MPG and MPH after lift.

[Arctic-Rodz]

So after lifting my Tahoe and adding the 35" Toyos, its obvious that my Speedo was off. But then I began to think that if my speedo is off, im sure my MPG calculator was off too, since its reading "slower" from the taller tires.

Got the tire size calculator and compared the stock size tire to the new 35's and it calculates that with the bigger tires, my speedo reads 9.58% slower.

So I crunched the #'s.

@ 158 miles marked on my trip meter (just under half tank of gas)

158 x 9.58% (.0958) = 15.13
15.13 + 158 = 173.13 (actual miles driven)

Added 12.9 Gallons of gas to top off, which tells me how many gallons of fuel I used to go 173.13 miles

173.13 / 12.9 = 13.42 MPG

What do you guys think? Thats about 75% city driving. The MPG calculator on the truck says 11.9 MPG but thats reading the "slower" speed.

Not too bad, id say.

 

[DenaliAK]

Hey, nice calculating. I'm not a math whiz...I'll have to do that with mine since according to my computer my mileage sucks now even though the tires are only slightly over-sized. I know my speedo is only off a couple of percent, though...I used a GPS to calculate speed and compared it to what the speedo said. There wasn't much difference.

Edit: Yep, my mileage actually does suck. There's only a 1.26% difference in the speedo according to the calculator.

 

[Arctic-Rodz]

Yea, this is a good way to find out your ACTUAL MPG until you get your speedo calibrated to read the new tire size.

After seeing the MPG im getting, im wondering if I should consider lower gears? 13.4 doesnt seem too bad and im not sure if getting lower gears will make it better or worse. Ive heard 35" tires call for 4.56 or 4.88 gears. Im currently on stock gears (3.73 i think)

 

[dwmmatt23]

Shit if thats the case you still get better mileage than I do. 11.5mpg around town on 33''s

 

[jdpber]

DenaliAk - remember your AWD drice train have a greater loss than a free spin 4wd front diff.. take that into account also.. and i have this same issue and set up as ARCTIC-RODZ and my computer is all screwed up on the gas estimator.. and mine states higher than actual.. the past month i have been using the trip and speedo on the Garmin as a test comparison and i am getting about the same as you in city. 14 and change some times 15 area on tank.. but i have tune so that may make the extra mile i dont know.. but 13 sounds about right to me that seems very close to my actual.. after further investigation after a discrepancy brought to my attention buy various board members.. just cant trust the GM calculator after modification..

 

[redemn93]

i get 14.5 mpg stock. city highway mix. driving like a granny or not. im mounting 275/65/18 nittos tomorrow. and getting my tune by next week. just a traditional BB. if i get 13.5 i will be happy. the more the better though. especially since its a 91oct tune.

 

[brucebruce45]

Tried to tell u that

 

[Arctic-Rodz]

John-
My truck is tuned... i remember you said you have a lot of straight roads. I dont. Lot more stop and go traffic. Also, I have M/T tires. Im sure your A/T's are considerably lighter.


Im debating right now about swapping gears to (4.56 - 4.88) not really sure how it will impact MPG. Ive heard its suppose to be better cause it wont struggle as much to keep the same speed (due to the extra weight and larger tire diameter).

Anyone ever heard of Ron's Machining Service?

 

[jdpber]

Yea man. The AT tires toll easier than the MT tires. I will have to see if I have a different economy. 3rd an 2nd gear died Friday. I'm having a new trany built from scratch for me. With beef to handle the larger tires and added power. I don't know if it will change economy. I doubt it but. Should be Bullet proof with all the upgrades. I also drive easy. In town and That helps.