H3 MPG < H2 MPG
 

WHy is my H3 with 35" tires getting 3-4 mpg worse than my H2 with 37" tires? I'm only geting around 9mpg in the H3 and am getting 12-13mpg in the H2. They both have the same tire tread, both have stealth GOBI racks, both get gas from the same station, and I drive both the same.

:confused:

Re: H3 MPG < H2 MPG
 

Could it be that with the H3 only having a 3.5L engine and trying to move 4700 lbs of vehicle with taller tires is more taxing on the engine than a 6.0L (or whatever is in the H2) trying to move around a slightly heavier vehicle with taller tires, but not as taxing to the engine?

Seriously though, the little H3 is overworked to begin with, and the addition of taller tires makes it have to work just that much harder. That extra work comes at the cost of the fuel economy, whereas the H2 has power to spare and can handle the taller tires easier.

Re: H3 MPG < H2 MPG
 

In case you didn't know, Hummers are not about saving Gas. Maybe you have this site confused with the jeep or VW site. Rebel

Re: H3 MPG < H2 MPG
 

Have you had your H3 odo recalibrated? If you're running 35" with factory calibration on odo, then you are getting more miles than you think.

Re: H3 MPG < H2 MPG
 

9 mpg sounds REALLY low! I'm still averaging 14-15mpg with my 35's. Granted I don't have a roof rack, but I doubt the Gobi will account for 5-6mpg.

Re: H3 MPG < H2 MPG
 

The 35" tires are severely over-working the hamsters.:jump:

Re: H3 MPG < H2 MPG
 

Something's wrong with your H3 maybe. I'm running stock 32's on my H3 and averaging 14-16mpg over last 16 months.

Don't think the 35's should hurt the mileage that much, just make it more gutless from a street acceleration standpoint.

S.

Re: H3 MPG < H2 MPG
 

IMO two things may be at play here, first is the diameter difference in tires, since w/315/75/16 you are going 3.5 mph faster than w/285/75/16 therefore farther distance traveled with each revolution your odo is not showing true distance making your mpg caculations off (to my knowledge no one recalibrates speedo for h3 as of this time) second when you went to 35's did you also go M/T I was getting about 17.5mpg on highway w/stock 33's, changed to 33 in bfg mt and dropped to 14.85 mpg on highway(higher resistance tire = worse mpg)

Re: H3 MPG < H2 MPG
 

wondering if I should but fat tires on the beatch

Re: H3 MPG < H2 MPG
 

:iagree:

Just guessing, but another problem could be the torsion lift changing the aerodynamics of the front end and underbody.

Re: H3 MPG < H2 MPG
 

It's pretty obvious. The less MPG your vehicle gets, the cooler it is. The cooler your vehicle is, the less MPG it gets.

Re: H3 MPG < H2 MPG
 

Just did some calculations on your estimated tire diameter (C = pi * d). Assuming an actual diameter of 33 and 35 inches, your tire circumference changed from 103.62 to 109.9 inches, so you're now travelling 6.28 inches further with each tire revolution than your odometer reads.

To convert your mpg, find the ratio of one circumference to the other and multiply by your odometer's mileage.

109.9/103.62 = 1.06%

9 mpg * 1.06 = 9.5 mpg (corrected)

That's not very much. Maybe aerodynamics from the t-bar lift makes a bigger difference. Other factors could be tire pressure, cargo load and driving patterns.

Somebody please check my math. My algegra's a little rusty.

Re: H3 MPG < H2 MPG
 

the engine has nothing to do with how much its going to burn relatively. Its called the conservation of energy. If you have the same mass, and try to move it with a smaller engine, it will be at higher rpm, but use less fuel per revolution because of the smaller size. A larger engine would do it at less rpm (thus seems easier) however because of its larger size uses more fuel per revolution. 3.5L to 6L almost double per revolution. Although its more complicated than that, i just wanted to make the point.

Tires however could be an issue.

Re: H3 MPG < H2 MPG
 

I have a 5 turns on t-bar as well as roof rack w/pull pall and highlift jack I noticed a slight drop after t-bar crank (1/4 mpg) but never put crank/aerodynamics together. figured I was just getting a little more into the skinny pedal than before. major drop after I added M/T's

Re: H3 MPG < H2 MPG
 

Well, we found the issue. One of the mahsters under the hood was tired so we added another.

http://www.transoniq.com/images/ham40.jpg

I hope this solves the problem.

Re: H3 MPG < H2 MPG
 

I still think it's the Gobi. I don't know about everyone else, but I'm going to spread the word that it will cut your MPG in half, that's ridiculous.

Re: H3 MPG < H2 MPG
 

Timgo,
Check and see if one of the Hamsters is lodged in your intake manifold:beerchug:

Re: H3 MPG < H2 MPG
 

:jump:

Re: H3 MPG < H2 MPG
 

i have the rancho lift with 35 inch superswampers and i get an indicated 10-11 mpg.
cant see hpw ur getting an indicated 9mpg.
i realize the odo is off, but guys like us are hurting.
if i knew the gas mileage would be this bad, i would have gotten an h2 and lifted that..:)
probably my next vehicle, but i really like how the lifted h3 offroads.

Re: H3 MPG < H2 MPG
 

Have you checked your Influx Regulator (or the Soil Compilator if you do a lot off roading)?

It could be the Muffler Bearings....if that is the case, you MUST use a Left-Handed Hammer to repair it.

Re: H3 MPG < H2 MPG
 

TRUST on old man...

IT AIN'T the:
tires
roof rack
torsion bars

OR

hamsters

Its one of two things:

#1 YOUR ANCHOR is DRAGING
#2 You have a tuning problem

RYD

Re: H3 MPG < H2 MPG
 

One thing to keep in mind is that as you increase the height of the front of the vehicle, the front axles/CV joints become more misaligned. The efficiency of the CV joint drops as the ends become more off axis. This increases your drivetrain losses resulting in less power to the wheels and lower fuel economy. This is the same philosophy as setting the proper driveshaft and pinion angle or torqueing a bolt using a universal. This may not may the complete cause of the issue here though.

For example, the Corvette (IRS rear) has about 2% worse drivetrain loss than an F-body (solid axle) due to the 4 CV joints in the Corvette's IRS.

Re: H3 MPG < H2 MPG
 

Gee
I hope Corvette doesn't go back to a solid axle :)

It's the 35" tires causing the drop in mpg. The hamsters can't take it
Not likley the cv joint angle in your case.

Re: H3 MPG < H2 MPG
 

The size of the engine has everything to do with how much fuel it consumes, assuming everything else is equal. Power= PLAN where P=Pressure in the cylinders, i.e. air pressure past the throttle body, L=Length of stroke, A= Area of the piston head, and N= number of times. Since the air fuel mixture reamians constant reguardless of the throttle position or RPM, for every given volume of air going into the cylinder there is a proportional amount of fuel. Air pressure in the cylinder is regulated by the throttle plate. When it is closed, and the engine is at idle, very little air makes it past the plate and you have low pressure in the cylinders. This shows up as high vacuum on a vacuum gauge, or low pressure Manifold Absolute Pressure (MAP) gauge. When the throttle plate is fully open, then there is high pressure, almost full atmospheric pressure, in the cylinders. This shows up as very low vacuum, or high pressure on the MAP.
Now, to put this in prespective of the Hummers, the 3.5L is at a certain throttle position and a certain RPM producing a certain amount of power during cruise. Put the 6.0L at that same RPM and throttle setting and it will produce more power because of it larger size. Thus, the 6.0 can perform more work for the given RPM and manifold pressure (throttle position), but at a cost of more fuel. If you want it to consume the same fuel as the 3.5L at the same RPM, you must change the throttle setting to one with lower manifold pressure to match the power output of the 3.5L (That may be physically imposible depending on the RPM, target fuel consumption, and the brake fuel consumption of the 6.0L). If you increase the load on the 3.5L, it will require a higher manifold pressure (throttle open wider) and consume more fuel to maintain that same RPM. So, if the H2 cruises with a certain aerodynamic load, mass load, and rolling resistance and gets a certain fuel economy, it is entirely possible for the H3 to increase its aerodynamic load, mass load, and rolling resistance to the point that the engine is working hard enough to consume more fuel that the larger underworked vehicle.
As to gearing, assuming everything is eqaul, and the engines are producing an idential percentage of their total power, then yes, the smaller engine would have to have gearing to work in it's favor, and it would have a higher RPM. But, by changing the tire size without regearing the axles, you have changed the effective gearing to something unfavorable to the smaller engine, thus increasing it's load and throttle position just to maintain the same RPM.

Re: H3 MPG < H2 MPG
 

In short one f'ed up H3. Worst of both worlds, both gutless and getting 9mpg. That H3 needs to be returned completely back to stock configuration for a fresh start.

S.

Re: H3 MPG < H2 MPG
 

Don't feel bad Tim. Sometimes I forget and leave the E-Brake on too.

Re: H3 MPG < H2 MPG
 

I have 35's

I have four turns on the t-bars

I got 15mpg on my latest long distance trip, 1223 miles, at 80mph.




Tim,
have you changed you air filter????:giggling:

Re: H3 MPG < H2 MPG
 

Re: H3 MPG < H2 MPG
 

yep...

Re: H3 MPG < H2 MPG
 

I have the stock 33s, t-bar turns levelled to rear, a brush guard, rear bumper bar, factory off road lights, and vent shades. My mileage had been in the estimated range and still is, for the most part, on highway trips. However, after the 6,000 mile mark, I have noted a definite decrease in city mileage. I am not quite sure why although I had been driving it quite aggressively in expressway conditions, frequently kicking high rpms. On my current tank, I am going to try to stay out of "afterburn" and see what the mileage is as I suspect of you drive it like a granny, you'll get the best MPG, but if you drive it like Ricky Bobby.... well, you get the point.

Has anyone ever conducted a test on gasoline grades and what gets the best mileage in the H3 under normal driving conditions?

:dancingbanana:

Re: H3 MPG < H2 MPG
 

Well this proves the H2 is better than the H3.:D :D :D

Re: H3 MPG < H2 MPG
 

A Pathfinder with a 4.0L 270 hp V6 weighing almost the same as the H3 can get 16/23 mpg and is still pretty quick(0-60 in 7-8secs) for an SUV. Why can't the H3? I have my fingers crossed the 08 H3 comes close. Of coarse the H3 kicks it's arse in the off road dept., but why can't the H3 excel in both on and off road?