I have a 2007 f250 5.4 4x4 with the 3.73 gears. its at about 97,000 miles. its sluggish stock but Its lifted 6 or 8 in. with 35x12.5r18 toyo a/t tires now its really sluggish. going 65 mph if the wind blows hard it downshifts. I want to change the axle ratios but stuck on which ones I should get. I want it to be a lot more powerful but not to much that the rpms get to high on the highway that it causes the engine to wear out faster. any help is greatly appreciated.

 

Stock tires I would do 4.56....So 4.88...I would love to do 4.56 on mine.

 

4.30 is a great effective ratio for these gas engines, better for towing and general all round performance. With 35" tires you will need to go with 4.88 gears to get to an effective 4.30-ish ratio. That is the combo I am running on my '05 V-10 EX, 4.88 gears and 35" tires with an effective ratio of 4.39. I use this EX for towing almost exclusively, the improvement in towing performance was night and day with the new gears vs the stock 3.73s. Your RPMs will not be super high on the highway, at 65 MPH I am turning 2230 RPMs in OD. With 32" tires (near the stock 31.6" size) it was spinning at 2430 RPMs and even that was perfectly comfortable and didn't seem too buzzy.

 

thanks for the help. iv read other posts similar to mine but no one has really touched on the point if going to this low of gears will wear out the engine before its time. thx

 

I don't really see how turning a few extra RPM which will have the engine NOT working as hard would wear it out sooner, making life easier on things generally tends to extend their lifespan.

 

ok. I was thinking that but also thought maybe because of the extra rpms over time it may wear more. that makes since though. thanks

 

Piston ring wear is directly correlated to piston speed and piston travel, ie feet per minute and feet per mile, as well as other things like fuel rate and piston temperature.

Simply put, the faster the engine speed and vehicle speed, and the more fuel you burn, the greater the engine wear.

You hear a lot of talk about an engine "working too hard", but there's really no engineering reason an engine would last longer by going to steeper gearing.

It's urban legend at best.

Part of the reasons modern engines last longer is that modern drivetrains with overdrive transmissions reduce piston travel per mile driven.

There are obviously many other material and design improvements over the years through improved modeling and understanding, also.

 

Next time your going down the highway, at about 60 mph, turn your OD off. This should put you really close to how you will be geared with 4.88's at 70mph. See if you are comfortable with that if you go on a long trip. My opinion, if you tow heavy and often, or 99% of your driving is local and 55mph highway, get 4.88's. If you travel the interstate empty or light a lot, go with 4.56. 4.56 will put you real close to a factory geared 4.10 truck.

 

Counter thought.
Stop saying 60-65 mph my rpm is...

In much of the country 70 or 75 is the posted speed limit. Some folks still go 5 (or more) mph faster. So, realize when not towing, you will be turning much higher rpms if you are going 75, but with your lift, maybe you should stay at 60-65?
I grew up with 55 mph speed limits, so going 70-75 legally feels awesome, I have no need to be the fastest vehicle any more. I like cruise control and just going faster than the slow vehicles while enjoying the drive.

 

If that's geared towards me at all, you need to reread my post. And when I'm in the truck, I do try to stick to 70-72. The fuel mileage drops off terrible after that because of wind drag on big azz brick. I also don't tow over 65, as most trailer tires are only rated to that.

 

Not "aimed" at anyone. Just pointing out to the OP, and anyone else, considering regearing with large tires and a big lift to consider driving hundreds of miles on interstate highways (not towing) where speed limits are 70+, it is tough to drive 60-65, and going 75 will greatly increase rpms, and destroy fuel mileage.

 

I also see the op is from Florida, this has me to push the 4.56 over 4.88 even more for him.

 

To the OP do you tow or off road your truck? If no I'd go 4.56 gears since your in Florida,like and it's flat, IF you tow or go offroading defiantly do the 4.88 gears. Like stated above a 4.88 gears will give you the feeling of stock tires with the factory optioned tow gear which is 4.30, my truck had 3.73 and I had 4.30 installed and now low the combo from my 5.4. I'm will be adding a 4"n lift with 35" tires hopefully before summer and I'm trying to save up for a gear swap AGAIN because I feel the 4.30 won't be enough for the 35" tires and for the fact that I do tow trailers, I'm in South jersey but we go to Pennsylvania a lot so I'm always up in the hills so I'll need a 4.88 gear. I'm just trying to say think long and hard about this, when I did 4.30 gears I just jumped into it because I didn't think about the future with adding a loft and larger tires. Now that I'm ready for that I know it's going to make the truck sluggish and when I do go off road 4wd high is going to be useless

 

Or just go back to factory size tires..thats what I did ..left me 20 inch 34 in tires behind and when back to factory 18 in wheels around 31 in tires with 4.10 gears...add a tune and its way cheaper then re gearing which is a major expense - just my 2 cents

 

Go with 4.88's. Especially if you tow relatively heavy.

As you can see in our signature that we're running 4.30's behind our 5.4 with stock 31.5 inch tires. We tow heavy about 80% of our yearly mileage. Occasionally I wish I had gone with 4.56's or even 4.88's. The 4.30's made a world of difference but if we're bucking a stiff head wind while towing the steeper gears would be helpful.

In your case with the tall tires it's a no brainer. 4.88's should be your optimum choice.

Good luck and let us know what your choice is and how satisfied you are.