1995 f-150 currently running 3.08 gears. The truck has a 4 in susp lift and is running 33's. Needless to say, 5th gear is useless.

I want to get back to a best mpg without sacrificing drivability. Originally I was thinking 3.55's would do the trick. I don't tow much but I do use the bed to haul. However, after reading threads here it seems that 3.73 might be better.

Currently I get only 10-13 mpgs. I think part of that is the poor gearing/tire combo.

So what gears to get me back to a more stock performance and better mpgs.

 

I have 3.55 gears and 35"s with a 7 inch lift and 5th gear is useless too.. I barely ever drive on the highway for very long but I want 4.11's. I had 3.55's and 33's and it was hard to stay in 5th only if it was flat and not windy...

 

Do a search.

 

Thanks for the help chief. I did a search already but I was unable to find much that addressed my question. I've also run the calculators. However, most guys seem to want "more power" and that's not what I'm after. I need mpgs and drivability and if possible I'd like some experiential feedback before I go looking in the yard for another rear end... that just sounds weird.

 

What the fuzz.. I enjoy the conversation.

Okay man let's start with the basics. I already know you have the M5 and 3.08 gears. The important missing peice to this puzzle is what engine do you have?

 

Nevermind. I just realized this is in the I6 part.

3.73 gears would give you the best for fuel mileage.

 

I too enjoy the conversation. I don't mean to come off harsh.

Anyway, Doing the calculators (4lo) 3.55's would put me at 2000 rpms at 70 mph. 3.73's would be 66mph. I'm assuming here that 2000 mph would be about the optimum cruising rpm. Am I right in that assumption?

My driving takes me mostly in the 50-60 mph range on smaller country highways. I only drive about 10 miles at a time back and forth to school (chem teacher :-) ).

So according to that logic the 3.73's would be right. However, according to the gear change after tire swap calc on the ranger station I get a ratio closer to 3.55's for stock performance.

Hence my questioning.

Factor that in reality these are relatively minor changes in ratio.... will I see much difference in mpg's and driveability?

Thanks for bearing with my semi-coherence and relative harshness.

 

You didn't come off any harsher than I did. I'm just tired tonight, sorry!

A 33 inch tire is a big tire. You will need a 3.73 gear set to really get the best mileage out of you 300. I don't care what the calculations say.

I'm going to give you my own specs. Maybe they will help you out. Other men will chime in here and be able to give you a more intelligent answer than I can. I'm horrible at explaining things.

Okay, here's mine.

300, 4-speed automatic with OD, 31'' tires, 4.11 gear set.

60 mph @ 2,200 rpm. Fuel mileage at this range is 16.5. Power in the bottom end is great. Top end power isn't great but this isn't a hot rod truck.

I really believe that if you're looking for fuel mileage with your large 33 inch tires, 3.73 would be perfect for you. A lot of guys run 33's with 3.55's.

Thing about it, there's not much difference between 3.55 and 3.08 when it comes to a large tire like that. You're going to put the money and effort into two sets of gears - for very little change in power and fuel mileage. You will also still need to give it plenty of GO pedal just to get the truck moving.

Remember, the taller the tire, the higher the gearing.

You want fuel milage. 3.73 will give you that but you will also be surprised at how much power you get back.

I'm sorry if this sounds like a drunk post. I'm completely spaced out tonight - just tired.

I hope I helped!

 

i def agree with bill. 3.73 with 33" would be perfect. thats what i plan on for my truck, when summer comes around (too much ice for those tires in germany). my buddy has 3.73 and 33" on his silverado and he drives 45 min from his house to work on the interstate everyday. he said he gets decent mileage

 

Alright, sounds like I'll be scoping the bone yard for 3.73's. Thanks for the help guys!

 

It's a big tire but if you're geared for it and have OD, I don't see why someone couldn't get a solid 15 mpg highway!

 

One thing to keep in mind is that just because the gear is overdrive doesn't mean it's necessarily going to merit better mpg at highway speeds.
Look at it this way: (4th gear is a 1.00 ratio and 5th is a 0.80 ratio)

4th gear, 33 inch tires, 3.08 rear end, 60mph = 1900 RPMs
5th gear, 33 inch tires, 3.73 rear end, 60mph = 1850 RPMs

All your going to change is what gear you're going to be cruising in at highway speed, but your engine RPMs are going to be pretty much identical. It'll be a lot of swapping work to end up right where you are now (at least at highway cruising).


What you will do, though, is increase your acceleration in lower gears, which will definitely help with around town mpg and regain the use of your whole transmission.

Just some food for thought.


One thing you may want to try is hooking a vacuum gauge up to the intake. When at the cruising speed you like, go through the different gears and get a feel for what RPM range gives you the highest vacuum, and then figure which rear end ratio will put you at that RPM range in 5th and go from there.