New tires killed my milage..:(
 

Just replaced my BFG Rugged Trails with some Nitto Dura Grapplers...same size "technically" 265/70/17 and the milage dropped almost 2 mpg. The Nitto's stand about an inch and a half taller. I'm pretty bummed....I thought with the new tires...not cupped or anything..the milage would increase. I had read the Dura Grapplers were delivering decent milage but I got barely over 15mpg averaging 73mph for a tank. Any idea's???

Be sure to adjust for the difference when you calculate the mileage.

Something sounds wrong. If you stayed with the same size you should have not lost any. The Duras are only slightly more aggressive than your original Rugged trails. If you had gone to an aggressive mud tire I could see losing a little. The size difference (1 1/2 total) is 3/4" from center and should have very little affect.

I went from 265 rugged trails to 285 Duras and did not lose any mileage.

Duras are a highway tread. You either didn't adjust your speedo or got a load of winter fuel.

They are both 265/70/17's why would I have to adjust the speedo?...:conf:

Regardless of what the tire numbers say, If they are physically larger you will lose true MPG's. The larger tires are traveling farther with each rotation so they read less miles traveled. 1 1/2" may not sound like a lot but if you do the math you will find it really adds up. Also your speedo is off by 2 or 3 mph.

Anyone know of a formula or calculator I can use?....also can the speedo be recalculated?....Thanks

Your best bet is probably gonna be to get a GPS and compare the mph numbers between it and your speedo.

You said they stand an inch and a half taller !!! Look up circumference in the dictionary.... And you based this on one tank of fuel?

Never mind...
Good luck.

Stock BFGs are 661 revs per mile. 265/70 Dura Grapplers are 654 revs per mile. Not really much of a difference at all.

I have 285/75 Dura Grapplers and my mileage is pretty close to what I got with the stockers...

Do a search for tire size calculator ... I think a Miata forum has one that will gice you the % difference. This will allow you to figure in your actual miles driven difference that you can then add to the total of your miles. This will increase your calculated MPG figure. Also make sure that each time you fill up you do so until you see fuel in your filler neck...not foam....fuel!

Are you really wound up that tight?...Jeezz...... I based this on a 800 mile trip...the GPS reads the same as the speedo. Never mind...and thanks for the good luck.

Thank you!!

Rolling resistance… assumedly your old BFGs were worn down in their remaining tread. So diameter decreases, resistance against the road decreases, add to that BFGs use a harder rubber compound, which again result in less rolling resistance. Same reason many race cars run slicks. Your new tires (new rubber) changed all these variables and you get more contact & adhesion with the road = less MPG - JMO.

That was my first thought....and I agree. I guess what was making me think was that in quite a few posts I had read that users had an increase in mpg when switching from the BFG's to the Dura Grapplers...live and learn I guess. As far as slicks go....my mpg is far worse in my other ride...[laugh]

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