Larger circumference tires better mileage?

[joe_julie81]

I am wondering if this could be true. I ordered my dually with the 4.10 rear axle for more power pulling the heavy 5th wheel. At 70 mph I'm over 2000rpm. Now that I'm getting a TC I don't need that much torque. But I don't want to change the rest axle. So would bigger circumference tires get better mpg at top end? I have 235/R80/17 now. If the answer is yes, what size would be recommended?

[Ski_Pro_3]

Grit dog wrote:

skipro3 wrote:

Grit dog wrote:
^Sure, gear ratio change is a solution, an expensive one. So is driving slower or putting up with 2700rpms down the freeway.
Without tearing the truck apart, taller tires satisfy the request for lower rpms and are almost a "free" upgrade. (In that if you need tires, taller cost only marginally more than shorter)
That was my point. My strong preference would be easy vs difficult or costly to arrive at the same solution.

I'd challenge that gear swap is any more expensive than a tire size swap. 19.5" tires and wheels are NOT cheap. I'd have to say I spent about $3,000 for my 19.5 set up.
Toyo M608Z are $500 each plus.
Rickson steel wheels are about $300 each plus.
That's $3,200 plus any extra charges like tax, mounting, stems, etc.

I didn’t say anything about 19.5s, but go ahead and do a gear swap......I could spend 5grand on wheels alone if I tried. That wasn’t the point.
Although I’m probably talking to a wall, in general here. Bet most of the members in this forum don’t run out of gears with 4.10s and pizza cutters. Hard to at 58mph.

OP has a dually, I forgot.

[Bedlam]

If you do mostly highway, taller tires may help your mileage. If you drive winding back roads, those same tires will give you worse mileage than shorter ones.

[Ski_Pro_3]

Kayteg1 wrote:

skipro3 wrote:


I'd challenge that gear swap is any more expensive than a tire size swap. 19.5" tires and wheels are NOT cheap. I'd have to say I spent about $3,000 for my 19.5 set up.
Toyo M608Z are $500 each plus.
Rickson steel wheels are about $300 each plus.
That's $3,200 plus any extra charges like tax, mounting, stems, etc.

and assuming you threw away good wheels with good tires?

Just about. Resale market for used truck tires/wheels is pretty low. $50 each. Which is why I said I spent about $3K for what amounted to about $3.2K

[Grit_dog]

skipro3 wrote:

Grit dog wrote:
^Sure, gear ratio change is a solution, an expensive one. So is driving slower or putting up with 2700rpms down the freeway.
Without tearing the truck apart, taller tires satisfy the request for lower rpms and are almost a "free" upgrade. (In that if you need tires, taller cost only marginally more than shorter)
That was my point. My strong preference would be easy vs difficult or costly to arrive at the same solution.

I'd challenge that gear swap is any more expensive than a tire size swap. 19.5" tires and wheels are NOT cheap. I'd have to say I spent about $3,000 for my 19.5 set up.
Toyo M608Z are $500 each plus.
Rickson steel wheels are about $300 each plus.
That's $3,200 plus any extra charges like tax, mounting, stems, etc.

I didn’t say anything about 19.5s, but go ahead and do a gear swap......I could spend 5grand on wheels alone if I tried. That wasn’t the point.
Although I’m probably talking to a wall, in general here. Bet most of the members in this forum don’t run out of gears with 4.10s and pizza cutters. Hard to at 58mph.

[Kayteg1]

skipro3 wrote:


I'd challenge that gear swap is any more expensive than a tire size swap. 19.5" tires and wheels are NOT cheap. I'd have to say I spent about $3,000 for my 19.5 set up.
Toyo M608Z are $500 each plus.
Rickson steel wheels are about $300 each plus.
That's $3,200 plus any extra charges like tax, mounting, stems, etc.

and assuming you threw away good wheels with good tires?

[Ski_Pro_3]

Grit dog wrote:
^Sure, gear ratio change is a solution, an expensive one. So is driving slower or putting up with 2700rpms down the freeway.
Without tearing the truck apart, taller tires satisfy the request for lower rpms and are almost a "free" upgrade. (In that if you need tires, taller cost only marginally more than shorter)
That was my point. My strong preference would be easy vs difficult or costly to arrive at the same solution.

I'd challenge that gear swap is any more expensive than a tire size swap. 19.5" tires and wheels are NOT cheap. I'd have to say I spent about $3,000 for my 19.5 set up.
Toyo M608Z are $500 each plus.
Rickson steel wheels are about $300 each plus.
That's $3,200 plus any extra charges like tax, mounting, stems, etc.

[deltabravo]

joe&julie81 wrote:
So would bigger circumference tires get better mpg at top end? I have 235/R80/17 now.

Slight advantage. Same as having a higher axle gearing ratio.

Going to bigger tires throws aff the speedometer, so you'd have to get that re calibrated to maintain its accuracy

[Kayteg1]

OH, I am sorry. With all the adds popping on the site, I missed there is more than 1 page
I can only conclude how nice is to have motor running at low rpm.
My 2017 F350 cruise at 1400 rpm.
The first truck I can listen to a radio in, without turning the volume very high.

[jimh406]

Kayteg1 wrote:
7 years and the guy never come back to report final result.
I just wasted time reading it.

I guess you missed it.

Well, I have made a few trips, unloaded, and out on the freeway at 70-75 mph I would average about 18-19 mpg. Before I would never get over 17, usually 16.5 or something. I was always in a real hurry, so driving for MPG was not a priority. If a guy set the cruise at 70, I bet he would get better than I got. I was racing the clock.

So it definitely did improve the mpg, but also it is nice to not be revving the motor so crazy. I just drives much nicer, more relaxed.

I haven't put many miles on, pretty busy in the summer here on the farm. I think when I do need new tires someday, I'll probably go up a size or two to even further lower my rpms. I know I was trying to avoid larger tires when I started this thread, and I still am, so we'll see.

I would like to make a long trip on a highway, 60 mph, and see what kind of mileage I get then, but I don't know when that will ever happen.

[Kayteg1]

jimh425 wrote:


For those who might want to read more about someone doing a swap on a '06 from 3.73 to 3.42, here's a thread. http://www.cumminsforum.com/forum/3rd-gen-powertrain/385747-3-42-gear-swap-questions.html Obviously cheaper if you only did the rear and was a 2 wheel drive. The OP implied changing rear only in his first post.

7 years and the guy never come back to report final result.
I just wasted time reading it.

[jimh406]

Grit dog wrote:
My strong preference would be easy vs difficult or costly to arrive at the same solution.

Me too, but it isn't the "same" solution or same set of problems/fixes which was my point. In my case, I could go slightly higher, but the cost of 6 tires vs the gear change would be a few hundred dollars different. It also wouldn't change the gearing as much as a gear change.

For those who might want to read more about someone doing a swap on a '06 from 3.73 to 3.42, here's a thread. http://www.cumminsforum.com/forum/3rd-gen-powertrain/385747-3-42-gear-swap-questions.html Obviously cheaper if you only did the rear and was a 2 wheel drive. The OP implied changing rear only in his first post.

[Kayteg1]

Somewhere on this forum you should find old thread where 1 of the members, who drove dually in his bussines - decided to convert it to SRW as he had no more use for dually and did not want to buy new truck.
He did not go cheap and spend some serious money on new adapters and other stuff, but come back reporting huge mpg increase.
I could not believe such big difference was possible, as I don't complain about dually mpg (beside old GMC with 454 carburated engine making 5-6 mpg)
but the guy did not buy the "mpg is what it is" mentality and went for it, winning big in the result.
There is a risk in everything.

[Grit_dog]

^Sure, gear ratio change is a solution, an expensive one. So is driving slower or putting up with 2700rpms down the freeway.
Without tearing the truck apart, taller tires satisfy the request for lower rpms and are almost a "free" upgrade. (In that if you need tires, taller cost only marginally more than shorter)
That was my point. My strong preference would be easy vs difficult or costly to arrive at the same solution.

[jimh406]

Grit dog wrote:
Your truck with 4.10s NEEDS the tallest tires you can fit on it for your intended use and sane engine rpms at freeway speeds.

Or, just change the gears as has been noted and don't raise the center of gravity, have fitment including spare tire issues, and don't change your braking characteristics. BTW, I have only 2 pages. Must be your setting for how many posts to show per page.