Old 07-23-18, 08:14 AM
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Thank you for your excellent suggestions and references.

It took me awhile to realize there are predominately three types of axles.
(1) Thread on axle which requires a bushing and nut attached to the chair. In the past, this axle required tools to put on and take off.
A revamped version of the above is the standard for off road bicylces. It is called a Thru Axle. Instead of having a bolt head which requires a wrench, the
design has an integral handle which allows one to screw the axle into and out of the nut attached to the chair. The advantages of this approach is
that the solid axle is strong and the connection to the wheel chair very solid. Disadvantages are that removal and attachment requires more effort and bearing
replacement requires special tools.

(2) Quick Release (wheel chair design).....which is the axle you described. A hollow shaft with balls or pins that prevent the wheel from coming off.
Various methods (rods or wires) permit the locking balls or pins to retract into the hollow shaft allowing the wheel to easily come off. This approach requires
NO nut on the wheelchair. Only a bushing. Its advantage is ease of wheel removal or attachment. The drawback is that the inner race is not press fit onto the
axle and hence the wheel can sometimes turn on the axle and not on its inner race.

(3) Quick Release (bicycle design). This design can not be easily cantilevered as the rear wheels on wheel chairs are. The axles are hollow. a small diameter rod
tightens up clamps on both sides of the wheel hub clamping the wheel to the the bike fork. its advantage is light weight and the ability to use open bearings
which permit balls, inner race, and outer race to be separately maintained and replaced. I mention this approach as it is the current standard for road (not off
road) bikes and could be adapted for use on wheelchairs.

I favor the Thru Axle for my friend. He does not have a need to remove his wheels and wants to go fast. In that case, I want his wheels to rotate on the bearing
races. I believe, that wheel chair users give up the performance of a bearing for wheel removal convenience. I believe tthey could have better performance if they
had press fit bearings instead of the slip on fit they use. I may be wrong. I have been wrong many many times in my life. But I would like to point out that in most
mechanical designs incorporating bearings, both inner and outer races have interference fits intended to guarantee rotation takes place IN the bearing and NOT on
the axle. Have you ever wondered whey so many Quick Release axles are sold? Maybe the bearings gawl the axle? I have no idea.
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