Hypertech or?

[SF Jakey]

I've got a 2002 ccsb4x4 d/a with 60k miles on it. I've run 285's since new and can't get over 16 mpg unloaded. Yes, I do add 8% to my mileage to compensate for the larger diameter, so my figures are accurate. When towing I get 8mpg max, 9000lb boat, triple axle trailer. My question is, will the hypertech reprogram anything besides the speedo, like shift points etc, to get normal mileage, or am I pretty much screwed. I don't want more power, I really don't see the need, but I would like to see the truck perform like everyone says. My other thought is go get a new 06 6spd and hope for better results, although I can't see the truck being any different than what I have. Can oversize tires really take away 3-4 mpg on a truck this size? It just hasn't ever added up to me. thanks for the input

[More Power]

I saw about a half mpg improvement while towing after installing an Edge Juice some time ago. This, I attribute to less downshifting with more power.

Hypertech advertises better fuel economy, but I'd like to see an accurately run longterm fuel economy evaluation to see the big picture.

The only way you'll see what effect larger tires have on fuel economy is to switch back, then compare the fuel economy to when driving the same speeds.

Most people report varying degrees of fuel economy loss when going to larger tires. Your report is within the range of mpg loss... Aside from the math error when going to larger tires, the engine and drivetrain have to work a little harder, and larger tires increase rolling resistance. Wind drag is also increased a bit due to the truck being a couple inches taller.

Jim

[SF Jakey]

Would going down to 265's help with towing and mileage, or would I have to go back to 245's, which isn't really an option since I drag over rocks now? I didn't notice this big a mileage loss going to 33's in my Rubicon, seems strange that a high hp motor like this would even be affected.

[More Power]

What effect larger tires might have on fuel economy depends somewhat on how fast you drive. My guess is most would drive a 2500HD faster on the Interstate than say a Jeep Rubicon.

Additionally, fuel economy in a typical diesel powered vehicle can be affected more by the engine rpm range than a gas engine - due to the much wider dynamic rpm range available to a gas engine. Try to run at your engine's torque peak of 1800 rpm for best fuel economy.

I run 265 Mich LTX tires on my 2001, and I run them at about 70 psi front and 60-65 rear (or a little higher when towing). My fuel economy is very similar to when running 245's, but there was a slight loss.

I get about 12-14 while towing the loaded trailer in this image (depending on speed).

http://www.thedieselpage.com/images/towingproject01.jpg

Jim