K so we recently bought my girlfriend a 2001 cummins auto has 94,000 miles on it and its a really nice truck runs great. It has an edge ez, 4" turbo back mbrp exhaust, and 35 inch tires. Hand calculated the truck gets 10-12 mpg with 3:55 gears in it. We have replaced the air filter and fuel filter and are lost onto why its getting that bad could it be the tires? i have a 2000 5 speed with stock tires and i get 18 around town. any suggestions would be greatly appreciated

 

tires is throwing your odometer readings off, my 33s on my truck throw my odometer reading off by roughly 8 percent for mile.

but yes the tires can and will affect gas mileage. although my stock 98.5 auto i used to have only got 13-15 mpg around town

 

My friend Dukeboy has a point. Your tires are throwing things off a little and I have provided a calculator that I came up with last week to figure my own fuel mileage. I get an average of 14.7mpg, thats an average of everything, from interstste to city to romping on it. If you can I would go through and change a few fluids. Try using a thinner synthetic oil in your engine; change your tranny fluid, filter and adjust your bands; change all your gear oil; and lastly make sure your tire pressures are set to factory spec, as I see most people who run larger tires only keet them at 50psi.

The Tires that come on our trucks from the Factory SRW - LT245/75R16 and DRW - LT215/85R16 Circumferance is right at 8ft. and it takes that size tire to roll 660 times to reach one mile. You will need to calculate the new circumferance of the larger tires.

215/85R16 - 8ft
235/85R16 - 8.35ft
255/85R16 - 8.7ft
245/75R16 - 8ft
265/75R16 - 8.34ft
285/75R16 - 8.66ft
305/70R16 - 8.65ft
315/75R16 - 9.13ft

So I'll give you an example. I run 235's on my dually and the factory are 215's.
My last fill up took 29gal for 412 miles.

8.35*660=5511

5511/5280=1.04375

1.04375*412=430

So I actually went 430 miles on the 235's instead of 412. Then you just have to devide the true mileage by gallons to fill up the tank.

430/29=14.8

So, I actually got 14.8mpg instead of the 14.2mpg as figured with my IPC.

I hope this helps some people.

 

Yep, tires.

 

okay, topped off my truck this morning,used 11.103 gallons, topped off to the brim as always. odometer showed 194.8 miles. so without using the above formula, i averaged 17.549 mpg, thats country and city driving. using the above formula, with my 305/70/16s at 8.65 feet

8.65*660 = 5709
5709/5280= 1.08125
194.8*1.08125=210.6275
210.6275/11.103=
18.97 mpg!!!!


I like this forumula, I always just used a rough estimate of 7.5 percent to convert, this is much better. , now it worked to reduce the fuel costs by 90%, I'd be thrilled


btw: my tires are set at 60 lbs

 

my 01 still has the stock Exhaust is mostly stock i get 18 in town and 21 on the hiway

 

OP,

Depending on how much tread is left on the tires, if they are in need of being replaced in the near future, you could always get some smaller ones if the mileage is of most importance. Just a thought...

oudive

 

What gears do you have?