Ok guys I need some advice. I am looking to maximize my fuel milage on my truck. I have read and heard that a larger tire size can get my RPMs down and improve milage. I have a 99 3500 5 speed, I haul cars with it (1 and 2 car trailers) I was wondering what the best tire size would be for me to get better milage. I am currently getting around 17 with stock size tires. Diesel is $2.49 a gallon here in southern ohio! Any help would be GREAT!

 

In 28 years of driving and modifying cars/trucks etc big tires never got me anything but less power and poorer mileage. Consider the wind resistance, rolling resistance and weight and gearing issues. This will affect the brakes also to some extent.

 

Slightly larger and much much thinner would get you a little better mileage.

Most bigger tires are also wider, so the gains are negated by the losses.


phox

 

depends on ur mileage

is it mostly highway? or city.. Yes larger tires will give u more resistance etc etc etc, but in the highway once u get them goin its more tire revs per mile, and lower rpms at 70, in the city it might hurt u more than what its worth..

Tx

 

In the city I get about 13-15 normally. On the highway I can get 17-20 depending on speed. Big difference there due to the tires.

 

I lost about 2 mpg going to 35's, and that is on the highway.

 

Lowering engine RPM on a diesel (via slightly taller overall gearing) will have very little effect on overall fuel economy.

Lowering rpm using taller tires will NOT help mpg, as the increased rolling resistance easily offset any insignificant gains from taller gearing.

Gas engines see better mpg from taller gearing because the air:fuel ratio of the engine is pretty constant.

Diesels don't see this because taller gearing just means the engine has to work a little harder and it runs richer (hotter). They VARY fuel ratio in accordance with engine load. So as long as the engine is operating within its comfortable BSFC rpm range, there's nothing to gain from taller gearing.

Fuel economy is all about tire rolling resistance and aerodynamic drag. For max mpg, find some 235/85r16 hockey pucks with rib tread and air them up to high pressures (at the expense of treadlife).

Reduce aero drag by slowing down. I can knock out 25+mpg empty anytime I want to-- *IF* i am content to run 50mph in 5th gear. I'm not, so I drop it down to 20mpg or so by running 70+ mph.

jlh

 

W

 

Sorry, Why would high tire pressures have a negative effect on tread life?

 

i did the chip and tires pretty much at the same time. and if i'm full out down the highway like 180 sorta deal then i get better milage but for the most part i lost a lil bit
if i do the speed limit its about the same

 

High pressure alone will not-- IF the load on the tire is high. At normal loads, high pressures (overinflation) will cause the centers of the tread area to wear prematurely, as they carry the load while the outer tread barely touches the road (if it touches at all).

jlh

 

Gee you guys talked me out of the 285's i was going to buy this fall?? but thanks for the information tho--glenn

 

I'm really starting to look at throwing a set of Big O XT 235/85 R16 next time to se if it help with MPG... I'm currently running 265/75 R16 Big O XT and the fuel milage is about 17.47 MPG... Not to great...

 

it sure looks a lot better though! i couldn't believe the diffference

 

The difference in mileage going from a 265 to a 285 is negligible. I doubt you'd see any difference one way or the other. The looks alone are worth any loss in mileage.