No speedo difference between stock 265/60/20 and new 285/60/20?

Hello,

New member here...just brought home my 25 Tundra Limited TRD. So far really liking the truck.

I swapped tires out from the stock 265/60/20 Wildpeaks to 285/60/20 Toyo AT3 (SL). Like many others, I always swap tires out for one size up. My new tires are 33.5" and the stock were 32.5". Revs per mile stock 639 and new 621.

What I don't understand...I expected (like always has happened) that my speedo would be off a couple MPH. No biggie. However, it's not off. I used google maps and two different apps to test speed vs my trucks speedo. It's dead on. I seriously don't understand how that can be the case, unless the new trucks have a way of knowing the new tire size and recalculating? What am I missing!

 

Probably because you increased width not height

 

Before and after views...not huge tires but world of difference in looks IMO

 

They should be different in height. New are 33.5 vs stock 32.5

 

check here

 

That’s not how metric sizes work. Increasing the width, 265 to 285 in this case (width in mm of the tire), while keeping the same aspect ratio (ratio if width to sidewall height), 60 in this case, increases the overall diameter of the tire. The diameter calculation for the stock tire is 265mm*.60*2/(25.4 mm/in) +20 in = 32.5 in. Similar logic follows for the diameter of the new tire.

In this case, the speed being nearly the same is a result in the small change in tire diameter. For what it’s worth, going to 35s on my 2.5 gen results in ~3 mph difference at 75 mph. The speed difference generally increases as speed increased due to gear ratios within the transmission.

 

I did not know that

 

Someone posted that you can't calibrate the odometer in these since it is set via GPS. No idea if that is true, but that would explain speed reading.

 

That would totally explain it. Being 1 inch taller tires I should be a couple MPH off at 65-70 but its dead on.

 

Same for me when I made the change to 285/60. It’s 1-2 mph off over 75, nothing for me to worry about

 

OP - This is a KNOWN issue that Toyota/Lexus speedometer is SLOWER than the actual speed (about 3%) so at 285/60/20 you are dead on. I have tested this on 4 Toy/Lex and they are behaving the same way.