4psi rule

Submitted: Saturday, Jun 26, 2004 at 09:52
ThreadID: 14146 Views:5220 Replies:5 FollowUps:4
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Can anyone tell me what the 4 psi rule is for tyres if you have say a difference 7psi from cold to hot does that mean that your original psi was to low or to high.
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Reply By: Mad Dog (Victoria) - Saturday, Jun 26, 2004 at 10:07

Saturday, Jun 26, 2004 at 10:07
4psi just right
More than 4psi then under inflated
Less than 4psi then over inflated

AnswerID: 65195

Reply By: Hedonist - Saturday, Jun 26, 2004 at 12:47

Saturday, Jun 26, 2004 at 12:47
To add to the succint explanation above:

The change in pressure is an indication of the amount of heat generated by the tyre as the carcass flexes under load.

If a tyre is underinflated the flexing of the sidewall will be excessive and the tyre will generate a lot of heat which will cause a larger increase in pressure that would occur if it was correctly inflated to start with.

Conversly, if the tyre is overinflated, there will be very little flexing of the tyre carcass and a correspondingly smaller increase in the inflation pressure...

Cheers,
Pete
AnswerID: 65210

Reply By: Topend - Saturday, Jun 26, 2004 at 12:47

Saturday, Jun 26, 2004 at 12:47
Tyre pressure should be checked when cold, although sometimes this is not possible. Try your high and low pressures when cold then go for a decent drive. Then recheck them and see what they read when hot. Remember your hot pressures for those times when you have to alter the them while hot.

As for the 4psi rule, I sometimes vary my pressure by more than this depending on weight etc.

Topend
AnswerID: 65211

Reply By: Member - Meggs - Saturday, Jun 26, 2004 at 20:24

Saturday, Jun 26, 2004 at 20:24
I read somewhere a while back that it was 4 psi for car tyres and 6 psi for 4 x 4 tyres. Does anyone know what is right?
AnswerID: 65251

Follow Up By: Member - Brett H (QLD) - Monday, Jun 28, 2004 at 17:59

Monday, Jun 28, 2004 at 17:59
Bridgestone told me 10 years ago that 4 psi was good for 10R 15's
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FollowupID: 326480

Reply By: DaveNJude - Monday, Jun 28, 2004 at 15:01

Monday, Jun 28, 2004 at 15:01
Eric

Check out this link to the NRMA http://www.mynrma.com.au/travel/do/cc4/cara3.shtml

Cheers

Dave n Jude
AnswerID: 65515

Follow Up By: Rosscoe - Monday, Jun 28, 2004 at 15:33

Monday, Jun 28, 2004 at 15:33
Hi DaveNJude,

Read the articlle.
Now, how do you define a "Large 4WD Tyre". I run 265/70/R16 on my 4WD and 265/75/LT16 on my dirt road caravan. 4 psi or 6 psi test?????

Rosscoe
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Follow Up By: DaveNJude - Tuesday, Jun 29, 2004 at 12:37

Tuesday, Jun 29, 2004 at 12:37
Rosscoe

My guess is the article is aimed more at car style tyres so I would imagine the heavier sidewalls etc on Light Truck etc tyres would have to generate more heat - so 6psi would be the go :)

Dave
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Follow Up By: Member - Glen O (NSW) - Thursday, Jul 08, 2004 at 07:04

Thursday, Jul 08, 2004 at 07:04
6 psi

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