New wheel and tire combo

i am running stock 18 in steel wheels and the factory michelins are now needing replacing. 255/70/R18. How much bigger of a tire can I run without affecting the speedo? or can that be reprogrammed? wanting to move to a A/T type tire and would like to stick with the 18 in rim but not opposed to a 20. looking for new rims 2019 4X Crew Cab SR5. Stock suspension at the moment.

 

The ride will lessen some with a 20 inch wheel. I'm running 34's on 18's and mine isn't off by hardly anything at all.

 

Welcome

 

Any increase in tire diameter will throw the speedo off by the same percentage as the size increase. 10% larger tire throws speedo off by 10% etc. You can get the speedo reprogrammed.

This is IF your speedo is accurate to start with. Mine was not, so going to a 275/70R18 put mine dead on with the speedo.

 

while this is likely true to a certain extent the seat of the pants difference is negligible provided you're not airing down and taking it on hairy trails. I've yet to meet the person that sits down and can discern 18's from 20's based on vehicle ride.
the bigger difference is availability of wheels and tires where there is definitely more choices at 18"

 

Nothing to worry about. I run 275/70-18s and my speedo is closer to accurate than with the stock tires. Before was about 3 mph low, the tires had 30K miles so were worn some(smaller), now I am 1ish mph above. Basically, my accurate speed is at the right edge of the needle now so very, very close to GPS verified accurate with the 33inch tires. I run wildpeaks, which do run large for the size, 33.43 tall in my case.

But do know, moving to a larger tire on a tundra generally means moving to an E load tire, which are heavier than the stock standard load tires and they have more pyles, so expect a little MPG hit when installing larger meats with more aggressive tread pattern.

 

Go with a 275/70r18 and your speedo will be just fine. Hell mine stock was about 1-1/2 mph off. 275/70's probably would make it dead on.