Need some advice:

Live in Houston (super flat), travel 70 miles to work and back daily all highway, have an '02 F250 4x4 crew 6" lift w/ 35x14.50x16.5 SSRs. Already have gauges, upgrades in the intake/exhaust depts., and a programmer set @100 HP.

That's the setup, here's the question - currently, I have stock ring and pinion gears 3.73. MOST of my time is and will be in the future, unfortunately, on pavement, flat pavement. I sorely miss my low end accelleration. I want to replace my stock gears with a lower ratio to compensate for the larger tire diameter and get the feel back more towards stock. I have purchased a new set with a 4.56 gear ratio but now I'm having "cold feet" about changing them at all because of the concern that I have bought a gear ratio that's too low.

Should I go ahead and install (gear ratio OK) get a higher replacement set (4.10 or 4.30) or leave the 3.73s?

Keeping in mind that I'll probably get some taller, narrower tires and 18-20" rims in the future....

COMMENTS, ADVICE, RECOMMENDATIONS, and SUGGESTIONS are WELCOME!

Thanks, Bill

 

Bill,

I'm running a V10 with 36's and 4.56's and I still think I should have gone 4.88's.

Try out the calculator in my sig, it might help you out a little bit. It's pretty self explanatory.

It the calculation puts you between available gear sets, go to the numerically higher one. Remember that you are taking into account not only the larger size tire, but the width and rotating mass as well.

EDIT: If you are planning on going larger than the 35's, I would definitely go with the 4.56's.

 

Great reference, thanks! I see what you're saying...I used the gear ratio chart you'll find on 4Wheelparts.com - go to any tire or wheel page and you'll see the gear ratio chart hyperlink. I wanted to get the gear ratio in the low overall performance bracket and high in the economy bracket. If the 4.56 is a little higher than stock I'll be OK with that; just wanted to ensure that it wasn't going to be too, too low because of all the highway driving I do. Thanks for the help!

 

I have a V10 and just installed 4.88 with my 33s, my original plan was to move up to 35s in the future. Primary objective is easier towing of my boat over the grades. Eaton posi in the rear and a LockRight in the Dana 50 - the truck is like a cat with its claws extended when the 4x4 is engaged.

I like the 4.88 with 33s so much that I don't want to go up on tire size. Just installing Bilstein 71000 on all four corners, so no lift and no new tires for me. V10 tachs 3100 at 80mph and seems very happy.

 

Holy Cow, what a difference! I'm going to have to get used to this....the jury is still out. The 4.56s has made the truck very responsive; the spongy low end feel that was there with the 3.73 has vanished - this is a good thing. But, it seems that my highway driving cruising at 70-75 days are over. I'm way out of the sweet spot of 2000 rpm at that speed - I hear the gears whirring just over the tires' singing (SSRs). Feels like the gears are holding the motor back, I know it's a skewed perception because it's different, but it is what is! After paying that huge bill to get the gears changed, I'm not too hip on changing them again any time soon (my wife is on the verge of doing something, I'm keeping her in my peripheral vision...). I've got 35x14.5x16.5s on there now (6" lift), when the tires need replacing, I'll sell the rims and get larger ones with taller, narrower tires, like 37x12.5x18 w/right backspacing - do ya'll think that would take care of getting me back to the "sweet spot" at 70 mph? Hope so because right now I feel I've over-geared, should have went with 4.11 or 4.30? Or, is all my panic much ado about nothing?

 

Hi Guys, I have been wondering the same thing about changing gearing. I have an '04 F250 PSD 4X4 with a 6" lift running BFG 35" 0n a 17" rim. If I was to change the gearing to bring it back closer to stock would it effect the milage for better or worse? and do you have to change the gears in the front pumpkin also? I was told you did? Yet I havn't heard any mention of this here. Thanks for the input.
Richard

 

Yep, change the back, you got to change the front, package deal. From where I'm sitting, my 4.56s didn't help with mileage - yowza. I can't provide any real advice yet, too soon post 3.73 changeout. Ask me again in amonth or so.

 

Thanks Bill

 

Do not ever expect to make up the cost of the gears and install with ANY mileage you may / may not get. Think about it, let's say you did your gears and install for $1500 (conservative). That is gonna take a good little while to ever make up.

The purpose of gearing is to put the engine in the correct power range. Lower RPM does not always equate to better mileage, having the engine in it's proper range for the driving style will though.

I like stealing Monsta's line, "Choosing gears for economy is like getting a Diet Coke with a Whopper Meal!"

Bill, you'll get used to that power real quick.

 

Lookin' forward to it, Beefer! Thanks for the clarification (and hand-holdin'). B

 

Thanks for the reassurance, KC - I'm feelin' better already! You're right, I found a bit of soil this afternoon and stomped - I about jerked my fillings out! I've got Bilsteins all around too, 5100s, duals in front - very wise of both of us!

I'll be installing a Superlift Tru-Speed Calibrator this weekend so I'll know exactly how fast I'm going and at what RPMs (yeah, I know there's a formula). B

 

What RPMs are you turnig at 70, Bill?

 

Want to be accurate, Cokeman, so I'll send a note to all after I install my Tru-Speed. To answer your question now, though, without oversize tire adjustment at 70 I'm at approx. 2200 rpm.