"Real" Tyre Pressure for Land Cruiser 79 Dual Cab

Last set I ran was on a 105 series which needed at least 55 psi to keep it going in a straight line on the highway with a slight crosswind. They like air pressure and lots of it. We used to deflate to 35 for gravel roads and corrugations.

Ask your Toyota dealer if they have a service bulletin from Toyota saying the pressures should be changed to 45 psi. If they can't produce anything then the pressures should be as per the book.

Your standard specification tyres and the handbook pressures are a combined part of the whole suspension design, providing you still have a standard suspension. Those pressures. when adjusted correctly in accordance with the load, will determine the front to rear tyre slip angle ratio. It is almost always slightly higher at the front than the rear so the car understeers.

Look through the charts mixed in with the photos on this page and you will see how easy it is to change the car's handling characteristics.CHARTS Tyre pressures should not be altered unless you know exactly what you are doing and how it will affect handling, particularly in an emergency situation..

You should learn the 4psi rule.

Essentially you choose a starting pressure, try what's on the placard if you have standard tyres, and if not, then pump them up to a point where they are only just bagging out....

then go for a drive for an hour or so, and measure the increase in pressure from cold to warm....if its is less than 4psi, then your starting pressure was too high, if its more than 4psi, your starting pressure was too low, so wait for your tyres to cool off, then drop/raise them 1-2psi from your original starting pressure, and rinse and repeat....

if you get an 8psi increase from cold to warm, obviously you are way to low, so try 4-5psi higher, if you get a 1psi increase, then drop 3-4psi out....

I've always figured that these large companies spend millions in test and development so should have a relative idea on the correct tyre pressure to run their vehicle at. They are also standing by that, by printing it and having it on the vehicle. Will the mechanics put their claim in writing?
While pressure may vary due to loads, one of the first things checked after an accident is the tire pressure, so I would tend to keep within a reasonable range. After having a caravan I was unsure what pressure to run the tyres and found a site which describes how to work out the best pressure. I can't see any reason the same formula can't be applied to a car.
http://www.withoutahitch.com.au/caravan/correct-caravan-tyre-pressures/

Tony.

Laz - For tyre advice, there are good referral places - in the following respective order ...

1. Tyre size and pressure advisory decal or plate mounted on your vehicle (usually on the door frame) ..

2. Tyre load capacity and inflation tables put out by the manufacturer (usually on their company website or on their tyre agency websites) ..

3. The maximum tyre pressure and tyre load capacity, stamped on the wall of the tyre ..

Of all these, No 1 is the first one to refer to. The vehicle manufacturers advice, is usually fairly good advice. However, the tyre manufacturers advice is usually better.

Two - you adjust your tyre pressures according to your current load level, and road conditions and speeds.
If I'm going for a extended country run at 110kmh, I'll bump up my tyre pressures by around 4 psi, all-round.

If I'm carrying a good load, the rear tyre pressures get increased, by up to 20-25 psi, if needed.
I use wall bulge, as a "rule of thumb" indicator, and attempt to roughly match wall bulge between front and rear tyres.

I never exceed the tyre manufacturers recommended pressure.
To do so, risks tyre carcass failure, or fractured rims (and yes, I've seen rims split from excessive pressure)

For 7.50R16's, 40 psi all-round is a fairly good, average-road-condition, tyre pressure.

The vehicle manufacturer always advises the lowest suitable tyre pressures for good road suburban conditions, to give a comfortable ride - and they always advise raising tyre pressures when extended high-speed driving, or substantial load-carrying, is going to be carried out.

The 36 psi rear tyre pressure recommendation by the tyre shop is obviously a recommendation merely to improve the ride, when completely empty.

Most "commercial" vehicles, particularly those with leaf springs on the rear, give a harsh ride when empty, and many owners complain about that feature.

The tyre shop is only trying to improve the ride comfort for owners, and is not taking into account, any load carried, or high speed driving, being indulged in.

A good "rule of thumb" guide to correct tyre pressures under the prevailing road conditions and ambient temperature, is to put your hand on your tyres when you stop, after an hours driving.

The tyres should only be cool to comfortably warm to the touch, at most.

A tyre temperature that exceeds 75 deg C will result in the commencement of tyre/rubber degradation that hardens rubber and breaks down the bond between the rubber and the steel/rayon/nylon plies in the tyre.

50 deg C is reasonably hot to the touch, but you can usually keep your hand on the tyre at that temperature.
75 deg C is too hot to hold your hand on, for any length of time.

It also pays to feel the difference between tread temperature and side wall temperature, after a steady period of driving.
If the sidewalls feel noticeably hotter than the tread, the tyres are under-inflated for the conditions.

Interestingly, Michelin state that tyre under-inflation, below the manufacturers recommended pressure, by 30kpa (about 4.5psi) results in 6% additional rolling resistance, and around 1% increase in fuel consumption.

All the above advice is based on 53 years of experience with tyres, ranging from wheelbarrow tyres, to hard-worked ute tyres, to heavy trucks, to huge front-end-loader and dump truck tyres - and just about every road and track condition, one could experience - and it's worth exactly what you paid for it. [;-)

No doubt, other forum users will provide alternative and conflicting advice and experiences. You be the judge, and adjust your tyre pressures to give a comfortable ride, without overheating the tyres, or causing odd wear patterns.

It's a good idea to try out various tyre pressures to gauge the comfort level and driving/handling response.

Cheers, Ron.

65,000kmout of a set of Road Grippers is very good indeed.
They must have changed the compund/wear rate from the earlier ones I had on a Cruiser.
They did a bit over 30,000km all smooth road and no high speed because of family illnes and subsequent travel to hospitals over a few years. Nothing else. The tyres were dangerous and had poor grip near the end.

From my perspective, the only authority to listen to in regards to tyre pressures is the tyre manufacturer and even then you MUST know the load being carried to get the pressure correct.
Without that, everything else is speculation and guess work.

Cheers,
Peter
OKA196 motorhome

Laz, what ever you are doing don't change a thing, getting 65,000k out of a set of road grippers is excellent

Yup.
Its very much a grey area isnt it.
I mean look at what part of the country your in.
Like up north where asphalt tar heat could get to 70deg in summer.
Let alone such as melb in a peak heat summer wave.
Or your driving across the nullabor....gees spelling nazis will come out soon but you get the name.
Different states and wide varied of temps
You just wonder do you drop a couple psi in a stonking hot heat wave.
It was soo bad on the hume the asphalt even melted on the way to melb.
Couldnt imagine the tyre temps getting around.
Let alone towing and carrying a massive load

I have been told for 33 inch 12.5w 15 diameter 40psi is good.
And a few psi less in the front

As one of the essential auto parts, the best way to find out the real tyre pressure is ask the tyre manufacturer. They must give you a some sort of a chart or something about the pressure based on road conditions.

I agree that 65,000kms from Road Grippers is awesome.
My split rims/tyre combination is 60psi front and 70psi rear for bitumen and 40/45psi dirt and 30/35psi for sharp rocky roads and sand.
25/30psi for talc type sand.
Tyres have done 85,000kms and are around 65% worn.
BFG A/T 235/85/16.

Sorry to come in late on this, but something that doesn't seem to have been mentioned is why your tyre pressures need to be higher than you are used to.

You are running split rims and tube type tyres.
The tube type cannot dissipate heat as efficiently as a tubeless tyre because of the extra thickness and friction between the tube and carcase.
You will find that when loaded and travelling at the limit on the highway the tyres will feel hotter. By increasing the pressure, you will reduce the heat.

To get 65,000k off the grippers is excellent - I'm guessing you do a 5 tyre rotation but I'm also wondering whether you do a fair number of kilometres not loaded.