I just changed my tires from the stock 275/65/R18 to 275/70/R18s. Do you think that will throw the speedo off by muc Anyone know from personal experience?

 

It will be about 3mph behind. It will also through off all of your fuel readings and things like that.

 

According to this:

http://www.1010tires.com/Tools/Tire-...5R18/275-70R18

Your speedometer will read 3.27% too slow. That means when your speedometer reads 100, you're actually doing 103.27.

Anywhere up to that you'll be around 2mph faster than what the speedometer says you're doing.

 

At 65 mph on the speedometer you will be traveling 67.1 mph

 

Thanks for the info guys.

 

If you find it affects transmission your shift points and speedometer, you can always use the Hypertech Speedometer Re Calibrator, does the trick. I used on my F-150 and worked fine, once I determined correct inflated tire diameter. Checked speed with Speed Box GPS App.