Advice: Change from 285 to 255?

I,d get rid of the tyre for sure. Unfortunately too many believe bigger tyres mean better off road performance and its not until they fit the tyres that maybe, just maybe, the manufacturer knew what they were doing with the original size.. I still have a laugh at the youngens in the twin cab hiluxes with 4 inch lift and 35 inch tyre. YES..you will have better fuel economy, less stress on the drivetrain and probably better braking and handling as well.

Larger diameter typically improves off road performance . Width is of much less importance and can be a hindrance.
Any extra stress on the drive train will only be in first gear low range. There will be a reduction in braking (but an increase in road grip).
I don't agree that fuel consumption is worse with larger diameter tyres. The oddometer will under register and that may give that impression. Fix the oddometer first before asessing fuel economy. It may actually improve.
Cheers,
Peter
OKA196 motorhome

Much of a muchness.



Bob

MrRichard, may I ask how you measured the power loss?

Problem with the 255/85R16 are they are only available in Mud Terrains and only in a few brands such as BFG, Toyo and Yokohama. They are less common and therefore more expensive. You will not see an improvement in fuel consumption but they are a nice tall tyre.

If you want less power loss and better fuel consumption, you need to go even skinnier - to say the 225/95R16 that is fitted to the current 76/78/79 series. It is still a nice tall tyre with that big 95 profile - diameter is 827mm (285/75 is 835mm). But you'd need new 6" or 7" rims.

The 80 series is geared so low that some taller rubber can help the rev area at cruise speeds. Brakes - not so good.
You need to know the carcass weights of the tyres to have any sort of informed decision about which to buy. Ask any cyclist about rotating mass - it sucks power.
If they weigh the same I’d take the 285/75 simply for on road handling and load carrying. Higher internal volume means less psi required to carry the same weight, and skinny high profiles squirm if not blown up hard anyway. Off-road biased I’d probably take the 255/85’s.

Hi Richard,
Maybe my experiences (without specifics) may add some clarity to your thoughts on this....As everything is a compromise with offroad tyres - consider this. You wanted clearance mainly for sand driving. I believe that most people have trouble in soft sand these days and it is not just the vehicle set up. Mainly the driver - but I digress. From someone who has driven 2wds up to very capable lifted, locked and prepared 4wds since the early 1970s, I can only suggest you go for the higher profile and larger width tyres (more sq inches to lift vehicle with less internal air pressure). The myth that narrow cheese cutter style tyres are better in sand only applies to very specific situations. You certainly will not acheive a technically difficult recovery with a vehicle fitted with narrower or cheese cutter style tyres in soft sand - I can speak from much experience on this! (Certainly if you yourself are stuck sometimes 8psi will get you moving but you cant do much about recovering your mate behind you and this speaks volumes about tyre profile). You are not changing much with your 2 suggested sizes so there will be little extra stress or changes to the vehicle performance - nothing that you cant change by altering your driving technique. If it costs a fraction more to be better off in sand then it is worth it (eg fuel wise etc) - 4wheel driving is not a cheap pastime anyway. Importantly, the less times you get stuck, stress yourself/vehicle or have to make difficult choices - the better! I can only suggest you spend plenty of time "playing" around in soft sand with your vehicle - it is the only way to learn how capable your vehicle "really" is. (Irrespective of the driver). Remember a lot of us managed quite well with only 2wd vehicles in soft sand - if they can be capable of moving through sand then have faith in your 4WD and become master of its capabilities.

If I may suggest, 4XOverland doea a few great you tube videos discussing tyres. A man with a LOT of experience with off road touring. Ronny Dahl also. They explain what tyre for where and why.