Highway tire pressures?

[Cristian G]

So, we’re off on our trip to West Oz, and probably a bit late to ask now, but I am wondering what run our tires at on the highway?
Tug is a 2014 150 Prado, 4 kids to adults and about 100kg of gear, on BF Goodrich All terrains
I’m currently running them at 36 front and 40 rear.
Camper is Ezytrail Lincoln LX, full tanks, gear, food, kids bikes, on 16”ATs. I’ve currently got these at 40.
We are not expecting to go off road on this trip with the camper, so should be sealed roads all the way.
What would you guys recommend?
Thank
Cristian

[edz]

As everyones rigs tyre types / weights etc are different, you will have to do a bit of Experimenting on your set up ### Check out the 4 > 6 PSI rule bit on here https://www.coopertires.com.au/media/1400/cooper-drivers-guide-tyre-pressures.pdf

[GBC]

You aren’t saying if the tyres are LT or not which makes a difference. Our MDC trailer has 265-75-16 LT MT Goodrides which I run at 55 lb on the highway - they max out at 80 so they like a lot of pressure. I would probably be adding more air to the rears of the car with a nose heavy trailer as well if they are LT’s. If they are p metrics, 40 psi is about right.

[Cristian G]

You aren’t saying if the tyres are LT or not which makes a difference. Our MDC trailer has 265-75-16 LT MT Goodrides which I run at 55 lb on the highway - they max out at 80 so they like a lot of pressure. I would probably be adding more air to the rears of the car with a nose heavy trailer as well if they are LT’s. If they are p metrics, 40 psi is about right.

Dumar$$e question, what is the LT & P code for?
I just checked and out camper tires are the same as yours, brand and size.

[GBC]

Dumar$$e question, what is the LT & P code for?
I just checked and out camper tires are the same as yours, brand and size.

LT = light truck
P = passenger

LT tyres have more plys in the sidewall to carry more weight but require much more air pressure to do so.

P tyres come in all terrain (AT) tread patterns too. They are more comfortable, lighter, better on fuel, easier on suspension but not as strong and generally have less tread depth so they don’t get a lot of love from 4wd ers.

The letters and numbers really are important and if people dont ask what tyre construction you have I would suggest their advice isn’t worth a lot. The LT or P or nothing will be on the sidewall next to the tyre size. A load rating is also on the tyre  which will also help if you can get that info?

You are asking the right questions not dumb ones

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[Cristian G]

Check out the 4 > 6 PSI rule bit on here https://www.coopertires.com.au/media/1400/cooper-drivers-guide-tyre-pressures.pdf

Thanks edz.
I don’t know why I didn’t consider that! We do it on the race cars to check setup, so why not on road cars.
Thanks for the link.

[Cristian G]

LT = light truck
P = passenger

A load rating is also on the tyre  which will also help if you can get that info?

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Thanks GBC.
I’m used to the load and speed ratings, but hadn’t considered those parts of it.
I just checked the car and it LT as well.

[GBC]

Thanks GBC.
I’m used to the load and speed ratings, but hadn’t considered those parts of it.
I just checked the car and it LT as well.

My original numbers stand then. I’d try 45 in the car rears for towing. Enough to be stable in an emergency, not enough to drive you mad. I tend to run a bit more than others though. There isn’t a magic number.


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[Cristian G]

Great, I’ll try that today.
I did notice our fuel consumption was more than I expected yesterday, but I put that down to our our high all up weight and the roof pod more than anything else.

[Bird]

Great, I’ll try that today.
I did notice our fuel consumption was more than I expected yesterday, but I put that down to our our high all up weight and the roof pod more than anything else.

judging by how low the arse end is, I'd say its ****in heavy - get used to it

[Cristian G]

judging by how low the arse end is, I'd say its ****in heavy - get used to it

The camper is the heavy bit.
I didn’t get to fit helper springs before we left. A victim of poor planning and competing priorities, my prep is well below what I wanted for this trip.

[scott13april]

I’d swap to HD rear coils or airbags, not a big job, 2/3 hours perhaps have it done on the trip?


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[OldPaj]

I follow the guidance on the manufacturers placard on the drivers side door frame on my Pajero.
Up to 5 Passengers:  29 PSI Front 32 PSI Rear (Highway tyres fitted generally)
Up to Max Load: 35 Front 41 Rear
Trailer Rowing: 38 Front 44 Rear (LT tyres fitted normally)

For the camper trailer (Vista RV Crossover XL) the manufacturer recommends 36PSI (LT tyres) and adjust as necessary at the same time as the car on lesser roads.

Seems to work well, no heat or over/under pressure issues.

[GeoffA]

I’d swap to HD rear coils or airbags, not a big job, 2/3 hours perhaps have it done on the trip?

I can swap the rear springs on my Patrol in 30 minutes.....fronts in 45.....

[gronk]

I have a 200 series, even though it's not the same 4wd, but tyre pressures are similar from car to car for a normal type of load and comparing the tyre placard that is on the door sill.

I run a couple of psi more than the placard ....35 front ....39 rear....140kgs on the ball.. tyres have never run hot and wear is even across the tread !!

[Fizzie]

LT = light truck
P = passenger

The LT or P or nothing will be on the sidewall next to the tyre size. A load rating is also on the tyre  which will also help if you can get that info?

Similar question to Cristian.

Tyres on our van are 195/70 R15C, which apparently stand for Cargo, so can I assume that's the same as LT

Also have a (I think) load rating of "104 / 102R" - I can see that 104 = 900kg per tyre, while 102 is 850kg - why 2 ratings Interestingly enough, the van's ATM is 1960kg, but, both those ratings, the 2 tyres would only allow us to load to max 1800kg, & possibly only 1700

[edz]

This may explain it for you Fizz https://www.bobjane.com.au/info/load-index-speed-symbol/   
From what I understand the two different load ratings on LT tyres, apply to Single tyre use and being used in a dual tyre set up  .. 
EDIT : Found it ..   http://www.tyresizecalculator.com/tyres/tire-speed-rating-and-load-index-for-the-light-truck-tires

[GBC]

Similar question to Cristian.

Tyres on our van are 195/70 R15C, which apparently stand for Cargo, so can I assume that's the same as LT

Also have a (I think) load rating of "104 / 102R" - I can see that 104 = 900kg per tyre, while 102 is 850kg - why 2 ratings Interestingly enough, the van's ATM is 1960kg, but, both those ratings, the 2 tyres would only allow us to load to max 1800kg, & possibly only 1700

Yes, they are delivery van tyres which go fine on trailers assuming you aren’t overloading them. I’ve run them on boat trailers before. Your load rating on a single axle is the 1st one. They are derated slightly on duals because of road camber and bumps meaning they end up not equally loaded. It looks like your tyres might be a bit light on for capacity. They will need to be at max inflation and it may be an offence to use them. What does your compliance plate say?

[Fizzie]

Thanks for that fellas.

Plate gives:

Tare 1600kg

GTM 1800kg

ATM 1960kg

Axle load capacity 1800kg

All of a sudden I'm (quite) a bit worried

[Fizzie]

Just went out & had another look at the van tyres.

Had only looked at the spare previously as that's easy to read , but this time checked the actual tyres as well.

They're actually 106 rating = 950kg each so 1900kg, so, if I'm reading all this correctly, would that make them illegal as they're then over the plated axle capacity

As mentioned, the spare is only 104 rating so I'm guessing it shouldn't be used in conjunction with a 106 on the other side

Also noticed that the plate gives cold tyre pressure as only 275kpa = 40psi. First couple of times we used the van & checked the tyre pressures they went from 45 to 51psi then 49 to 54, so we're now running at 52 (forgot to check the hot pressure after our last run ) so they're now way over spec's as well

This is getting messier & messier all the time

[GBC]

Your GTM is all that the trailer can put onto the tyres - the rest goes onto the ball/jockey wheel. Strictly speaking your spare is rated at precisely enough and the two main tyres have a little in reserve. Forget the 4 psi rule, you need to be at the max inflation number written on the sidewall to achieve that load rating. I have no idea what your load situation is, but with such a small payload allowance I’d be surprised if you don’t blow straight past those Gtm numbers when loaded for touring. I don’t want to cause alarm but it would be worth weighing it in touring trim. If you are within those numbers then all good. Worry about the alternative when you have some facts and figures.

[Fizzie]

Forget the 4 psi rule, you need to be at the max inflation number written on the sidewall to achieve that load rating.

66psi! Bloody hell! Isn't pumping the tyres up to that pressure then going to shake the absolute living crap out of the van

& if it's so important to run at max pressure (& it obviously is), then why all the discussion re the 4 psi idea, why isn't it just a hard & fast rule - inflate to max rated pressure

I don’t want to cause alarm but it would be worth weighing it in touring trim.

We ran it over a weighbridge on our way out on a trip & came in at 1.8t, so right on the limit, but that was only packed for 4 days so minimal groceries -- wouldn't be good if we were really touring so carrying a fortnight's worth Guess the planned second water tank, battery & solar panel have all just gone out the window

[edz]

Could always do a slash and burn Jenny Craig on the gear you take or the easy way out with an axle upgrade      ..  http://www.candm.com.au/atm/

[GBC]

66psi! Bloody hell! Isn't pumping the tyres up to that pressure then going to shake the absolute living crap out of the van

& if it's so important to run at max pressure (& it obviously is), then why all the discussion re the 4 psi idea, why isn't it just a hard & fast rule - inflate to max rated pressure

We ran it over a weighbridge on our way out on a trip & came in at 1.8t, so right on the limit, but that was only packed for 4 days so minimal groceries -- wouldn't be good if we were really touring so carrying a fortnight's worth Guess the planned second water tank, battery & solar panel have all just gone out the window

I dont see that you have too many other options. Shakng a van to retain control in an emergency doesnt seem like a huge compromise to me. A simple swerve on outclassed sidewalls could end badly.

[edz]

https://www.youtube.com/watch?v=nd-hUX8memY