Tyre pressure measurement 22 September 2022 at 8:48PM edited 22 September 2022 at 8:53PM in Motoring 55 replies 1.7K views

Car_54

RobM99 said:

Beer in pints, football pitches are in imperial, horses in hands, fathoms still in use? Feet for altitude. 

The laws of the game have used metric since 1997, with imperial equivalents in brackets.

chrisw

Ectophile said:

The tyres on your car show the rim size ... in inches

But the first figure on most tyres is the width in millimetres.

The three numbers are the width in millimetres, then the ratio of the sidewall height to width (as a percentage), followed by the rim size in inches.

They do that because rims have been made in inch sizes for so long that it would be a major hassle to go metric.  The manufacturers would have to come up with a completely new set of tyre sizes.

I seem to remember that the early Rover Metros had metric wheels and the tyres were hideously expensive. I presume they are now impossible to find.

Grumpy_chap

chrisw said:

I seem to remember that the early Rover Metros are now impossible to find.

Correct (almost) - most of them rusted away from the front wings backwards.
But, I managed to find this one:
https://www.autotrader.co.uk/car-details/202209069489643
Top of the range model, too

facade

sevenhills said:

Ectophile said:

They do that because rims have been made in inch sizes for so long that it would be a major hassle to go metric.  The manufacturers would have to come up with a completely new set of tyre sizes.

I believe cycle tyres all used to be 20" and 26" but we now have metric, 70cm

Cycle tyre sizes e.g. 26" are the tyre diameter not the rim- the ISO rim diameter is 559mm. (22")

The 700c is also known as 29" and fits a 622mm rim.

The 27" tyres we had on our racers in The Olden Days are still available, and fit a 630mm rim

sheramber

For many years fabric was sold in inches width but meter lenghths.

So bought x meters of 36 inch wide material.

Iceweasel

shiraz99 said:

Iceweasel said:

Are we now metric - we've been metric since 1972. No school in UK has taught in Imperial since then.

Yet we still measure distance in miles not km.

Yes - totally stupid.

MalMonroe

The reading on the OP pic is around about the pressure for the tyres on my car, I was originally told.

I have a Toyota Aygo and just googled 'tyre pressure and size guide' for its year of manufacture -

"165/60 R15, 2.3 bar or 33 psi, 2.3 bar or 33 psi"

Thank you so very much.

Without all the flim-flam, I believe that means the PSI (pressure per square inch) on a tyre gauge (but please don't make me use one) should read 33 and the radius of the tyres needs to be 15 inches. Nope, not gone metric there at all, then.

My car is collected by the dealer every so often for an MOT and service and they tend to fiddle about with tyres and other things, wash it thoroughly and do a valet service, after which it is returned to me at my home - all nice and sparkly clean. What goes on behind the scenes is nothing whatsoever to do with me.

If anything breaks down (but it doesn't with my Aygo!) - I call the lovely RAC people.

I do know how to put petrol in, though because that is really handy to know.  Maybe even a splash of windscreen wash, at a push. . .   Well, after all, I'm a driver, not a mechanic.

Iceweasel

chrisw said:

Ectophile said:

The tyres on your car show the rim size ... in inches

But the first figure on most tyres is the width in millimetres.

The three numbers are the width in millimetres, then the ratio of the sidewall height to width (as a percentage), followed by the rim size in inches.

They do that because rims have been made in inch sizes for so long that it would be a major hassle to go metric.  The manufacturers would have to come up with a completely new set of tyre sizes.

I seem to remember that the early Rover Metros had metric wheels and the tyres were hideously expensive. I presume they are now impossible to find.

And in the early 80's both Ford and BMW (there may have been others) equipped their top-of-the range models with TRX tyres and wheels - 390mm diameter they were. My 528i had tyres that were 220/55 WR 390 Michelin TRX,

MalMonroe

sheramber said:

For many years fabric was sold in inches width but meter lenghths.

So bought x meters of 36 inch wide material.

I used to buy fabric in yards, 3 feet wide. Never bought it in meters. Maybe I'm a bit old.

I don't make much now though, as it's not as cost effective as it was in the 'olden days'. 

Buying curtains can be a bit of a pain sometimes now as they're always in cms. I use google to convert though so it's not too bad.

I do generally prefer the metric system though - all those 10s. Metric money certainly is easier. I don't know how we used to manage before decimalisation, it was a crazy system. 

k3lvc

Loved watching someone who should probably have known better trying to get their BMW tyre to 31 bar and wondering why the garage pump didn't go up that far - I kept a safe distance