Tyre Pressures

[sturmovik]

I tend to run 35 or 36 psi. Higher the pressure, the lower the rolling resistance so a small mpg advantage compared to 30-32. Also helps to avoid premature shoulder wear, which can be caused by underinflation. I know some run maximum pressure as indicated on the sidewall less 10%. I wouldn't go as high as 40 psi as I think this can harm grip in adverse conditions such as black ice and standing water.

Kevin

[Leander]

Originally Posted by sturmovik

I tend to run 35 or 36 psi. Higher the pressure, the lower the rolling resistance so a small mpg advantage compared to 30-32. Also helps to avoid premature shoulder wear, which can be caused by underinflation. I know some run maximum pressure as indicated on the sidewall less 10%. I wouldn't go as high as 40 psi as I think this can harm grip in adverse conditions such as black ice and standing water.

Kevin

If 40psi is good enough for the rozzers it's good enough for me

Seriously, my understanding is that it is under inflation, rather than over inflation, that increases hydroplaning.

As for black ice by far the biggest factor is the kind of rubber in your tyres, and I use winter tyres now for precisely that reason.

[Chris Broughton]

Agree with the consensus on here use the manufacturers advised settings. It mentions in my had book for high speed driving 34 all round for a connie se tourer automatic. I tend to put 33 all round as guages can be innacurate and believe slightly over is better than under.

Chris

[Kearton]

The tyre pressures listed in the Rover / MG manuals are those worked out for common tyres at the time of the car's development. In some cases tyre manufacturers may specify different values for their tyres on specific vehicles. I such cases it is probably best to stick to those.

For example Vredestein quote 39/38 psi F/R of the 225/45 x 18 Sessantas for the ZT-T diesel.

One reason might be that the tyre has more flexible side-walls (which reduces noise) and so extra pressure may be needed to support a heavy car that handles well.

Regards,
Kearton

[Leander]

Chris and Kearton - I agree that the manufacture's figures are the 'safe' way to go, but I take them as a guide. Obviously, road conditions, ambient temperature, the weight in the car, and the tyre itself, could all be seen as nudging those figures up or down a psi.

For example 10 degrees of temperature (F) will raise or lower the psi by 1.
So a hot summers day at 30 (yes, I know that's very rare) versus the -10's we've had this winter, is a 4 psi difference.

I see driving at 40psi as just one more 'mod' to the car (and we all know how popular mods are for our cars!) and one that improves mpg

[Devilish]

I used to put 46psi in the rear when I had the mother in law in the back.

[COLVERT]

Originally Posted by Freebyrd

Does anyone know how manufacturers workout recommended tyre pressures? There must be some formula used, I expect

Yes. They test them on a rolling road at different pressures, speeds and temperatures to obtain the best overall figure for general use.



Colvert.

[Dave Goody]

Originally Posted by Devilish

I used to put 46psi in the rear when I had the mother in law in the back.

You just liked to see her false teeth vibrating

[Jay]

I've looked in the hand book for a contemporary 75 saloon 2.0 Deisel it says (34) front (32) rear. It also has a page devoted to tyre pressures above 100 mph (38) (36). Quick trip to the shops and back I suppose.
Does that mean if I want to do 70 plus I've got to stop and put air in the tyre
Jay

[Devilish]

Originally Posted by jay2112

I've looked in the hand book for a contemporary 75 saloon 2.0 Deisel it says (34) front (32) rear. It also has a page devoted to tyre pressures above 100 mph (38) (36). Quick trip to the shops and back I suppose.
Does that mean if I want to do 70 plus I've got to stop and put air in the tyre
Jay

I did notice everyone lining up to pump up their tyres at Bruntingthorpe