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stefu

Car physics: tire pressure

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Too much pressure will lose grip.

I think low pressure has better grip on looser surfaces, like dirt, but uses up the tires faster..

I can't remember exactly, but I think I learned things like this with the NASCAR racing series.

As for the formula, I dunno.

[edited by - Waverider on June 18, 2003 12:02:40 PM]

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In a very simplified, "ideal" friction calculation, there''s no difference. Otherwise, here''s the deal.

Let''s say that your car has mass m kg. Gravity is g m/s. Now, the gravitational force between the car is, of course, m*g N.

Let''s say that the tire pressure is p N/m2. (yes, you can convert pressure to these units.) Since the pressure from the contact patches must be equal to the gravitational force (otherwise the car would sink into the road) the contact patches have, total, area m*g/p, and each tire has a contact patch of size m*g/4p.

Of course, that doesn''t give you a final equation; but it does give you the size of the contact patches, which will be useful in determining one.


How appropriate. You fight like a cow.

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Well, I think I''ll take just approximation fuinction approach like this:

float tyre_pressure_fact(float pressure_at_20C, float temperature) {
const float max_p=300;
float p = pressure_at_20C * (temperature+273.15) / (20+273.15);
if (p<0) p=0; if (p>max_p) p=max_p;
return 1.0+cos(PI*p/max_p)/2.0;
};

Should be reasonable start. Later I had to add some other effects that too low pressure causes.



3D Racing Game Updated June 16 2003

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http://www.theuspits.com/news/race/index.html

This is a collection or articles hosted by a race sim site (don''t know if you''ve heard of the US pits or not), but it''s a phenomenal guide to car physics, and is also somewhat geared toward simulation developement. You will probably never need anything else.

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Thanks!

I also found that tyre pressure affects slip angle. Higher pressure makes tyre''s slip angle (the peak point) smaller.

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quote:
Original post by tmoneyksu
http://www.theuspits.com/news/race/index.html

This is a collection or articles hosted by a race sim site (don''t know if you''ve heard of the US pits or not), but it''s a phenomenal guide to car physics, and is also somewhat geared toward simulation developement. You will probably never need anything else.



yeah, that''s the classic Physics Of Racing Series articles (PHORS, phoarrr!!). Brian Beckman should be canonised as a saint

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