I've been researching several threads on different gearing options for 35" tires but still haven't found an answer that I'm looking for. I have a 4" lift and 35" tires.

First of all, at the present time my truck is not my daily driver. I've owned it for over a year and only have 6,100 miles on it. However, my round-trip commute to work is 80 miles of nearly all freeway. My daily driver ('92 Grand Marquis) certainly isn't going to last forever, and is going to crap out on me one of these days.

I was under the assumption that my stock 3.73 gearing would actually give me better gas mileage at higher speeds (70-75mph) with 35's because the RPMs are lower at that speed than stock. I recently got back from a 1,000 mile round trip of all highway/freeway driving and only got 15 mpgs compared to about 17-18 with stock wheels/tires.

So, my question is: Was I wrong in assuming I would get better gas mileage at higher speeds with stock gearing and 35's? My truck is probably going to be my daily driver at some point so would it be better to get 4.56 gearing for my commute or just stick with stock 3.73s?

I know the 4.56s would help out a ton around town....it's the freeway driving I'm wondering about. If the 4.56s will put my gear ratio back to nearly stock, will I get about the same mileage on the freeway as I was with stock tires?

Thanks.

 

I'm running 35s with 3.73 gears and on the open highway it downshifts on hills, because my rpm about 1200 rpm. My stock tires it doesn't downshift. When you add bigger tires ,you raise gear ratio and weight(tires).I'm planning on getting 4.56 this spring.

BTW; Thats a nice setup 4" with 35s. If I didn't tow a camper thats my choose of lift. I'm afraid my drop isn't low enough for a 4" inch lift.

 

While many will say that an F-150 is not ideal commuting vehicle no matter what gears you have, I would have to say that the 4.56 gears would be a good combination for your 35" tires. I was in the same situation as you when I upgraded from 3.55 to 4.56 on my 2002 F-150 and was told that going to 4.56 would put me pretty close to stock (3.55) while running 35" tires.

I'm currently running 33" tires with plans of going to 35" tires once these wear out. I average around 15 mpg but my truck is not my daily driver. My RPM's are a bit higher but I rarley take my truck over 70 mph where I'm running slightly over 2000rpms.

 

http://www.4lo.com/calc/geartable.htm

chart to help you out

 

Thanks for the replies so far guys....after looking at that chart I'm thinking maybe the 4.10s will be a little better for the highway. Of course, the 4.56s would be better in stop-and-go rush hour. :o

I'll probably just start saving up for the 4.56s and get those eventually.

 

No matter what gears you get, the lift and the big heavy tires are going to kill mileage. I'd look for something else to replace the Tankury with for a daily driver when it dies, like some 4 cylinder sh1tbox.

 

I too, am thinking of doing the same thing. Something Ive ran into is that 4.10s are hard to find for the front diff. (if you have 4x4). If anyone knows anything bout that...

Also, heres another site for calculations....
http://www.izook.com/gearcalc.htm

 

Here's a front/rear package if you're interested:

http://www.4wheelparts.com/PDT291600.aspx

 

My mistake, its the 4.30's Im having a hard time finding for the front.

But hey, thats a pretty good deal. Thanx for the link.

You know, Im new to this forum, but im likin it quite well.

 

get 4.56's

only thing i dont like about them is i cant take 3ed gear to fast

im at 110-113 at 5k

but me and my 35's would never go lower then 4.56's
some times i want 4.88's

 

That's because they don't make them for the front that i know of. That is the ratio i would like also but nobody makes them yet that i have found

 

Mine is a DD with V6 4.2L & 4.56s with 35s does fine just not the best gas millage...
Most of my driving is freeway about 1.5K a month

 

how do u find out if your front Ring and Pinion are reverse cut?

 

I am in somewhat the same boat. I also agree that any full size truck is not a daily driver(unless you use it for your business) with the price of gas, I will look at an economical 4 banger. I think I will be getting 4.88 gears for my truck. I was told it is only a 7% difference over the 4.56, and I definitely want the truck to have some more power for going in the mud, sand, towing and hills. Also I have read some guys wished they had gone 4.88 instead of 4.56. In some instances, I have seen the 4.88 cheaper also. It is a few hundred RPM at highway speed higher, but again, she is NOT going to be my daily driver. I think you should stick with the 3.73 if you will do alot of highway driving. You'll easily spend close to a grand on gears and install and that could be gas money for the next few months on your 3.73. It won't feel as powerful, but you can stay at 70 while keeping the rpm's down. JMO

 

Definately go with the 4.56s. I have them now and am running 37x13.5 and with i had 4.88 sometimes. Quick question for the other guys reading this though, does anyone know how hard it is to replace the rear pinion seal on a f150?