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Tyre pressure - front vs rear


Alec Leamas
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I have a Defender ´98 HI CAP pickup with recently mounted 265/75R16 Cooper S/T MAXX and am trying to find the optimum pressure. When it came back from balancing at the tyre shop, it offered quite a harsh ride, and after a few weeks I figured out they had set the pressure to 3.2 bar all around. My own initial pressure was 2.2 in the front and 2.4 in the rear. I have referenced my Haynes manual, but there are no tyres in this size mentioned there. What I notice is that they propose very high pressures for the rear vs the front.

I understand the best way (or at least a good way) is to mark the tyres with chalk or something and see how the chalk wears.

Is the reason Haynes and others are proposing substantially higher pressures for the rear that they are assuming one regularly load max?

If so, if I almost always ride alone with nothing on the rear bed, shouldn't I have the same pressure or maybe even higher pressure in the front (with the weight of the engine)?

Any input highly appreciated.

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Most vehicle manufacturers give a range of pressures for different loads.  LR may have done so, but that may be missing from the Haynes manuals.  It certainly still applies.

Your pressures may need to be higher than standard because of the extra tyre width - standard pressures would probably allow the centre of the tread to deflect upwards, riding on the shoulders.  Higher pressure combined with larger cross section is going to be more jarring a ride - you have both increased "p"si and increased "i", so the tyres can't respond as supply as normal size and pressure tyres.

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The major factor to address before trying to decide on a pressure is what is the weight each end ?

   The front will run pretty close to standard at all loads , due to the relatively small weight increase

the engine being the major component .  The rear is a very different matter .

With 265/75 I have used 25 to 30 psi depending on how comfy I want the ride  and if very heavy in the rear .   If you are running empty (more or less ) in the rear then 25to 30 will work well . If you run partly loaded most of the time then 30 to 40 psi , if  you are running well loaded then try higher pressures 

upto max load pressure (shown on tyre)  to ensure stable handling .

     The best way to get the absolute accurate tyre pressure for any given load is a bit long winded but works well  , start with cold tyres  set what you think is correct pressure  , drive the vehicle for a long enough period to stabilise  tyre temp (say ten miles)   Check tyre pressure , you are looking for a rise

of 4C  if its more then you need to increase pressure (when cold) by 1psi per 1C  , if it is less than 4C rise then lower by 1psi per 1C   This can then be repeated if required to obtain an optimum for that particular weight .  HTSH

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I run my 265/75/16 bfg AT on the 110 at 28psi front and 36psi rear unladen and find I get excellent ride, handling and wear at those. If I'm towing the trailer or loaded the rear get increased to 46-48psi. (I've done this for over ten years now without issues) 

I know mine are a different pattern, but they're the same size as yours so may provide some reference. 

 

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