brentlakatos

Hi

Dan Burkhart 

Once an axial force is introduced, any friction advantage of a deep groove radial bearing is lost in addition to subjecting it to accelerated wear. I think angular contact is the only suitable option here.

brentlakatos

Thanks for the reply!

I understand the accelerated wear, and in training that makes complete sense. I guess I am most interested in is what will be faster for a one race situation where I dont care about any wear?

EDIT: Eg Would a radial bearing allow the wheel to change angle slightly during a push, which would 'toe-in' the wheel, which would slow us down

Iride01 

I'm thinking that it's not going to matter much either way. Certainly one could find all sorts of engineering and technical reasons why one is better, but since you aren't spinning those wheels at 21,000 rpm, it doesn't amount to much.

You aren't assuming because it's a cartridge bearing it's not angular contact are you? Cartridge bearings can be angular contact also.

WizardOfBoz

I think Dan's answer is spot on. AC bearings will likely give you lower friction and longer life.

I grew up working in a machine shop and the precision machines (lathes, milling machines) typically use AC bearings. I'm also a big guy and use AC bearings in my bike bottom brackets and (if I can find them in the right size) in my wheels. My old Campagnolo Nuovo record wheels lasted 40 years and they are essentially AC.

I can't imagine increased friction, and i see only benefits to AC (except that they cost more, and you have to be sure to install them with the correct orientation).

3alarmer 

.
...I watched your video link, which was pretty interesting. In terms of the race itself, it looked like there was a lot of strategy and drafting going on. I cannot imagine a way in which the small theoretical difference in these two types of bearings, in your application, could give you enough of a practical advantage in such a race (at the sprint for the finish), that it would be worth trying.

I guess maybe if you were time trialing, it might be worth the expense to run this experiment, but I tend to agree that this is not a good plan for improving the mechanical performance of your machine.

3alarmer 

...with regard to this particular question, I'm not 100% certain on the answer. O honestly don't know whether enough preload would prevent this with a wheel so slanted in use.

brentlakatos

Me neither That is what I am most interested in. Will the angular contact bearing provide a positive impact on performance or just a longer life.

The latteral stiffness of the wheels is extremely important as each push does toe in the wheels by about 5mm. Reducing that would help is a big way.

brentlakatos

Sometimes it might not in a race like the 5000m in a peloton. But in the races in your own lane then any performance boost is good. And even in the peloton distances marginal gains always add up.

brentlakatos

Thank you for the reply. Do you know the answer to my latteral stiffness question? Right now each push toe's in the wheels. Do you think any of that could be coming from the radial bearings and could it be reduced by AC bearings?

blamester

You could dish the wheel so that the push and subsequent bending put the wheel in the correct plane.
Do you have special tyres? Do they run square with the wheel or the road.

WizardOfBoz

Ok, I'm giving you a theoretical answer (I have a PhD in Engineering, but I haven't analyzed wheelchair dynamics). The quick answer is that the toe-in may be caused by your frame flexing, or by the axle (including axle to frame joint) flexing, or by the bearings having some play. If you are swapping out bearings you might try a subjective test: accelerate as fast as you can with the old deep-groove radials and then do the same test with the AC bearings. Can you tell any difference?

I did a search on wheelchair structural rigidity and was a bit dissapointed in the lack of results. Ideally, one would do a structural analysis and create a computer model to see how the forces (stress) cause structural deformation (strain, as in the toe-in you mentioned). Then you'd instrument up several wheelchairs and have different athletes test them to measure the strains observed. This would allow you to calibrate the model and then optimize the design. I'm sure that this has been done (there were some pretty slick looking CF chairs I saw online) but I found nothing published.

One question: do they make wheelchair wheels with the inboard bearing (and axle diameter) larger than the outboard bearings? I ask because I suspect that the biggest contributor to flexibility is that axle. It's what engineers call a cantilever design: One side (inboard) is fixed, the other (outboard) is free. Bike pedals have this same design and an added feature sometimes: the axle tapers down and the outboard bearing is smaller). This gives you more stiffness in the pedal-to-crank joint with lower weight and friction.

One last speculation from someone with gray hair: The old bike wheels used AC bearings and the cones were adjustable. IMHO, this (and other design aspects, such as not needing as much space for the replaceable races) made the old design far superior to modern replaceable bearings. Again, its MHO. Actually MNSHO: I think I'm right. At least my 40 YO campy nuovo record hubs, which are properly preloaded and still run great, would seem to suggest so. I would think that wheelchair wheels with a tapered axle, built-in AC races, and an adjustable preload would offer a lot of advantages to the racer.

brentlakatos

Its quite tricky because we are only pushing part of the time. Maybe 50% of the time our arms are in recovery/drive phase before making contact again.
We just use standard bike tires. Eg Vittoria Pista Speed for tracks and Corsa Speed for roads.

smashndash

Shimano, campy and chris king use angular contact bearings for their wheels. Those are also three of the most reputable hub manufacturers in the world. And also pretty much the only 3 manufacturers that actually make their own bearings as opposed to buying off the shelf stuff. So I think it's fair to say that in a situation with actual constant axial/cantilever load, the choice is obvious.

I also think one reason angular contact bearings aren't popular for hubs is that you need a real preload adjustment mechanism for it to work. And that costs money. It's cheaper to err towards too little preload or use a wave washer () and use a radial bearing and pretend bike wheels never see axial loads.

brentlakatos

na

CliffordK

I would think that round ball cup and cone bearings would still do reasonably well with the offset forces on the wheelchairs.

I've had sealed bearings that didn't do well with the axial load from over-tightening. But, that wouldn't be unexpected either. I'm having troubles envisioning how wheelchair forces would impact them.

If you have the ability to build test equipment and run an experiment, I'd build a test setup somewhat like this.



Measure spinning change in RPM, or revolutions to stop with a uniform starting speed.

I'll try to get back to this later today to comment on potential forces acting on different bearing types.

Dan Burkhart 

If we are designing the ideal solution for this application,, ie, cambered wheel with one side mounting , larger inner bearing, adjustable preload,I would be considering tapered roller bearings.

WizardOfBoz

Dan is suggesting tapered roller bearings. These have some advantages, but I thought I'd point out one more advantage of Angular Contact bearings (and I consider tapered roller bearings in this class).

When you make deep groove radial ball bearings (that is, standard, good old ball bearings), you grind the inner and outer races and select a set of identical (or as near as you can get 'em to identical) balls. You put the inner race inside the outer race, but not concentrically. This leaves spacing that allows you to insert balls. You put in enough as many balls as you can fit (making sure the races and balls are all pre-lubed) and then you fiddle with the balls until they are equally spaced and so now the races are concentric. A spacer is added to keep the balls separated. This means that you can't have 100% fill of balls in the radial grooves. Put another way, there is always considerable spacing between balls in a deep-groove radial bearing.

In an angular contact bearing, you fill the larger outer race with grease and balls - they can almost be touching. Then the inner cone is applied and preload is applied so that there is no play. There is minimal spacing between balls in an AC bearing.

All this means that an AC bearing of the same size has higher load rating and wears more slowly than a deep-groove radial ball bearing. A non-operational consideration is that AC bearings are rated for higher speeds (no offence, but neither you nor cyclists are getting anywhere near the max rpm of any bearing on a bike or a wheelchair*). The extra balls give more support radially and axially. AC bearings come standard in 15° and 25° (also 40° but I don't think you want that). I think I'd go for the 15°, provided your camber is less than that. You may want to talk to a bearing expert (as in people who sell these things) to verify that.

One specific thing is that the larger the bearing the more parasitic drag you will have. May not be very operational in your case, and it may be that you choose axle diameter (and hence bearing size) based upon stiffness considerations rather than (a minimiallly small) difference in bearing friction. Given that bike cranks are in the 24mm size range, and that your wheels are essentially both wheels and a crank, and that some of you wheelchair guys have arms the size of gorillas, I think your 1 inch inboard ID sounds like a good diameter to try.

If axle diameter was arbitrary, I would think that you could go with tapered roller bearings to give stiffness, in the smallest possible size to reduce friction and weight. Tapered rollers will have higher parasitic friction for the same size. Because they are designed for high loads, the races will be more heavy duty and heavier. Because the axle diameter may be set by other (stiffness) considerations and because a 1 inch ID TRB will be pretty heavy, I'd respectfully disagree with Dan and would probably tend towards AC ball bearings. Happy to learn something new if if I've missed something, Dan.

This is really interesting stuff. Good luck - let us know how this proceeds.

*A dynamo might be a counterexample.

blamester

How standardised are the machines?
Why are the wheels canted?
Is it for steering and stability?
Or to get a good push or both?
Can you feel the tyre deflecting?
That's the where I would be looking for gains.
Looking at the video you would gain very little by changing the bearings.
Good tactics and fitness win

​​​​​​

CliffordK

Ok, I was thinking of tapered roller bearings (like cars use in wheel bearings).

But, a little research of angular contact bearings.

https://www.skf.com/us/products/roll...-ball-bearings

The single row angular contact bearings look a lot like the cup and cone bearings that I suggested earlier.



Although, that diagram indicates a mighty tight curve on the cup & cones.

Can you get something like a Shimano hub built into the wheels?

Dan Burkhart 

No, I don't think you missed anything, and thinking this over and doing some more reading, I think I have to agree with you. No question, for strength and durability, tapered roller wins, but the goal here is minimum drag and weight and I think we have to give the edge to the ball bearings on that.
To minimize drag, I would run the bearings open,(no seals) with as light a lube as possible like a 00 semi fluid grease, or even oil, and preload set to the absolute minimum. Another advantage of the angular contact type is the ease of disassembly for thorough cleaning and lubrication. In a racing environment, this would need to be done frequently when running open bearings.

brentlakatos

na

Dan Burkhart 

If you could source spindles from Cannondale lefty forks, I think those would work great. Alternatively, you could have a machine shop make copies.
The Lefty hubs use a 15 x 28 x 7 outer bearing and a 25 x 37 x 7 inner. Those sizes are available in angular contact.

79pmooney

A thought I just had and I better get down before I forget - those bearing race sets - of two, right and left. How convenient.. You have two wheels. A larger set of bearings for each inboard bearing and a smaller set for the outside.

Another thought - your racing is very similar to bicycle time trialing. You might find it interesting to see what the pro mechanics have done for decades to optimize the AC bearings in the hubs of the bike wheels. (A lot of work for the mechanics. After the last road race before the all important time trial in a three week grand tour, he spends a sleepless night cleaning all the grease out of the bearings and reassembling with light oil, only to undo this work that night for the following road race.

I'm no expert on racing wheelchairs but I do have a deep interest in more conventional "sport" wheelchairs. I have a friend who suffered spinal damage in her mid-20s and watched her decline from crutches. She knew and told me in the early '80s she would eventually need a chair when wheelchair technology was still in its infancy. 1986 I was on a ride in Michigan and had to stop for the Dexter 1/2 Marathon. Was told the wheelchairs would be by first in a couple of minutes. Watched the leader, minutes ahead, fly by at ~18 mph, arms like my legs in my racing days on a canted wheel sport chair with bicycle race wheels and tires. I knew immediately this chair weighed like a racing bike. Also that a chair very close to it was what my friend wanted though she was still angry at the thought of losing her crutches mobility and I knew she wasn't ready to her this from me.

Seven years later I spent a long weekend with her after she came home from the massive surgery to rebuild her back. Her new life in that chair. She'd discovered the sport chairs and had one made for her. Though she was still very weak, she did her best to be a good host and tour guide to a city I'd never seen. We went to the observatory with its huge telescope. 20' wheelchair ramp up, no landings. I was not allowed to push. (Growing up, she was the athlete, I was the klutz.) Twice she had to stop, hold onto the guardrail, then push with all she had to re-start. Watched those re-starts and it was obvious to me; a hardcore fix gear rider, that this was someone "riding" in too big a gear. Then, "why couldn't the hub have a reduction gear a al the Sturmey Archer 3-speed that had been around for 60 years?"

More thought and I realized it wouldn't be easy. The hub would have to be light, bulletproof and quick-release (while having a torque connection to the wheelchair frame). (And no wider than a standard wheel. Any excess width means not being able to use the bathroom without squirming in on one's stomach.) Bulletproof because athletic young men would take it far into the wilderness to places they could never get to before and a mechanical failure meant being stranded and perhaps dying.)

This took me on to a long journey I won't describe here and to a start-up, Magic Wheels building a wheel of my inspiration and their design. I got to be invited to the un-veiling at a trade show and spend much of my two days there wheeling around on their two-speed wheels. A blast! (At the tradeshow I listened to a young woman describe the "bathroom squirm".) Sadly, Magic Wheels didn't survive the financial and regulatory challenges. I still feel that a world where the users of wheelchairs could have in their closet a pair of 2-speed wheels for post injury/sickness use and to handle going to places with real hills or deep carpet would be a better place. (I do this now on my fix gears. All but one offer the choice to flip the wheel and use a lower gear.)

Oh, and for those forumites who wonder about the cant of racing wheel chairs - it all about ergonomics. The canted wheel puts the handwheels in the plane of our arm sweep, much like conventionly located bicycle pedals do the same with our leg sweep. For regular chairs, it is a balancing act between more cant = better ergo dynamics and less cant = more doorways that chair can get through. I knew users with a comfortable around-the-house chair (doorways having been modified) and their office chair with less cant to get into the office bathroom.

brentlakatos

na