2004 TD5 Landmark wheel/tyre question

Good morning all. I wish to purchase 4 new Goodyear Wrangler Duratrac 255/55/18 tyres but it apears the only size available for my wheels is 255/65R18. (my wheels are 3 spoke Land Rover Alloys)
I realise that this will throw speedo out slightly, but as I live on a farm having extra grip whilst on frosty and muddy fields would be an advantage. The car has only covered 71,000 miles from new so is not abused and is fully serviced. Can anyone offer any advice? I've heard people have remaps etc but is this strictly necessary?
Thanks in advance

Smiffy

Why limit yourself to one make... plenty of other manufacturers offer the correct fitting... Try Black Circles.

https://www.blackcircles.com/tyres/255-55-18?id=11679

Whats your budget....

https://www.blackcircles.com/catalo...rrain-ta-ko2/255/55/R18/R/109/f?tyre=34716872

tilly2 said:

Why limit yourself to one make... plenty of other manufacturers offer the correct fitting... Try Black Circles.

https://www.blackcircles.com/tyres/255-55-18?id=11679

Whats your budget....

https://www.blackcircles.com/catalo...rrain-ta-ko2/255/55/R18/R/109/f?tyre=34716872

Click to expand...

It's a very good point and I have decided to go for the Avon AX7 on the correct size. They seem to be well priced and well respected. Thank yiu