Tyre pressures (I know, sorry)
Discussion
I'm sure this is 'one of those topics' on here, but I thought I'd ask anyway.
Every time I go to the free air pump at Sainsbury's, I have to change the digital pressure selector from some catastrophically low number (tonight it was 26 PSI) up to the 32 or 34 at which I run my tyres (because that's what the manufacturer says they should be at).
What's the craic? Am I running tyres which are far too hard? Do these people who go immediately before me have some sort of death wish, setting their pressures so low (I'd consider 26 PSI almost bloody flat!) Are tyres run at 26 or so PSI much more common than I think?
The real thing for me is: how low do they have to get before they're pumped up to 26? Given the extremely casual attitude of the majority of motorists to maintenance, I can't imagine these people checking their tyres all that regularly, so how flat do they have to get before a trip to the pump is undertaken?
Simon.
Every time I go to the free air pump at Sainsbury's, I have to change the digital pressure selector from some catastrophically low number (tonight it was 26 PSI) up to the 32 or 34 at which I run my tyres (because that's what the manufacturer says they should be at).
What's the craic? Am I running tyres which are far too hard? Do these people who go immediately before me have some sort of death wish, setting their pressures so low (I'd consider 26 PSI almost bloody flat!) Are tyres run at 26 or so PSI much more common than I think?
The real thing for me is: how low do they have to get before they're pumped up to 26? Given the extremely casual attitude of the majority of motorists to maintenance, I can't imagine these people checking their tyres all that regularly, so how flat do they have to get before a trip to the pump is undertaken?
Simon.
4G63T said:
if you go on a long motorway run, its good sense to lower it a few psi as hot air expands making the tyre pressure higher.
but its probably more likely that the people who use the pumps are idiots.
I think that the people setting the tyre pressures might have taken the pressure rise with temperature into account, they might be even using the pressure increase to improve the durability of the tyres.but its probably more likely that the people who use the pumps are idiots.
So if people are going to do a 100 mile motorway shlep you alter the air in the tyres? Unless you are loaded to maximum and doing 120mph the whole way I think that's pretty overkill.
Merc runs 32/36
MK1 Focus runs 30 all round
110 Defender runs 28/36
If i'm fully loaded in the Defender i'll put the rears up only to 42psi.
I've never had uneven wear and regularly do long motorway runs in all 3 cars.
Dave!
Edited due to brain fart.
Merc runs 32/36
MK1 Focus runs 30 all round
110 Defender runs 28/36
If i'm fully loaded in the Defender i'll put the rears up only to 42psi.
I've never had uneven wear and regularly do long motorway runs in all 3 cars.
Dave!
Edited due to brain fart.
Edited by Howitzer on Sunday 4th May 07:50
What I find more annoying is that my local Sainsburys now has a timer on the air pump which means you can only just about manage to do a tyre before it runs out. If anything that makes people wait to use it for longer, especially if a doddery old dude has to go from car to pump an extra 3 times.
Tyre pressures are entirely dependant on the car, and which axle, and the tyres size.
The weight of the car needs to be supported by the tyre, but it needs to deform correctly at the base to maintain the correct shape contact patch, and to generate the right amount of heat in the tyre.
The correct size and shape of the contact patch is determined by the tyre and pressure needs to counter the weight to ensure the contact patch is right. Thats why the same tyre fitted on different cars have different pressures, or why the car has laden and unladen pressures.
26psi at a garage is around the minimum a car will have, so is a safe level. If they set is at the more common 30-34 psi, then quite a few people who know nothing about cars will be driving around with less grip than the should have pecause they went with the default.
The weight of the car needs to be supported by the tyre, but it needs to deform correctly at the base to maintain the correct shape contact patch, and to generate the right amount of heat in the tyre.
The correct size and shape of the contact patch is determined by the tyre and pressure needs to counter the weight to ensure the contact patch is right. Thats why the same tyre fitted on different cars have different pressures, or why the car has laden and unladen pressures.
26psi at a garage is around the minimum a car will have, so is a safe level. If they set is at the more common 30-34 psi, then quite a few people who know nothing about cars will be driving around with less grip than the should have pecause they went with the default.
Edited by 98elise on Sunday 4th May 07:35
Edited by 98elise on Sunday 4th May 08:25
It does depend on the type of tyre. My 185,75,13 are supposed to be 23/26 PSI. I do admit to running them at 28 PSI all round, & I do have 205 65s on the back of the 330 BHP TR8.
The lower the profile the higher the pressure required, the Ford Fiesta shopping trolley runs 32/30 normally & 2 PSI higher if to be loaded heavily.
Just for perspective, in 1968 we ran the Formula 1 BT 24 Brabham Repco on 16 front 17 rear, [cold], which became 18 19 at full operating temperature.
These pressures were recommended by the Dunlop technicians, after checking the temperatures across the tyres with a pyrometer each time we came off the track, to make sure the full tread was working. They worked well enough at just on 180 MPH down Conrod straight Bathurst, for me to win the Bathurst 100 F1 race.
The lower the profile the higher the pressure required, the Ford Fiesta shopping trolley runs 32/30 normally & 2 PSI higher if to be loaded heavily.
Just for perspective, in 1968 we ran the Formula 1 BT 24 Brabham Repco on 16 front 17 rear, [cold], which became 18 19 at full operating temperature.
These pressures were recommended by the Dunlop technicians, after checking the temperatures across the tyres with a pyrometer each time we came off the track, to make sure the full tread was working. They worked well enough at just on 180 MPH down Conrod straight Bathurst, for me to win the Bathurst 100 F1 race.
zygalski said:
What I find more annoying is that my local Sainsburys now has a timer on the air pump which means you can only just about manage to do a tyre before it runs out. If anything that makes people wait to use it for longer, especially if a doddery old dude has to go from car to pump an extra 3 times.
Local supermarket has a timer on it. I view it as imposing a tax on people who aren't organised enough to remove valve caps before they drop their 20p in...A compressor and decent pressure gauges at home makes keeping pressures correct much easier.
Willy Nilly said:
4G63T said:
if you go on a long motorway run, its good sense to lower it a few psi as hot air expands making the tyre pressure higher.
A softer tyre will flex more generating more heat which is why you need to increase the pressure for motorway driving. "At high speed, (defined as driving at 120km/h for over one hour), your tyres will wear out twice as fast as when you drive at 70-80 km/h. If your tyres are under-inflated by twenty per cent tyre life can be reduced by thirty per cent. The rule here is to add 28Kpa (4PSI) from your Minimum Compliance Plate Pressure. Don't inflate your tyres above 40 psi or 280 kPa. When the tyres get hot from driving, the pressure will increase even more."
From a Bridgestone website.
m8rky said:
Lowering pressures for high speed driving,possibly the worst advice on the internet ever.
"At high speed, (defined as driving at 120km/h for over one hour), your tyres will wear out twice as fast as when you drive at 70-80 km/h. If your tyres are under-inflated by twenty per cent tyre life can be reduced by thirty per cent. The rule here is to add 28Kpa (4PSI) from your Minimum Compliance Plate Pressure. Don't inflate your tyres above 40 psi or 280 kPa. When the tyres get hot from driving, the pressure will increase even more."
From a Bridgestone website.
How does the above fair when it comes tofilling them with nitrogen. Mine recommend 42psi for load/speed"At high speed, (defined as driving at 120km/h for over one hour), your tyres will wear out twice as fast as when you drive at 70-80 km/h. If your tyres are under-inflated by twenty per cent tyre life can be reduced by thirty per cent. The rule here is to add 28Kpa (4PSI) from your Minimum Compliance Plate Pressure. Don't inflate your tyres above 40 psi or 280 kPa. When the tyres get hot from driving, the pressure will increase even more."
From a Bridgestone website.
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