regear?

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Feb 2, 2011 | 09:18 PM

#16

Fordfanatic4life

Postmaster

Joined: Oct 2008

Posts: 3,924

Likes: 6

From: Richmond BC

Quote:

Originally Posted by dkf

Wrong on both parts. The 3.73s suck with the stock 31.5" tires so larger 36" diameter tires are WAY worse. The mpg difference in stock form between 3.73s and 4.30s is negledgable. All those 3.73 gears gears are doing with those 36" tires is causing the transmission to hunt more and increasing the engine load. Hunting between gears all the time and driving with the TQ unlocked for long periods of time kills mpg.

To the OP you need to regear with those tires. You will gain performance and the transmission will thank you for the steeper gears. As for mpg you may pick up some with the swap it depends on your driving conditions. The 5 Star tuner will help with the performance but don't expect a mpg increase from it. The tuner will not make up for the poor gearing that you currently have with those 36s.

^^^agree with all of this ^^^

Feb 2, 2011 | 10:08 PM

#17

CraigOutdoors

Elder User

Joined: Mar 2010

Posts: 544

Likes: 2

Quote:

Originally Posted by sanders46

thanks. and any advice on the speedometer being off affecting mpg reading?

Yes, it will affect apparent mpg, because you're reading fewer miles than you are actually going, since the spedo and odo are calibrated to the stock tire/gear size. With the larger tires, you are going a further distance for each wheel rotation than you were stock. Thus, your computer thinks you are traveling a shorter distance than you are. If you correct the calibration, your apparent mpg will increase to your actual mpg. I believe it is done in the computer nowadays. Used to be done with a gear in the trans.

Feb 2, 2011 | 10:30 PM

#18

cmullins

Junior User

Joined: Mar 2009

Posts: 66

Likes: 0

From: Rochester, MN

Quote:

Originally Posted by sanders46

thanks for the anwsers and i was considering a 5 star programmer. what mpg did u gain with it?

I was getting 10.5 max before the tune. I put on an intake, ypipe, and the tuner all at the same time. I now get 11 to 11.5 pretty consistantly and can get over 12 if I can keep my foot out of it. That is really hard to do because the tuner made it a totally different truck. The best I have done is 13.2 mostly highway and empty. Many tuners can adjust for the tire size but I believe from Mike that there may be a limit. I just put 33s on a while back and changed the revs per mile in the tuner and my speedo is within 1 mph through the traps. Mike is a great guy and excellent resource. I would recommend a call to him if nothing else he could help you sort through whether that is an mod you want or not. He is not a high pressure guy and full of info and there is a ton of info on his site as well. Check it out and make your own informed decision.

Disclaimer: Past performance is not necessarily an indication of future outcomes but I could not be happier with the mods I have done so far on my SD. And, if I go any bigger than the 33s I plan to gear to keep the rpm/speed ratio where it is designed to be.