Have 265/60/18s on my truck now. I'm thinking about going 265/70/18 in a Nitto Terra Grappler. Is it going to throw my speedo off a lot and how much should I expect to lose in MPG?

I am debating on those or 275/65/18... I want the aggressive look but I spend most of my time on the hwy and don't want to sacrifice too much.

 

Anyone?

 

It will throw the speedo off by about 3 mph. MPG depends on the weight of the tire.

 

Your stock tire is about 30.5".
265/75r18 is about 33.6".
275/65r18 is about 32".

Both will throw your speedometer/odometer off probably 3 to 7 mph at around 60-70 mph. For example, if your speedo reads 60, you will be doing between 63 to 67 mph (obviously the 7 +/- would be for the 265/75's)

It's best to also get a programmer to adjust for tires. The garage can also do it, but it's easy to justify getting a programmer for a little more performance.

Sticking with a standard P-metric shouldn't decrease your MPG because your aren't changing the weight by much. Going a little wider, like to the 275 will be minimal. That's only .4". I'd say you will see less than .5 MPG loss.