isn't putting as much weight on the wheels and won't feel the pellets. If she is fine with it, I'd say leave it.
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Old 10-21-05, 12:08 PM   #4
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Quote:
Originally Posted by neil0502
I don't in any way mean to dissuade you from making your inquiry here ... and I wish you all the best of luck with your daughter (hard enough to raise a kid without obvious physical challenges....), but have you tried looking for forums specifically for wheelchair-bound people, too?

This sounds like the wheelchair-world's equivalent of "what chain lube should I use?"

Best of luck.
I posted the question here for two reasons. One is that the wheels of a wheelchair are structurally the same as bicycle wheels, (i.e. hub, rim, tire and spokes), so the knowledge carries over quite effectively. The second is that I don't frequent any wheelchair specific sites, but I lurk around the BF everyday. As such, I know there are members here who know their stuff.

It really is just a question about the functionality of non-pneumatic tires.
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Old 10-21-05, 01:31 PM   #5
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Silly question: is it a 26" or other common bike size rim, and is there a valve hole etc? I guess the trouble is, if you get the thing off and you can't make the pneumatic setup work, you won't be able to reassemble it with the plastic filling...

The tyre might not be capable of holding the relatively high pressure used in bike wheels, and the rim might not a have bike-style clincher ridge inside...
I'd wait to see if it's uncomfortable for her and ask the manufacturer and ppl who have experience with the wheelchair if it's possile to convert the wheels.

Pneumatics are definitely more comfortable, though, and not that much of a pain to maintain. Maybe solid filled tyres are used for fear of punctures. But you can put a tiner in to minimize the risk, and, as she can walk if need be, it's not that big a problem, I suppose.
Good luck.
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Old 10-21-05, 03:03 PM   #6
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Did you have your wife ride the wheelchair? Try pushing her down a steep cobblestone driveway...
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Old 10-21-05, 03:31 PM   #7
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I think your wife is right: air-filled tires are probably nicer to ride a wheelchair on, but it's gonna be a small disaster at the first puncture: either your daughter is alone and she won't be able to fix it, or she's with you and you'll have to fix the flat in the middle of the street. Either way, not an enjoyable situation for her. Being in a wheelchair is tough enough without having to deal with that sort of thing, there's a reason most wheelchairs have solid tires.
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Old 10-21-05, 03:36 PM   #8
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Keep in mind that most wheelchairs are not operated at speeds like a bicycle so there is less jarring from a rough surface. I would certainly not fool with the thing unless your daughter complains about it. A little rougher ride is probably better than your daugeter and your wife having to deal with a flat at a shopping mall.
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Old 10-21-05, 04:04 PM   #9
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Quote:
Originally Posted by DannoXYZ
Try pushing her down a steep cobblestone driveway...

Certainly that would free him up to do as he wants with the wheels, but think of the child!


I'm gonna have to side with your wife, though. It might be a little less comfortable, but it's going to be a gigantic PITA if she blows a tire. Think about it: if you blow a tire 1/2 a mile from home and have no spares, you can walk home. What would she do?

There is a guy on campus here with a lime green wheelchair with what I swear are 26x3" knobbies, and rock shox on the front. That's probably pretty comfortable
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Old 10-21-05, 04:14 PM   #10
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Originally Posted by Eatadonut
There is a guy on campus here with a lime green wheelchair with what I swear are 26x3" knobbies, and rock shox on the front. That's probably pretty comfortable
Probably not Have you ever ridden a MTB with serious knobbies at very low speed? it goes thud-thud-thud and rattles your teeth, until you go fast enough to smooth out the ride. Not to mention rolling resistance, and s@%&-flinging abilities when you roll in a turd, which incidentally is a constant annoyance for wheelchair users in dirty city streets.
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Old 10-21-05, 04:48 PM   #11
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i'm no physical therapist or psychologist, but i tend to feel rolling around on two beanbags is going to be awfully tiring, and that a more normal tire/tube set-up would enable her to move by her own power longer/farther, and promote more sense of independence and well being for your daughter in the long run. she's going to have to overcome obstacles greater than the occassional flat when she gets older, and i imagine at this age somebody accompanies her a fair amount of the time anyhow. look into what flat-prevention options are available in the wheel size before you do anything, of course, and perhaps discuss it with your daughter.
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Old 10-21-05, 05:18 PM   #12
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Originally Posted by dafydd
i'm no physical therapist or psychologist, but i tend to feel rolling around on two beanbags is going to be awfully tiring
The two main differences between solid tires and air-filled tires are hysteresis ratio and penetration resistance response curve.

The former concerns how the tire behaves when it rolls on a flat surface. When a tire rolls, the section of tire immediately in front of the contact patch starts to deform itself, which takes energy, and the section right behind the contact patch "pushes the road back down", which releases about the same amount of energy it took to deform the tire about to make contact with the road, minus a little something (rolling resistance).

An air-filled tire has very low hysteresis, meaning that it releases most of the energy it has acquired by deformation instantly. A solid tire also releases most of the energy it has acquired, but with a small delay. That's because air itself has a low hysteresis and the tire walls are thin, but rubber has a high hysteresis.

Therefore, when a wheel turns slowly, there isn't much difference in rolling resistance between solid and air-filled tires. It's at high speed that a solid tire will start to steal all your energy and heat up, because the energy you put in to deform it gets released too late, after the rubber has left contact with the road. This means that solid tires are adequate in low-speed applications such as an everyday wheelchair, and air-filled tires are better for fast wheelchairs used in handisports.

As for penetration resistance, an air-filled tire gets deformed at the contact patch, but uses all the air inside the tire as shock absorber (the pressure in the tire doesn't rise significantly when a wheel hits a bump). In a solid tire, only the material right under the contact patch is deformed, which gives the wheel a much harsher ride. Again, in a low-speed application like an everyday wheelchair, the difference in harshness is certainly there, but it's not a huge problem like it would be hitting bumps with solid tires at 15mph.

So no, in an everyday wheelchair, it's not significantly more tiring to roll on solid tires than on air-filled tires. Even if it is a little, the pro of never getting a flat outweigh the con of pushing a bit harder. When a wheelchair user engages in a sport however, that's different, and air-filled tires are much better. A flat in that context is much more acceptable.
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Old 10-21-05, 05:18 PM   #13
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Point out to your wife that you can handle flat changing, so what's the problem with a rare puncture?
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Old 10-21-05, 06:53 PM   #14
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Point out to your wife that you can handle flat changing, so what's the problem with a rare puncture?
Changing a tube on a wheelchair is easier then a bike. You usually don't have to remove a wheel. I replaced a tubular 24" tire on a racing wheelchair, never needed to remove the wheel.
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Old 10-21-05, 06:59 PM   #15
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Quote:
Originally Posted by ppc
The two main differences between solid tires and air-filled tires are hysteresis ratio and penetration resistance response curve.

The former concerns how the tire behaves when it rolls on a flat surface. When a tire rolls, the section of tire immediately in front of the contact patch starts to deform itself, which takes energy, and the section right behind the contact patch "pushes the road back down", which releases about the same amount of energy it took to deform the tire about to make contact with the road, minus a little something (rolling resistance).

An air-filled tire has very low hysteresis, meaning that it releases most of the energy it has acquired by deformation instantly. A solid tire also releases most of the energy it has acquired, but with a small delay. That's because air itself has a low hysteresis and the tire walls are thin, but rubber has a high hysteresis.

Therefore, when a wheel turns slowly, there isn't much difference in rolling resistance between solid and air-filled tires. It's at high speed that a solid tire will start to steal all your energy and heat up, because the energy you put in to deform it gets released too late, after the rubber has left contact with the road. This means that solid tires are adequate in low-speed applications such as an everyday wheelchair, and air-filled tires are better for fast wheelchairs used in handisports.

As for penetration resistance, an air-filled tire gets deformed at the contact patch, but uses all the air inside the tire as shock absorber (the pressure in the tire doesn't rise significantly when a wheel hits a bump). In a solid tire, only the material right under the contact patch is deformed, which gives the wheel a much harsher ride. Again, in a low-speed application like an everyday wheelchair, the difference in harshness is certainly there, but it's not a huge problem like it would be hitting bumps with solid tires at 15mph.

So no, in an everyday wheelchair, it's not significantly more tiring to roll on solid tires than on air-filled tires. Even if it is a little, the pro of never getting a flat outweigh the con of pushing a bit harder. When a wheelchair user engages in a sport however, that's different, and air-filled tires are much better. A flat in that context is much more acceptable.
i'm no physicist either, but you argument seems to hear some merit. however, it ignores at least one major factor and brings on a few questions/comments. first, that a solid tire is not more tiring ignores that a girl in a wheelchair will accelerate and deccelerate to and from a full stop more often than, for instance, a road racer. the great rotational mass of a solid tire versus you average pneumatic requires more energy to reach a certain velocity. second, that it's not a true traditional solid tire, which tends to make me believe at least one engineer thinks a "semisolid" tire will have the benefits of a pneumatic tire without the flatting problem. last would be that while i haven't been able to verify this at the moment, i doubt the average nonpneumatic safety bicycle traveled faster than 15 mph, they were quite willinlg accepted due in large part to the comfort factor (keep in mind the wheel diameter of a safety bike versus that of a wheelchair).

anyways, i'm no brandt or brown, but there seems to be so logic behind the use behind of pneumatics in many if not most real-world applications (ie, not perfectly smooth surfaces). of course, more opinions and data are welcomed and awaited.
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Old 10-22-05, 04:36 AM   #16
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Try it and let your daughter decide the risk/ benefit factor. Im sure she will appreciate the concideration.

Could be more of a parental thing going on here.

I would think that a good set up would be a pleasure but a flat tire would be at worst a nuisence. If one had to they could simply pull it off the rim a get around just about as well.
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Old 10-22-05, 06:40 AM   #17
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Make one wheel pneumatic. Then see if your daughter notices a diff, and which one she prefers. QED.
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Old 10-22-05, 08:28 AM   #18
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Thanks to everyone for taking the time to respond.

The points that stand out for me are:

I do weigh twice what my daughter does; thus a rougher ride.

When I took it for a spin, I did make it go considerably faster than Madison ever does; again a rougher ride.

The thought of her having to deal with a flat, while away from the house is quite disconcerting for both my wife and me.

Lastly, my daughter is perfectly satisfied with the performance of the wheels the way they are. Plus, she's afraid I'll gink something up if I start taking things apart, (I do have a history of tinkering until I break something and then having to tinker more to fix what I broke )

So I'm going to leave the chair the way it is. My daughter does love the chair and I know she'll get a lot of miles out of it.

Funny how I thought I needed input to sell my wife on the change over and I ended up being swayed the other way.

Thanks again everyone!
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Old 10-22-05, 10:36 AM   #19
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Glad you got that taken care of.

Remember that Dunlop invented the pneumatic tyre after his kid complained of a rough ride from solid tyres...
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Old 10-22-05, 10:59 AM   #20
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Adding: It's true that you do weigh more. Due to your daughter's conditon, she may not be aware of the rough ride that may later cause sores or muscular aches.

How about a foam tire instead. The folks at airfree have been making them for years. Not sure about your area but most tire stores can order those for you and put them on.

http://www.airfreetires.com/Medical/Default.htm

Note: From personal experience on severa brands, I do not recommend air-free style tires for fast biking conditions esp on wet pavement. But I've heard they are save to wheelchairs etc.
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