Hello everyone.
I recently got new tires for my truck and ended up getting a different size from the original. The tires I wanted didn't come in the same same size or a comparable size that had the same diameter. That and I couldn't find a good 14" tire that was good in the snow and ice. I drive 120+ miles a day and going off the road in the winter is a big concern. Having to pay a tow and repair bill eats up any fuel savings a LRR tire or lighter rims might gain me.
I know the speedometer will be off by about 3mph and I'm sure the odometer will also be off. I am having trouble with the math in trying to figure out if the new tires are going to hurt my FE or not. I know I can put 10 gallons in the tank and drive 300 miles for a 30mpg average. This is fairly consistent as I drive the same route everyday. The new tires are heavier so I would expect some FE loss, but with the larger diameter it may be offset from the final drive being slightly taller?
Here are the particulars on the old (22/70/14) and new (215/75/15) tires.
The old tires are about 764 rev/mile and the new are about 728 rev/mile and the old diameter is 26.4" and the new is 27.7" (about 5% larger)
The question is.....with the odometer being slightly off because of the larger tires......if I put 10 gallons in the tank approximately how many miles (on the odometer) should be equal to the 300 I used to see? The simple answer seems to be 5% less or 285 miles, but is it really that simple? I just want to see if I'm still getting about the same FE with the new tires or just how much I have lost. I know this isn't the best time to try and figure out exact FE numbers as it's winter and I'm burning winter blend fuel, but I have to start somewhere.
Thanks for any help.