Today is the moment of truth. I can get a nice set of 265 Michellen's for under $300 by trading in the 245 BFG's on my new truck, under 450 miles. The most important quality in a tire for me is saftey and durability, combined with fuel economy.

If I decide to go with the 265's will I have to recalibrate the odometer to get accurate miles and DIC fuel economy? How will my hand calculated fuel economy change, if any, by moving to 265 tires? Any suggestions are appreciated.

That's exactly what I did when I first bought my truck. Traded in the stock 245s for Michelin 265s. The 265s are ~3.85% larger in diameter than your stock tires, but I found with my GPS that with speedometer error factored in, my speedometer (& odometer as well) was reading about 4% too low. So to get your true MPG, add 4% to your miles driven, divided by gallons used.

My DIC was never very close to begin with, but as always, your results may vary.

Did the same here for my last two trucks - drove straight from the dealer to the tire shop. But luckily you have the BFG's which will net you more money - I have the Bridgestones and no one would give me more than $75 per tire. BTW don't forget your spare - Suprising how some people do :eek: !

Ditto on adding the 4%. It's become simple habit now to take mileage x 1.04 / gal used. I have to say though, I hand calc. every tank, and usually it is only different than the DIC by 0.5 MPG (lower). Anyway, the 4% does very little to your speedo - 2mph @ 50, and the benefit of not recalibrating is that you are actually extending your warranty albeit by just a little bit!

You will achieve better MPG with 245s, Due to less tread patch contact. It would be minor tho.

good day

That's not entirely true. Because the added surface contact of the 265 tire can equal, or even offset the larger overall diameter of the tire. It all depends on what kind of 265 tire it is.

I, myself went from the crappy bridgestones to General Grabbers. Now, that's more of a rock climber than highway tire. Great in the winter. But I do get less mpg, but not because of the wider tire, but because of it's way higher rolling resistance.

A very low rolling resistance, say, Michelin 265/75 tire on the stock 16's will get better mpg than the stock bridgestones...given that they're both hand calculated to attain correct mileage figures with the bigger tires.

I have a GPSr in my truck and did some testing in different trucks. Stock, the truck seem to be about 1% off the actual speed at about 50-60mph. It is off more the faster you go. And a 265 tire over the 245 from factory will be (as mentioned above) 3.85% bigger. All in all that would make the actual speed 4.85% greater with 265's over speedometer reading.

Now, those nubmers are nothing more than theoratical values. In real-life the offset can be as little as 2% or less. Variables can be the tread left on the tires, among other little things. Around 60-70mph, on my truck, the GPSr will give me a speed of about 2mph more than what speedo says. With the speedo being off almost 1mph at that speed, the difference is close to 3mph, or maybe more like 2.5mph.

Now, when I max it out, it doesn't just go 98mph anymore (actual speed would be more like 96mph), but an actual speed of 100mph. Feels good to be in the 3-digits :cool:!

Good discussion. Bullydog, good point on the rolling resistance of tires. Tires that provide great fuel mileage normally don't provide much in the way of traction due to their low rolling resistance. Conversely tires that grip the road or have agressive tread patterns tend to hug the road tighter and yield less mpg's. You can actually hear high traction tires gripping the road while you are driving. Totally cool!

Per Tirerack.com the width of the tires can adversely affect mpg's as well. Putting a wider footprint traction tire on a vehicle can result in poorer fuel economy than with a narrower footprint traction tire. Aerodynamics stuff or something like that, way over my head. However, this has been my personal experience when changing to wider tires on my vehicles.

JJ is big on safety and will opt for traction everytime, fuel economy can come in 2nd or 3rd. Later. JJ