I'm going to buy and run for the first time a winter rally spiked tyre of 145 80 r13, and I was wondering what pressures do people generally use rallying in low winter temperatures on snowy terrain?

Does running a low pressure increase the grip? Does the air inside increase or decrease volume just like a summer tyre increase pressure inside it as it gets warm?

Note: I am asking about a rally tyre, not a road one

Edit: The manufacturer recommended 1.5bar front and 2.0bar for rear (2.5bar for high oversteer) for my current setup, fwd light car with 75% weight on front

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Generally speaking, reducing the pressure will be a dangerous idea - underinflated tyres don't stop anywhere near as well, and steering will be more of an issue.

It's actually supposed to be quite a rigid tyre - snow tyres aren't meant to ride on top of the snow (like a large, fat, low pressure tyre would) but cut into the snow for added sideways grip.

Yes, pressure will increase with heat, but because these tyres are probably lower volume than your summer tyres, the effect should not be as marked. You'll still expect about 1 psi for 10 degrees increase in ambient temperature, which isn't as significant on more rigid snow tyres as it is on a broad slick, for example.

Two of my friends who race winter rallycross suggest up to 40psi for short stages and 35-ish for longer stages to take into account the increased temperatures.

  • I appreciate the answer, but it doesn't really answer my question, manipulating the tyre pressure to suit course condition is a common practice, i don't really use the manufacturer's specifications. For example, when running semi or full slicks, using the recommended pressures is a sure way of ending up in a ditch. They get to higher temperature than normal compound tyres and the air gets to expand so much as to overinflate the tyre causing severe loss of grip. Adjusting the air is a crucial part, as air is volatile, and in most racing from it is illegal to use more stable gases such as NO2 Nov 16 '16 at 14:48
  • For short reference: tirerack.com/tires/tiretech/techpage.jsp?techid=58 Nov 16 '16 at 14:50
  • I get it, but i'm interested in some numerical values, and obviously for a competition use. For the amount of money there tyres are worth, using them on public roads is out of the question :) Nov 16 '16 at 14:55
  • cory - that clarification did come in after I wrote the post, to be fair, and only from this comment thread.
    – Rory Alsop
    Nov 16 '16 at 15:11
  • there you go - now the question actually asks about running on a winter rally course with spiked tyres. The original one didn't have that context. I agree - pretty funny though
    – Rory Alsop
    Nov 16 '16 at 15:21

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