larger tires

snarkee · February 17, 2005

i know that going from 265 70 17 to 285 70 17 is a bigger tire and my speedo is effected.....my question is...my speedo will read slower than what i am actually travelling, so in return, my odometer will read a little lower than it should if i had the stock tires???? ( i know it isnt much but just wanna make sure i understand this or not?)

thx

potz1999 · February 17, 2005

you got it bud.

silverado19 · February 18, 2005

Going from the 265 to the 285 should not really do anything to your speedo. 265 and 285 are the width of the tire. 285 is a bigger tire but only the widht, not the height. If you do nothing to effect the height which is the 70 in your example, or the rim size which I believe was the 17, your speedo should be the same.

snarkee · February 18, 2005

its still a taller tire because the 70 is 70 % of the width

so 70% of 285 is more than 70% of 265

or am i messed up?

Mule · February 18, 2005

Try this website:

http://www.miata.net/garage/tirecalc.html

Plug in the new and old tire sizes and it will give you the speedo difference.

snarkee · February 18, 2005

thanks!

99-2door · February 18, 2005

Going from the 265 to the 285 should not really do anything to your speedo. 265 and 285 are the width of the tire. 285 is a bigger tire but only the widht, not the height. If you do nothing to effect the height which is the 70 in your example, or the rim size which I believe was the 17, your speedo should be the same.

<{POST_SNAPBACK}>

WRONGO!

The 70 is an aspect ratio

70% of 285 is more than 70% of 265

Even though the 285s are slightly taller you speedo won't be affected much. Probably not even enough for you to bother changing anything. On my 99 the 285s actually made my speedo more accurate than with the stock tires.

Wingnut · February 18, 2005

Same thing with my '02. The speedo is correct now (with 285/75/r16's), dead on at 40-50-60-70 and 80 mph. I've also checked the odometer on long-hauls as well as short trips with the GPS. It's dead on as well.