Using the 4psi Tyre Inflation Rule

Submitted: Tuesday, Feb 14, 2012 at 14:14
ThreadID: 91867 Views:11382 Replies:12 FollowUps:12
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Care must be taken in using the 4psi inflation rule as often the pressures measured 'cold' and 'hot' may be affected more by ambient temperature than tyre heating through vehicle motion.

The 4psi rules states that “if your tyres are inflated correctly then the tyre pressure measured when the tyres are hot (after travel) will be 4psi greater than the pressure measured when they were cold (before travel)”.

See Blog for actual caluclations.

Changes in tyre pressure due to typical ambient temperature changes show:
Example 1. Morning ambient temperature 15c, Midday ambient temperature 30C, pressure change due to temperature change alone is 2.6 psi.
Example 2. Morning ambient temperature 10C, Midday ambient temperature 35C, pressure change due to temperature change alone is 4.4 psi.

I am not saying that the 4psi rule is right or wrong, I am saying that caution needs to be taken in how it is applied.
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Regards Rob

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