Over-inflated car tyres?

lunacity · 10 August 2018 at 9:34AM

Hi- something I've noticed is that whenever I buy a new car, or take a car to a garage for a service, the car tyres always come back overinflated. For instance- my current car came with tyres inflated to 37psi at the front and 34psi at the back, against a recommendation of 30/26 psi respectively.

Does anyone know why this is?

Also - how exact to the recommendations should the pressure be? I have started to follow the advice that on "hot tyres" you should inflate 4psi above the recommended spec and check later (this is because I have to drive to the garage to use the inflator). Is this correct? I checked my tyres cold at home with a neighbour's device the other day and they are now 32pis/28.5psi (front/back) - a little above the recommendation. Will this significantly effect safety / comfort / wear or should I just leave be and not be so OCD about this?

Many thanks.

Aylesbury_Duck · 10 August 2018 at 9:48AM

Are you sure your measuring device is accurate? If this always happens to you, it would seem likely that your device reads incorrectly. The plastic dials that are on many domestic foot/hand pumps are very cheap and not properly calibrated. The older-style needle gauges are usually more accurate but in a proper testing environment, they will be checked and calibrated regularly. Getting yours out of the shed once in a while for several years isn't going to lead to accurate and reliable measurement.

marlot · 10 August 2018 at 9:52AM

I'd recommend one of the little digital gauges - they tend to be pretty accurate.

The gauge on my airline can easily be 5psi wrong.

neilmcl · 10 August 2018 at 10:13AM

lunacity wrote: »

Hi- something I've noticed is that whenever I buy a new car, or take a car to a garage for a service, the car tyres always come back overinflated. For instance- my current car came with tyres inflated to 37psi at the front and 34psi at the back, against a recommendation of 30/26 psi respectively.

Does anyone know why this is?

Also - how exact to the recommendations should the pressure be? I have started to follow the advice that on "hot tyres" you should inflate 4psi above the recommended spec and check later (this is because I have to drive to the garage to use the inflator). Is this correct? I checked my tyres cold at home with a neighbour's device the other day and they are now 32pis/28.5psi (front/back) - a little above the recommendation. Will this significantly effect safety / comfort / wear or should I just leave be and not be so OCD about this?

Many thanks.

Because sometimes the garages are useless. I always double-check my tyres when back from the dealer or tyre fitters because they always seem to get it wrong. You need to check and inflate your tyres to the recommended pressure when cold. I'd recommend getting yourself a tyre inflator/compressor and do it at home.

FYI, a few PSI either way is not going to affect safety.

AndyMc..... · 10 August 2018 at 10:20AM

marlot wrote: »

I'd recommend one of the little digital gauges - they tend to be pretty accurate.

The gauge on my airline can easily be 5psi wrong.

This, while my airline is brilliant and inflating and had a button to deflate the gauge is 8 psi out.

lunacity · 10 August 2018 at 10:38AM

I'd recommend one of the little digital gauges - they tend to be pretty accurate.

Thanks - I used my neighbour's which was digital to get my 32/28.5 reading but I'm starting to think I should get one that can inflate for home.

lunacity · 10 August 2018 at 10:40AM

FYI, a few PSI either way is not going to affect safety.

Thanks- I was wondering whether to let it down a couple of psi or just leave it and check again in a month - I have a couple of runs with other people in the car to do anyway so maybe better slightly overinflated atm?

marlot · 10 August 2018 at 11:01AM

Sometimes it can be helpful to run a few psi different to the recommendation.

On my last car, the official setting was 29psi, but when I ran the tyres at that the edges wore terribly. When I changed to 34psi they wore evenly across the tread, so lasted much longer. I couldn't feel any significant difference on the road.

Similarly, if the tyres are wearing mostly in the centre, you could try lowering the pressures a little.

https://www.tirebuyer.com/education/tire-pressure-and-performance

agrinnall · 10 August 2018 at 1:04PM

neilmcl wrote: »

Because sometimes the garages are useless. I always double-check my tyres when back from the dealer or tyre fitters because they always seem to get it wrong.

It's this. The dealer that services my car seems to always put the same pressure in all tyres, even though the difference between front and rear should be 6psi, so at least 2 tyres are wrong, and possibly all 4. As neil says, I check them myself and deflate/inflate as necessary, although at my next service if I remember I will check before taking the car away and complain if they've done it again.

UncleZen · 10 August 2018 at 2:29PM

lunacity, you're not the only one, this is quite common, Ive used several garages over the years and it happens a lot.
I believe its because they assume most people dont check their tyre pressures, so they overinflate them, so that over the course of the year the average pressure will be correct! - just a wacky theory of mine, base on no science whatsever.

Jackmydad · 10 August 2018 at 3:23PM

The thing about tyre pressures, garages, and inaccurate gauges has been going on for years.
I seem to remember one of the newspaper having a go about it at one time, and at least one magazine that I can remember.
Garages don't get their equipment calibrated, the gauges get kicked around on the floor, and some of the people doing the checks will have a "that'll do" attitude.
The advice was always to keep a separate tyre gauge, and use that to check your tyres. Also treat it like the instrument it is, and don't leave it kicking around loose in a pile of crepe.
I pulled the gauge apart on my tyre inflator and reset the hand to as near as I could get it to the digital gauge. It was about 8psi off. . . I wonder if they all are.

Over-inflated car tyres?

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