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 Post subject: Tyre Pressure
PostPosted: Sat Nov 27, 2010 10:09 
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How much difference does ambient air temperature make to tyre pressure?

If one inflates their tyres to the correct pressure on a cold day such as today, does the tyre warm up enough to over inflate them under motorway driving conditions?

Is it taken into account when tyre pressures are determined?

Does it matter?

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 Post subject: Re: Tyre Pressure
PostPosted: Sat Nov 27, 2010 11:17 
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Yes it makes a difference. My car is usually parked sideways-on to the sun. The two tyres on the "sunny side" are usually half a PSI more than the ones on the shady side (as accurately as my cheapo gauge can measure)!

Yes it's taken into account when determining tyre pressures (within reason)! I guess that if you inflated them to the correct pressure in the Antarctic and then air-lifted the car to Death Valley and took it for a fast run, you'd have problems, but for most normal running there wouldn't be. Manufacturers tell you not to check your tyre rpessures after a long run at high speed - that usually puts them up a few PSI but they have huge safety factors. It's also self-limiting, up to a point. A soft tyre generates more heat because of sidewall flexing, so if they end up being slightly over-inflated at high speed, that would help reduce the flexing, thus the temperature, and the pressure.


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 Post subject: Re: Tyre Pressure
PostPosted: Sat Nov 27, 2010 21:44 
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Mole wrote:
Yes it makes a difference. My car is usually parked sideways-on to the sun. The two tyres on the "sunny side" are usually half a PSI more than the ones on the shady side (as accurately as my cheapo gauge can measure)!



For interest, what is the accuracy of the average owners / garage gauge expected to be . Not being pedantic or funny, but could the expected accuracy and the possibility the frequency of checks on commercial forecourt ones be one reason for the sudden increase in tyre pressure machine chargers .( or something else for petrol stations to milk :wink: ).Would expect that in this day and age that forecourt gauges would be subject to TSA checks - ( if for no other reason than that they exist)

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 Post subject: Re: Tyre Pressure
PostPosted: Sat Nov 27, 2010 22:10 
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I believe that a few years ago forecourt airlines were brought under the aegis of Trading Standards who insisted that the gauges be accurate. That was when the garages started charging, presumably to cover the fees charged by TS. I find it more convenient to have my own compressor and gauge

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 Post subject: Re: Tyre Pressure
PostPosted: Sat Nov 27, 2010 23:08 
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Given the wide range of recommended presures dependent on anticipated speed, loading etc, I dont imagine in most cases that the "correct" tyre pressure is anything of an exact science anyway.

On my (rather heavily loaded) van I have the rear tyres up at the maximum (65) and the fronts at 55, both these are somewhat higher than the handbook recommendations but if I set them at the "recommended" presures they look flatter than a cowpat from a very tall cow and the steering becomes almost impossibly heavy!

I have done over 270,000 miles like this without issue!

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 Post subject: Re: Tyre Pressure
PostPosted: Sun Nov 28, 2010 00:11 
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dcbwhaley wrote:
I find it more convenient to have my own compressor and gauge



So do I , as the charges are now on average 50p - whether or not you need to adjust the pressure .

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 Post subject: Re: Tyre Pressure
PostPosted: Sun Dec 05, 2010 19:12 
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dcbwhaley wrote:
I find it more convenient to have my own compressor and gauge


Those plastic bike stirrup pumps fit and go up to 80psi. They pump quickly too.


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 Post subject: Re: Tyre Pressure
PostPosted: Mon Dec 06, 2010 12:57 
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billyfat wrote:
dcbwhaley wrote:
I find it more convenient to have my own compressor and gauge

Those plastic bike stirrup pumps fit and go up to 80psi. They pump quickly too.

Yes, I have one of those; a Joe Blow thingy. I find them really good, certainly better than those crappie twin-tub foot pumps, and they make me feel like I’m on one of those pump action mine carts. :P

If we are pedantic, the tyre pressures should be adjusted to the load and number of passengers but no-one ever bothers and in the real world it probably doesn’t matter anyway.

I’m supposed to put an extra 6 psi in the back tyre of my motorbike when I take a passenger but since 99% of my riding is solo I don’t bother and it doesn’t feel dangerously different either way.

:welcome: billyfat

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 Post subject: Re: Tyre Pressure
PostPosted: Tue Dec 07, 2010 00:00 
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Er, this is probably quite a sad thing to admit, but, I, er, DO actually put the pressures up a bit if I'm doing a long run with the family compared to my one-up motoring! Mainly for fuel consumption reasons though.


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 Post subject: Re: Tyre Pressure
PostPosted: Tue Dec 07, 2010 10:41 
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Oh I would in your situation Mole or if I have my honeybunchkins on the back for a long jaunt but if we’re just nipping out fairly locally I don’t bother. She’s only a size 6 anyway; I’ve seen more meat on a butcher’s apron. :D

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