# I Tire dynamics

#### LLT71

http://imageshack.com/a/img923/733/FJKAqj.jpg
so here is the deal. is rolling resistance N+Ft or are they "separate" in a means of: N part is for static friction = mu*N and Ft is part of rolling resitance=coefficient of rolling resistance*Ft so that in order for tire to start rolling without slipping do I need to apply such force that overcomes Ft*coeff of rolling resistance. but at the same time that applied force has to be less than mu*N?
2. is N equal for every point from point C to B (see picture) and why?
3. why its the point of most interest just point B (like in this picture, and similar ones explaining rolling friction)?

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#### haruspex

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http://imageshack.com/a/img923/733/FJKAqj.jpg
so here is the deal. is rolling resistance N+Ft or are they "separate" in a means of: N part is for static friction = mu*N and Ft is part of rolling resitance=coefficient of rolling resistance*Ft so that in order for tire to start rolling without slipping do I need to apply such force that overcomes Ft*coeff of rolling resistance. but at the same time that applied force has to be less than mu*N?
2. is N equal for every point from point C to B (see picture) and why?
3. why its the point of most interest just point B (like in this picture, and similar ones explaining rolling friction)?
See if section 4.1 of https://www.physicsforums.com/insights/frequently-made-errors-mechanics-friction/ helps.

#### rcgldr

Homework Helper
I"m not sure how you calculate rolling resistance from that diagram. Part of rolling resistance is due to hysteresis, and part due to sliding friction. The force during radial deformation is greater than the force during recovery, lost to heat (hysteresis). There's also loss due to deformation along and across the tread, some of this loss is due to hysteresis, some due to sliding friction as the tread deforms and recovers.

The normal force at A and C is zero. The maximum normal force occurs near B.

Correction - the normal force at B and C is zero. The maximum normal force occurs near A.

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#### LLT71

I"m not sure how you calculate rolling resistance from that diagram. Part of rolling resistance is due to hysteresis, and part due to sliding friction. The force during radial deformation is greater than the force during recovery, lost to heat (hysteresis). There's also loss due to deformation along and across the tread, some of this loss is due to hysteresis, some due to sliding friction as the tread deforms and recovers.

The normal force at A and C is zero. The maximum normal force occurs near B.
say I am stupid but why forces at point A and C are zero? and how do I know whitch force I must apply to tire in order to roll it without slipping? what I must overcome with that force? so confusing... also, can you recommend me some books that explain tire kinematics? thank you!

@haruspex thank you!

#### haruspex

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2018 Award
The normal force at A and C is zero. The maximum normal force occurs near B.
I think you have A and B swapped over relative to the diagram.
The maximum normal force should be right in the middle, no? But it will be greater a small distance x in front of that than at the same distance behind it.

#### rcgldr

Homework Helper
The normal force at A and C is zero. The maximum normal force occurs near B.
Correction - the normal force at B and C is zero. The maximum normal force occurs near A.
forces at point A and C are zero?
I think you have A and B swapped over relative to the diagram.
I forgot the ordering of points in the diagram, I had thought it was A, B, C, right to left, not B, A, C right to left, so I got A and B swapped. I struck through the incorrect statement and added what should be a correct statement.

how do I know whitch force I must apply to tire in order to roll it without slipping?
It's complicated. You have hysteresis effects related to deformations along the sidewalls and across and in the direction of tread. There's also some sliding friction along the tread surface as it deforms, but according to wikipedia, most of the losses to heat are due to hysteresis.

http://en.wikipedia.org/wiki/Rolling_resistance

#### LLT71

It's complicated. You have hysteresis effects related to deformations along the sidewalls and across and in the direction of tread. There's also some sliding friction along the tread surface as it deforms, but according to wikipedia, most of the losses to heat are due to hysteresis.

http://en.wikipedia.org/wiki/Rolling_resistance
ok,and what about my picture in first post; is it decently okay if I say that I must apply moment (Mo=Fo*rd) that will overcome N*f in order to have just pure rolling but at the same time I have to be careful that force Fo=Mo/rd has to be ≤μstatic*N (cause it will cause additional slipping, something like burnout)?

"Tire dynamics"

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