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Discussion Starter #1
So I bought my truck with 305/70R16s on the stock 16" rims. They are LRC or D and actually have less load capacity thatn the OEM 265/75 LRE tires. They are the standard BFGoodrich AT tires. They are nearing the end of their life and I tend to overload the truck and like long tows with an RV so I want good tires. I have 3.73 gears and an auto.

The choice I have is between 285/75 and 265/75 tires.

My question is, what mpg differences can I expect to gain by downsizing to 285 or 265 tires. I have chosen the General Grabber HTS all season highway tires with "Low Rolling Resistance".

Are the 265s the ideal mpg tire?
 

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From what I can tell, either 265-75x16 or 235-85x16 are the optimum sizes for MPG.

Hey! One MPG for just tires is a nice difference.

Be sure and recal your speedo.
 

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From what I can tell, either 265-75x16 or 235-85x16 are the optimum sizes for MPG.

Hey! One MPG for just tires is a nice difference.

Be sure and recal your speedo.
True, it does add up. But I didn't really pay attention to it because I'm not sure how much the odometer was thrown off by the bigger tires.
 

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My best mpg experiences have came from BFG rugged trails. Also, the wider tire will get worse mileage (the 285s) not going to affect it by much, but I'd say 1 mpg is a good estimate
 

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285's are the same height as your 305's just a little narrower. The 265 is narrower and smaller just fyi :D
 

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You should have no problem getting 1 or 2 more mpg with the 265's. I lost about 4 mpg when I went from 265/70/17 to 375/50/18. There is a ton more unsprung rotating weight.
 

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How much difference do you guys think there is in like an AT tire versus like a highway tire?
 

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Discussion Starter #9
Perfect info, it was what I had read elsewhere but more specific to our engines and gear ratios. The height difference (305/70 to 265/75) is very small, like less than an inch overall, but the width is 40 millimeters. I would like to bump up my RPMs for a given speed a bit as well but I don't expect the speedo difference to be much, like 4% or 2 mph at 50 mph.

1 mpg is a big deal for a big truck. It's between a 5 and 10 % improvement.

Easier on brakes, our unit bearing hubs, and the steering system as well.
 

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A green web site did an extensive test on tires and MPG for all size vehicles. At the time the BFG Long Trail 245s gave the lowest rolling resistance for pickup-sized vehicles. Don't know if that's still true or not.
 

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I went up to a 285 from a 265. Hand calculated I'm still getting the same mileage, no change. Since I didn't recalibrate the speedo, I figure I'm getting a little bit better now with the bigger tires.
 

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Discussion Starter #13
I went up to a 285 from a 265. Hand calculated I'm still getting the same mileage, no change. Since I didn't recalibrate the speedo, I figure I'm getting a little bit better now with the bigger tires.
Hmmm, that's the opposite of what Dave is saying. So is most of your driving highway? 285s look better, no doubt about it but not 5-10% of my fuel bill better.

I require LR E tires since I have been known to regularly use every bit of the rear axle rating.
 

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285 vs. 265 are just tire widths. You'll only need to recalibrate your speedo if you've also gone up in tire diameter.

I went from a RUGGED 325/60R18 to an AT/MT hybrid 295/65R18 so I kept my diameter pretty similar. I've noticed a 1.5 or so mpg increase in town. Didn't really get a good highway test on it yet.
 

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Bigger diameter tires have bigger rotational moment of inertia.

Once you correct your speedo, you'll see lower MPG.
 

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Hmmm, that's the opposite of what Dave is saying. So is most of your driving highway? 285s look better, no doubt about it but not 5-10% of my fuel bill better.

I require LR E tires since I have been known to regularly use every bit of the rear axle rating.
They are load range E. I'd say 85% or so highway driving, 30 mile one way trip, 3 stop signs, all county roads, with some city driving at the end.

I know that the 285 is the width, but going from a 265/75R16 to a 285/75R16 I increased both width and diameter.

Bigger diameter tires have bigger rotational moment of inertia.

Once you correct your speedo, you'll see lower MPG.
I don't get it. I understand what you are saying, but with my slightly larger tires, I am actually going faster than what the speedo says (slightly). Hand calculated, I am still getting identical mileage. So, since I am going faster and farther than what the speedo/odo is showing, it would seem my mileage went up (slightly). It could be that the slight increase in diameter has allowed me to keep the engine RPM's in the sweet spot for the speed/style I drive?

That's my thoughts.
 

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Staying with a singular tire size doesn't guarantee that it is the same tire size as other manufacturers. If you're really going to try and make your data accurate, it's important to look at the manufacturers individual specs for their tire, and that's probably easiest to see from "Rev's Per Mile".

As an example...this tire is 683 RPM's...
Michelin LTX M/S2

This tire, same "size" is 662...
Dunlop Grandtrek AT20

This tire, different "size" specification is 683...
Dunlop Grandtrek AT20
 

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If your tire size is larger your odometer should be reading lower.
 

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I don't get it. I understand what you are saying, but with my slightly larger tires, I am actually going faster than what the speedo says (slightly). Hand calculated, I am still getting identical mileage. So, since I am going faster and farther than what the speedo/odo is showing, it would seem my mileage went up (slightly). It could be that the slight increase in diameter has allowed me to keep the engine RPM's in the sweet spot for the speed/style I drive?

That's my thoughts.
If your tire size is larger your odometer should be reading lower.
That's what I said.
 

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Ah, misread.

Sorry!
 
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