How many miles per tank of gas?
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93yotasr5
Come and take it
got 233 on this last tank today. gas light came on. averaged 11.5 mpg.
Last tank was 290 miles on 24.5 gallons (cutting it close, I know) -- just shy of 12 MPG. That was predominately city driving. Hoping I can get 375 on a highway only tank.
HI Im ganna bring this back from the dead! I'm new to mudd, I bought my 80 about 2 months ago. So far I've done the basic tune up (cap, rotor, plugs, wires, rear 02, and cleaned the maf/ throttle body). I was wondering how I corrected for the 35s? OH and my ultragauge says I'm averaging 11.1 mpg. Thanks!
If you have an UltraGauge, you need to calibrate it for your larger tires.
Secondly, your 35's are 12.9% larger than you factory tires so your REAL gas mileage is 12.9% HIGHER than what was recorded on your odometer because it is now running 12.9% slower than you are actually moving.
So, your REAL mileage is 12.53 MPG, right on the mark. No issues, that's about normal.
If you want to find out how to get better gas mileage, buy a Subaru. Also do a search for "gas mileage for my 80" and they all end up in the same place.........
COYS
SILVER Star
Hey BILT, how would the calc change if one is running 315/75/16s aka 35s, but regeared from stock to 4.88s?
You're looking at final drive ratios.
Turn off your overdrive and you'll have your RPM at a given speed. OD off, you will assume that gear (4th in this case) is 1:1 on you input to output from engine to driveshaft.
Assume your transfer case is in high so it is also a 1:1 input to output.
Let's pick an RPM. 3000 RPM
Input to the rear axle is 3000 RPM (due to 1:1 ratios throughout.)
Output to the rear tires is 3000 / 4.88 = 614.75 RPM
Tire Diameter = 35" = 109.96" circumference.
Speed = 614.75 x 109.96" = 67595.29 inches per minute.
67595.29 IPM x 60 = 4055717.58 inches per hour
4055717.58 IPH / 63360 inches per mile = 64.01 MPH
So, let's do the same for your FACTORY set-up of 31" tires, and 4:10 gears.
Let's pick an RPM. 3000 RPM
Input to the rear axle is 3000 RPM (due to 1:1 ratios throughout.)
Output to the rear tires is 3000 / 4.10= 731.70 RPM
Tire Diameter = 31" = 97.39" circumference.
Speed = 731.70 x 97.39" = 71260.26 inches per minute.
71260.26 IPM x 60 = 4275615.78 inches per hour
4275615.78 IPH / 63360 inches per mile = 67.48 MPH
So your REAL difference between your original setup and your current setup is:
67.48-64.01 = 3.47 MPH at the SAME RPM.
So, you're actually going 3.47 MPH SLOWER than your speedometer
Lets make this a percentage so you can use it for your gas mileage adjustment:
3.47/67.48=0.0514 = 5.14%
What does this mean?
You are actually traveling SLOWER than your speedometer shows, which means you ODOMETER is racking up the miles FASTER than it should, so your gas mileage is 5.14% WORSE than you have been calculating!
So, if you THINK you've been getting 12.5 MPG, you're actually getting 11.85 MPG.
At 20 MPH, your speedometer is running 1.08 MPH FASTER (21.08 MPH) than you're actually going.
At 60 MPH, your speedometer is running 3.47 MPH FASTER (63.47 MPH) than you're actually going.
At 80 MPH, you're speedometer is running 4.11 MPH FASTER (84.11 MPH) than you're actually going.
There are a number of ways to do the math and you can calculate it starting at a speed and working backwards to the RPM and calculate the difference there, but it all works out.
OD is a moot point because it will be the same in both instances and will be a constant.
Your ACTUAL tire diameter will affect this some, as varying tire brands have varying tire OD's.
I happen to running 285's on stock 4.10 gears and my speedometer runs 5% SLOWER than I am actually moving, so I have to watch for LEO's. At 60 on the speedo, I'm running 63. At 80, I'm running 84.
I enjoy final drive ratios.
For example, FOO, the trail rig for @2fpower , has an A343F automatic transmission.
His first gear is 2.804:1
His transfer case , in low range is 2.488:1.
His differential gears are 5.29:1 (I think)
His Portal gear ratios are 2:1
His tires are 39.5" Diameter
His final drive ratio in first gear, low range is 73.81:1.
In first gear, low range, at 4000 RPM he will be moving at 54.19 RPM axle shaft output.
54.19 x 10.34 FT/Revolution of the tires = 560.32 FPM = 0.106128 miles per minute = 6.36 MPH
On the opposite extreme, in 4th gear with OD engaged:
4000 RPM
0.753: 1 OD
HF2A transfer Case high range = 1:1
His differential gears are 5.29:1 (I think)
His Portal gear ratios are 2:1
His tires are 39.5" Diameter
In high range, with OD, at 4000 RPM, he will be moving 502.09 axle shaft output.
502.09 x 10.34 FT/Revolution of the tires = 5191.61 FPM = 59.00 MPH
He has a 9.26:1 turn down ratio from the lowest to the highest. Call it 10:1 for easy math. At any given RPM, he will travel 1/10th the speed in low-low as he will in OD-High.
For example, FOO, the trail rig for @2fpower , has an A343F automatic transmission.
His first gear is 2.804:1
His transfer case , in low range is 2.488:1.
His differential gears are 5.29:1 (I think)
His Portal gear ratios are 2:1
His tires are 39.5" Diameter
His final drive ratio in first gear, low range is 73.81:1.
In first gear, low range, at 4000 RPM he will be moving at 54.19 RPM axle shaft output.
54.19 x 10.34 FT/Revolution of the tires = 560.32 FPM = 0.106128 miles per minute = 6.36 MPH
On the opposite extreme, in 4th gear with OD engaged:
4000 RPM
0.753: 1 OD
HF2A transfer Case high range = 1:1
His differential gears are 5.29:1 (I think)
His Portal gear ratios are 2:1
His tires are 39.5" Diameter
In high range, with OD, at 4000 RPM, he will be moving 502.09 axle shaft output.
502.09 x 10.34 FT/Revolution of the tires = 5191.61 FPM = 59.00 MPH
He has a 9.26:1 turn down ratio from the lowest to the highest. Call it 10:1 for easy math. At any given RPM, he will travel 1/10th the speed in low-low as he will in OD-High.
COYS
SILVER Star
Class is in session!
What I’ve been doing is whatever miles at fill up x .97 / gallons pumped to get my approx mpg. I’ve been sitting at 12 mixed, 13 hwy on my 250K powertrain.
K02s are more like 34-34.5.
Thanks, BILT!
What I’ve been doing is whatever miles at fill up x .97 / gallons pumped to get my approx mpg. I’ve been sitting at 12 mixed, 13 hwy on my 250K powertrain.
K02s are more like 34-34.5.
Thanks, BILT!
Last edited:
Change it to .95 and you'll be right on.
ewillis
SILVER Star
I'm getting close to 500 miles between fill ups...LRA FTW! 
forum.ih8mud.com
Long Range Automotive LRA 24 Aux Tank Meets an 80 Series Land Cruiser
Well...here we go! There are a number of these tanks in the wild on 40s, 60s, 100s, 200s, GXs, Taco's etc. There are also a few I've seen on the 80 series in the U.S., but only a couple threads here on Mud...so here's another for anyone considering adding a LRA tank. Musings below… The why...
forum.ih8mud.com
I'm running what I think are stock gears (but very well may not be as I haven't had to dig in there, yet) but I get about 200-250 a tank depending on driving conditions. I've personally had the best luck (based on observation alone) running 91 from Chevron stations. 35 inch Duratracs with a decent amount of weight. Fr/R bumpers, 4 inch lift, winch, full size spare, Yakima RTT, usually loaded with camping gear (no idea what my overall weight is).
BILTs awesome posts are now going to haunt my dreams. I've never thought about it in such a manner. My speedo was never recalibrated so I'm about 10 percent low. My prior understanding (or lack thereof) was that it meant my odometer read less than actual miles. For example, if my speedo says I'm doing 80, I'm actually doing 88. At least that's what speedometer apps tell me.
Going to reread his posts again when I have more time to actually think. At the end of the day, I suppose I don't really care, but curiosity always gets the better of me.
BILTs awesome posts are now going to haunt my dreams. I've never thought about it in such a manner. My speedo was never recalibrated so I'm about 10 percent low. My prior understanding (or lack thereof) was that it meant my odometer read less than actual miles. For example, if my speedo says I'm doing 80, I'm actually doing 88. At least that's what speedometer apps tell me.
Going to reread his posts again when I have more time to actually think. At the end of the day, I suppose I don't really care, but curiosity always gets the better of me.
I get about 0.9gph on the trails.
And in case it hasn't been mentioned, the following link will do the math for you and presents a good illustration of what happens when tires change size.
tiresize.com
And in case it hasn't been mentioned, the following link will do the math for you and presents a good illustration of what happens when tires change size.
Tire Size Comparison
Tire size comparison the easy way. Use our tire size comparison calculator to compare diameter, width, sidewall, circumference and revolutions per mile.
Awesome thank you!
Definitely not buying a Subaru, I came from jeeps (flame suit on) and definitely like the freedom that the bigger/ more capable 80 gives. I saw that thread but didn’t see how to calculate it. Definitely might have missed it though.
I did 363 miles from Moab to Boulder on ~23 gallons, no stops, never stopped rolling. Can anyone top that without an additional fuel tank? Stock engine, stock gears, 285/75/16 Duratracs, bumpers, thick rack and RTT, me and one passenger and gear. Drafted a semi from a safe distance for a really long time on I-70 on the Western Slope. Otherwise I definitely wouldn't have made it.
Three weeks ago I did 385 miles on mine with the same setup sans roofrack and still had two gallons. I was shocked!8
i am right around 200 miles when light comes on a mixture of highway and city. Factor in 37s around 565rpm vs stock factory 31s around 675rpm. 200 x (675/565) = 200 x 1.195 = 240 miles per 20g. so avg around 12mpg
super charged, 4" lift, 315 AT tires, calibrated speedo, mixed driving with highway under 70mph, last tank was 289 miles with a MPG of 14.18
Current tank has185 miles and the needle is still touching the half full mark.
Current tank has185 miles and the needle is still touching the half full mark.
