True pressures

Submitted: Monday, Nov 09, 2015 at 20:50
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Can anyone help me with correct tyre pressures ? i have a Toyota Prado and a Jayco 17 ft pop top Caravan. Thanks johno
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Reply By: cruiser 3 - Monday, Nov 09, 2015 at 20:59

Monday, Nov 09, 2015 at 20:59
Usually vehicles have the tyre pressures clearly marked on a plate inside the drivers door, follow the manufacturers recommendation.
Also Jayco vans have a similar plate attached showing the recommended tyre pressures. On my Jayco that plate is inside the front boot.
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Reply By: Member - Will 76 Series - Monday, Nov 09, 2015 at 21:38

Monday, Nov 09, 2015 at 21:38
Johno, you may start a long thread here as tyre pressures can be a bit like tyre brands themselves in regards to opinions. The tyre placard is good place to start from the vehicle manufacturer, but I usually run 40 psi on tar roads, 26-30 on dirt and 16-18 on sand. This is the start pressures for me then I adjust to the conditions to let them down or put more air in. You need to drop the pressures in your van as well as your car for offroad. Hope this helps.
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Follow Up By: vk1dx - Monday, Nov 09, 2015 at 22:41

Monday, Nov 09, 2015 at 22:41
Similar here in a heavy 100 series.
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Follow Up By: Member - Wildmax - Monday, Nov 09, 2015 at 23:15

Monday, Nov 09, 2015 at 23:15
Same here in my Hilux, with a canopy and towing an AOR Eclipse (about 1800kg). Look to equalise how much tread is actually meeting the road surface on all six wheels, as you may need a bit more pressure in the vehicle rear tyres if you have a heavier weight on that axle.
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Follow Up By: Member - tazbaz - Tuesday, Nov 10, 2015 at 07:25

Tuesday, Nov 10, 2015 at 07:25
Ditto on my Ford Ranger and Billabong 2200kg
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Follow Up By: Frank P (NSW) - Tuesday, Nov 10, 2015 at 09:31

Tuesday, Nov 10, 2015 at 09:31
Ditto on my BT50 and 200kg Kimberley Karavan.
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Follow Up By: Gramps - Tuesday, Nov 10, 2015 at 16:29

Tuesday, Nov 10, 2015 at 16:29
Frank,

You do mean 2000kg Kimberley Karavan don't you ?

Regards
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Follow Up By: Frank P (NSW) - Wednesday, Nov 11, 2015 at 09:55

Wednesday, Nov 11, 2015 at 09:55
Bu**er! 2200kg

Thanks Gramps
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Reply By: Member - Trevor_H - Monday, Nov 09, 2015 at 21:44

Monday, Nov 09, 2015 at 21:44
Standard is known as "4psi rule".
Start with the recommended, as per plate.
Measure cold, then measure after 100km.
Should be 4psi increase.
If more, then is too low (flex causes more heat, more increase)
If less, then is too high (not enough flex).
Check front and rear, Prado will vary up to 20psi dependent on payload carried.
Regardless, drop to 20psi and drive slower on corrugations.....feels like a different vehicle.
Based on 30.000km on all road types last year. I was running 40psi front and 50psi rear for near max payload.
AnswerID: 592531

Reply By: Batt's - Monday, Nov 09, 2015 at 21:53

Monday, Nov 09, 2015 at 21:53
The best bet is to weigh your car separately and then together with the van hitched to get their true weights loaded up like your going away don't forget to add extra for water, fuel if the tanks are low, passengers and how the vehicles are loaded. Then you could ask a couple of different tyre outlets for their opinion on pressure because without knowing weights and tyre sizes it would be a pure guess.
AnswerID: 592532

Reply By: Member - Robert1660 - Monday, Nov 09, 2015 at 22:38

Monday, Nov 09, 2015 at 22:38
Hi Johno,
On the bitumen I run on my Toyota 200 series fully loaded towing a Tvan 45 on the front and 55 on the rear. The Tvan will be at about 35. When on the dirt I will run 25 at the front and 30 on the rear, 20 on the Tvan. My speed is limited to 80 km/ h. The key is to check your tyre temperatures frequently. The difference in the ride you will get is quite dramatic. It is still rough but the suspension "bang" is gone. The other thing to consider is tyre choice. Not a particular brand but "type". With the LT (light truck) construction the tyre wall is considerably stronger and the flexing that occurs with all tyres is much less thus tyre heating is reduced and thus lower pressures are possible. With standard tyres the issue of sidewall damage and over heating is always an issue. You will find many people do not believe in reducing tyre pressure, however I consider that it is an essential aspect of off bitumen driving and also a mechanism of helping to preserve non bitumen roads and tracks.
Robert
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Follow Up By: Member - Mark (Tamworth NSW) - Tuesday, Nov 10, 2015 at 06:32

Tuesday, Nov 10, 2015 at 06:32
Robert I was told by Bridgestone tyre engineer that LT tyres must be held at higher pressures than passenger construction tyres as they are less able to dissipate heat which leads to tyre wall failure.
The e mail came from his Bridgestone e mail address, not a private one from someone purporting to be working for Bridgestone.
LT tyres are capable of much higher pressures than passenger tyres, those details are on the tyre wall
Mark
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Follow Up By: gbc - Tuesday, Nov 10, 2015 at 07:13

Tuesday, Nov 10, 2015 at 07:13
Damn straight. Lt rated tyres need significantly more air to carry the same weight as the equivalent sized p rated tyre.
No one yet has even bothered to ask the OP what construction tyres they are running on the Prado or the van.
No one can issue advice before knowing the tyres on the car and the van, the load state and the terrain. Anything else is a wild guess.
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Follow Up By: gbc - Tuesday, Nov 10, 2015 at 07:15

Tuesday, Nov 10, 2015 at 07:15
And the 4psi rule is correct for racing and p rated tyres. Lt's on 4 wd's are more like 6-8 psi differential at correct inflation due to sidewall heat buildup.
There is no one correct rule for all.
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Reply By: TomH - Monday, Nov 09, 2015 at 23:00

Monday, Nov 09, 2015 at 23:00
I had TPMS in my 100 ser and used to pump them up so that I got a 6 lb increase from cold to hot Usually ran rears at 45lb hot and fronts about 38 Van about 45-50 but van was probably 50% heavier than yours.

Interestingly the sunnyside ones were always a couple of pound higher than the dark side.
AnswerID: 592535

Follow Up By: Allan B (Member, SunCoast) - Tuesday, Nov 10, 2015 at 00:17

Tuesday, Nov 10, 2015 at 00:17
I have a tyre pressure monitor using internal sensors which provide accurate temperature indication. It is interesting to observe the elevation of temperature on the 'sunny' side which is typically 10 degrees higher. This is accompanied by a small pressure increase.

Cheers
Allan

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Follow Up By: Les - PK Ranger - Tuesday, Nov 10, 2015 at 11:35

Tuesday, Nov 10, 2015 at 11:35
Indeed Allan, I find sunny side is usually about 2psi more, after equal pressures all round when set before sun comes up.
Negligible in the scheme of things, but still good to be aware of.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Nov 10, 2015 at 15:10

Tuesday, Nov 10, 2015 at 15:10
Yes, that would be right Les. The relationship between pressure rise and temperature is about 5 degrees C for each psi.
That ratio is from tyre technical sites and I have also observed similar.

I cannot find tyre temperature limits on any manufacturer's website. At times mine are in the low-mid 50 degrees and I change my pressure/speed to control that. But I would get nervous if they got to 60C. Maybe higher than 60 is OK but I just don't know that. I would appreciate the advice of a tyre manufacturer but not just someone who claims to know.
Cheers
Allan

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Reply By: Member - KeithB - Tuesday, Nov 10, 2015 at 07:15

Tuesday, Nov 10, 2015 at 07:15
For about $15 you can buy a digital thermometer on Fleabay. I use it at rest stops to check tyre and bearing temps.
Going over the Simpson in May at 13/16 psi cold and 13 in the trailer, temps stayed at about 50-60 degrees. Same at higher pressures on bitumen.
Keith
AnswerID: 592540

Reply By: Slow one - Tuesday, Nov 10, 2015 at 08:52

Tuesday, Nov 10, 2015 at 08:52
Johno, to work out the pressure you first have to weigh the combination with your wdh on if you use one. Get the individual weights for each axle and from this you can work out the tyre pressures for those axles.

The pressure will be a percentage of the maximum weight carrying capacity for the tyres. An example of this is, say the tyre has a maximum capacity of 1000kg at a 65 psi then if the weight on that individual tyre is 600kg then the pressure should be 39 psi. There should be tyre pressure calculators out there for this. Naturally there is a minimum pressure you shouldn't go below, except when off road at reduced speed.

We have one of the best temperature gauges on us all the time. The hand is a very good gauge to use and I have used this all my life. I run a hand over the tyres and bearing caps and you soon pickup any abnormal temps.

AnswerID: 592544

Reply By: Keir & Marg - Tuesday, Nov 10, 2015 at 11:40

Tuesday, Nov 10, 2015 at 11:40
van tyre pressure calculator
You could try this link which gives you a way to calculate the pressures for your van tyres based on the tyre designation and the axle weight.
AnswerID: 592550

Follow Up By: Keir & Marg - Wednesday, Nov 11, 2015 at 11:06

Wednesday, Nov 11, 2015 at 11:06
Forgot to mention that using the tyre pressure calculator on this link for the tyres on our van at its maximum axle weight gives exactly the pressure that Jayco has put on the van's compliance plate.
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Reply By: Member - Terry W4 - Tuesday, Nov 10, 2015 at 17:22

Tuesday, Nov 10, 2015 at 17:22
On a 2008 Prado 120 D4D and with the vehicle being near max weight on Toyo Off Country A/TIIs I use 35 psi (cold) around town. This gets up to close on 39-40 psi at running temperatures. On gravel using HL I run at 25 psi (cold) which climbs to about 28-30 at running temperatures. This will also be enough for some LL work as well but if consistent hard off-road LL work required I will drop pressures to 20 psi (hot) when required.

I keep the tyres on my camper at the same pressures as the Prado.
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