Tuner or what?
Fleet Mechanic
Joined: Oct 2003
Posts: 1,371
Likes: 10
From: Green Springs, OH
In the past for me it was the other way around. Once you get the bigger tire rolling it turns the motor turns less rpms. Harder to get them going will cause slightly less city driving.
Postmaster
Joined: Aug 2015
Posts: 3,146
Likes: 32
From: Maryville, TN
Bigger, wider tires will decrease fuel mileage in all situations. But gearing with big tires in both instances is what I'm talking about. The 4.30's will motivate those heavy tires a lot easier than 3.73's. And it puts you right back in the sweet spot with less down shifting on the highway. It will be comparable to a 3.73 truck with the smallest factor optioned tire. My opinion, at least for my driving needs, is 4.56 for 35's. I run a 4.88 with my 37's. 4.56 would also allow you to go up in tire size if that's something you are considering one day. If you install 4.30's and go up in size, you will be right back in the same boat. Don't fear the gear. Some people seem to think you will be spinning 3,500 rpm going down the interstate with 4.56 and 35's. You are just talking about @200 rpm jump in rpm in overdrive. My truck cruises at 75-80 all day long in comfort. I average 10-10.5 around town with a heavy foot, and 12.5-14 on the interstate. I don't consider that bad with 37's versus the factory numbers. If you search you tube with "6.2 4.88", I've got several videos posted.
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Gassports
1999 - 2003 7.3L Power Stroke Diesel
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Jun 28, 2010 01:27 PM
