Tyre Pressure/Ply Rating

[B.S.F.]

The recommended tyre pressure for a bias-belted 7.00-16 tyre under normal condition is 25 Psi. Is that regardless of the ply rating; whether it's 4 or 12 ply ?
.W.

[JDNSW]

I assume you are talking about a specific application? In my view the more plies the higher pressure needed to reduce heat buildup.

And worth noting that the same tyre on the essentially the same vehicle, went from about 25 to 30 from Series 2 to Series 3 - and on my County as high as 65 depending on speed and load.

I don't think there is a simple answer to your question

[B.S.F.]

Right, I will elaborate. Recently we did a 2500 km trip, about 2/3 on sealed road , the rest dirt roads, about 40 rocky river crossings, about 4hrs steep uphill driving on washed out deeply rutted tracks, mostly in 1st and 2nd low, and some mud. We carried a load of well over 400 kg. The tyres were brand new 7.00x 16 rags 12PR.mud tyres. Pressure rear 32psi.as per manual ,front also 32 psi because of extra weight of 2.25l engine instead of 2l plus extra spare on bonnet and winch. When we got back home and I changed the tyres back to normal road tyres for everyday driving I noticed that some of the little pimples were still present near the outside edge of the new tyres but were all worn off in the centre of the tyres, which to me indicates that the tyres at 32 psi were over-inflated. Hence my question.
Excerpt from 54-58 instruction manual.
.W.

[whitehillbilly64]

I believe Tyre companies are running high pressures, so tyres wear quicker.
My Daughters 'Little' Diahatsu Feroza, came back, after new tyres, with 38psi in them. 'That's what you should be running'
I have dropped them to 28psi, and use a little tyre depth gauge to keep an eye on wear.
The depth gauge checking wear on other vehicle I have, indicate over inflation, from tyre companies.

whitehillbilly

[JDNSW]

Any tyre pressure is a compromise between handling, ride and tyre life. As a general rule, the higher the pressure the longer the tyre life, as the higher pressure reduces heat build up, which is what reduces tyre life. Centre wear without wear on the edges can be a symptom of over inflation, but it has to be by a wide margin - the reverse is more common, and quite unusual on radial or belted bias tyres. Uneven tyre wear on front tyres of Series Landrovers is almost always a wheel alignment issue - toe-in, bent axle, sagged or non-standard springs, worn swivels or TREs, bent wheels.

[S3ute]

As a general rule, the higher the pressure the longer the life.

Hello from Brisbane.

My late father-in-law successfully ran an earthmoving operation for years and consistently ran his fleet of Toyotas on very high tyre pressures (~60 psi). Ditto the family cars. Getting 60k plus out of a set of 7.50 x 16” Grand Treks was the norm rather than the exception.

He thought I was crazy only putting 32 psi into my Falcon’s tyres - typically stuffed at around 25k.

Cheers,

Neil

[goingbush]

I paint/ chalk a line across my tyre treads , go for a short drive , if the mark its worn in the centre its over inflated. if it worn on the edges its under inflated .

My Series3 Lightweight with 6.50/16 cross plies , ideal pressure using that method is as per book, 24psi

I put 225/75R16 radials on as requested by Vicroads engineer for my EV conversion , tyre guy pumped them to 40PSi , I did the paint line test and 40psi is spot on .

It rides a little firmer but much less rolling resistance .

[JDNSW]

To add to your comment, it should be realised that the rolling resistance and heat generation (and hence tyre life) are directly related, in fact, different ways of measuring exactly the same thing - the loss off energy due to the tyre flexing.

But the point still remains, as I commented earlier, that tyre pressure is a compromise - if you optimise on rolling resistance (a good choice for your EV!) you are compromising on ride, and may also be compromising on handling, both of which will depend very much on the vehicle.

[goingbush]

Very good point John, I am reading about new tyres becoming available for EV's , less rolling resistance but also not compromising on braking / handling .

Most likely just marketing , otherwise they would have been suitable for ICE vehicles that also want better economy and / or performance , The tyre does not know what kind traction unit is in the car.

Goodyear EV concept hopes to the tire that your EV deserves - Roadshow (https://www.cnet.com/roadshow/news/goodyear-tire-concept-electric-car-problems-ev/)

Des pneus au service de l’electrique | Michelin (https://www.michelin.com/eng/media-room/press-and-news/michelin-news/Innovation/Electric-Tires)

[JDNSW]

Probably simply that rolling resistance has not featured largely on factors for specifying tyres in the past, but comes into focus when you start talking EV.

If you think about it, most tyre choices (by manufacturers) over the years have been for styling reasons - for example, there is virtually nothing to support the tyre width on the current Rangerover being any better than that on the first Rangerover, and low profile (<85%) tyres have no measurable advantage for most motorists. Both are selected because they do have advantages for racing cars, where ride is irrelevant as is cost and durability of tyres.

About the only really worthwhile basic innovations in tyres were the introduction of tread in the Edwardian period, the change to balloon tyres in the 1920s, and the introduction of radials in the 1950s. None of these were really supported initially by manufacturers, and the last only ever saw production because a tyre company owned a car manufacturer!

[chazza]

...
About the only really worthwhile basic innovations in tyres were the introduction of tread in the Edwardian period, the change to balloon tyres in the 1920s, and the introduction of radials in the 1950s. ...

What about carbon-black added to the rubber compound?

[JDNSW]

What about carbon-black added to the rubber compound?

I'm not absolutely certain, but I think that predated motoring - wasn't it introduced when the only users of rubber tyres were cyclists?