"Real" Tyre Pressure for Land Cruiser 79 Dual Cab

Submitted: Tuesday, Apr 10, 2018 at 11:28
ThreadID: 136527 Views:1236 Replies:12 FollowUps:17
Hi, guys. I need your help.

I am running Dunlop Road Grippers F 7.50 R16 on my Landcruiser 79 series dual cab. The last set lasted 4 years and 65,000km. I am happy with the tyres and I want to keep using the same type.

But, I am totally confused about the tyre pressure. I was religiously following the Toyota Manual, telling me to keep the front tyres – 36 and the rear – 38 (for unloaded vehicle). And, of course I adjust the pressure to suit the road condition.

However: every time TOYOTA serviced my truck – they pump all four of them up to 45, saying “That’s the way they should be”.

Recently, I changed the whole set at the tyre shop, where they said to me “You should be keeping them at 40 – for the front, and 36 – for the rear”.

I was unable to find anything to confirm or deny any of those points. I really appreciate your input.

Cheers,


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Reply By: Gbc.. - Tuesday, Apr 10, 2018 at 12:30

Tuesday, Apr 10, 2018 at 12:30
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.
AnswerID: 618203

Reply By: splits - Tuesday, Apr 10, 2018 at 12:40

Tuesday, Apr 10, 2018 at 12:40
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..
AnswerID: 618204

Follow Up By: Frank P (NSW) - Tuesday, Apr 10, 2018 at 13:39

Tuesday, Apr 10, 2018 at 13:39
Splits,

You post a lot of good technical info on suspension, including the above which I for one appreciate. So I have a question the answer to which may help the OP.

When someone decides on a modified suspension - eg in my case a 2 inch lift, GVM upgrade to 3500 for my BT50 which necessarily incurs stiffer springs and different shocks - and then fits aftermarket tyres different from OEM (but within the limits allowed by the state rego authority) where can that person get info on the correct tyre pressures for the altered setup? Or how can they be determined?

Lacking that information I have to admit that my approach has been quite unscientific.

I start with my tyreshop's advice. I read forums like this and gather opinions. I try to get a feel for how the vehicle is driving (but how qualified am I or any other Jo Blow to assess that?) and I look at tyre wear.

With my heavily loaded BT50 on BFG TA KO2 LT265/70-17s I've come up with front 40 PSI, rear 45 PSI for highway, 33 and 35 and max speed 80 for good dirt, 23 and 25 max speed 60 for corries, the last being variable and driven by comfort as much as anything else.

How far off the mark is this, and is there a better way?


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Follow Up By: splits - Tuesday, Apr 10, 2018 at 21:17

Tuesday, Apr 10, 2018 at 21:17
Frank

The engineers who designed the original suspension supplied written instructions on what to do with tyre pressures. The people who fitted your modified suspension should be able to do the same.as well as answer any question you have about it. They should not leave their customers to try and work it out for themselves.

If they can't then they are just parts installers, not suspension design engineers. I suspect the vast majority of them are in that category.

The right pressures for the load could most likely be obtained from the tyre manufacturer, not the dealer. Check on their web site. They usually have a customer information service.

That may solve your pressure problems but they are not going to know how the car is going to handle, particularly in fast corners or sudden swerves. It may run the front out a little wider or slide the tail out. Unfortunately your modifications have changed a lot of the original design

One example is the rear springs. The originals are usually near flat when loaded and don't look right in the eyes of many owners. You will notice the front eye of the spring is mounted down low under the chassis and the rear shackles are up much higher. The original spring will bend even more in corners and has been designed to swing the axle up in an arc and forward towards the front of the car. The other spring will drop down slightly as weight comes off it and pull the axle back.

This changes the angle of the axle slightly and assists in cornering stability but chances are your lifted higher arc spring will flatten and take the axle back in the wrong direction on the outside of the corner and pull it forward on the other side. That is the reverse of what the car manufacturer intended.

The only other thing I can suggest is if you live in Sydney to contact this company.HEASMANS They were THE place to see for both street and competition suspensions back in the days when I was busy screaming at Elvis and the Beatles. Click on the word "About" at the top of the page to see their history.

They could look at what has been done and maybe recommended moving a few pivot points or whatever to improve on road safety and handling..

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Follow Up By: Frank P (NSW) - Wednesday, Apr 11, 2018 at 13:30

Wednesday, Apr 11, 2018 at 13:30
Thanks Splits.

The GVM upgrade kit is a Lovells product and their head office is not far from me. The kit is a DOTARS-approved SSM kit for my vehicle. I might have a chat with them.
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Reply By: Malcom M - Tuesday, Apr 10, 2018 at 12:55

Tuesday, Apr 10, 2018 at 12:55
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....
AnswerID: 618206

Follow Up By: RMD - Tuesday, Apr 10, 2018 at 15:20

Tuesday, Apr 10, 2018 at 15:20
I always wondered about the 4psi rule, but it is only a rough guide.

What if the increase in temp and pressure are because of the hot road surface or the speed and it increases themp/pressure more than just normal tyre molecular activity creates?
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Follow Up By: Batt's - Tuesday, Apr 10, 2018 at 16:44

Tuesday, Apr 10, 2018 at 16:44
The old 4psi rule again it's not as accurate as you may think and is more aimed towards passenger cars as a guide and not 4WD's and not for off road I would ignore it and stick to what works for you and your vehicle. If your tyres are wearing evenly and you are having no problems you must be doing something right.

When you take the vehicle in for a service or tyres your the paying customer so tell them what tyre pressures you want if they change them I would take to their supervisor and get them to adjust them back to what you want at their inconvenience not yours.
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Follow Up By: AlbyNSW - Tuesday, Apr 10, 2018 at 17:38

Tuesday, Apr 10, 2018 at 17:38
Agree with Batts, the 4 psi rule is of little value. If you have a TPMS system fitted you will soon see how much pressures fluctuate with outside influences, you can get a 4 psi change without even driving your vehicle with just the change of ambient temperature during the day.
Even tyre wear is the best indicator of correct pressure
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FollowupID: 890134

Follow Up By: Batt's - Wednesday, Apr 11, 2018 at 17:11

Wednesday, Apr 11, 2018 at 17:11
I actually read it on the Cooper tyres site some time ago.
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Reply By: tonysmc - Tuesday, Apr 10, 2018 at 12:55

Tuesday, Apr 10, 2018 at 12:55
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.
AnswerID: 618207

Reply By: Ron N - Tuesday, Apr 10, 2018 at 13:08

Tuesday, Apr 10, 2018 at 13:08
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.
AnswerID: 618208

Follow Up By: splits - Tuesday, Apr 10, 2018 at 20:24

Tuesday, Apr 10, 2018 at 20:24
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,
-------------------------------------------------------

I looked at a lot of car handbooks back in my days in the motor industry many years ago and I can only remember seeing one instruction for increasing the pressure for high speed driving.

The car was a new mid 1970s Jaguar XJ6. The book said for sustained speeds above 120 miles per hour (not ks per hour) increase tyre pressure by 2 psi. I doubt if any Australian owners ever increased their pressures.

The manufacturer of the new set of standard size tyres that I put on my 4x4 ute soon after buying it told me during a phone call to their customer information service to use the pressures in the hand book and if I really must increase them then never go any higher than 4 psi. They also said never reduce them below the handbook pressures.

Toyota's pressures were so low that I thought why would I want to? I have used those pressures for around ten years on everything from mountain tracks to freeways to a few Beadell tracks and they work perfectly with no sign of outside edge wear due to under inflation.

The only exception was to drive to the top of Big Red and back down again. I used 14 front and 18 rear as opposed to 25 front and 32 rear that I used for the whole trip. That was in accordance with the handbook. The 32 rear was a little under maximum because the car was under GVM.

-----------------------------------
or substantial load-carrying, is going to be carried out
----------------------------------------------------------------------

Increasing pressures in accordance with an increase in load maintains the front to rear slip angle ratio. The pressure in my front tyres does not increase at any time. The rear is the same as the front when the car is empty but can be raised progressively by an additional 9 psi as the load increases.

Adding weight to the rear will increase the tyre slip angle to the point where it can exceed the front angle. The car will now be prone to oversteer which is sliding its tail out and even spinning if the driver can not control it. By increasing the pressures in accordance with the load, you stiffen the tyre sidewalls and progressively reduce the slip angle. If done correctly, you will end up with the original; front to rear ratio being restored and the car under steering as the manufacture intended.



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Follow Up By: Ron N - Tuesday, Apr 10, 2018 at 20:39

Tuesday, Apr 10, 2018 at 20:39
Well, here's the Tyrepower website advice ...

"On your placard you may also see pressure information for heavy loads and sustained high-speed operation. This is only a guide and if you have any questions it's a good idea to consult with a professional."

Tyrepower - tyre placard

Virtually every tyre placard image I see below, has a recommendation for increased tyre pressure for increased load.

It doesn't take long to find a placard that reads ...

"For speeds above 140kmh, inflation pressure shall be increased by 60kPa (9 psi)".

Granted that there are only a few places in Australia where one can sustain in excess of 140kmh for an extended period - but they do exist.

Google images - tyre placards

The VN SS and Calais tyre placard clearly states - "Where shown, 30kPa (4 psi) to be added for consistent high speed operation".

Tyre placard - VN SS and Calais

Cheers, Ron.
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Follow Up By: splits - Tuesday, Apr 10, 2018 at 21:48

Tuesday, Apr 10, 2018 at 21:48
Virtually every tyre placard image I see below, has a recommendation for increased tyre pressure for increased load.
------------------------

That is what I just said in my last post along with the handling related reason for it. There is also the need for more air to support the additional load. There is more than just one reason for increasing rear pressures as the load increases.

-------------------------------------
Virtually every tyre placard image I see below, has a recommendation for increased tyre pressure for increased load.
---------------------------------------------------------------

That does not surprise me. Unfortunately we did not have an endless supply of customers at work years ago with seriously high performance cars so it was not mentioned in all the books that I looked at except for the Jag.

One question that comes from increasing the pressure for sustained high speed is what is considered to be high speed, if the manufacturer does not state a figure, and what is the starting point for each owner?

Many owners use their own pressures and there will most likely be a wide variation from one car to the next.. Do they add two or maybe four psi to those pressures or go back to the factory ones in the book and add a few psi?

There are a lot of screwed up cars on the road that are running on their owner'ssuspension mods.. Some will get away with it while some wont. If a suspension alteration does contribute to an accident, most owners will still be none the wiser.

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FollowupID: 890146

Reply By: RMD - Tuesday, Apr 10, 2018 at 15:24

Tuesday, Apr 10, 2018 at 15:24
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.
AnswerID: 618210

Follow Up By: mike39 - Tuesday, Apr 10, 2018 at 15:48

Tuesday, Apr 10, 2018 at 15:48
I have used 750r16 Road Gripper F tyres on the HZJ75 trayback since new in '97.(came fitted with them)
A workhorse, pretty much always with a van or heavy trailer on the back, a lot of travel in SW Qld. breakaway country, off road amongst the gidgee spikes, they are the tyre for those conditions.
However, as RMD has found, they do have a limited life. I have found that running 55psi in the front and 65psi in the rear carries the load I put on the old girl with replacement around 30-35000km.
Saves them falling apart from UV damage!
mike


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Reply By: Peter_n_Margaret - Tuesday, Apr 10, 2018 at 17:24

Tuesday, Apr 10, 2018 at 17:24
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
AnswerID: 618212

Follow Up By: Baz - The Landy - Tuesday, Apr 10, 2018 at 17:33

Tuesday, Apr 10, 2018 at 17:33
Agree!

Cheers, Baz - The Landy
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it can be done shouldn’t
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Reply By: 9900Eagle - Wednesday, Apr 11, 2018 at 06:21

Wednesday, Apr 11, 2018 at 06:21
Laz, what ever you are doing don't change a thing, getting 65,000k out of a set of road grippers is excellent
AnswerID: 618217

Reply By: mountainman - Wednesday, Apr 11, 2018 at 07:26

Wednesday, Apr 11, 2018 at 07:26
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
AnswerID: 618219

Follow Up By: RMD - Wednesday, Apr 11, 2018 at 08:32

Wednesday, Apr 11, 2018 at 08:32
Spelling Nazis? It is the "SSS'" you have to worry about.

Nullabor has a Big N, and yor not getting it write.
Didn't know the asphalt was on it's way to Melb, Big M this time. No not the Milk carton.
Unused Dickshunry for sale. Contains proper words, good value.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Apr 11, 2018 at 08:58

Wednesday, Apr 11, 2018 at 08:58
.
It's Nullarbor anyway!
Hang on to the dictionary.

Cheers
Allan

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Follow Up By: Ron N - Wednesday, Apr 11, 2018 at 13:07

Wednesday, Apr 11, 2018 at 13:07
Geez, and here's silly ol' me, thinking it was spelt Nullerbore!

It can get pretty boring after a couple of solid days of flat featureless terrain!

Cheers, Ron.
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Reply By: Lucas R - Wednesday, Apr 11, 2018 at 15:21

Wednesday, Apr 11, 2018 at 15:21
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.
AnswerID: 618225

Follow Up By: Peter_n_Margaret - Wednesday, Apr 11, 2018 at 17:13

Wednesday, Apr 11, 2018 at 17:13
Correct pressures for a particular tyre are based on load and speed which are the main parameters that create heat build up from the flexing of the tyre components.
I have the Michelin charts for the tyres on the OKA and they quote pressures for a wide range of loads for 20kph, 65pkh and 130kph (the rated maximum speed).
I use the tyres strictly in accordance with these charts.
These charts also include using the tyres at higher loads that those that the tyre is rated for (at very much reduced speeds).
These are some of the benefits of using tyres from the best manufacturers.

Cheers,
Peter
OKA196 motorhome
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Reply By: Been-Everywhereman - Saturday, Apr 14, 2018 at 16:18

Saturday, Apr 14, 2018 at 16:18
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.
AnswerID: 618289

Reply By: Member - Phil G (SA) - Tuesday, Apr 17, 2018 at 12:33

Tuesday, Apr 17, 2018 at 12:33
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.
2012 Landcruiser 200 Altitude
2015 New Age MR16E Deluxe
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AnswerID: 618354

Follow Up By: Ron N - Friday, Apr 20, 2018 at 21:39

Friday, Apr 20, 2018 at 21:39
I still use quite a number of tubed tyres every day, and I discovered one very useful trick for tubed tyres, many many years ago - that no tyre dealer or retailer will ever tell you about - because they all want to sell you new tubeless rims, and new tubeless tyres.

When you assemble your tubes into your tyres, pour a goodly amount of French chalk (powdered talc) into the area between the tyre and tube.

Pour in enough to give the tube a good slippery coating over its entire surface area.

Then assemble the tyre and rim, and pump it up to your desired pressure, and fit it.

You will find the French chalk is such a good lubricant between the tube and the tyre, that your tubed tyre and rim will now operate at temperatures similar to a tubeless tyre, under equivalent loads and operating conditions.

I have personally experienced the difference this makes to tubed tyres when getting a stake at high speed on dirt roads.

This is common to have happen after the road has been maintenance-graded, and the grader operator buries pieces of sharp sticks in the new road surface.

If you stake a tyre at speed, with no French chalk in the tyre, the tube will be rubber salad by the time you come to a halt.

If you have put a satisfactory amount of French chalk in the tyre, the staked tube is always useable again, after you've come to a halt with the flat.

The only downside with using French chalk, is that you need to take special care when repairing holed tubes, that all the French chalk is removed from the patch area, before you put the patch on.
If you abrade the patch area properly, before installing the patch, this should pose no problem, anyway.

Cheers, Ron.

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