How Does Tire Inflation Affect Resistance in Bicycle Motion?

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A Physics Enthusiast
If friction is independent of area of contact, how do less inflated tires of a bicycle experience more resistance towards motion than the well inflated tires?
 
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T13091999 said:
If friction is independent of area of contact, how do less inflated tires of a bicycle experience more resistance towards motion than the well inflated tires?
Take an uninflated tyre and 'knead' it with your hands. When you cycle on a soft tyre, you are actually doing this to every bit of the tyre as it comes into contact with the ground. A hard tyre may rattle your teeth but it takes much less energy.
P.S. Steel wheels on steel rails are highly efficient.
 
sophiecentaur said:
Take an uninflated tyre and 'knead' it with your hands. When you cycle on a soft tyre, you are actually doing this to every bit of the tyre as it comes into contact with the ground. A hard tyre may rattle your teeth but it takes much less energy.
P.S. Steel wheels on steel rails are highly efficient.
I have failed to understand this. Do you mean that the deformation of the tyre takes away the "effort" ? (Sorry for the not-so-proper terminology)
 
A Physics Enthusiast said:
I have failed to understand this. Do you mean that the deformation of the tyre takes away the "effort" ? (Sorry for the not-so-proper terminology)
The forward motion of the bicycle requires continual deformation of the tires as they roll. This deformation consumes energy beyond what is required to overcome friction.
 
A Physics Enthusiast said:
I have failed to understand this. Do you mean that the deformation of the tyre takes away the "effort" ? (Sorry for the not-so-proper terminology)
The hysteresis in the deformation involves a loss of energy. So the deformation takes away Energy. The word "effort" is used to describe a Force so it is not appropriate to apply it here, I think. Best to talk in terms of Work Done and work returned to the system.
 
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A Physics Enthusiast said:
Do you mean that the deformation of the tyre takes away the "effort"?
Did you read the link in post #2?
 
Friction is generally not independent of area of contact. That's an oversimplification used in introductory physics, and it's generally fairly accurate for hard objects sliding against each other, but when you get into complex situations like modern tires, both the contact area and the shape of the contact patch matter.

In addition, rolling resistance is yet another phenomenon that is independent of ordinary sliding friction. A wheel which is rolling is not sliding, so the sliding friction formula does not apply. Instead, rolling resistance has more to do with the deformation of the wheel and surface, and the energy needed to cause that deformation. As a result, a wheel which deforms less will have less rolling resistance, leading to the tire pressure dependence you talked about.
 
A.T. said:
Did you read the link in post #2?
Yes. Wikipedia says that deformation of the tyres contributes to rolling friction. I got confused as I wasn't able to link that concept with the concept of friction being independent of area.
 
A Physics Enthusiast said:
Yes. Wikipedia says that deformation of the tyres contributes to rolling friction. I got confused as I wasn't able to link that concept with the concept of friction being independent of area.
Some wikipedia articles are quite good, some not so much, and some are generally OK but carelessly written so can be confusing. You've been victimized by one of that last kind.

(Stuff like this is the reason why wikipedia is not a generally accepted reference under the PF rules, although we will routinely refer people to particular entries that do fall in the "quite good" category.)
 
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A Physics Enthusiast said:
I have failed to understand this. Do you mean that the deformation of the tyre takes away the "effort" ?
Yes, energy is lost in the continuous deformation of the underinflated tire as it rotates. It has nothing to do with the friction between the tire and the road. Have you been able to start understanding this effect now because of the responses in the thread? :smile:

https://www.physicsforums.com/threads/awesome-motorbike-skills.937405/#post-5928180

tirepressurestory_04-jpg.jpg


EDIT/ADD -- Bonus Quiz Question related to the question in your first post -- Why is underinflating tires good for climbing over rocks or riding/driving through sand? :smile:
 

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berkeman said:
Have you been able to start understanding this effect now because of the responses in the thread? :smile:
Yes. I need some time (exams are going on).
:blushing:
 
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A Physics Enthusiast said:
Yes. Wikipedia says that deformation of the tyres contributes to rolling friction. I got confused as I wasn't able to link that concept with the concept of friction being independent of area.
Why are you trying to link it to something you learned about "friction"? The wiki article explains right at the start why "rolling friction" is a misnomer.