I installed a 4" lift and installed 315/75/16 mud tires. The stock gear ration is 3.73. By going to a bigger tire and not regearing my truck how bad did I hurt the performance. The reason I ask is I took my new 32 foot travel out this last weekend and well I was a little disappointed, on the flats it was hard to maintain 70 mph with out it wanting to shift down into second. On the hills I was in first at 35 mph at 4000rpms, not sure on the grade but steep. I am going to change the gears with some 4.56. Will this help in towing my TT.

thanks
Orlie

 

Howdy Orlie,
My buddy found himself in the same situation as you (same tire size and gear ratio). Aftering switching to 4.56's he saw immediate gains in both daily driving and especially in towing his 12,000+ lb. toy hauler.

Roach

 

Get tyself to a gear CALCULATOR! If you can not google one some body here will post the latest and greatest.


I bet you either suck up the $700-$1900 for a 4.30:1 gear set of the relativly less expensive drop back to 265 series tires... your choice...

To Haul a 5000 to 19,000 lb load you need the motor to turn 2250RPM in top gear

THIS IS A SERIOUS HINT ...... do nto blow off this ADVICE....

The 2 v v10 REQUIRES 2250 and HIGHER rpm to provide enought torque to haul a load!

 

Here ya go on this one. Here's a couple things you can use to figure out your gearing needs.

This one will give you what gears you need to get back your STOCK performance.

(new tire size / old tire size) x current gear ratio = what gears you need to get back to STOCK performance

EXAMPLE: (35 / 31.5) x 3.73 = 4.14 (4.10 is closest to this)

This on will give you the effects that different gears will have in RELATION to your ORIGINAL setup. EFFECTIVE GEAR RATIO is what your truck would perform like if you still had the stock wheels and tires.

(old tire size / new tire size) x gear ratio = effective gear ratio

EXAMPLES:

(31.5 / 35) x 4.10 = 3.69 effective ratio
(31.5 / 35) x 4.30 = 3.87
(31.5 / 35) x 4.56 = 4.10
(31.5 / 35) x 4.88 = 4.39

So if you want your truck to perform like it was originally equipped with 4.10's, you would need to install 4.56's. If you want 4.30 performance, install 4.88's. You get the point.

 

So what your saying is when I'm pulling my TT I need to be at 2250 rpm, now I do not pull in over drive so is that 2250 in overdrive or 3rd gear.

So today I took the truck on the freeway and at 65 mph in overdrive I was running 2000 rpm's. Does this sound right, can anybody give me feedback as to what rpms you guys are running in overdrive, what speed, and what gear ratio you have installed.

I went to the gear calculator and at 65mph with 35in tires and 4.56 gears I should be at 2015rpms, and thats what I am reading on my tach. When I enter in the 3.73 gear ratio which the tag on the pumpkin reads then I should be at 1650rpms which I am not.

I did not buy the truck new and it did not have the lift or the 35" tires when I bought it. Is there an easy was of finding out what gear ratio is installed with out removing the pumpkin cover.

I hope some one can take there truck for a ride and record the rpm's at 65mph and post the info with tire size and gear ratio.

thanks
Orlie

 

Check the tag in the door jamb - there'll be an axle code, write that down and check it against the data in the facts thread that's stickied at the top of the super duty forum. That will tell you the factory gear ratio.

I've got 3.73 and 265/70's and I run about 1850 rpm @ 70 mph. Hope that helps.

David

 

Most 99-2004 V10 with auto trans and 3.73:1 gears with the typical 30.6" tall tires (265 series) would run between 1900-2100rpm in OD (.71:1) 0r 2300-2500rpm in high (1:1) at 70mph. This is pretty far down in the power band but good enough for empty cruising. In OD most slight hills force a Torque Converter unlock and perhaps a down shift out of OD to high gear.

Whenever you change effective gear ratio by putting on taller tires there is a point where you force the cruise rpm too far below the optimum (2250rpm in OD empty cruise at 70mph) and need to consider re-gearing the differentials.

This is a place where more is not better. The costs of 4.10/4.30/4.56/and 4.88 gear sets are all within $10. If you go all the way down to 4.88 you will be screaming along at 70mpg in OD sucking great gobs of gasoline.

If you just work from empty weight cruise rpm and re-gear for optimum then you put the beast back to best configuration for the occasional heavy load up steep hills.

The dynamic here is leverage (torque) and a tall gear 3.73:1 and a tall tire reduce the torque applied to the road. By re-gearing you can gain back a significant amount of that leverage. (of course it is always cheaper to add a set of 225 tires and wheels just for heavy towing days) Yea yea yea I KNOW... dinky tires looks stupid on a lifted truck....

FWIW I have yet to find the off road hunting or fishing grounds that made me think I NEEDED any lift on a standard Ford 4x4 truck... but hey that is just me. Yes I think lifted trucks are cool.... but it follows that "you wanna play you gotta pay"!

 

I understand bigger tires require gears, but what I really need is rpm at what speed and gear ratio, it would be nice if someone with 35" tires would take there truck for aride and let me know the info above.

thanks
Orlie

 

This will calculate any combo you can imagine:
http://gs.tolan-hoechst.com/tirecalc.htm

 

Man, using that gear calculator was a real wake up call for me. With my 37's and 3.73's, that put me at about a 3.08 effective gear ratio (ugg!!). Looks like I'll be asking for some 4.56's for christmas this year.

Now that I think about it, if I regear, am I going to have to reprogram the computer? I had my local shop adjust my speedo/tranny with my bigger tires (I don't have a programmer/chip) years ago so I'm thinking now if I get gears, that'll effectively take me back to a "stock" ratio and my speedo and shift points will all be wrong, correct? I could be way off, just thought I'd throw it out there.

 

Re-gearing on the Superduty's does NOT require a computer re-program.

Changing tire size DOES.

At one point in this thread, you said 2000RPM at 70MPH? That's not a 3.73 with 35" tires, I bet you didn't re-calibrate for the larger tires, did you?

 

Now im getting some answers, I did not know that changing tire size you needed to re-calibrate. So what your saying is my rpm is wrong on my gauge. Correct me if im wrong.

How do I get my re-calibration for my truck.

thanks
Orlie

 

Yes, your RPM is right, but the speedo is wrong! You are going much faster than you think! 13% wrong, or thereabouts, 35" (your current size) divided by 31" (or actually smaller for stock tires), equals 1.129 - or 13% increase in speed.

The dealer can re-cal the computer, but the Superchips tuner and others can do it too. Get a GPS, they can measure actual speed.

But still, that 3.73 is going to kill you with 35" tires.

 

ORLIE-
http://www.onlineconversion.com/tire...conversion.htm
Above is a tire size calculator. Stock tires (265) are about 31.5 and 35" differ by brand. Some 35"s are only 34.2 inches in diameter so the website is a great guestimate. I have a V10 and 35" tires with stock rims and 3.73 gears. See gallery for pics. I did not adjust the speedo for the new tires and mine is 9% off where the website shows about 10.7%. Close enough. My truck is turning about 2000RPM at a stated 71MPH which is an actual land speed of about 77MPH. The way to check without fancy tools is to use the interstate mileage markers compared to your odometer. The more miles the better. 50 miles traveled but only 45 miles on the odometer is a difference of about 11%. I usually check mine in 10-50 mile increments and do it every so often as the tires wear down. Yours at 65 at 2000 is a little different than mine but our 35" tires may be a little different in actual size. Gears will deffinitely help you towing. I do not tow much weight and am happy with what I have. If I did tow, I would change gears or add a supercharger. The blower would add enough power to offset the gears but then I am sure the tranny would be the weaker link. If you tow often, deffinitely get lower gears.