Taller tires affect MPG
 

Hello y'all,
just wondering about changing to taller tire to get better fuel mileage. I have a frind that went to taller tires on a 7.3 power straoke that is chipped and is getting 22-24 highway with his rig. I have a 6.7 Cummins that has been fully deleted and using the Smarty Sr programmer. I'm running my stock 17's but just wnadoring if I would have any trouble fitting 35's on my rig? It is stoc with no lift kit on it. Any help would be appreciated.

Yes it will result in different MPG. you are essentially changing the gear ratio in the rear-end. the truck will travel farther with each revolution of the axles because the outer diameter of the tires is larger. One thing I would ask about you friend is how he figured his MPG. if he is chipped with larger tires, is he going by the readout on the truck for what MPG he is getting? Does he have the speedometer compensated to adjust for larger tires? if he has a programmer on it then keep in mind that power is added by lying to the trucks ECU to get it to adjust timing and fuel rates so any readout that the truck gives is derived from false input. the overhead readout on my 01 5.9 CDT with my old Hypertech tuner on stage 3 would say I was getting about 24mpg when I was truthfully getting about 12 and that my 30 mile ride to work was actually 36 miles.

Thanks uglytruck. Jhis truck is old enough it doesn't have all of the fancy computer stuff in it. All of his mileage is hand calculated.

bigger tires equals less mpg its the nature of the beast. expect 1-3 mpg loss from my experience.

Well a wider tire will give you less mileage. A taller tire will give you better mileage on the highway, but around town the more torque required and the additional mass will hurt fuel mileage. Also it depends on just how much bigger...bigger rims? or taller tire, you kinda want to keep the sidewall the same height as stock. Now if your going for 22.5 rims and heavy truck tires all bets are off. :scare2:

My next tire will be the 285-75-18 Toyo or Nitto.
My G-56 0.79 final drive yields the same as a 4.10 auto so it should slow down the tach some.
Our '98 Honda Accord 4sp manual barely got 26mpg city/highway combined
My friend's 2000 4wd F-250 with factory blades and $6.5K of Bank's barely yields 17 mpg highway.

I'm gonna put Terragrapplers on my stock 20's. Wider than my stock tire but I think they look good.

I agree it will surely affect your MPG also the speedo reading.

Just changed my tiers in Nov. Went from 32 to 35. Milage is down about 2 mpg. Power seems down too.

Larger tires = more rotating mass = less fuel mileage. It is very rare that a taller tire will yield better fuel mileage unless you are starting with a very deep gear already.

https://cimg8.ibsrv.net/gimg/www.die...5a88f789ef.gif

https://cimg1.ibsrv.net/gimg/www.die...ced0e6fc3a.gif
chart to help you decide tire heoght and axle ratio for fuel milage

My 2007 G-56 has the lower ratio final drive that yields super high rpms at freeway speed.
To get a 35" approx tire diameter in a 17" I'd have to go 35-12.50-17's. I may have to go with an 18" rim and 285/295-75-18. I'd like to keep the narrower tread width. Problem is getting an 18" wheel in an appropriate backspacing so they're not sticking out.

Interesting charts, however it is all relative. Are these charts based upon traveling at 60mph on county roads, or 70-80MPH on the freeway?

Engines are generally the most efficient at their peak torque RPM, so if you cruise at that specific RPM you should get your best economy. If your engine does not have enough torque to cruise at the speed reached with your gear ratio at that RPM, you will have to down shift and lose economy. Also, if the engine is struggling to maintain peak torque RPM, parts of the engine will likely fail early due to excessive heat generated or excessive vibration.