Hey guys. I have ditched my edge tuner so now I am trying to figure out my mileage. I went from 255 70 17 to 265 70 18. I just want to know when I have gone 100 miles according to my truck what have I really gone. All the tire calculators only tell me my speed difference and I am not sure what math I need to do.

Here is a tire calculator: http://www.1010tires.com/TireSizeCalculator.asp

 

mileage is the same proportion as the speed difference

in other words, if the truck is actually traveling 60 mph, and the speedo says 57. then when your trip odometer says 57, you actually traveled 60 miles

or go by percentage., your odometer is 6% lower than actuall ( as an example)

Ramb

 

Your 18s are 4.98 % slower.

If you drove 100 miles with the 17s, you would have covered 95.02 miles with the 18s.

100 miles with the 18s would = 104.98 miles on the 17s.

 

I just changed the 275-65-18s on my 04 Lariat to 285-60-18s and used this tool to work it out

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

 

I feel retarded. LOL So if my speedometer says I traveled 300 miles how do iI figure what I actually traveled with my 18's. Would the answer be I traveled roughly 315?

 

Yep, you got it. What ever mileage your odo says you travel, multiply by 1.05 and that is the "true" mileage - (assuming the odo was correct with the stock 17's) - which may be a bit of a stretch based on what I have seen.

Anyway 300 x 1.05 = 315 so you are right on.

 

So bigger tires will save mileage on the truck odo. Another advantage to bigger skins.