'99 4x2 Suburban gas milage

ncsuburban · September 19, 2003

I just purchased a '99 C1500 4x2 Suburban with the 5.7, 255/70/15 tires, 3.42 rear end and 45k miles.

I am wondering what other owners with a similiar setup are getting for gas milage? I haven't driven it enough to gauge my milage, yet.

Mike

plrod · September 21, 2003

My wife drives a 99 LT C1500 sub mostly around town on kid taxi duty and I get to fuel it up for her. She does alot of iddling from what I can tell bc mileage around town is in the 10 to 12 range; when we travel it gets around 17 on the highway. I put the largest 15" tire I thought I could fit on it which is a 31x10.50-15 for it's curb hopping ability and increased ground clearance.

99-2door · September 22, 2003

My wife drives a 99 LT C1500 sub mostly around town on kid taxi duty and I get to fuel it up for her. She does alot of iddling from what I can tell bc mileage around town is in the 10 to 12 range; when we travel it gets around 17 on the highway. I put the largest 15" tire I thought I could fit on it which is a 31x10.50-15 for it's curb hopping ability and increased ground clearance.

Wow that is a big tire for a 2wd. It is also the reason you are getting such poor gas mileage. It has your truck geared up too high for town duty, plus it gives you an inaccurate mileage reading that is too low ( your increased circumference means more distance traveled per revolution). Your change in tire size has given you something like a 3.15 rear-end with stock tires(assuming you have the 3.42). I have a feeling this has an adverse effect on your gas mileage, especially in a vehicle as heavy as a Suburban in stop go traffic, not to mention perceived power loss. Get some smaller tires back on that thing and you will see your mileage around town pick up a bit. I think you will see your mileage pick-up on long trips also because the faster you go the more your mileage will be off, plus with the bigger tires your truck will be more likely to downshift on slight grades instead of just larger ones. I know it seems backwards sometimes to think that a lower rear-end ratio will result in higher gas mileage but it is true sometimes.