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Simple Question for all

chevyCowboy said:
las tsummer i was getting close to 19 very cosistantly with 245 75 16 tires i put 285 75 16 on this winter and i lost about 2 mpg i was getting 16-17 on winter fuel and now im getting 14.5-15 anxious to see if it cums back up this summer
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Probably the tire size is screwing with your odometer. I know mine changed going from 245/16 to 265/17's.
 
Dieseldad97 said:
Probably the tire size is screwing with your odometer. I know mine changed going from 245/16 to 265/17's.
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Good point, he didn't mention if he is correcting for the new tire size.

Assuming you don't change your speedo calibration, going to bigger tires will make the mpg figures appear lower unless you adjust for the tire size. The circumference of the 245/75-16 is 95.7", and for the 285/75-16 its 103.1". That is a 7.7% increase, so if you calculated 19 mpg with the old tires it should drop about 1.5 mpg with the new tires, but the real result is the same.

In my case going from 235/85-16 to 265/75-16 the tires are very close to the same so my calculations wouldn't change, in both cases I'm about 4% over stock size.
 
last summer my very best was 15 with 4.10's and bone stock. Now, I'm curious to see what kind of numbers I'll be working with a decent amount of upgrades and changes. Coming up depending on extra funds will be a custom fabricated intake, custom suspension lift(in progress now), new tires(going from 245's to 265 Mickey thompsons:D), and hopefully, rockin an A-Team turbo by the end of fall.
 
The best i've gotten was 28mpg. It was in a 91 k2500LD with a 6.2 n/a 3.70 gears,245-16 tires. This was on a straight interstate run from minneapolis to millwaukee at 75mph+. I never got that good any other time. Steady speed is the reason. I haven't checked my 6.5s
 
im getting 13.8 MPG on the one tank i checked. but that was when i first got it and i had been towing about 4500 pounds and when it was unloaded i was "Testing" to see how much horespower this thing had. plus i doubt the previus owner recalbriated the odo for upsizing to 265/75/16 tires from the 245s that were on there before. but on the TDI i get 42 MPG
 
Dave01 said:
Good point, he didn't mention if he is correcting for the new tire size.

Assuming you don't change your speedo calibration, going to bigger tires will make the mpg figures appear lower unless you adjust for the tire size. The circumference of the 245/75-16 is 95.7", and for the 285/75-16 its 103.1". That is a 7.7% increase, so if you calculated 19 mpg with the old tires it should drop about 1.5 mpg with the new tires, but the real result is the same.

In my case going from 235/85-16 to 265/75-16 the tires are very close to the same so my calculations wouldn't change, in both cases I'm about 4% over stock size.
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could you explain that some more im not following? so i am actually traveling 7.7% more distance than what my odo says?
 
The first 2 tanks on my new engine averaged 18.9 mpg. 2nd tank w/ similar hiway driving (~ 65 mph) was 19.5 mpg. Stock 245/16 sized tires. Still w/ OEM exhaust (left it on to ensure passing inspection to get it licensed). The 3" DP, 4" Heartthrob system going on this weekend.

Not really enough samples yet to draw conclusions; I try to log mileage/gallons every fill for more data/better conclusions.

Figured going to 18:1 might have given up some combustion efficiency at cruise conditions. Don't have before/after to compare but so far, it appears lowering compression didn't hurt fuel economy that significantly.
 
could you explain that some more im not following? so i am actually traveling 7.7% more distance than what my odo says?
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Yes. By going with the bigger tires but your odometer still calibrated for the stock tires, when it says you've gone 100 miles you've actually gone 107.7 miles.

I re-read my post and it wasn't all that clear. Here's a simpler way to look at it. When you calculate mpg, and come up with a figure for example of 17 mpg, to get your real mpg add 7.7% to the 17 and you get 18.3 mpg. Also, when your speedo reads 65 mph, you're really going 65 plus 7.7% = 70 mph. Does this make sense now?

David
 
14.xx mpg (cant remember, but it was close to 15) in the 92 HD, that is empty bringing it home from the auction we bought it at.
 
I get consistent 17.5 - 18.5 running back and forth to work. I just came back from a 800 mile round trip to N. Georgia and got 19.9 mpg on the way up running 70 mph and 21 on the way back. I'm also running HHO - which at this point I'm getting about 2 mpg increase.

When empty I try to keep the boost below 5 psi (it takes fuel to make boost!). It was a little hard to do that when I started getting into some long grades around Atlanta - was sustaining 12psi with a lot more pedal to go.....man, that little GM-3 can whistle when it gets over 10 psi.:thumbsup:
 
I used to run Cooper SRM2s, a highway tread, outstanding wear -
averaged about 18.5 with them, over last few years.
Just went to Cooper ATRs, great looking tires, very good wear rating,
but mileage went down just over 1 MPG with them :sad:
 
Tire effect on mileage

Tookie said:
I used to run Cooper SRM2s, a highway tread, outstanding wear -
averaged about 18.5 with them, over last few years.
Just went to Cooper ATRs, great looking tires, very good wear rating,
but mileage went down just over 1 MPG with them :sad:
Click to expand...

I found some Goodyear HPT 235/85-16 (on craigslist) that I'm going to put on for the summer so I can compare mileage with the BFG Long Trail 265/75-16 I've had on for the last 2000 miles. Same height with about one inch less tread and of course a bit different pattern, both are load range E. I'm expecting a slight increase, we'll see.
 
plus one with ATT so far

Only the 750-mile-light-duty-report but with my new A Team Turbo installed and a bit over 800 miles on it now, I can say that it gained about one mpg. This is only running empty at this point so no data yet from me with the horse trailer on back. Huge drop in intate air temp, about 50 degrees accross the board, (again only running empty). My average mpg is now at 18.5 with about 70% of that on the highway. I'm looking for an excuse to hook up the trailer and head up Mt Hood just to see how it does. I just need a better excuse than going to burn some diesel :thumbsup:.
 
I get 13-15, depending on conditions. I have 3.42 gears, 200k injectors and NO working gp's. So the age of my engines components lead to poor mileage. Hopefully with this new engine i would be very happy with at least 18....
 
DieselSlug said:
I get 13-15, depending on conditions. I have 3.42 gears, 200k injectors and NO working gp's. So the age of my engines components lead to poor mileage. Hopefully with this new engine i would be very happy with at least 18....
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No working GP's? Ouch - how many starters have you replaced> ):h

I ran ole blue down to three working GP's and when one of them died, with only two remaining - she would not crank...period.
 
21-22 on the highway.
17-18 driving like a sane person around town.
all other driving not looked at from a mpg viewpoint. ):h
 
See signature for details......

Constant 55-60 mph highway, 17 mpg.

Around town, driving sanely (hey, it happens on occasion) 15 mpg.

Most of the time, -around town, driving like I usually do (foot in the fanbelt), 13-14 tops.

My setup does NOT lend itself well to mileage, but she runs very strong.
 
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