Heating up of tyres on the road

[vcsharp2003]

Homework Statement

Why do the tyres of a car get hot when one drives the car on a road?

Relevant Equations

None

I have searched online for this and found that it's due to friction. But for a rolling tyre there is only static friction acting and static friction produces no heat. For heat to be produced the two surfaces in contact must slide over each other i.e. there needs to be kinetic friction.

Perhaps the bottom part of the tyre gets compressed by the road continuously causing -ve work on the thermodynamic system of tyre and inside air. Perhaps, the negative work is causing the internal energy to increase of the thermodynamic system made up of tyres plus inside air.

 

[Steve4Physics]

Read-up on 'rolling resistance'.

 

[berkeman]

Homework Statement:: Why do the tyres of a car get hot when one drives the car on a road?

But for a rolling tyre there is only static friction acting and static friction produces no heat.

The correct answer will come from the hint by @Steve4Physics but it also depends on "how" you drive on the road...

https://www.carwow.co.uk/blog/best-drift-cars#gref

 

[vcsharp2003]

Read-up on 'rolling resistance'.

Rolling friction will always produce heat like sliding friction, it seems. But shouldn't the constant deformation of the tyre by the road surface also be responsible for producing heat.

 

[Steve4Physics]

Rolling friction will always produce heat like sliding friction, it seems.

Yes.

But shouldn't the constant deformation of the tyre by the road surface also be responsible for producing heat.

It should and it does! The continuous deformation of the rubber, as the tyre rolls, causes local heating inside the rubber.

The rolling resistance force and the conversion of mechanical energy to heat inside the rubber are intimately linked.

Kudos for using the correct spelling of 'tyre' by the way!

 

[hutchphd]

The contact patch of the tire on the slightly convex road has a different area and shape than when not in contact. This repetitive "squirming" causes various heating mechanisms of the rubber.
My guess is that the gas is not much heated directly (but is heated by the rubber). I would be interested to know.

 

[haruspex]

Rolling friction will always produce heat like sliding friction, it seems. But shouldn't the constant deformation of the tyre by the road surface also be responsible for producing heat.

Rolling resistance is the better term; it is more widely used, avoids confusion with friction and is more appropriate since it encompasses several causes - in particular, the deformation you mention.
See https://en.wikipedia.org/wiki/Rolling_resistance for a good discussion.

 

[hutchphd]

I have always been appalled by the terminology surrounding "friction forces". It is even worse for things that roll. Is "rolling resistance" the same as "rolling friction" etc etc.? I pity the first year Physics student (not to mention her erstwhile professor) trying to rationalize these terms. No wonder confusion reigns.

 

[jack action]

The word you want to look for is hysteresis.

Hysteresis. A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis. As the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber.

 

[Chestermiller]

The word you want to look for is hysteresis.

Yes, this is due to rubber viscoelasticity which converts deformational mechanical energy to internal energy.

 

[Lnewqban]

Go to the 5:00 minutes mark:

 

[Tom.G]

If you want a hands-on demonstration of heating by deformation, try this experiment.

1. Get a clothes hanger that is just metal wire, the larger the wire diameter the better, but you have to be able to bed it with your hands.
2. No plastic covering or remove the plastic.
3. ) You need a straight section of the wire long enough to hold with both hands.
4. Grip the wire with both hands close together.
5. Now rapidly make a sharp bend in the wire then immediately straighten the bend.
6. Do this several times and notice that the area of the bend has gotten warm.

That is the same process that heats the tyre you asked about.

Cheers,
Tom

 

[vcsharp2003]

If you want a hands-on demonstration of heating by deformation, try this experiment.

1. Get a clothes hanger that is just metal wire, the larger the wire diameter the better, but you have to be able to bed it with your hands.
2. No plastic covering or remove the plastic.
3. ) You need a straight section of the wire long enough to hold with both hands.
4. Grip the wire with both hands close together.
5. Now rapidly make a sharp bend in the wire then immediately straighten the bend.
6. Do this several times and notice that the area of the bend has gotten warm.

That is the same process that heats the tyre you asked about.

Cheers,
Tom

Deformation of the rubber of the tyre should be the real reason of it heating up rather than rolling friction/resistance between the road and tyre.

 

[haruspex]

Deformation of the rubber of the tyre should be the real reason of it heating up rather than rolling friction/resistance between the road and tyre.

As I wrote in post #7, deformation is one aspect of rolling resistance, not something separate. In the case of car tyres, it is the major reason for the tyres' heating.
For other aspects, road deformation heats the road, while axle friction heats the axle.

 

[jack action]

Deformation of the rubber of the tyre should be the real reason of it heating up rather than rolling friction/resistance between the road and tyre.

Rolling resistance has nothing to do with friction. It is a moment due to the misalignment of the normal force acting at the axle vs the one acting at the contact patch.

 

[jbriggs444]

Rolling resistance has nothing to do with friction. It is a moment due to the misalignment of the normal force acting at the axle vs the one acting at the contact patch.

Indeed, this is correct.

If all wheels are driven in a coordinated fashion, the result can be that the drive train counters rolling resistance directly and static friction does not enter in.

If one or more wheels are free, the result is a tendency for those wheels to slow their rotation. On a frictionless surface, this would result in slipping rather than pure rolling. Static friction acts to prevent this. The drive wheels (if any) then have static friction providing a forward force on the car while the free wheels have static friction providing a rearward force.

 

[hutchphd]

So the tire is functiong as a cyclic heat pump using the hysteresis of the rubber as the working medium?

 

[jbriggs444]

So the tire is functiong as a cyclic heat pump using the hysteresis of the rubber as the working medium?

I am not sure that I understand what you are getting at. Cars seem to have more in common with resistance heating than with heat pumps.

 

[hutchphd]

Do you know the rubber band heat engine?

It strikes me that the tire is a driven (heat pump) version of this engine.

 

[hutchphd]

If you want a hands-on demonstration of heating by deformation, try this experiment.

But the rubber is fundamentally different because it is elastic and the deformation is repeatable. Thus the process can be made mechanically cyclic. Here's some Feynman:

 

[jbriggs444]

Do you know the rubber band heat engine?

I see a similarity in that both involve a rotating object constructed with rubber. In the case of the rubber band engine, I see a cold reservoir (the air into which which we are pouring heat) and a hot reservoir (the lights from which we are drawing heat).

In the case of a tire on the road I do not see a cold reservoir from which we are drawing heat. We are not pumping heat. We are just thrashing around generating thermal energy.

We could try to turn a tire into a heat pump if we optimized the process and adjusted the operating margins so as to drop some portion of the rubber below ambient temperature. But no actual production tire is optimized in such a way. The typical operating point is quite far away from such conditions.

 

[hutchphd]

The typical operating point is quite far away from such conditions.

Very interesting. Looking at a revolution in the thermodynamic cycle it is the inevitable waste heat from the cyclic process (because of the response hysteresis) that is causing the tires to warm up. I didn't see that this could be called, if one has to, "internal friction" in the rubber. All "frictiion" terms give me agita.
I now think we agree on the Physics. Thanks.

 

[haruspex]

Rolling resistance has nothing to do with friction. It is a moment due to the misalignment of the normal force acting at the axle vs the one acting at the contact patch.

View attachment 320676
View attachment 320677​

That's rather too restrictive.
Rolling resistance certainly encompasses losses due to deformation of the substrate, e.g. a rigid wheel on carpet.
I believe many, particularly engineers, would include axle friction, e.g. https://en.wikipedia.org/wiki/Rolling_resistance#Definitions:
"In the broad sense, "rolling resistance" includes wheel bearing resistance, energy loss by shaking both the roadbed (and the earth underneath) and the vehicle itself, and by sliding of the wheel, road/rail contact."
The "shaking of the vehicle" would arise from unevenness in the road surface. I was surprised to learn recently that this leads to an ideal pressure on a given surface for cycle tyres. At lower pressure there is increased loss in deformation of the tyre, while at higher pressure the increased vertical jitter from the road surface becomes the problem.

The 'sliding' mentioned I take to be of a microscopic nature, rather than outright skidding. Certainly rubber is prone to creep. As a part of the tyre joins the contact patch, it is under tangential compression. As it subsequently leaves the ground, and the normal force on it tends to zero, it will tend to slip slightly.
Something similar may happen laterally at the sides of the contact patch. The reason rubber tyres work so well on asphalt is that as the rubber is forced against the ground it contracts laterally and tangentially, gripping the ground.

 

[jbriggs444]

vertical jitter from the road surface becomes the problem

Riding bicycle down a fairly steep hill with a left hand curve and washboard type corrugations in the asphalt was a frightening situation the first time I encountered it. The wheels slid right out from under and I was left trying to figure out what had happened.

 

[jack action]

@haruspex , I may have been too restrictive in my definition by eliminating the word "friction", but I did so because I felt the OP believed that rolling resistance is some sort of "rolling friction", i.e. the resulting heat is mainly caused by the tire sliding on the ground (which it does, otherwise the tire wouldn't wear).

But the main source of heat is the constant deformation of the tire and it can be evaluated by a moment, not by some friction coefficient and normal force.

 

[hutchphd]

Riding bicycle down a fairly steep hill with a left hand curve and washboard type corrugations in the asphalt was a frightening situation the first time I encountered it. The wheels slid right out from under and I was left trying to figure out what had happened.

As a cyclist I would advise avoiding that........

 

[hutchphd]

Of course I would be remiss if I did not point out that certain members of this community (@berkeman ) would seek out such a geometry and be challenged by it only if it were also slathered in mud.

 

[berkeman]

Of course I would be remiss if I did not point out that certain members of this community (@berkeman ) would seek out such a geometry and be challenged by it only if it were also slathered in mud.

I already have a thread about how rattlesnakes alter tire traction in high-speed downhill banked turns, so I won't repeat the discussion about that variable...

 

[haruspex]

I may have been too restrictive in my definition by eliminating the word "friction",

No, I'm with you on that. I hate the term "rolling friction", when friction is a minor component at best.
My main issue with the link you posted is that it ignores substrate deformation, as would be encountered by a ball rolling on grass; and secondarily, in the case of a vehicle, axle friction.

 

[hutchphd]

This is why I am an abolitionist when it comes to the terms "friction" and the "work done by friction". Attempts to define them absolutely end up involuted and inutile. I propose that we are far better served by simply defining "non-conservative" approximate forces and then specifying them when necessary. "Frictional Force" means nothing unless otherwise specified. I believe the existance of the term to be driven by lazy pedagogy.

 

[Lnewqban]

When the asphalt is very hot, a lot of heat is transferred into the tires and the internal pressure increases.
When it is raining, the tires cooldown and the internal pressure decreases.

Strong braking and acceleration, as well as cornering, also transfer heat into the tires.

Internal friction of tube against carcass, or even inside delaminating plies of a damaged carcasse, also increases temperature of the tire.

A normal tire can become very hot (to the point of destruction) simply by underinflation combined with high static (weight) and dynamic (speed associated) loads.