Bigger tires more hwy mpg?

[Rockcrawlindude]

depending on how you look at the physics, it could be argued that a larger diameter tire could give you better highway mileage by effectively raising (lower numerically) your final drive ratio. Every revolution of the tire you travel further saving you rpm at a given speed

But, an important thing to remember about physics class is all the things that are ignored like rolling resistance, air resistance, etc. hell, i once asked a physics professor “if friction is independent of surface area, then why do drag cars have super fat tires?” She had to reach out to colleagues and they didn’t have an answer. In physics class this is an assumed rule when you calculate a block sliding down a ramp but all of us know that contact patch matters in real life

In the real world, where we live, everybody who is being completely honest will tell you larger tires hurt mileage. It takes more to get them going and you downshift more frequently and that cancels out the hundred RPM cruise savings.

If you want bigger tires definitely get them. Couple percent lost mpg is nothing compared to a good looking truck with meaty rubbers

 

[Great White North Eh]

I am enjoying reading some of the responses from people that have no clue but decided to answer anyway.

Ya as soon as I read the title of this thread I knew it was going to end in tears and cinders.

 

[BikePilot]

These engines are actually pretty efficient even at higher rpms. If you look at all the 4.10 vs 3.73 posts on mpg there's not much difference. Imo just let it rev. There's not enough milage improvement to be had by messing around with effective gearing to matter. Gearing does make a huge difference in towing performance though.

Fwiw I run 37s and 4.10s on my SRW 3500 and love it. For my purposes the combo just feels right.

 

[Docwagon1776]

But, an important thing to remember about physics class is all the things that are ignored like rolling resistance, air resistance, etc. hell, i once asked a physics professor “if friction is independent of surface area, then why do drag cars have super fat tires?” She had to reach out to colleagues and they didn’t have an answer. In physics class this is an assumed rule when you calculate a block sliding down a ramp but all of us know that contact patch matters in real life

A physics teacher didn't grasp that a given force spread over a larger area is less abusive than the same force spread over a smaller area? She was reading from a book she didn't understand. A super skinny tire would have the same friction, but it would be destroyed because the energy would be concentrated on a smaller area and the material couldn't handle that 'energy dump' without being destroyed. The fat tire can get better traction because the energy is spread out over a larger surface and it isn't instantly turned into a liquid due to heat concentration...so deals with the same friction in a manner better suited to accomplish work.

Inexact analogy, but more intuitive to understand. Let's say I'm going to hit you in the stomach with 50 ft/lbs of force. Would you rather I do that with a knitting needle or a manhole cover? Instinctively you know that the force concentrated on a knitting needle means metal in your guts but a manhole cover will be a tap with zero risk of penetrating trauma. Why? Same energy applied over a larger area.

 

[Dave01]

I am enjoying reading some of the responses from people that have no clue but decided to answer anyway.

I'm running 42" tires on my 6.4 and getting 32 mpg on the highway. Are you saying I have no clue? I hand calculated it on a 3 mile downhill stretch between a Shell station and a Sinclair station.

(just kidding )

 

[A6t8vw]

Thanks for all the reply’s guys, I knew this thread would be semi provoking and what I expected.
I went ahead and installed Toyo AT3 in 255/80s on the stock steel’s. I only have 250 miles on the truck so I don’t have a good sense of a before /after . It did drop RPMs slightly at hwy speed . From 4.1 to an effective ratio of about 3.9 with these 33.1” tires.
Looks a lot better that’s for sure. I’ll be headed out to the desert next week and I’ll find out how they do in sandy roads finding a camp spot.

Cheers!

 

[phatboy64]

Definitely look better Then stock!

 

[ClawSS]

Those look good. Pretty good amt. of weight, tho.

 

[gimmie11s]

He said on the highway fellas....at a constant speed....a taller tire means lower rpms....yes your mileage will improve ....all you'd be doing is effectively lowering your gear ratios to around 3.9 which these trucks also come with 3.73's...and we all know 3.73 gets better mpg's than 4.10's....so yes...it'll improve....slightly....it's not going to be a huge increase....iirc when I went front the stock 32's on my HO drw with 4.10's up to 33's I picked up a half a mile....if you go to 34's...some where around 1 mile a gallon is where I'd guess you'll be....

False largely due to the added weight and width of your new, larger tires.

If, theoretically, you could find a taller tire that was the exact same weight as your OEM tire and the exact same width -- then yes, you'd realize a gain on the highway.

 

[gimmie11s]

Thanks for all the reply’s guys, I knew this thread would be semi provoking and what I expected.
I went ahead and installed Toyo AT3 in 255/80s on the stock steel’s. I only have 250 miles on the truck so I don’t have a good sense of a before /after . It did drop RPMs slightly at hwy speed . From 4.1 to an effective ratio of about 3.9 with these 33.1” tires.
Looks a lot better that’s for sure. I’ll be headed out to the desert next week and I’ll find out how they do in sandy roads finding a camp spot.

Cheers!

View attachment 64880

Looks great!

 

[2001WS6]

Have any more pics with the new tires?

 

[Dave01]

Just picked up a 23 3500 HO dually with the 4.10 gearing, I'm considering 255/80R17 (33") or 255/85 (34") "least aggressive tread" tires on the stock wheels.

Not sure Toyo AT3's qualify as "least aggressive tread" tires . Don't get me wrong, great choice, they look terrific, and me personally I wouldn't put highway tread tires on unless I was only on the road, only running in decent weather.

 

[IndyRamMega]

False largely due to the added weight and width of your new, larger tires.

If, theoretically, you could find a taller tire that was the exact same weight as your OEM tire and the exact same width -- then yes, you'd realize a gain on the highway.

Happened to me....they are barely wider due to the dually situation and we're basically just taller....it's not like there's a weight difference because I went to 37's from 32's....you guys and your 17 different ways to calculate this are hilarious.....I stand by my previous statement....if you don't like it....oh well...

 

[Dave01]

I don't think this is off topic, if so I apologize in advance ...

We all care about mpg, but then again most of us sort of don't care at all because most of us don't change driving habits to increase mpg. Here's what I mean.

If you drive 100,000 miles with a 6.4 and let's figure gas at $3.70/gallon, and let's not get into towing miles, just for grins figure all miles the same
at 13 mpg you'll spend $28,461 on gas
at 14 mpg you'll spend $26,428 on gas
Savings is $2,033 if you achieve the 1 mpg higher fuel economy

How many of us will drive in a way to achieve that? Gaining that 1 mpg is pretty easy, just keep your foot light from a stop, anticipate stopping ahead of time, drive 10 mph lower speed on the highway and you'll get it. I know there's no way I'm driving that way, even if I can save 2 thousand bucks over 100,000 miles (which is under 4 years for me). I don't think many others will do so either.

Still fun to discuss mpg, and I'm interested enough to watch mileage when highway driving or towing, but in truth I bought my truck, really happy with it, I drive it how I drive it, way too late to decide I want more fuel efficiency.

 

[ClawSS]

I love all the maths. I got mine to drive for the looks. Never gonna pull anything or even haul anything more than my 37" spare and some crap in the Ramboxes.
My truck gets the best $/mi than any of my others in the fleet. I drive the piss out of it.

'79 square body gets 8mpg
'93 3500 SCLB SRW 454ci TBI gets 10mpg
'09 cammed SRT 300 6.1 gets 12mpg on 93oct.
'10 cammed Camaro SS 6.2 gets 12mpg on 93oct.
'15 cammed Sierra 1500 5.3 gets 8mpg on E85 or 14 on 93oct.
'22 Ram 2500 MegaHemi on 37's gets 13mpg on 87oct.

 

[Blythkd1]

I don't think this is off topic, if so I apologize in advance ...

We all care about mpg, but then again most of us sort of don't care at all because most of us don't change driving habits to increase mpg. Here's what I mean.

If you drive 100,000 miles with a 6.4 and let's figure gas at $3.70/gallon, and let's not get into towing miles, just for grins figure all miles the same
at 13 mpg you'll spend $28,461 on gas
at 14 mpg you'll spend $26,428 on gas
Savings is $2,033 if you achieve the 1 mpg higher fuel economy

How many of us will drive in a way to achieve that? Gaining that 1 mpg is pretty easy, just keep your foot light from a stop, anticipate stopping ahead of time, drive 10 mph lower speed on the highway and you'll get it. I know there's no way I'm driving that way, even if I can save 2 thousand bucks over 100,000 miles (which is under 4 years for me). I don't think many others will do so either.

Still fun to discuss mpg, and I'm interested enough to watch mileage when highway driving or towing, but in truth I bought my truck, really happy with it, I drive it how I drive it, way too late to decide I want more fuel efficiency.

I definitely get what you're saying and agree with you for the most part. A few folks do worry about mileage though, probably mostly guys that are making a living with their truck. Over the years as I was hauling, I did lots of things trying to maximize mileage, and profit, including rolling lightly into the throttle and slowing down, especially when towing.

Don't get me wrong. If I was running with someone else and they wanted to run 80mph back from Arizona, I ran 80mph back from Arizona. It's just that my normal habits were to watch my fuel mileage and try to maximize profits.

 

[Great White North Eh]

I love all the maths. I got mine to drive for the looks. Never gonna pull anything or even haul anything more than my 37" spare and some crap in the Ramboxes.
My truck gets the best $/mi than any of my others in the fleet. I drive the piss out of it.

'79 square body gets 8mpg
'93 3500 SCLB SRW 454ci TBI gets 10mpg
'09 cammed SRT 300 6.1 gets 12mpg on 93oct.
'10 cammed Camaro SS 6.2 gets 12mpg on 93oct.
'15 cammed Sierra 1500 5.3 gets 8mpg on E85 or 14 on 93oct.
'22 Ram 2500 MegaHemi on 37's gets 13mpg on 87oct.

Way to go man…you just gave Greta an ulcer when she read that list!

 

[gimmie11s]

Happened to me....they are barely wider due to the dually situation and we're basically just taller....it's not like there's a weight difference because I went to 37's from 32's....you guys and your 17 different ways to calculate this are hilarious.....I stand by my previous statement....if you don't like it....oh well...

There is absolutely a weight difference. Youre not serious, are you? Stock tires to 37's???

I can promise you, you are not getting better milage.

 

[Rockcrawlindude]

I don't think this is off topic, if so I apologize in advance ...

We all care about mpg, but then again most of us sort of don't care at all because most of us don't change driving habits to increase mpg. Here's what I mean.

If you drive 100,000 miles with a 6.4 and let's figure gas at $3.70/gallon, and let's not get into towing miles, just for grins figure all miles the same
at 13 mpg you'll spend $28,461 on gas
at 14 mpg you'll spend $26,428 on gas
Savings is $2,033 if you achieve the 1 mpg higher fuel economy

How many of us will drive in a way to achieve that? Gaining that 1 mpg is pretty easy, just keep your foot light from a stop, anticipate stopping ahead of time, drive 10 mph lower speed on the highway and you'll get it. I know there's no way I'm driving that way, even if I can save 2 thousand bucks over 100,000 miles (which is under 4 years for me). I don't think many others will do so either.

Still fun to discuss mpg, and I'm interested enough to watch mileage when highway driving or towing, but in truth I bought my truck, really happy with it, I drive it how I drive it, way too late to decide I want more fuel efficiency.

Gas is $2.69 here but I get what you’re saying. Also it would take me like 15 years to get to 100k miles on the ram

 

[Docwagon1776]

False largely due to the added weight and width of your new, larger tires.

If, theoretically, you could find a taller tire that was the exact same weight as your OEM tire and the exact same width -- then yes, you'd realize a gain on the highway.

Not in reality. At the end of the day, the only thing that matters is reducing the overall energy requirements. Taller tires are still at a mechanical disadvantage due to the longer lever of the increased radius. That's why people need to regear to move them. If they were more efficient you'd accelerate faster and maintain speed *easier* with larger tires, which obviously you don't. Even ignoring minor factors like sidewall flex and increased wind resistance, if no other factors change the shorter tire will get better fuel economy. Now, if you go to a taller tire with much stiffer sidewalls and lower rolling resistance, THOSE variables may make up for the others and you end up with better fuel economy. Going from a 33" mud tire to a 35" road tire, for example. Cleatus lore may confuse that with getting better fuel economy due to the taller tire, but it's not what happened.