physics of bike wheel

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Mike Kirney
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re: physics of bike wheel

Post by Mike Kirney » Tue Sep 06, 2005 5:22 pm

The bicycle rim is a box beam, albeit with a complex and often aerodynamic profile. Old wooden rims from 1930s racers show exactly the same profile as modern carbon fibre track rims. Larry, bicycle rims ARE rigid. Have you ever smacked somebody in the head with one? It hurts. Why? Because the rim does not deform under load, rather it is your skull that deforms slightly and this is what causes the pain. It is true that there are no objects in this world that are truly and completely rigid. By applying enough force, any object can be deformed. It is all a question of degree really. Aluminum bicycle rims will 'taco' from hitting a hard bump, but many times they will tear or crack. They crack because they are rigid and that is the only way the stress can be relieved. In the 1920s, many cycles had wooden rims which were superior to aluminum ones in many ways except that they were much more likely to crack from shock loads rather than simply deform. Steel rims were once very popular too but although they are much stronger than aluminum ones they are significantly heavier, get very slippery when they are wet (making rim braking nearly impossible), and corrode to the point of failure with little or no warning.
Trig IS fun.

Ray(GB)
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re: physics of bike wheel

Post by Ray(GB) » Wed Sep 07, 2005 4:58 pm

Thanks all,
It's still a very complex system to my brain.
I agree with Larry, that its a marvellous piece of engineering.
I wonder what genius invented the tensioned spoked wheel.
The wooden cart wheel seems so simple by comparison,as the spokes are always in compression.
I wonder what the derivation of the word 'tyre' is, as its spelled 'tire' in N.America.
Ray.

larry cottrill
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Re: re: physics of bike wheel

Post by larry cottrill » Wed Sep 07, 2005 5:51 pm

Ray(GB) wrote: I wonder what the derivation of the word 'tyre' is, as its spelled 'tire' in N.America.
I'm betting it comes from the tyre worn on the head by Bedouin to hold their bernousses in place, and named after the ancient Mediterranean seaport city.

L Cottrill

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Re: re: physics of bike wheel

Post by Bruno Ogorelec » Thu Sep 08, 2005 12:00 pm

Ben wrote:Why make false guesses when it's so easy to find the correct answer?
Ben, you are being Ben again! For a while, I thought you had undergone a change of character or were under sedatives. :o)

Now I have to be careful what I write again.

Ray(GB)
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re: physics of bike wheel

Post by Ray(GB) » Fri Sep 09, 2005 6:54 pm

Thanks for that derivation,Ben,and that intelligent guess,Larry.
Ray.

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