True pressures
Submitted: Monday, Nov 09, 2015 at 20:50
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johno59
Can anyone help me with correct tyre pressures ? i have a Toyota Prado and a Jayco 17 ft pop top Caravan. Thanks johno
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: 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.
AnswerID:
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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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860714
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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860715
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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860716
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.
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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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