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What should be the direction of friction acting on both tyres of a running bicycle? My friend said that the direction of friction will be opposite for both tyres. My view is different, I think the direction of friction will be the same for both tyres as their slipping tendency is towards the same direction. Which of us is correct?

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  • $\begingroup$ "Their slipping tendency is towards the same direction"? When i ride my bike on ice and pedal too hard, the back wheel slips backwards. I can't imagine that happening with the front wheel. $\endgroup$
    – JiK
    Sep 8 '16 at 14:12
  • $\begingroup$ and what about riding on a normal road???? $\endgroup$ Sep 8 '16 at 14:13
  • $\begingroup$ Do you mean that the read wheel has tendency to slip forward when you're riding it? What exactly is the situation here, is the cyclist pedalling or not? $\endgroup$
    – JiK
    Sep 8 '16 at 14:19
  • $\begingroup$ sorry i forget to mention that, cyclist is not paddling. $\endgroup$ Sep 8 '16 at 14:25
  • $\begingroup$ JiK, i think you have interrupted the situation incorrectly maybe(maybe i m wrong), when you paddle your bicycle you say back wheel slips backward, if it happens then you will not be able to move forward ever.i m a little bit confused with the situation you discussed. $\endgroup$ Sep 8 '16 at 17:14
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If a bicycle is coasting along, the front tire and rear tire will have friction in the same direction. If you are pedaling, you are applying torque to the rear wheel that propels the bike (friction pointing forwards); the front wheel meanwhile continues to experience only rolling friction, and would therefore experience a net force of friction that slows the bike down.

So "it depends". Coasting = same; pedaling = opposite.

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