SuperRhino

I just purchased a 2005 F150 Supercab 5.4L, It looks like the previous owner sunk a lot of money into the truck, as almost everything on it is custom.

It is lifted with 37X13.5 open country toyo MT's. acording to the sticker in the door the factory gear ratio is 3.73, but the truck has way to much kick in it to be running those gears, when I step on the gas, it gets up and goes!! (I test drove a 2002 screw with 35" tires and it was like driven miss daisy to get up to 75 on the interstate, obviously had the stock 3.55 gears in it)

can anyone tell me a educated guess as to what my gear ratio might be, I check the speed vs my gps and the gauges are accurate so it had to of been chiped or tuned to compensate for the larger tires.


37X13.5x20 tires

around

1800 to 1900 RPM @ 60MPH
2400 to 2500 RPM @ 75 mph

these RPMs are in overdrive.

I am getting around 12 MPG on the fuel is that about right?


Loves the truck so far pictures coming soon!

My only complainet is at around 60 to 70 MPH when I step on the gas I here a loud whinning noise from the front of the truck (assume its a loose hose or air leek?) when I take my foot off gas noise disappears, when cruising at 75 mph I dont here the noise seems only at certain speed/rpm this happens.


anyone help would be awsome. This is the 2nd ford I have bought, and my first full size truck. (1st was a 2002 mustang gt still have it and love it!!)

Thanks!!

driver444

Educated guess... 4.56

Easy to chech though, jack up the back of the truck, turn the tire exactly 1 revolutoin, and count how many times the drive shaft goes around.
If it goes around about 4.5 times, you have 4.56's. If it goes around about 4 times, you have 4.10's ETC.

SuperRhino

it was about 4 1/2 turns didn't check it exactly to the T.

I assume 4.56 gears are the ideal setup for 37" tires?

Mph is about 12 does this sound right?

With this gear tire setup would I be able to occasionally pull a two horse trailer saftely about 500 mile round trip during hunting season (about 6000 pounds loaded).

Any comments about the noise I am hearing and specific RPM/MPH range.

ak_cowboy

Check the fluid in your front differential. The 4.56s should work fine for towing and everything else.
Also, is your speedometer correct for the larger tires? I'm getting 12mpg on stock tires with 4.10s, up to 14 on the highway. So I wouldn't worry about your fuel mileage too much

SuperRhino

I checked my speedometer with my gps, and everything appeares to match up. cruising at 75 on the highway I stay consistent with the flow of traffic.

the previous owner must of had it chiped or tuned to compensate for the tires, so I dont know if buying a edge or a gryph would help me much.

Larryw1

I have BFG 36" 35.51 according to the specs 4:56 gears

at 70 mph in OD with the cruise set and with my speedo cal. with my programmer. 70 mph 2000 rpm if I was to go to a taller tire as in a 37" my rpm would drop.

Now here is a chart from 4 wheel parts. but I would guess this would be close if you were out of OD and they don't account for sizes like 34.9 or 35.51 but it could be close. this would give you a close idea.

http://www.4wheelparts.com/aux_incl/gear_ratio.html

SuperRhino

well I don't have it exactly narrowed down, but I have at least 4.56 if not 4.88 gears. I love how the truck drives! This weekend gonna flush all the fluids in the differentials and the tranny hopefully clear up that whining I am hearing occasionally, and if it doesnt guess it wouldnt hurt anyway with 102k miles on the truck to do it.

Larryw1

you led me to believe you had 4:88 by your rpm's but then you said by counting the drive shaft rev's it might be 4.5

use the chart and do readings out of OD so you are 1:1 ratio and do the speeds on the chart. What were they 65 mpg. on a standard trns
so don't use OD? that may be close. bu tcount your turns on the dr shft. mark the shaft if you have 4:88 it will be just a hair over 4 3/4 of a turn or between 4 turns then the last turn should be .88 of the turn just under 90% around 10 or 11 o'clock

does this make sense?

SuperRhino

Thank you guys so much for your help! Soon as I get off work tommarrow tommarrow gonna get the exact revolutions, and rpm out of overdrive.

SuperRhino

Confirmed 4.88 gears!