Tyre pressure - low profiles

[aaronng]

Thanks for all the advice!

I ended up pumping all tyres to 36 psi. However.... I've seen a loss in fuel economy. Could be because it revs much better now.

Fill up to a full tank and then drive. Fill up again and then measure fuel consumption. I doubt you would be able to see the difference in fuel economy over a span of only a week unless you are a sales rep and finish your whole tank of fuel in 5 working days.

[DNY*BOY]

im running 205/40/17 also, i inflate 40psi no probz and regulary check once a fortnight.

[dahondr98]

The idea that high tyre pressures typically cause excessive / rapid wear in the middle of the tread is a hangover from the days of cross-ply tyres (which have rather flexible treads due to the lack of reinforcing steel belts). With modern steel radial tyres it typically takes very excessive pressures to cause centre tread wear (because of the inherant tread stiffness of a radial ply tyre).

However, even with radials, the wider the tread happens to be the more prone it may be to becoming 'crowned' due to higher psi (i.e. it's easier to flex / bend a long stick than a short one), and this leading to somewhat increased wear in the middle of the tread. Fitting a wider tyre to a narrower rim also tends to 'crown' the tread to some degree, possibly contributing to increased central tread wear.

So, a radial tyre is more likely to wear in the middle if:
A) It's quite wide
and
B) The wheel rim is relatively narrow (for the tyre)
and
C) The pressure is quite high

Actually, the bit about tyres wearing in the middle when over-inflated is more to do with running tubes, as all tyres used to long ago, than anything to do with crossplies vs radials. Just for the record, radials also wear in the middle when running tubes and they don't need to be running very high pressures for it to happen. Tubeless tyres generally wear relatively evenly across the tread at most pressures. The fact that you were more likely to hear stories about over-inflated tyres wearing in the middle 50 years ago is because most tyres were tubed back then, not because they were crossply tyres. Because the tubes have a round cross-section, they are higher in the middle than at the edge, which pushes the centre of the tread up.

I only know all this because I had a wheel rim develop a slow leak some years ago, and the local service station mechanic fitted a tube, until I could find a rim for the relatively rare European car I was driving at the time. That tyre wore more in the middle, but the other tubeless tyres (all radials) didn't, even though they were all running at the same pressures. When I worked out what was happening I banished it to spare wheel duties, and bought a good rim off an interstate wrecker to eventually replace the leaking one.

And for the record, I would say 35 psi would be a good pressure to start at. When I did an advanced driving course some years ago, the recommended minimum pressures for safety were 32 psi in all tyres. Some years ago I owned a 1984 Holden for which, according to the tyre placard, 26 psi was the ideal tyre pressure. That wasn't my experience - I ran them at 35 psi. So following what the tyre placard says for pressure isn't always ideal, although recent model cars, from the last 15 years or so, tend to have more realistic (safe....) pressures on the placard.