Topic: Reliability of posted mpg figures.

[Canada]

I would like to know the following. Why is a 4WD GM product with a curb weight of 2560kg/5645lbs with a 5.3L OHV V8 rated at 20mpg city and 30mpg highway while another 4WD GM product with a curb weight of 1913kg/4218lbs with a 5.3L OHV V8 get a rating of only 19mpg city and 27mpg? If anything it should be the other way around? I find it hard to believe that something that weighs more than 1400lbs gets better gas mileage with practicaly the same engine. Perhaps a typo? I have found others also that just don't make sense, although, this one is the best example since it is the same manufacturer with a similar engine. The GM products are the 2011 GMC Canyon/Chev Colorado and the 2011 Chev Avalanche as per this website.

[bridgecity]

Transmissions? 

I'm guessing that the Avalanche has the six speed while the Canyon is still using the 4 speed??  However, I would bet in the real world the Canyon would get better mileage, regardless of transmission.

[EV Dan]

Sounds about right. The truck comes with an ancient 4 spd auto and might have a higher differential ratio. Check fueleconomy.gov for US, more real life numbers.

[Canada]

I was not aware that a tranny could make that big of a difference? My logic would have been even with a superior tranny/gearing the 1400lb lighter vehicle would have easily surpassed the bulky brute? If that is the case then why not put a better combo on the lightweights and make something to be proud of, as far as fuel econonomy is concerned? They (GM and others I am sure) go to great lengths to come up with the Volt but the stuff that is a no brainer (more fuel efficient tranny/gearing) falls short. My guess is cost wise there probably is not a big diff between the two trannies to make, afterall why not put the same setup in the Colorado since tey already are making it for the Avalanche? It  probably has something to do with sales and numbers, ie. if the Colorado was too good with the mileage it would cannibalize Avalanche sales. Which would they rather sell you a 25K to 35K product or a 45k to 55K product? Not sure how many people buy the smaller truck thinking/assuming better gas mileage. As you mentioned though real world driving is another ball game. Something to think about?

[KRS]

  What you are missing is the 5.3 liter in the full size trucks has active fuel management meaning up to 4 cylinders can have the injectors shut off which the Colorado/Canyon does not get, the full size vehicles where designed to take the engine where the smaller trucks had to have the V8 shoe horned in cutting the efficiency do to non optimal exhaust routing which is also why the small truck 5.3 is rated at 26 less horse power then the full size as well as already mentioned the small trucks gets the 4 speed auto and full size gets the 6 speed.
 
 While the real life mileage of either won't be what they rate it at (nor is any other vehicles) in comparison I would expect the full size to get proportionally that much better mileage over the small truck.

  I have had the experience last year of going on a trip with another few guys me in my Sierra and one of the other guys taking his Colorado with the 5 cylinder. we filled up before we headed out and after about 5 hours when we had to gas up cause he was out and he had to buy 6 dollars more then I did. he had 1 more person in his truck but that shouldn't need 6 bucks more to haul.

 
 

[airbalancer]

I have had the experience last year of going on a trip with another few guys me in my Sierra and one of the other guys taking his Colorado with the 5 cylinder. we filled up before we headed out and after about 5 hours when we had to gas up cause he was out and he had to buy 6 dollars more then I did. he had 1 more person in his truck but that shouldn't need 6 bucks more to haul.
Are the tanks the same size on both trucks?

I do not think I could go 5 hours in my truck

[Canada]

Active fuel management, optimal exhaust, size of gas tank? Good points. Why not put the afm in the Colorado? The exhaust may be better optimized in the Avalanche but I dont think the advantage would overcome the 1400lb disadvantage. As far as the tranny is concerned I believe they are similar units (correct me if I am mistaken). I find it hard to believe that most of us would be better off (gas mileage wise) driving an  Avalanche over the lighter Colorado? Just my (possible) misconceptions? I like both Avalanches and Colorados and about a hundred other cars / trucks.

[KRS]

Are the tanks the same size on both trucks?

No where close to the same size tanks. I still had well over a quarter tank and he was on fumes. Still when we when we were both full heading out and both filled up again it makes it a fair comparison. When you can get on the 400 highways in the early morning and not get stopped in traffic its amazing how far you can go between stops.  If I was driving in K-W with the truck all day I doubt I could go much over 4 hours of constant driving. Who knows the Colorado may shine in that kind of driving, but i would suspect you'd know a lot of gas station attendants by name if you where using a Colorado 4x4 as a delivery truck every day in the city.

Why not put the afm in the Colorado?

  I suspect that GM engineered this install on the cheap not expecting a large number to be sold and since it is not optimized didn't want to use the expensive bits when they didn't offer the full benefits. If I remember correctly the 5.3l was first adopted to the basic platform for the Hummer H3 (Hummerado if you will) where fuel economy doesn't seem to be a concern. I am guessing that the Canyon and Colorado got this option only because GM already paid to figure out how to fit the engine to the basic platform and want to amortize the cost over more vehicles. I have little doubt GM expects and probably even hopes that the vast majority of these trucks would be sold with the 5 cylinders and really the V8 is an after thought on a limited budget.

  Having driven the Colorado a few times with the 3.5l 5cylinder it had lots of power for most jobs you would use the truck for. I believe the 5cylinder is now 3.7l so it may be even more useful but even the 5 cylinder in my limited experience doesn't seem to match the 5.3l in the full size truck on a long trip for fuel economy. Unless I was towing heavy loads with a Canyon or modding myself a play truck I wouldn't see any need for more power then the 5 cylinder offers. I would expect and even hope that GM would start working on making the 5 cylinder more efficient as I have to figure with GM still recovering from bankruptcy they wouldn't have the resources to do both and the improving the 5 cylinder efficiency would seem to be the most bang for the buck.

[Canada]

Good arguments KRS for sure! Thanks for sharing. Just seems to me things haven't improved as much over the last 20 or 30 years as I had anticipated. I was hoping for something the size of an International CXT with the ability to pull a small house (almost) but could achieve the gas mileage of a Honda Civic or diesel VW Jetta.  I think I may have to wait another 20 or 30 for that. Appreciate everyones slant on this. Thanks.