Which thing determine friction in tyres of cycle?

1. Sep 20, 2011

vkash

Hello guys.

first question.
you must have done cycle ride. It's our common experience that when air pressure inside tires reduced it becomes harder to ride. But as usual my question is why it is so why we need to apply more force(more likely torque ).???????
As it is written in highlighted letters in books that friction is dependent on normal reaction of forces not on surface area(surface area of tires increase if air pressure decrease). so why it(friction) is changing with surface area change.

second.
It is also on cycle.
friction on back tire of cycle is in forward direction and on the forward tire in is backward. What if there is one tire cycle(one wheel with pandels on it) as shown in circus. I think it will be easier to ride that cycle if continuous force force is applied by rider. what you think. Will it have greater acceleration than excepted value.since friction will in forward direction.

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vikash chandola

2. Sep 21, 2011

rcgldr

The term used for the force opposing rolling motion is called rolling resistance, which is different than friction, which relates to the amount of grip between a tire and pavement (or whatever the tire is rollling on).

The rubber in a tire consumes energy if it's compressed or stretched and allowed to return to it's original shape. This process is called hysteresis. In the case of a rolling object, there is deformation that results compression and/or stretching of the rubber at and near the point of contact between tire and the pavement.

By increasing the pressure inside the tire, the amount of deformation is reduced, and the amount of rolling resistance is reduced. Reducing the pressure in the tire increases the amount of deformation and increases the amount of rolling resistance.

3. Sep 21, 2011

vkash

Can you tell something on single tire cycle's rolling friction?

4. Sep 21, 2011

JeffKoch

I personally don't really have a clue what you are trying to say, so I suspect you'll have to try again - there's either a language barrier or some major misunderstandings floating around in this paragraph.

5. Sep 21, 2011

vkash

have you ever seen a cycle with single tire.In cartoons or circus. For that's single tire to roll friction must act in forward direction. OK. So here friction is helping rider to move cycle.
In bicycle there is backward friction from front tire. so I want to say that will it easier to ride this single tire cycle with respect to bicycle?
Hope my English is better this time.

6. Sep 22, 2011

JeffKoch

The driven wheel, whether the rear wheel on a bicycle or the only wheel on a unicycle, is driven by pedal force, and wants to rotate forward. Because of friction it can only do this if the whole cycle moves, which it does unless you're trying to pedal on smooth wet ice with oil poured on top - in that case friction is tiny, and easily overcome by pedal power, so the wheel turns in place and you fall over.

The front wheel on a bicycle adds resistance primarily from being cyclically deformed, so some of your pedal power goes into heating the tire, the road, the air, etc. So you have to use a bit more pedal power to compensate, but in return you have the ability to steer in a stable manner using a wheel with trail.

So all other things being equal, you would have to use a bit more pedal power to ride a bicycle. But all other things are far from equal, and in fact it's far easier to ride a bicycle, primarily because it's stable and you can direct your energy towards pedalling - on a unicycle you have to constantly shift your balance to keep from falling over, which is tiring and wastes energy.

7. Sep 22, 2011

rcgldr

The term is rolling resistance not rolling friction. For a unicycle (single tire), there's only one tire, but it's deformed more since all of the weight is on the single tire. The hysteresis curve for rubber is complicated, and the rolling resistance with two tires could be less than the rolling resistance with a single tire (if all other factors are the same).

8. Sep 22, 2011

vkash

thanks to both for giving their valuable answers.