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Could someone explain this bit to me: "In traditional wheelchair designs up to 30 percent of expended energy is lost because they lack suspension." It sounds

Could someone explain this bit to me: "In traditional wheelchair designs up to 30 percent of expended energy is lost because they lack suspension." It sounds an awful lot like bullshit. I know nothing about wheelchairs, but I just can't see how you're going to increase efficiency by adding suspension. In bicycling, suspension reduces your efficiency when you pedal. It's why XC and all mountain MTBs have various mechanisms to lock out suspension during pedaling (some of which are quite clever), and high-end dedicated XC bikes have no rear suspension at all. I don't think there's anything magical about moving that suspension into the wheel that would suddenly add efficiency. As others have noted - this will never make it into mainstream cycling. The most noticeable weight on your bike is the weight on your wheels. If you added 2 lbs of weight to your frame, it would be much less noticeable than adding 1lb each to your wheels. Even if the article's claims of somehow increasing efficiency by adding suspension were true, I'll be they'd be more than negated by the added weight on the wheels.

reubenmorais 12y ago
Suspensions steal pedaling efficiency when going up, but they help a lot when going down. It's why top XC bikes are hardtails but downhill and trail bikes all have suspensions with long travel.
adsfasdf23f23f 12y ago
This could refer to high rolling resistance from tires maintained to a lower pressure to account for no suspension. That's my best guess.
msandford 12y ago
>"In traditional wheelchair designs up to 30 percent of expended energy is lost because they lack suspension." >It sounds an awful lot like bullshit. It's not necessarily bullshit and in fact could be quite true. This is one reason why cars drive on air inflated rubber tires instead of solid metal ones. It's also one reason why trains are more efficient than cars, they have a VERY smooth "road" to travel on and thus don't lose any energy to up-and-down movement. If you believe that suspension losses are trivial then I invite you to find a road with rumble strips (to wake up sleepy drivers who slowly veer off the road) and to ride it on a road bike with skinny tires at a very high pressure. Then ride it again with a non-suspended (or locked out) mountain bike with it's much larger tires. Then ride it again with a mountain bike with a suspension. Here is an informal study doing precisely that for different sizes of road bike tires: http://janheine.wordpress.com/2012/08/12/suspension-losses/ http://janheine.wordpress.com/2012/08/12/suspension-losses/ You'll find that the pedaling losses from a suspension might get swamped by the benefits. So it turns out that the optimal solution is relative. Furthermore a person in a wheelchair isn't going to have the same kind of 60-120 RPM cadence (1-2Hz, but then double it since there are two legs, so 2-4Hz) that a cyclist would. You can do a lot of higher frequency bump reduction for wheelchairs and not sap the users energy for the wheel-push stroke which takes multiple seconds. What this really has to do with is the size of the surface texture relative to the size of the wheels and the ability of the tire to deform. A lot of wheel-chairing happens on sidewalks which are fairly smooth but have expansion joints every 3-10 feet. Or on blacktop which is smooth relative to a car's tires which are air inflated but not relative to a wheelchair's which are solid rubber. Or what about older concrete, or tile, or one of any of the other myriad surfaces which aren't perfectly flat? > Even if the article's claims of somehow increasing efficiency by adding suspension were true, I'll be they'd be more than negated by the added weight on the wheels. It all depends on the kind of riding you do. I ride long distances on the road for training (not racing) so I don't have need of a wheel that has low rotational inertia. As such I could accept a weight penalty for the sake of comfort. I own a titanium road frame which is "heavy" by road standards and I put a tandem fork on it for extra strength, and I ride 40 spoke wheels. The idea that weight is paramount bar none might be true for professional cyclists but not for everyone. To a great many people it's only a small factor when making decisions. EDIT: formatting and moving the link
- vacri 12y ago
  a car's tires which are air inflated but not relative to a wheelchair's which are solid rubber. Plenty of wheelchairs have pneumatic tyres, including the ones in the article.
  - msandford 12y ago
    Point taken. I was thinking of the wheelchairs I've seen people pushed around hospitals in which don't necessarily correspond to what people buy for themselves for the long term.
    - lizzard 12y ago
      Those are absolutely terrible wheelchairs, built to the specs of 50 years ago, heavy and uncomfortable. They are very difficult to get around in. No one should have to use those.
DavidAdams 12y ago
Could be a bullshit stat, however, bikes with suspension lose energy because the rider's pedaling energy is absorbed somewhat by bouncing the bike up and down on its shocks. Because a wheelchair's operator makes it go by cranking directly on the wheel, a similar loss of energy wouldn't happen. A free-rolling vehicle is going to lose energy on a bouncy surface because some of its potential energy is expended bouncing up and down, so I'd say that smoothing out the ride will help.

reubenmorais 12y ago

Suspensions steal pedaling efficiency when going up, but they help a lot when going down. It's why top XC bikes are hardtails but downhill and trail bikes all have suspensions with long travel.

adsfasdf23f23f 12y ago

This could refer to high rolling resistance from tires maintained to a lower pressure to account for no suspension. That's my best guess.

msandford 12y ago

>"In traditional wheelchair designs up to 30 percent of expended energy is lost because they lack suspension." >It sounds an awful lot like bullshit. It's not necessarily bullshit and in fact could be quite true. This is one reason why cars drive on air inflated rubber tires instead of solid metal ones. It's also one reason why trains are more efficient than cars, they have a VERY smooth "road" to travel on and thus don't lose any energy to up-and-down movement. If you believe that suspension losses are trivial then I invite you to find a road with rumble strips (to wake up sleepy drivers who slowly veer off the road) and to ride it on a road bike with skinny tires at a very high pressure. Then ride it again with a non-suspended (or locked out) mountain bike with it's much larger tires. Then ride it again with a mountain bike with a suspension. Here is an informal study doing precisely that for different sizes of road bike tires: http://janheine.wordpress.com/2012/08/12/suspension-losses/ http://janheine.wordpress.com/2012/08/12/suspension-losses/ You'll find that the pedaling losses from a suspension might get swamped by the benefits. So it turns out that the optimal solution is relative. Furthermore a person in a wheelchair isn't going to have the same kind of 60-120 RPM cadence (1-2Hz, but then double it since there are two legs, so 2-4Hz) that a cyclist would. You can do a lot of higher frequency bump reduction for wheelchairs and not sap the users energy for the wheel-push stroke which takes multiple seconds. What this really has to do with is the size of the surface texture relative to the size of the wheels and the ability of the tire to deform. A lot of wheel-chairing happens on sidewalks which are fairly smooth but have expansion joints every 3-10 feet. Or on blacktop which is smooth relative to a car's tires which are air inflated but not relative to a wheelchair's which are solid rubber. Or what about older concrete, or tile, or one of any of the other myriad surfaces which aren't perfectly flat? > Even if the article's claims of somehow increasing efficiency by adding suspension were true, I'll be they'd be more than negated by the added weight on the wheels. It all depends on the kind of riding you do. I ride long distances on the road for training (not racing) so I don't have need of a wheel that has low rotational inertia. As such I could accept a weight penalty for the sake of comfort. I own a titanium road frame which is "heavy" by road standards and I put a tandem fork on it for extra strength, and I ride 40 spoke wheels. The idea that weight is paramount bar none might be true for professional cyclists but not for everyone. To a great many people it's only a small factor when making decisions. EDIT: formatting and moving the link

vacri 12y ago
a car's tires which are air inflated but not relative to a wheelchair's which are solid rubber. Plenty of wheelchairs have pneumatic tyres, including the ones in the article.
- msandford 12y ago
  Point taken. I was thinking of the wheelchairs I've seen people pushed around hospitals in which don't necessarily correspond to what people buy for themselves for the long term.
  - lizzard 12y ago
    Those are absolutely terrible wheelchairs, built to the specs of 50 years ago, heavy and uncomfortable. They are very difficult to get around in. No one should have to use those.

DavidAdams 12y ago

Could be a bullshit stat, however, bikes with suspension lose energy because the rider's pedaling energy is absorbed somewhat by bouncing the bike up and down on its shocks. Because a wheelchair's operator makes it go by cranking directly on the wheel, a similar loss of energy wouldn't happen. A free-rolling vehicle is going to lose energy on a bouncy surface because some of its potential energy is expended bouncing up and down, so I'd say that smoothing out the ride will help.