I hope to order gears for my 04' f250 6.0 friday. I'm still not sure which ratio will work best with my combo. Truck is cc sb 4x4, has 4.5" lift and 35's. Ofcourse axle ratio is 3.73 now. I would like to lower egt's when towing (less load on engine), and get back some of my low-end at the same time, but I hope not to loose to much in the way of milage. With the 35's and 3.73's my effective ratio should be around 3.43 now. If I go with the 4.10's it should be around 3.77. If I go with 4.30's, my ratio should be around 3.96. (ex. tire size as from factory 31.8"/ new tire size 34.5" x 3.73=3.43) I am leaning more toward the 4.30's even though my ratio will be a little lower than stock due to the fact the bigger tires and high vehicle generate more load and drag. Please double check me and let me know what everyone with similar set-ups are running, then I will order the most common choice!! Thanks for all opinions.......hc

 

If I am not mistaken, most guys have been running 4.30's and 4.56's to keep the ratio within near factory specs with 35" tires. Go back and check your calculations, something seems a little funky in the math there...

No offense, not calling you stupid or anything of the such...but I am 99% sure that 4.10's will be nowhere close to the correct ratio for 35 inch tires.

 

Actually 4.10 gears will be right on the money with 35's if you want a lower ratio the 4.30 gears is what you will need, but 3.73's and 31.8" tires and 4.10's and 34.5" tires will be about .5 MPH different @ set RPM,

Hope this helps,

 

Just a question, i was about to put some 315, 75's which is 34.7 inch. Starting to think truck would run better with a gear change. dont want to loose anything. Question is whats the ball park it should cost to change to a 4.10 from the 3.73?

 

When you say lose anything...
do u mean the speedometer correctness (which can be adjusted)
or do u mean the performance ?
If that, spend the money on a diablo predator tuner and it won't matter which gears you have in there

 

This is very true with the Predator. I was more curious about the lose of low end.

 

4.10 is right on the money and you are doing your calcs correctly. Don't let anyone call you stoopid!

4.30 will lower your gear ratio giving you more power (but this will most likely be offset with the increased rolling mass).

Remember, every pound of rotating mass you add is equivalent to 15 static pounds getting lugged around in the bed of your truck!

 

My stock tires have a rolling diameter of somewhere between 30.5 and 31 inches. I have the auto tranny and a 3.73 rear end.

But doing the math using 31.65 inches as the specified tire diameter and discounting the actual rolling diameter for now, each turn of the crank comes out to:

((1 * rev) / (0.712 * 3.73)) * 3.14 * 31.65 in = 37.44 in per rev

Doing it again for a tire with a 35 inch diameter, each turn of the crank comes out to:

((1 * rev) / (0.712 * 3.73)) * 3.14 * 35 in = 41.403 in per rev

To get to the same distance traveled per rev for the 35 inch tire, the rear end ratio would need to be adjusted to:

3.73 * (41.403" / 37.44") = 4.125

You can simplify this by just multiplying the current rear end ratio, 3.73 in this case, by the ratio of the two tire diameters in question.

I.e., 3.73 * (35" / 31.65") = 4.125

So if you happen to have different tires or know the rolling diameter of each tire, use those instead.

Then pick the closest available rear end ratio.

If you know that you will be towing lots of big loads, or might go with even larger tires down the road, go with a higher ratio like 4.30 versus 4.10. If you'll just be lightly loaded and doing lots of highway stuff, then the 4.10 would probably serve you better.

 

If you were alluding to my first post, let me just set this straight.

I did not call him stupid, and I did not say that he was wrong. I simply stated that 4.10's for 35's simply sounded a little odd, and for him to go back and doublecheck the calculations.

I am done posting for the day; I'm in the mood right now to blow my own head gasket and get kicked off this forum.

 

uh oh...
did the test not go well ????

I find that hard to believe... but even nice smart people have a hard day sometimes....
makes life more "interesting"

 

The test went fine, actually.

Just been a combination of things...topped off by coming within .01 nanometers of a knock-down-drag-out with the service manager at work.

 

...I went back through this thread and found nowhere... that ANYONE called someone stupid. I would appreciate, you not starting something by using those words.
.. We here in the 6.0 area respect each other’s beliefs and knowledge. Sometimes we disagree however we do not call people stupid.

 

"I'm not calling you stupid or anything" is insulting in itself

 

Difference in a qualifier or a directed statement

 

Listen, and listen carfully...I said that in case that my previous statement (being "something seems a little funky in the math") came across as insulting. I said that to make sure that noone THOUGHT I was insulting him.

You might ought to mind your own business. I am not in the mood to listen to a line of crap.