Wheel/ tyre swap speedo etc

I know it's another tyre question but I've been searching on here for an answer that would be understood by a numb nut like me but....

On defender 90 now I have standard issue 5.5inch wide steels with 205/80 r16's.

I would like to change to 235/85 r16s (on new wider rims)

I understand this will affect the gear ratio etc but what I want to know is will it affect it so drastically that I would need to do something about it? And if so what?

If it's a big deal I would prob just stick to what I have! I just prefer tyres a bit more substantial.

If you are asking about the speedo gear, then I would ask you , " how accurate is your current speedo on the tyres you have?"

I have 285's on mine and when I have checked with GPS, my speedo measues absolutely spot on.

Cheers

Same here - when I went up to 235/85/16's my speedo was far more accurate. It was miles out on the standard rubber.

Thank you v much - I was told a few conflicting story's but I'll go ahead and order the wheels now without having to change my gearbox....;-)

Thanks again !

frc3310 is correct speedo drive but as said try your first

Quite a difference in size, same swap as I did