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Posted by: pythagoras ®

12/31/2004, 04:41:09

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I am a student and try to make a plastic bicycle according to my homework. I'm trying to design a plastic rim. As I don't think about the tire while analysing of the rim, I get a problem of defining the loads acting on the rim. 
Weight of the person that sit onto the bicycle and the weight of the bicycle acts at the hub of the rim. At the ground there is a reaction force of the weight acting at the hub. This reaction force acts to tire and the pressure of the air in the tire increase because of the volume decrease at the tire. This pressure acts to the rim radially to the center of the rim.
I want to analyse the rim by the program AnSYS. I thaught to draw the rim without tire, but a big problem shows its face to me. I can't support the rim from any place as I don't draw the tire. I can't define the ground.
Asking to people that has information about this subject said me that any mathematical represantation of this tire acting is not known.

To make the analysis, some people offer me to analyse the rim with tire; in AnSYS program I would draw the tire and give the proporties of the tire like Elasticity modulus, poisson's ratio,... so that it would act as a tire according to the given elasticity modulus and poisson's ratio,... 
Now I need to get information from a person that has information or opinion about this subject. Would I get information?
Please help me in giving the mathematical model of the forces acting on the rim by the tires (if possible), or in giving elasticity modulus and poisson's ratio of the inflated tire of a bicycle. (the values could be approximate values that is similar to natural ones)
please contact also with e-mail: (use "Mail Author" at top-left

Modified by Administrator at Fri, Dec 31, 2004, 09:20:14

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Re: PLASTIC BICYCLE RIM -- pythagoras Post Reply Top of thread Forum
Posted by: manulal ®

01/13/2005, 02:22:46

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first of all the load of a bicycle is not supported by the air inside the tyre but by the tyre walls, the rim, the spokes at the top(not at the bottom), and the hub.

when you load a bicycle wheel the load is supported by the vertical spokes at the top and the deformation of rim is prevented by the horizontal spokes. The vertical spokes at the bottom are freee of any load, practically.

If these informations are useful please contact me and i shall send a detailed mail.


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Re: PLASTIC BICYCLE RIM -- pythagoras Post Reply Top of thread Forum
Posted by: zekeman0 ®

01/06/2005, 11:40:18

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I would treat the force of bike plus rider as a point force acting on the rim and rotating. The tire pressure is constant around the rim and as a first approximation, it would be equal to the initial pressure.

The design would therefore involve the hoop pressure around  the rim and the rotating  point  force and the forces in the supporting spokes. The spoke forces may be fun.

If  you want to get the pressure more accurately, it becomes a geometric problem of  putting a flat, A on the toroidal section and getting its volumetric change,V1-V2 ,applying the gas laws and writing



Good luck

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