I have a new set of Goodyear Duratracs size 235/85/16. I was wondering if anyone has experimented with different tire pressures to see what works the best. Or should I just use the recommended 26 front 36 rear?
Vehicle is a 95 Discovery with little to no load and mostly road use with a 2 inch lift.

 

There should be an equation for you based on the original OEM Michelin Tires and the weight distribution of the front and rear of the vehicle axles.

Duratrac Tires based on your model are rated 'E', which means that the maximum each tire will do is 3,042 lbs @ 80 PSI. This is the most you can inflate the tire before it explodes from too much air pressure.

Following Land Rover Discovery's difference in tire pressure (it was engineered that way for a reason) the long and short should be around the following numbers below, provided your tire is the 'E' rating (Meaning the 10 PLY SUPER DUPER TOUGH TIRES)

Goodyear Duratracs size 235/85/16 inflation for Land Rover Discovery 1

Front Tires: 36 PSI

Rear Tires: 50 PSI

I have the BFG All-Terrain T/A KO and has a similar rating to yours, just my size is slightly different (245/75/16). I played with the PSI and found that I found it comfortable for me at Front 32 PSI Rear 44 PSI, mind you I need to replace my bushings.

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The madness... I mean... Math is below

Land Rover Discovery 1

- 4,400 lbs (Total Curb Weight Stock)

Front Axle Curb Weight is roughly 40% of the total Curb Weight of the Discovery.

Front Axle Curb Weight : 4,400 lbs x 0.40 = 1,760 lbs


Rear Axle Curb Weight is roughly 60% of the Total Curb Weight of the Discovery.

Rear Axle Curb Weight : 4,400 lbs x 0.60 = 2,640 lbs



Lets' test that shall we to make sure the math adds up thus far

Front 1,760 lbs + Rear 2,640 lbs = 4,400 lbs (Correct!)


The OEM tires were Michelin LTX MS if I am not mistaken, and they had a load rating per tire of...

2,365 lbs @ 44 PSI

Therefore lets do some more math...

Original Front Axle Curb weight was 1,760 lbs divided by two (each axle has two wheels) which leaves us with 880 lbs per tire as the load weight we have to account for in the front.

Lets do more math again

Original Michelin LTX MS tire ratings:

2,365 lbs divided by 44 PSI gives us 53.75 lbs/PSI

Therefore, Land Rover states that the stock front tires require 26 PSI for best fuel economy and safety (has to do with steering, that's why the front tires have less air in them than the rear tires).

That means 26 PSI x 53.75 lbs /PSI and each tire would be able to support 1,397.5 lbs at that pressure.


Lets go back to the new Duratrac Tires:

3,042 lbs @ 80 PSI

3,042 lbs divided by 80 PSI = 38.025 lbs / PSI

so we know that we would like to be similar to the weight distribution of the original OEM inflation ratio/weight at 1,397.5 lbs for each front tire.

Final Formula for new Front Duratrac tires based on your size and spec:

1,397.5 lbs divided by 38.025 lbs/PSI = 37 PSI (Rounded from 36.75 PSI)


Rear axle 2,640 lbs divided by 2 (two tires) = 1,320 lbs per tire

Original rear tires needed 36 PSI per tire as per manufacturer for best fuel economy and safety.

Original Michelin LTX MS Tire Manufacturer rating:

2,365 lbs divided by 44 PSI gives us 53.75 lbs/PSI


Rear OEM tires required 36 PSI

So 36 PSI multiplied by 53.75 lbs / PSI = 1,935 lbs



Go back to new tires... 3,042 lbs @ 80 PSI

3,042 lbs divided by 80 PSI = 38.025 lbs / PSI

so we know that we need 1,935 lbs for each rear tire therefore...

Final Formula for new Rear Duratrac tires based on your size and spec:

1,935 lbs divided by 38.025 lbs/PSI = 50 PSI (Rounded from 50.88 PSI)

 

WOW! Thanks man! Great information and can't wait to try it!

 

Original tires on D1 (at least all that I've seen) and early D2 were Michelin XPC 4x4.

 

I did the recommended tire pressure adjustment and I feel like it tightened up the steering. Hopefully it will help slightly on fuel economy as well.
Thanks again!

 

Glad to have helped. If it feels too stiff, it may also be a sign that your bushings need replacing (I know mine do).

An under inflated HD tire is also a bad thing for fuel economy so you should see a bit of an improvement

 

Is the slightly less inflated front tires simply a factor of the axle weight or does it directly relate to the steering performance as well?

 

Axle weight bc you have the engine and all accessories plus driver. Rear is just empty cargo most of the time.

 

So in the next few months when I get around to installing the ~800lb 6.2 some more math might be in order...