A Shock-Absorbing Wheel for Bikes and Wheelchairs | Hacker News Reader

A Shock-Absorbing Wheel for Bikes and Wheelchairs

wired.com

45 pointsjdnier40 comments

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.

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.

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

>"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/

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

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.

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.

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.

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.

So.

Suspension wheels have been around for quite a while now. The most well known is the Pantour.

http://www.atob.org.uk/bicycle-accessories/pantour-suspensio...

The Pantour does suspension inside the hub. That's not a lot of room so we're talking a centimeter of suspension. But that's all that many bikes can take anyway, since they have rim brakes and more suspension than that would move the rim too far from the brake.

A similar approach, albeit more high-tech and intended more for efficiency, was recently showcased by Gosiko.

http://www.bikerumor.com/2013/03/05/nahbs-2013-gokisos-amazi...

Though Softwheel gets credit (?) for using what amounts to shock absorbers, a much lighter and more robust approach has been done for a while now, using leaf springs:

http://www.gizmag.com/loopwheels-suspension-bicycle-wheels/2... https://www.youtube.com/watch?v=O11hFiu43RQ

Here's a few problems I see with the Softwheel, at least for bikes (I have no idea about wheelchairs).

1. It would appear to be very very inefficient. As the wheel is turning, each suspension spring is constantly being pushed and pulled. One would think that a single suspension, like a suspension fork or the Pantour hub, would be much more efficient.

2. It's likely heavy. Rotational inertia could be a problem.

3. It's likely not very strong. Perhaps the suspension compensates for this a bit.

4. It'd only work with disc brakes.

1 is the real deal breaker here. People fill their tires to 140 PSI just to get rid of a little bit of the friction caused by the tire deforming as the wheel turns. That has to be nothing compared to actual shocks. It must feel like riding through dry sand.

I think the whole bicycle wheel thing is just a ploy to scam clueless investors. No one who had ever tried to ride one of these wheels up a hill would think they were a good idea on a bicycle. And the descending stairs thing? I've descended much steeper on my regular old hardtail.

Since motive force is applied to the rim of wheelchair wheels, it probably works fine for those.

There's also the time 10 years ago when we used a design like this on another freakin' planet: http://marsrover.nasa.gov/technology/is_autonomous_mobility-...

For wheelchairs where the angular velocity is fairly low, it looks like a great product. For bikes, you can see on the demo video how the back wheel is out of alignment. The faster you go the more noticeable it would be. Even if you take care of the original factory calibration, over time I would think it would get worse from uneven performance from the shocks as they wear.

This seems like it might work well for wheelchairs, where performance is not a large issue. For bicycles though, it's turning a component that was once static into one that's rotating. This means the rider will have to overcome a whole new set of forces just to get the wheel moving. There's a reason people pay such a huge premium for very light rims and tires, and go through the trouble of not having inner tubes.

Is performance really not a large issue for wheelchairs? I would think the elderly would not have the strongest arms, and younger, powerful riders would in many cases prefer speed over comfort. Yes, it might be useful in rough terrain, but that is precisely the terrain where the loss of power due to inefficiencies in the wheel might mean the difference between getting over that bump or not getting over it. I think there is little room between this and just mounting (much) wider tires and using less tire pressure.

Performance is a huge issue. A better performing wheelchair makes a difference in our independence and range we can go on our own. It also makes a big difference in the wear and tear on our shoulder joints and hands.

Both videos are lame. Lots of shots of people riding around being all inspiring, and almost nothing about how the wheel actually works to absorb shock.

And nice music. Don't forget the music.

I can't press Ctrl-F to initiate a search on this page without it pulling up a picture slideshow, taking me away from the content that I wanted to search. What a stupendously senseless display of hostility to users.

For anyone else who was wondering, there seems to be no mention of rolling resistance.

A commenter on the article stated, "Putting the wheel's axle off center through a system of articulated links is bound to increase effective rolling resistance." and another said "This is going to feel like you're riding on sand."

Yeah, that is my suspicion as well. Even just the difference between street tires and mountain bike tires is very noticeable on a bike.

This product might be worth it if you are using a wheelchair over rough dirt/ground, but I doubt this sort of wheel will become very popular with bicyclists (bicyclists already have shocks built into their bike frames, if that is the sort of thing that they need for their particular application).

The value of shock absorbing for manual wheelchairs isn't just in efficiency, it would be also quite valuable for making it less painful to go over bumps. Even going down a relatively city sidewalk is exhausting from the bumps and cracks, because jolting adds to the pain of sitting upright if your spine or pelvis are already in pain. Efficiency is also great though!

If the suspension elements don't wear perfectly evenly or are not perfectly evenly charged to begin with, it will be like riding on an out-of-round wheel. That is, instead of absorbing bumps, the suspension will feel like you are riding over regularly spaced lumps. It will be fiddly to maintain.

You also use one third of the suspension at a time. Trading what the suspension spokes weigh versus a suspension with a single spring and shock per wheel, is also probably going to be a favorable trade-off.

Some quick Googling shows there are existing suspension wheelchairs that look like they use mountain bike rear suspensionspring/shock components, and it looks like there is sufficient room under the seat to accommodate a suspension.

I am shocked at the (very high) quality of comments on the article. (Just scroll down).

Better than HN. I didn't notice what domain I clicked through to, made me do a double-take, am I on Scientific Mechanics or some super specialized blog? Kudos to the Wired comments team.

Not really sure what kind of bikes this would be useful on. The most basic form of shock absorption is the tyre, and you can run with higher volume tyres and lower pressure to make it more comfortable. Of course on the road this will slow you down so people don't tend to do it. For the kind of urban obstructions in the video you could ride perfectly well (and with more fun) on a fully rigid frame (like a BMX). For more serious mountain style riding you need rims that will not be deformed by rocks etc and just keep rolling over obstructions.

Other than the spiral flexures that NASA uses this seems to be rather unique in that shock is absorbed in two dimensions rather than one. No matter from what direction jerk is applied the wheel will absorb it in the same or a similar direction rather than just absorbing the vector component that is along the direction of a linear shock absorber.

That means it will absorb more of the shock and be more comfortable. If people know of another mechanism that has this characteristic I'd love to know about it.

If there was a road bike version at a price I'd be willing to pay I'd be interested in something like this.

On training rides it would be a nice thing to have (and the increased weight would be less of an issue) not least because current road bike rims get buckled if you sneeze while riding on them (I exaggerate (slightly))

I would like to put it on a trailer, so the trailer would bounce around less behind you. One of these guys: http://travellingtwo.com/gallery2/d/44786-2/tombike.jpg

Is it just me, or has Wired completely failed to load on Mobile Safari for months?

Unless I missed it in the article, what's the advantage of this vs. mounting the wheel on a regular spring/shock? Other than needing minimal modifications to the base platform?

Compactness maybe? Backwards compatibiliy with old chairs?

That's a pretty big advantage already, if it's just a drop-in for existing mounts.

Assuming they can take disc brakes.

Though 3 shocks per wheel hits a very different price-point than 2 shocks per vehicle.

as a wheelchair user:

looks heavy, and spoke wheels provide suspension.

also there are tons of wheels built from a similar premise in the past ; they've all failed as long-lasting products.

I love this design, it puts the complexity in a part that already is and removes it from the frame. Lowering the total cost.

There were elastic wheels 110 years ago:the "roue élastique Roussel" for cars. it also inspired the lunar rover wheels back in appolo times. Hardly news.

How do you true those wheels?

Presumably there is not the same likelihood of them going out of true as with spokes.

Low spoke count wheels, like these, have substantially more material in the rim in order to make the rim stiff enough for the large gaps between spokes to work at all.

All that's needed is for all three spokes to have equal tension (and no excessive forces applied) and the wheel should stay true.

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