Question on the 4psi increase in tyres??
Submitted: Wednesday, May 21, 2014 at 16:11
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wombat100
To the tyre gurus here.
The theory of a 4 psi increase with hot tyre pressures would be for tyres running (say) about 40psi. So that's an increase of about 10%.
Would the same apply for pressures of 70psi cold?? This would be an increase of only about 6% (sorry haven't got a calculator here).
Or is the 4psi increase be applicable no matter what the cold pressures???
Thanks in advance
Reply By: Dennis Ellery - Wednesday, May 21, 2014 at 19:14
Wednesday, May 21, 2014 at 19:14
I have a brochure from Coopers that quotes 4 PSI for sedans and 6 PSI for 4WDs.
For sedans around town I have always used the tyre supplier’s recommended pressures.
For heavily loaded 4 WD I have always used the 6PSI rule.
It’s a rough guide but it’s simple and it suits me - I get an even wear out of my tires.
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Reply By: Alan S (WA) - Friday, May 23, 2014 at 10:36
Friday, May 23, 2014 at 10:36
Hi All
But is there another 4psi rule?. Because the one I am aware of takes into consideration speed and loading, as both these effect temperature which then also effects pressure.
If at what ever pressure you start at and you travel at a set speed, and the tyre pressure increases more than 4psi then you either need to slow down to reduce heat, reduce load or add more air to reduce tyre flex and heat build up.
Its olbvious to me that this would only work once past initial warm up. As a general rule i use it as a way of determing a suitable speed for the pressure I am running, and being able to reduce heat input into the tyre. You could use what ever pressure difference you wanted, and if you went higher you would have an associated higher speed for the pressure, and a lower pressure differential would give you a slower speed for the pressure.
Alan
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Follow Up By: Norm C (WA) - Saturday, May 24, 2014 at 18:45
Saturday, May 24, 2014 at 18:45
Well put Alan
That's been my understanding of the 4psi
Norm
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