Over inflating tyres..

[xreyuk]

Hey

For work I drive around with a lot of heavy stuff in the boot, and have my tyre pressures at 1 or 2 psi above the full load recommendations on the car.

At the weekend, I would like to take all of the stuff out of the boot to help with fuel economy. If I want to do this, will it be safe to leave the tyres inflated to their current PSI, or will I have to keep changing them every time I take all of the stuff out and put it back in?

[skene]

At 1 or 2 psi you'll be fine. May also increase your economy too!

[xreyuk]

That 1 or 2 psi, is above the recommendations for a full load though.

If I take everything out of the boot, it'll be more like 7 or 8 psi over what's recommended for that weight.

[skene]

You may experience a harder ride and wearing in the middle of the tyres but I shouldn't thing you have to worry about blowouts etc

[xreyuk]

Okay cheers.

It'll only be for the weekends then I'll be putting all the heavy stuff back in.

Looking at it, the fronts are meant to stay the same, but the rears would be about 7 or 8 psi over the recommended.

Edited by xreyuk on Sunday 8th April 13:33

[blank]

Unless you go over the maximum pressure written on the tyre (usually ~50 PSI) you'll be fine.

Might get odd wear patterns and a harder ride but you won't have a blowout.

[xreyuk]

Okay no worries cheers for the help. I suppose if I'm only doing low miles on the weekend (around 50) then Monday to Friday doing my usual 500-700 miles the wear pattern will stay pretty easy.

The main thing I was worried about was having a blowout, but if that won't happen, I was just wondering will there be any safety issues to consider?

[HustleRussell]

I use my mondeo for towing and I inflate the tyres to 40PSI or so to help with the extra load. If I don't reduce the pressures afterwards I get unpleasant jiggling through the steering and dodgy handling. I have had half a turn of opposite lock on completely unintentionally on a 'B' road at no more than moderate speed, which I'd never have had with the tyres at the right pressure.

[xreyuk]

Okay thanks

[EDLT]

Your pressure gauge probably isn't accurate enough to measure the 1-2psi difference anyway.

[jamei303]

Of course it will affect grip and handling, which will affect safety.

[Slapon]

jamei303 said:

Of course it will affect grip and handling, which will affect safety.

Get real.

[jamei303]

Slapon said:

Get real.

So a 20% deviation in tyre pressure from the recommended optimum won't affect grip or handling?

Pull the other one.

[davepoth]

jamei303 said:

Slapon said:

Get real.

So a 20% deviation in tyre pressure from the recommended optimum won't affect grip or handling?

Pull the other one.

It will affect the grip and the handling. A flat tyre has a very big contact patch, and a tyre inflated to infinity PSI (hypothetically) so there was absolutely no flex in it at all, would have an infinitely small contact patch. So as you increase pressure the size of the contact patch goes down. That's why higher PSI is better for economy. The extra weight in the back of the car with the full load would force the tyres to compress a bit, resulting in a contact patch close to normal size.

Higher PSI will also mean the tyre won't soak up as much of the bumps in the road, but that's not too much of a problem.

A few PSI over shouldn't be a tremendous problem, just be aware of the slightly reduced contact patch and you'll be fine.

[sday12]

jamei303 said:

Slapon said:

Get real.

So a 20% deviation in tyre pressure from the recommended optimum won't affect grip or handling?

Pull the other one.

It will affect grip, and potentialy handling.

jamei303 said:

which will affect safety.

Get real;)

[sday12]

jamei303 said:

Slapon said:

Get real.

So a 20% deviation in tyre pressure from the recommended optimum won't affect grip or handling?

Pull the other one.

It will affect grip, and potentialy handling.

jamei303 said:

which will affect safety.

Get real;)

[jamei303]

sday12 said:

Get real;)

Yeah, reduced grip doesn't affect safety, that's why everyone on this forum uses cheap Chinese tyres.

[Zad]

jamei303 said:

sday12 said:

Get real;)

Yeah, reduced grip doesn't affect safety, that's why everyone on this forum uses cheap Chinese tyres.

I bet you couldn't measure the grip difference. If you are going to get anal about a few % difference in adhesion, suspension performance etc then you'd never go out in the car for risk of killing yourself. This isn't an 1978 Morris Marina we are talking about.

[skwdenyer]

On anything modern and FWD, inevitably set up to understeer, the chances are that the proposed inflation would, at worse, result in better-balanced handling due to reduced rear grip. On anything RWD the same would apply, but a greater tendency to power-oversteer would be apparent.

I routinely play about with tyre pressures in order to balance handling; +10psi on the rear is fairly usual to get the balance better than manufacturer's standard in my experience, but your mileage (and handling tastes) may vary.

Don't forget that some manufacturers recommend the 'full load' pressures for sustained high-speed driving, too. What vehicle is it?

[deltashad]

We use crap, cheap Chinese tyres on the gay car. It was crap after having them fitted and they are now half worn and still terrible. It doesn't hold the road worth a poop with the recommended pressures, so I give it an extra 8 psi. Does the job, handles much better and it doesn't effect the handling.

Next time around though, I'll not be so tight with the budget.