Quick question and easier for me to ask then research ( and kinda lazy I guess ). Currently running 255/55/R20 Goodyear Eagle F1's - would the speedo be affected? if so then how far out would it be...
Whilst doing an indicated 80mph on the motorway I seem to be passing quite a few cars and rather easily to boot, concerned with all the "safety" cameras about I could get caught speeding without realising it.
Is there anything else that could be affected - steering geometry for example?

Put your tyre size in this and it should tell you all you need to know.

https://www.tyresizecalculator.com/tyre-wh...calculator

https://www.autopartuk.com/tyre-calculator/

Don't know what the original sizes were - car came with these fitted. Any idea?

* online check says same dims but on a 18" rim so now speedometer will be 6.9% too slow. May explain my thinking. Will try it against GPS system and look for inaccuracies.

if you had 20's to start with you should have had 275/40/20
But most people run 275/45/20 for a little more side wall and comfort..

I may be wrong but to confirm,
have a look inside the door and the info sticker for the sizes..

GL ===========================================
2012 Range Rover Sport Autobiography 3.0 SDV6 8 speed Automatic
Indus Silver with Hockenheim premium two-tone leather Ebony/Lunar,

Here's the door pillar info - none state 255/55/R20 however R18 displayed so I'm guessing I am 6.9% out to true reading. Do i need the IID tool to rectify or could I simply meet someone local to Ashford who has one and they could re-calibrate on my behalf?

worked it out......