Beside my posts on the subject regarding the effect of bigger wheels on the EGT, ABS related functions and how the the whole management is mixed up which were based on my own experience and many tests here's a very relevant article which confirms my findings in a simple way https://www.carthrottle.com/post/how-does-wheel-size-affect-performance/ the gist of it is in the following statement at the middle of he article

"To summarise, a car’s engine finds it more difficult to rotate larger wheels, making for a decrease in overall acceleration. This is all assuming that every other component like the engine, driveshafts, gears and differentials are kept stock, making them specifically engineered for the original wheel size. Fuel economy will inevitably suffer as well due to the engine having to work harder to rotate the wheels, but I’d imagine that’s the least of worries for the generic modifier."

I can tell you are a worrier John! Just move those D3 wheels on and get a set of tidy 16s with some BFGs on. Thats not simple by the way second hand. I looked for months and a lot were stupidly priced. I bought some modulars ffrom Paddocks or Craddocks? In the end and bought tyres off Camskill, fitted locally.
Those D3 wheels are great but the rolling radius is excessive if you are after something close to stock. You would hate the gearing I suspect.

Thanks all, some great info there. So smaller wheels is not the same as overall diameter (rolling circumference). Of course, obvious when you think about it, but i wasn't when I bought these wheels! They are 17" which is an inch smaller than mine so I just jumped in, but the tyres are huge and the extra circumference has to make a difference. If they don't foul the body, I suspect I could actually really like them. But that means buying wheel nuts and I am already having second thoughts so I think you're right. Time to look for 16" wheels!

I supposed I am a worrier, but this isn't so much about worry, more about not haing time or money for more mistakes. One was too many! Plus not having experience (or the resources to just try the ideas out). I need to plump for something and after everything I have read it seems 16" wheels with 255/65 tyres is the best setup, the most stock, and the closest to the current rolling circumference (practically identical).

Fuel economy is an issue, at least insofar as I would like to optimise it if possible. The remap may help, but I wondered if narrower tyres might help too. I will start by finding wheels, then consider the tyre widths as i keep on reading before buying tyres. Thanks again chaps

john snoo said:

I have read it seems 16" wheels with 255/65 tyres is the best setup, the most stock, and the closest to the current rolling circumference (practically identical).

Click to expand...

For 16" rims there are two standard dimensions: 255/65 and 235/70, if you want the best stick to standard but what ever you do dont exceed it with more than 5%(that's the highest limit), a decent allternative which is slightly bigger would be 245/70/16...even with 255/70/16 which is below 5% the EGT difference can be noticeable, depends on other things too which can affect the vehicle's weight

Its interesting how much more a mud terrain adds to rolling radius also. Same size tyre can be quite a lot bigger with deep treaded tyres. So going 235/70/16 on new BFG ATs would be a good option if you want to retain your gearing as close as possible.
Best of luck with it all

Thank God you posted that pic. I had not considered this 7j 8j businesses, no idea what it even means. But i see on that sheet it says the 70 profiles will only go on 7j, and not the 8j. I better check that before I buy any wheels