OT? Tyre pressures

[Malcolm Race]

I have recently bought a Zafira. I was surprised to see that the tyre pressures were 36psi. I previously owned an Astra Estate (similar size and weight) whith tyre pressures of 29psi. When I looked in the manual, two pressures were quoted - 29psi for 'comfort' and 36psi for 'eco'.

I understand that running tyres at higher pressures meant that there would be more wear in the centre of the tyre.

My inclination is to reduce the pressure to 29psi to obtain the maximum tyre wear.

Does anyone have any views on this?

Malcolm Race

[Adrian]

Yep - and that'll also improve the ride, by allowing the sidewalls to flex more. But raising the pressures will reduce the rolling resistance, and increase the fuel economy.

[polygonum]

Don't you want minimum tyre wear?

[Bill Wright]

It depends on how the tyre sits on the road at each pressure setting. Put some water on the drive, go through it, and look at the print on the dry bit of drive surface.

I find with vans that higher pressures reduce wear on the front wheels.

Bill

[news]

With tyres at about 50 quid for a small car, fuel at £1litre and tyres lasting 30k miles?? how do the costs work out?

AJH

[Johny B Good]

It's a trade off between fuel economy and the cost of tyre replacement. However, it does occur to me that if you're going for fuel economy, there's an implied desire to utilise a more economic driving mode, gentle acceleration and, if not cursed by an idiot automatic gearbox, short changing as you go up the gear ratios along with a heightened anticipation of the need to slow down or stop.

Such economy tactics will provide a side benefit of reducing wear and tear on the tyres other than when trying to carry maximum safe speeds around bends and corners (other idiot road users permitting).

In short, don't bother with the high pressure setting unless you're prepared to maintain or adopt a more economic driving style to get the most out of this "Life Choice".

[Tim+]

In the past I tended to run my tyres at their higher "Eco" pressure but never had problems with tyres wearing prematurely in the centre. I suspect that with radials you need pretty serious over-pressure to cause this problem.

Tim

[Lobster]

On 30 Jan 2015, Malcolm Race grunted:

Could it just be because as a larger vehicle with 7 seats, there's an assumption that you'll be carrying a heavy load? Most estate cars tend to show two sets of tyre pressures; one for 'normal' and one for 'heavily laden' - IIRC but CBA to go out in the snow to check mine, the Zafira shows only one set?

[Adrian]

Let's say 45mpg, because that makes the fuel cost a nice round 10p/mile.

£200 for four tyres every 30,000 miles is 0.67p/mile.

Reduce the tyre life by 10% and increase the fuel economy by 2% , and you're spending 2p/mile less on fuel but 0.07p/mile more on tyres - saving of 1.3p/mile.

Tyres are really, really, really cheap.

[Tim Watts]

And the low pressure setting will give you better grip under certain conditions

[Malcolm Race]

No, there is a further set for full load - 30 front and 38 rear?

Malcolm

[Nick]

I think you mean 1.97p/mile. It appears the fuel saving is the critical estimate.

[Nick]

Ahh! 1.93p/mile ;o)

[Adrian]

Or 1.93p, even.

Not really. The cost of the extra tyre wear is tiny compared to even the most insignificant saving on fuel. Of course, there's probably plenty of other ways to increase economy by one or more percent, just by improving driving style.

[Tim Streater]

Indeed. A bit of anticipation such as seeing that you're going to need to slow down and taking your foot off the pedal not only improves fuel consumption but also saves wear on the brakes. A much pleasanter experience for the passengers, too.

[Dave Plowman (News)]

Only if much higher than required for the load.

Which is why there are generally two figures given - one for light running, one for fully laden.

Generally, the higher one is to cover the possibility of running at a continuous high speed at full load.

A too low pressure can cause a heavily loaded tyre to overheat and fail. Too high may cause uneven wear. So it's better to err on the high side.

[Chris French]

In message , Lobster writes

We have a Galaxy, IIRC it has three suggestions (load related rather than performance/eco related).

To the OP's pont, whilst it's true that to high a pressure will increase tyre wear in the centre, I think that will be for significantly higher pressures, not a few psi

[Syd Rumpo]

If rubber isn't in contact with asphalt, it won't wear, obviously, so is the increased tyre wear at the lower pressure proportional to the resulting greater contact area?

Cheers

[Adrian]

Perhaps - but, in a way, it'd be irrelevant, because the life-limiting factor on the over-inflated tyre would not be the total wear, but the wear on a very limited part of the tread. The shoulders may still have 4mm left, but if the centre's down to

[Malcolm Race]

That few psi is a 25% increase

Malcolm