Hey guys. I didn't search through the whole site see if anyone has talked about his yet, so forgive me if I'm repeating someone. Just want to let you all in on the information I've come up with today.

I recently put 315's (35's) on my H3 with the 3.7l and leveled it out to 23 inches. I've seen some of you asking about how that might affect the mileage or driving quality. I can say that the driving quality isn't noticeably different from stock, so long as you get your camber angles readjusted at the alignment shop. You might notice that the wider tires will grab the grooves in the road a bit, but that's the way it is with any wider tires.

As for gas mileage differences, there appears to be a big difference AT FIRST. When i first swapped out the tires, I was averaging 12.6 mpg. BUT that is before it occurred to me today that my trip odometer information was inaccurate because the new tires cover more distance than the old ones.

I'll explain: My '07 H3 came with 265/75R16 tires which are 31.6 inches tall and have a circumference off 99.4 inches. The new 315/75R16 tires are 34.6 inches tall and have a circumference of 108.7 inches. This means that for every one full rotation of the tire I am covering 9.3 inches more than the stock tire.

The factory speedometer and odometer were calibrated to the specifications of the factory tires. As most of you know the bigger tires mean that you have to have your speedo recalibrated, but what I have never seen discussed is how this will offset your MPG calculation. So I did some math...

One mile = 5280 ft.
A 31.6 inch tire (99.4" cir) will rotate 637 times per mile
A 34.6 inch tire (108.7" cir) will rotate 583 times per mile
If the speedometer reads 55mph, with 35's I am actually doing 60 mph (conveniently exactly 5mph difference all the time).

This means that if the odometer says I've driven 91.47 miles, I've actually driven 100 miles. This equates to a 9.33% differential from what the odometer reads.

To put it in plain English: if I go to the gas station to fill up and I want to figure MPG, this is what I do to get it right:

Trip odometer reads: 250 miles
250 X 0.09333 = 23.3325 (real extra miles to be added)
250 + 23.3325 = 273.3325 (actual distance traveled)

273.33 / Gallons used = correct MPG.


*this also means that if I never get the speedo or odometer recalibrated then I will end up slightly retaining resale value: I can drive 109,333 miles and the odometer will only show 100k

 

Get more out of your bumper to bumper coverage!

 

very good point, didn't think about that!

 

supsam86 yeah I took that into account w/ my mpgs

Ive added alot of goodies to my rig, and I dont think a single one has helped my mpgs except for the CAI by airdoc lol...

 

Great news for a lease car...Thanks!