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Mik - 4psi tyre pressure test



Mik wanted to know about the old 4psi tyre setting routine, so here it
So, the manufacturer's calculated optimum pressures when warm are nearly
always 4psi above the recommended pressure when cold. You inflate to 32 and
when warm they are 36psi, and that's where Mr Dunlop/BFG/General et
al. wants them to be.
So if in doubt, set them to 32 early in the morning before it gets any heat
of the day, go for a ride for half an hour, and not in stop-go traffic, but
you don't have to do the Schumacker wiggly steering though. Then test the
pressure. If its 36 then you have it right. If its 38 and the car is full
of kids Labradors and chainsaws then it should be 34 cold for those loading
conditions. Likewise if its 34 when warm, then you should run at 30psi
cold. But in summer when its hot and you are going on a long autoroute
drive then inflate the rears more to get the best fuel consumption etc. The
only exception I have found is when it gets very - 40 degs - hot in summer
the fronts tend to squeal on tight corners and I put another 2psi in to
quieten them.
It is said that no 4WD car should run at much above 35psi otherwise the
tyres can't mould around the surface to get grip. But I am sure that it can
be proven otherwise by someone !
By the way, someone wrote less than affectionately about Dunlop Grand
Treks. Toyota have fitted them as OEM for years. My 80 has always worn TG
35 M2 pattern on 265/70 X 16's. I am amazed at the grip and wear I get from
them in very exceptional and varied conditions in a wide range of
temperatures, from minus 30 to plus 40. Even on the high speed tarmac roads
they are well behaved. I think I will replace them in respect of their
perishing rather than wear. (Maybe when Julian sees them next week he can
give me another opinion.) Each to his own I guess.
'92 HZJ80 ex UN surplus from Bosnia, now sharing time between Alfold Surrey
and Tring Herts.
Would've thought you can run a lot less off road unless you're banging
up rock steps in which case you may be worried about your rims. Now as
usual I don't really know much about off roading with 4x4's but I do a
lot on motorbikes. On the road I run 25 psi on the rear and off road
between 6 - 15 psi depending on conditions and type of tyre. Quads run
more like 4 psi. Now I know cars are different but I imagine the
principle is the same - if the going is soft or loose the pressure needs
to drop quite a bit to get maximum traction. I bet you could be running
more like 20 psi off road on a lot of tyres in UK soft stuff.
Saw quite a funny sight this weekend on Exmoor. I was green laning on
the bike with some friends and we were doing pretty much the same route
as a load of 4x4's so kept meeting them. They had all the kit, winches,
roll cages, mud tyres, lifted. We passed them up one steep rocky climb
and was dealing with a nail in a tyre at the top as they all crested out
onto the road. So all these pukka off road machines come out looking
impressive. Then at the back one of the locals comes out in his
immaculate spanking new Range Rover, absolutely standard, grandaughter
next to him, dog in the back, wearing his Sunday best, obviously just
off to town. He pulls alongside, lowers the suspension, selects high
ratio and off he goes. Put us all to shame.
toy80 wrote:
Thanks for the info Jon, sounds very logical. I must
confess, I never heard that one before, but it's copied and
filed in both my and the lap-tops (probably much safer)
memory now, thanks once again, I'll try it and let you
know the result.
Mik Kenney, (Cruisermik).
T.L.C.A. Member (Last 8 Years).
82 FJ 40 'Swagman'
97 80 1HD FT. 'Abe'
As a point of interest, Toyota have gone away from grand treks.
Regards, Clive.