Ok - I drive a 1987 Landrover 90 truck cab. It has just been fitted with Toyo All-Terrain 225 x 75 x R16 tyres. HMS Haddock (the name for her) is no longer used for towing heavy loads, pulling tractors and tourists' campervans out of ditches or towing anything beyond a light farm 1-ton trailer - she is retired from active service. I have just replaced all the springs and shocks with better-than-OEM which are for road use - no off-roading -. The roads here are in a terrible condition, many single-track and very bumpy. I set my tyre pressures at 30psi all-round. The new tyres are 225/75-R16 on old-fashioned plain steel rims. The inexpensive Toyo tyres are a revelation after the pretty mediocre General Grabbers they replaced. The ride is fantastic and for some reason the gearing seems smoother and crisper with the smaller diameter 225 tyres. She stops on a sixpence - very good grip at all times - unlike the GGs which were like driving a 2-ton roller-skate by comparison. If you are still awake, here's my question:

I am having to do a long road trip tomorrow for a week from the Isle of Skye to the bottom of England and obviously most of the driving is on dual carriageways and motorways. It strikes me that because the road surfaces are comparatively good, I could increase my tyre pressures significantly from their normal 30psi all-round and still have a reasonably soft ride - well, as soft as a Landy can make it. At higher tyre pressures, I am hoping to improve fuel consumption, currently 27mpg on the dreadful roads up here, falling to 24 mpg if I do a significant amount of bombing around on the even worse, heavily potholed single-track surfaces. Any suggestions and any opinions on the fuel consumption or any other side effects I should be made aware of? I can do quite high jailable speeds thanks to the diesel engine, a powerful 2.8-litre Isuzu brute of amazing strength. It goes like that stuff which is always falling off shovels.

Opinions and advice much appreciated, whoever is out there...

Sure I used to run 34 or thereabouts on my td5 110. I don't think you'll see much mpg improvement at all, especially cruising at 70+ you'll probably see a drop.

I think you're overthinking this tbh

Edit
Quick Google suggests 28 front 35 rear standard load

1988smithy said:

Sure I used to run 34 or thereabouts on my td5 110. I don't think you'll see much mpg improvement at all, especially cruising at 70+ you'll probably see a drop.

I think you're overthinking this tbh

Edit
Quick Google suggests 28 front 35 rear standard load

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Yes I’m definitely over thinking it! I keep a fairly meticulous track of fuel consumption as a possible guide to engine health and this tyre pressure query sort of springs from that. Of course one reason the long drive at higher pressures data are completely obscured is that the tub is pretty well loaded up with tools etc, which makes a nonsense of analysing this 1500+ mile, week-long trip. But I will find the answers interesting, thanks to the amazing knowledge members have - the sort of people who share on forums like this. So apologies to anyone out there who thinks my query boring and nerdish!

Like you I do a lot of single track road driving and Cooper 235 75 AT are tire of choice. Tend to run bit higher at the front say 32 and lower at rear 28as empty most the time.[SWB] The gearing and tire size suits this sort of back road work.
Best you can do for milage is unload anything not needed for the trip and most of all not to drive at 70mph.
Tests done some years ago by a 4x4 mag found that air pressure [ drag ] on the Landy front was double at 75mph what it was at 50mph

I'm back after fantastic 1300-mile plus road trip down to Devon via camping out in the Lake District and generally wandering around. Huge amount of motorway driving, mostly at 75-85mph, tyres at 30psi all-round, and returned 27mpg, so well-pleased. Toyo All-Terrain tyres were impeccable. Thanks to everyone who advised me...

Info for fuel consumption nerds! I have just done a 380-mile trip from the Midlands and up to Skye, a big chunk of it on the M6.I just chilled out and kept to the slow lane letting all the white-knuckle drivers zoom past me as I kept the speed to 60mph or under all the way and taking in the scenery which actually exists. It returned 34mpg. Result! If I'd done this journey as usual, at 75-85mph, it would have been 27mpg and on the single-track roads on Skye it can be as bad as 24mpg....

Hector the Bad said:

Info for fuel consumption nerds! I have just done a 380-mile trip from the Midlands and up to Skye, a big chunk of it on the M6.I just chilled out and kept to the slow lane letting all the white-knuckle drivers zoom past me as I kept the speed to 60mph or under all the way and taking in the scenery which actually exists. It returned 34mpg. Result! If I'd done this journey as usual, at 75-85mph, it would have been 27mpg and on the single-track roads on Skye it can be as bad as 24mpg....

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I soon learnt to chill with the wagons in my 110 they drink like **** above 65, high speed tractor after all!

Whereabouts in Midlands were you?

1988smithy said:

I soon learnt to chill with the wagons in my 110 they drink like **** above 65, high speed tractor after all!

Whereabouts in Midlands were you?

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I spent 3 nights camping on a remote hillside farm with spectacular views, in the Lake District, not far from Broughton-in-Furness. Beautiful rain, munching sheep and hardly a soul to be seen. By the way, I had been to LR Parts in Liverpool (the main reason for my trip) to pick up a safety roll bar as I’m converting my 90 to a ragtop over the next week or two. Can’t recommend them highly enough.