How Do Tractive Forces and Rolling Resistance Affect a Car Wheel's Motion?

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    Physics Tire
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Discussion Overview

The discussion focuses on understanding the relationships between tractive forces, rolling resistance, and the motion of a car wheel. Participants explore theoretical models, calculations, and the effects of various forces acting on the wheel, particularly in the context of constant speed and the presence of obstacles.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a diagram and seeks to understand the relations between forces acting on a tire powered by a motor, including static friction and rolling resistance.
  • Another participant provides a link to a Wikipedia article on rolling resistance as a resource for further understanding.
  • A participant questions how rolling resistance creates a torque opposite to the motor and how to include it in calculations.
  • One participant claims to have derived an equation relating static friction, rolling resistance, and the weight of the tire, but seeks confirmation on whether they are on the right track.
  • Another participant recognizes a mistake in their previous understanding and attempts to clarify the forces needed to move the tire, suggesting a new equation that incorporates static friction, rolling resistance, and weight components.
  • Participants express a need for resources, such as books or diagrams, to better understand tractive forces and rolling resistance.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct equations or models. There are competing views on how to accurately represent the forces acting on the tire, and some participants express uncertainty about their calculations and understanding.

Contextual Notes

Participants mention various assumptions, such as the direction of forces and the conditions under which the equations apply, but these assumptions remain unresolved. The discussion includes references to specific angles and coefficients that are not fully defined.

Who May Find This Useful

This discussion may be useful for individuals interested in automotive engineering, physics of motion, or those studying forces and mechanics related to vehicle dynamics.

cb951303
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Diagram = http://i.imgur.com/LaUO4.jpg

The tire is powered by a motor of torque T. It's weight is W and the static friction force is Fs. Consider that the tire is moving upwards in a constant speed of V.

I would like to understand the relations between forces on a model like above.
Also how can I show the rolling resistance? What's the direction?
For example what would be the value of Fs?

What resources/books can you recommend to better understand this?

Thank you
 
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Ok from what i understand rolling resistance creates a torque opposite to the motor but where from the force is applied? How can i include in my calculations?
 
See http://hpwizard.com/car-performance.html" (at the bottom of the page, Theory »» Longitudinal acceleration)

rolling-resistance.gif
 
Last edited by a moderator:
Ok I think I cracked it.
According to wiki page rolling resistance is applied in the reverse direction of the motion from the center of the wheel (somehow I missed it the first time sorry)

Since there is no acceleration the overall force should be 0 thus I can write this equation

F_s = F_{rr} + W.sin(\alpha) where F_s = T/r and F_{rr} = W.cos(\alpha).C_{rr} so the equation becomes:

T/r = W.cos(\alpha).C_{rr} + W.sin(\alpha)

Am I on the right track here?
 
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How would I have to change the above equation if let's say there is an obstacle in front of the wheel by the dimensions LxL like in below
QUc0r.jpg


thank you
 
Ok I now know that the above diagram and formula is false.
The force needed to move the tire is equal to the static friction between the tire and the road right. So F_s = W.cos(\alpha).\mu_s
But there is also W.sin(\alpha) and F_{rr} working in the opposite direction of F_s so the force needed to move the tire upwards is F = F_s + F_{rr} + W.sin(\alpha) am I correct? anyone know any books that explains the tractive forces and rolling resistance on a car wheel?
Or can you at least provide me with a free body diagram of a car wheel at constant speed?

thank you
 
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