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Where the rubber hits the road. Discussion about drive train; (locking) diffs; wheels; hubs; suspension and, of course, tyres

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Old 07-07-19
jimster99 jimster99 is offline
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Default How to adjust tyre pressure for ambient temperature

Question - do the manufacturer tyre pressure level recommendations remain correct in all ambient air temperatures? Or do I need to make an adjustment for the actual ambient air temperature?

In other words, if my manual tells me to use 30psi for all tyres (tested when the tyres are 'cold'), can I pump in 30 psi regardless of whether the air temp is 0 degrees c or 45 degrees c and then drive with the tyres being correctly pressurised (assuming the ambient air temp remains the same)?

Or should I (in theory) put extra pressure in when the air temp is hotter and lower it slightly when cold?

Answer doesn't seem obvious to me!

Thanks.
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Old 07-07-19
4ndy 4ndy is offline
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30psi is a different volume of air depending on the temperature.

My wife's Hyundai's TPM goes off every winter as it thinks there's a leak, it's just the ambient air temperature dropping causing the relative pressure to drop.

If you check your tyres every few weeks then you won't have an issue as you'll be adjusting in-line with the changing season.


Andy - from the colder and wetter UK!
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Old 07-07-19
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The answer is Yes, inflate you tyre's to the rested/cold inflation pressure regardless of ambient temperature.

As a general "rule of thumb" it is suggested that you are looking for a 4psi increase in tyre pressure for passenger construction tyre's (6psi for light truck construction), this is the pressure increase between the rested cold pressure (over night) and the tyre pressure after about 1 hour of driving. Depending on the load you are carrying, speed you are travelling, roads that you are traversing and the ambient temperature will all influence the pressure increase of the tyre to its optimal operating pressure.
Note this "rule" only applies to bitumen road driving.

As tyre tyre rotates it deforms and flexes, this causes heat to build up in the tyre and the pressure inside the tyre increases, if the starting/rested cold inflation pressure is too low then the tyre is flexing more than it should and the pressure will increase more than it should. If the tyre is over inflated at the cold pressure then the tyre will not flex and work how it is designed to. Severe over inflation results in accelerated wear in the centre of the tread and reduced handling and braking performance. The tyre is also the first shock absorber so over inflated tyre's not only result in a hard ride but also cause accelerated wear on shocker bushes. Under inflation will cause accelerated wear on the outside edges of the tyre and reduce handling. Severe under inflation will lead to tyre failure due to excessive heat build up and structural failure.

You do not need to get too hung up on pressures as long as you are within 2-4Psi of the manufacturers specifications. Several studies from Automobile Associations have reported that passenger cars are most likely to have under inflated tyre's where as 4wds are most likely to have overinflated tyre's. Most tyre shops inflate at the higher end of the range or even higher, as the majority of car drivers do not check tyre pressure regularly.

Nitrogen inflation is an expensive con job, if you are driving a race car or flying a high speed plane then yes it is important but for everyday driving the free air from the fuel stations is more than adequate, it naturally contains about 78% nitrogen anyway!
I have access to free nitrogen and and still do not bother using it!

OJ.
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Last edited by old Jack; 08-07-19 at 07:12 AM. Reason: spelling correction
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Old 08-07-19
jimster99 jimster99 is offline
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Thanks for the very thorough reply - that's interesting and it makes sense!
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Old 08-07-19
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Quote:
Originally Posted by jimster99 View Post
Thanks for the very thorough reply - that's interesting and it makes sense!



I have recently fitted a tyre pressure monitoring system to my Pajero and camper trailer. Very impressed with it. Simple to use and keep an eye on both pressure and temperature. It is the external valve cap screw on type and handles daily driving to off road travel.
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Old 08-07-19
signo1985 signo1985 is offline
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Originally Posted by Dicko1 View Post
I have recently fitted a tyre pressure monitoring system to my Pajero and camper trailer. Very impressed with it. Simple to use and keep an eye on both pressure and temperature. It is the external valve cap screw on type and handles daily driving to off road travel.

Hi Dicko1, have you got a link for it?
Wouldn't mind checking it out
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Old 08-07-19
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Hi Dicko1, have you got a link for it?
Wouldn't mind checking it out
I have the internal version of this system fitted to all 5 tyres.
The external cap 4 wheel version is n easy retrofit and cheaper.
https://www.digoptions.com.au/tpms-t...hoCHbsQAvD_BwE


OJ.
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Old 08-07-19
signo1985 signo1985 is offline
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Thanks OJ will check it out
One easy question though: are you happy with it?
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Old 08-07-19
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Originally Posted by signo1985 View Post
Thanks OJ will check it out
One easy question though: are you happy with it?

Yes so far, I was recommended the internal system by NJswb so when I fitted a new set of tyres 8,000kms ago I spent an extra $210 on the 5 tyre internal system. Only time will tell if it has been worthwhile over the next 70,000kms, I get out of a set of tyres, it only has to save a half worn tyre from destroying itself and the unit has paid for itself.
Last year when I was traveling with NJswb and his system alerted him to a higher than normal temperature which we tracked down to a frozen brake caliper and dragging brake. Earlier this year I ruined a 95% worn tyre on a beach run, when it rapidly deflated. Had I a TPMS I might have saved the tyre and been able to repair, reinflate and use as a spare rather than having a shredded tyre and no usable spare for the rest of the trip.



OJ.
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MM4x4 Auto Mate, Serial No 1 .
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Old 08-07-19
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Originally Posted by signo1985 View Post
Hi Dicko1, have you got a link for it?
Wouldn't mind checking it out

This is for the 6 sensor unit. Has no trouble picking up the trailers sensors as well as the cars. As I said..I went with external for ease of use. Any problems and I,m not paying a tyre store to take tyre off. You will have to do this when batteries need changing..12-18 months...external are easy. The pressure readings are almost identical to the tyre compressor I use as well.





https://www.digoptions.com.au/6-tpms...van-tru~175918
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