Suburban fuel economy vs gear ratio?

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Suburban fuel economy vs gear ratio? - 5/19/2007 3:58:54 PM    bracket boy   Posts: 1 Joined: 5/19/2007 Status: offline I have a 2001 5.3L 1/2T 2 wheel drive Suburban.  It currently has a 3.73 gear in the back with your typical 4 speed automatic trans.  The only thing not stock on the truck is a set of 20 wheels, but the tires are stock diameter.  Anyway, it gets an average of about 16.8 mpg's city/highway and flat out on the highway it will get about 18-19.  I rarely go faster than 70 on the highway which nets about 1950rpm.  I typically set the cruise in town at 40 so as to limit throttling just to keep up in traffic.  I am contemplating changing out the rear gears for something higher.  I called my buddy at the Chevy dealer and he looked it up on the computer and found 2001 Burbs could have been equipped with a 3.08, 3.42, 3.73 and a 4.10.  Do you think reducing the rear gears to a 3.08 would have an adverse affect on fuel economy due to the heavy vehicle or should I go with the 3.42's? Seems reducing the cruise rpm a few hundred would help and make the gear reduction worthwhile  About 12 miles of my 17 mile trip to work everyday is on the highway. If I could get closer to 20 city/highway and maybe 21-22 on the highway I think it would be worth the change.  I also have a 96 Vortec 350 extended cab and it rountinely gets 18mpg's with 3.42's and 27" rear tires which nets 1950rpm, 70mph cruise, and it has plenty of low end power.  Thinking of putting a 3.08 in it also.  The mods are cheaper than new trucks since one is paid for and one is close to being paid for.  In my area gas jumped almost .30 cents this week and is 3.29 a gallon right now. Thanks for any input!! Jay   Post #: 1

RE: Suburban fuel economy vs gear ratio? - 5/19/2007 4:31:40 PM    MalibuMaxxSS Posts: 598 Joined: 11/18/2006 Status: offline it will be worse....the truck is VERY heavy it will be working 3 times harder to get it going and maintain speed.... your truck is much lighter then the burb, going from 3.73 to 4.10 will be about 500 rpms more on the highway, typicall there is 1 MPG difference from a truck with 3.73 and 4.10.... Here in BC with the mountains 90% of trucks we sell have 4.10 why, they get better milage around here, up hills the truck dont work as hard.... I would not recommend going to 3.08 or 3.42 ESPECIALLY IF YOU EVER PULL, with these gears it will not pull anything very easily, and if you do you will find yourself in tow/haul all the time or downshifting all the time.... stay with 3.73, these gears work optimily for basically any kind of driving, the cost to replace gears, and the saving you may get IF you do all highway on FLAT roads, will be minimal, if you have any kind of hills or up and down terrain like around here, especially stay with 3.73.. not trying to come off abtuse but I regularly expain this to customers, in the end it is your decision and some people will tell you different but look on the internet, write ups things like that, it wont make a difference and end the end may get worse for you. _____________________________ 2006 Malibu Maxx SS, computer Flashed, undercar LED, Cold air intake, 18' Potenzas, Limo tint front to back 1990 YJ Lifted Locked and always muddy, posi loc, 33s TSLs, weber carb. drop tailgate... (in reply to bracket boy) Post #: 2

RE: Suburban fuel economy vs gear ratio? - 5/21/2007 8:09:03 AM    lost_in_alabama   Posts: 72 Joined: 7/17/2006 Status: offline With the larger wheels you are adding more mass.  Even though the overall tire diameter may be the same, the weight is more, needing more power to get them rolling.  A lower ratio gear axle will force the engine to work harder, consuming more fuel, to get started from a stop, and accelerate up to speed.  You may get slighty better overall fuel mileage, but the performance will drop off enough to make driving an unenjoyable experience. (in reply to MalibuMaxxSS) Post #: 3

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