riding a bike too small is damaging?

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Joined: Wed Aug 06, 2008 16:49 pm

riding a bike too small is damaging?

Postby cash77 » Sun Aug 10, 2008 21:43 pm

is it true that if you or a child rides a bike too small for them for a awhile it can damage their knees or back?

david 142
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Joined: Mon Jan 15, 2007 00:45 am

Postby david 142 » Thu Aug 14, 2008 00:00 am

As far as the back is concerned I think you are likely to be put off by discomfort before doing yourself any lasting damage. Its a different story for the knee.
The problems arise when the pedal is at the top of its stroke. When the leg tries to push it down it has a poor leverage to work with because the pedal is nearly in line with the bottom bracket spindle. Its hard to get that pedal moving, and even if the bike is moving this is still the point at which most force is involved.

If the saddle is too close to the bottom bracket (which is one feature of a too small frame) then the knee will have to bend more than it would on a properly sized bike. The more bent the knee is, the greater the force required from the extensor muscles to straighten it. (This is why its harder to climb stairs 2 at a time!) This force is channelled by the structure of the joint. As the force increases the contact pressures inside the knee joint increase, and so does the strain on ligaments, tendons, etc.

If you really overdo things then there is a risk of acute problems, such as torn ligaments.
However the real baddy IMO is the risk of accelerated wear on the bone surfaces. You dont notice it at first - and when you do, its a bit late...
Dont want to be a scaremonger - a little too smalll, a little while, is unlikely to amount to a disaster. Kids may be less likely to suffer simply because they weigh so much less.

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