H3 MPG < H2 MPG

[timgco]

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.

[Linus Gump]

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.

[lennyrebel]

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

[Khoolhandz]

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.

[Sewie]

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.

[DRTYFN]

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

[marin8703]

Originally Posted by Linus Gump

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.

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.

[timgco]

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.

[dеiтайожни]

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.

[timgco]

Originally Posted by dеiтайожни

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.

[wpage]

Originally Posted by timgco

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.

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

[Linus Gump]

Originally Posted by marin8703

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.

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.

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.

[Bully13]

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

[f5fstop]

Originally Posted by Steve - SanJose

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.

[Alan06SUT]

Originally Posted by timgco

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.

Well this proves the H2 is better than the H3.

[Diabolus]

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?