As you go bigger with tires, how does it affect your mpg? I am thinking of making the switch from 265's to 33's or 35's and i want to how my mpg will differ. Thanks

 

The bigger tires are heavier and take more power to get up and rolling. Driving around town they'll hurt it just because of all the stopping and starting out, it's just a lot more tire to pull.

Now if you are driving down the interstate at a constant speed on pretty flat level ground, it can actually help mileage a little bit by lowering your RPM's....but with any kind of hills I wouldn't expect it.

It also depends on what type of tire you go with....the meaty tread with soft rubber is going to hurt mileage the most. With a 33" tire with a pretty mild tread meant for the highway I wouldn't expect TOO bad of a loss in mileage.....

~Nick

 

It has allways been negative in my experience. IMO the higher gear ratio because of the larger diameter tires will not offset the extra rolling resistance. I believe I noticed a slight decrease just going to 285's. Larger tires are better for me for a lot of reasons but mileage is not one of them.

 

Another thing that hurts milage is tire width. The wider you go, the more resistance there is as well. I got my best milage ever with a set of 245/75R16 that were a very mild all terrain. Really more of a street tread. As was touched on earlier, the more agressive the tread, and softer the rubber the less milage you will get. With your 3.55 gears, I would say the point of diminishing returns is going to be about a 285/75R16. Any higher than that and your milage will suffer about 2MPG (that's what mine dropped). With a 285 you will get some decent size rubber on your rig, but still be able to pull good milage numbers.

 

Also the bigger tire will make your mileage seem to drop even more since your odometer will spin slower and so it will seem like you get even worse than actual. My 315's are 11% larger than stock tires so I have to add 11 % to my mileage numbers to get exact mileage. FYI my best of 24 mpg @ 65 mph non stop interstate was on 265's. My best to date, even with my 11% correction factor is 18 mpg all highway with these 315 soft buckshot mudders.

Truck looks way better but my next set will be 285's for sure. Mileage loss is killer! Now it's true that bigger tires help you turn fewer R's but it is too much extra friction to matter.

 

My 37" Toyos increased highway mileage from 17+ to 19+

The G56 and 3.73 ring & pinion really need taller tires, or you have to drive in the SLOW lane... the CTD's sweet spot is 1800-1900 RPM

 

That's true, 1800 R's or peak torque is peak engine efficiency but that is not the peak drag coefficeint or rolling resistence #. There is a sweet spot somewhere between 40 MPH and 65 MPH where loss of windrag is minimized due to loss off engine efficiency due to less than 1800 ish R's. Bigger tires do raise the sweet spot a little but no truck is more efficent at 65 mph than 55 mph. The taller tires allow you to be at 1900 r's or so when you're doing 65-70 but they are wider, stickier, heavier. If you want to see a maximum efficiency tire, look no further than a big rig. 100 Psi, skinny!

 

It's simple. Bigger tires = more weight, more friction (wider), and larger diameter = more torque to turn = more diesel used.

 

I wish the tire companies would manufacture a taller and slightly wider tire than the stockers that come on the new duallys. The above stated size in a load range "E" would be great. Maybe 9" wide x "33.5 tall.

 

a simple scenario,
if your mileage went from 18mpg avg. to 16mpg avg. as a result of going from a 265 to a 315 tire and assume you pay $2.90/gallon every time....over 30,000 miles its a $604 difference for only fuel.

calculate the additional expense for a 315 tire vs. a 265...

since youre the one paying at the pump (not us), is it worth it?

 

with 38's on my truck, i still get prolly about 18 mpg still. im going to 41's here pretty soon, and i will let yall know. the next step after the 41's will be 54's, and that will be the real test .

 

That sounds awfully high for your setup.

 

Yeah - that's amazing!

 

Hey Dean when you want to put on that leveling kit? We are gonna be in the Cave Saturday doing Leonards new tranny and Ernie's stack delete and new dual exhaust.

 

It's on my list of things to do...I wont be able to do it this weekend unfortunately. I think next weekend would be good. Let me know if you are available and i'll line up an alignment for the week after.