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a2k

tire temperatures for racing game

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does anyone know of a good source of how to model good tire temperature readings for a racing simulation? not talking about pressure stagger and camber just yet, just based on weight transfer, convection, conduction, material of tire, and friction. a2k

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I don''t know of any links, I''m not exactly an expert myself. but my dad used to drag race in NHRA. I''d just thought I''d throw out that there are different tires that they use. normal tires for everyday stuff, and slicks for rainy wether.

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newtons law of cooling/heating is some exponential function (which i can''t think of right now). you could probably just use C*e^(-a*x) and pick some values of ''C'' and ''a'' until you got it how you wanted it.

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If friction slows the car from A m/s to B m/s, then

heat energy gained = KE lost = .5 * mass * (A^2 - B^2)
temperature rise = heat energy gained / mass / heat capacity of rubber

temperature rise = .5 * (A^2 - B^2) / heat capacity of rubber

Unfortunately, I have no idea what the heat capacity of rubber is, so some experimentation will be needed.

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I have ''Tires, Suspension and Handling'' by John Dixon, which goes into some detail on how the how temperature effects tire properties, though not enough to construct a detailed model.

I think a detailed model would be overkill. Under normal driving (e.g. the tire not flat, not under heavy braking) you can assume the tyre symmetric, and then you are only interested in the temperature at the contact strip which you can treat as uniform. As the stresses are also applied at this strip you can treat it as a simple object in it''s own right.

Better might be something like:

dT/dt = f(stress) - k(T - T0)
or

T'' = T + timestep * (f(stress) - k(T - T0))

where f is a simple (e.g. linear) fn of the stresses on the tire, k is a constant (which takes account of heat dissipation to the rest of the tire) and T0 the ambient/air temperature. Then use a lookup table to translate the temperature to tyre properties such as grip and slip properties, one table for each tyre type/compound/design based on manufacturers data.

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quote:
Original post by Beer Hunter
If friction slows the car from A m/s to B m/s, then

heat energy gained = KE lost = .5 * mass * (A^2 - B^2)
temperature rise = heat energy gained / mass / heat capacity of rubber

temperature rise = .5 * (A^2 - B^2) / heat capacity of rubber



Doesn''t this formula apply to tyres only when they are locked (producing skidmarks and smoke :-)?
When tyres aren''t locked the temperature rise is gained by the braking discs.

/raddy

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quote:
Original post by Raddy

When tyres aren''t locked the temperature rise is gained by the braking discs.



I don''t think so. The brake''s dissipate thier own heat. They can get very hot and it would do the tires no good if this heat was transferred to the tires. Also the heat generated by the discs varies greatly depending on driving conditions, and it would be difficult to maintain a steady tire temperature having to take into account such variations.

Rather the heat comes from the internal and external frictional effects acting on the tire rubber. You can generate the same effect yourself - take a fork, bend it backwards and forwards repeatedly and it gets warm. That''s why to warm up tires drivers can be seen snaking from side to side to stretch the tire rubber and so warm it up, e.g. in the warm-up lap of a race.

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I would like to know what type of racing game you are making, tires react differently in different types of racing, if i knew what type of racing i could better help you.

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The heat build up in the tire is not only due to the work done on deforming the rubber but also due to the work done by the rubber on the road. The rubber imparts energy to the road and the road reacts imparting energy to the tire (that''s how the car moves!) This is all achieved because there exists a friction between the rubber and the tire. So, there should be a frictional heating term in your differential equation and a deformation heating term. Details of adequate models are above.

Cheers,

Tim

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