Fuel mileage vs. tire size

[jmoffatt]

I'm in the market for new tires still running stock size, I have a H3X Alpha so the wheels are 18 inch as opposed to the standard 16 inch, tires are 265 65 18. I've been reading a posting on a H3 facebook group where a guy ask everyone's mileage on a tank of gas, The guys with 35's are reporting anywhere from 25 to 50 miles less on a tank of gas than the standards, Question: how much fuel mileage difference will there be between 33 inch tires and 35 inch tires?
I'm definitely going up in size but just not sure if 35's are the way to go.

 

[08H3]

It really doesn't make much difference. I measured it once, but honestly don't remember the numbers. I think most people forget that unless you have your speedo recalibrated, you're actually travelling more miles on 35s than it will show.

 

[guruerror]

On my SUT I dropped from 12.0 to 11.8 when I went from the stock 35 BFG ATs to 37 BFG MTs...and that's with the speed-o re-calibrated.

The biggest difference was felt in performance...heavier tire = more effort to spin, and the size difference changed my power band by altering my final drive ratio. Re-gearing from 4.10 to 4.56 fixed that issue though.

 

[Happy Hummer]

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
265/65-18 6.8in 15.8in 31.6in 99.2in 639 0.0%
315/70-18 8.7in 17.7in 35.4in 111.1in 570 12.0%




Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
265/65-18 6.8in 15.8in 31.6in 99.2in 639 0.0%
325/70-18 9.0in 18.0in 35.9in 112.8in 562 13.8%


Above you'll see some basic information.
First 265/65-18 and 315/70-18 just samples....
Second 265/65-18 and 325/70-18

You can see the difference in the above valuation.:wink::emb::thumbs:

 

[alrock]

Larger tires are significantly heavier and take a measurable amount more energy to start (and to stop). I would estimate for myself that I lost about 1 mpg going to 35s from 33s. Add that 1 mpg to the loss from leveling and from the roof rack, and I'm about 3 mpg net loss vs. when it was stock.

 

[jmoffatt]

Happy Hummer ​

That hurt my head, lol

 

[jmoffatt]

Thanks guys, I think I'm going with the 33's

 

[08H3]

If I remember I'll check mileage when I switch over to snow tires (32s) and post the difference.

 

[cgalpha08]

Depends on now far you drive.

I just put on cooper MTPs, they are a 35 inch mud tire, weighing in at 63 pounds, one of the lighter M/Ts that I could find, compare that to the toyos that were 88 pounds a piece lol.

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[humvee]

Thats good advice, different brands have varying weights, Coopers and BF’s new all terrains are lighter than other 35s out there. Same applies for aftermarket wheels, some are much heavier than stock and will really push your truck.

The strangest thing is that my i5 on stock wheels spent more gas than my current v8 on 35s setup


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[Traxx]

If mileage is a concern then I would just opt for the oem 16" wheels at 21 lbs with 33's. It's kind of the happy medium for performance, cost, and looks. You take a significant hit with 35's in mpg and performance loss.

 

[alrock]

Good point on the tire weight. I've tried to stay closer to 60 lbs each tire vs the 80 like on the Toyos. But it also has to do with moving more weight farther outwards, requiring more torque to move the tires.

 

[JPaul]

Thanks guys, I think I'm going with the 33's

The pic in your sig is massive, it takes up all of my 24" monitor! Might want to shrink that a bit.

 

[humvee]

But it also has to do with moving more weight farther outwards, requiring more torque to move the tires.

Thats very true, Anyone has the math for this sort of thing?

Over here, they use desert tires called balloons, barely any tread on them, super lightweight, they look like balloons, zero grip, but plenty of wheel spin. Usually made in the UAE.

The locals drive them well, and can do wonders with them on the dunes, but they’re no match to AT tires when it comes to sticky situations.
And on pavement, if you park for longer than an hour, you get a flat spot that causes vibration, until it smoothens out after driving a few miles.

Their rounded profile makes it easy for them to drive their trucks on two wheels. I’m sure ya’ll are familiar with this street “sport” from youtube?

Anyway sorry for hijacking the thread.

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[4speedfunk]

I personally don’t think tire weight difference has much to do with mileage drop. I think it has more to do with the ratio change and tread design. I know swapping from BFG-MTs to BFG-ATs (same size) will get you one mpg improvement. And it will also let you hear the stereo!
The H3 seems to have a very narrow “tune range” (especially the 5-cly), so even minor changes in tire diameter can put the drivetrain out of sync with the factory tune. FYI, I run 37” BFG-MTs, 38psi, 5.13 gears, and ZERO aerodynamics. I have a PCMofNC tune and get 12.5 mpg at 70mph. I consider this outstanding compared to other similar vehicles. In fact, it’s hard to find a vehicle to compare it to. Most vehicles built to this level have numerous systems disabled, or are dedicated (trailer) off-roaders.

Regardless...any mention of mpg and Hummer in the same conversation is total madness. Buy the tire you want. Tune the puter to match. Drive it.


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[amrg]

Just wanted to add that one of the reasons you get less mileage is the fact that with bigger tires you stay longer in that rpm range where the torque converter is constantly slipping. This affects mileage and is the reason why with bigger tires the trans builds up more heat. The TC keeps slipping and generates more heat reducing efficiency/mileage.

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