Gear Ratio

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Oct 1, 2001 | 06:43 AM

Ripman

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Senior User

Joined: Jul 2001

Posts: 119

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Gear Ratio

what does it mean? like my 99 150 offroad has i think 3.53 and the standard f150 has i think 3.78,, is it something to do with axel to gear.. and does it mean i have in a 3.53 more torque to get up, across in thru the woods.

Nothing like using your truck for whats it made for and put it to the test while hunting.

Oct 1, 2001 | 03:36 PM

weldman

Fleet Mechanic

Joined: Feb 2001

Posts: 1,290

Likes: 15

From: Toronto, Canada

Gear Ratio

Rear axle ratio is the number of times that the engine turns to one revolution of the wheels.

Therefore if you have a numerically higher ratio, your engine will turn more times, giving you better takeoff, but slower topend speed.

Ihope I've explained it well enough!

Matt
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/weldman/3b8be147257a8888.jpg

1978 F250 4x4 - 351M
Don't crush them, restore them!

Oct 1, 2001 | 03:47 PM

JimCaudill

Junior User

Joined: Jun 2001

Posts: 77

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From: Dayton, Ohio

Gear Ratio

Weldman came close and did have the right general idea. The ratio is the number of turns the pinion gear will make (same as driveshaft revolutions) for each turn of the ring gear (the same as axle revolutions barring any differential action). The higher the ratio in numeric value, the greater torque that will be available at the rear wheels and the faster the engine will have to run to go down the road at the same speed. Actual overall ratio of engine rpm to road speed in mph is a function of transmission gear selected (and whether overdrive is in use), rear end ratio, and tire/wheel size.

Oct 3, 2001 | 09:50 PM

qwpo

Freshman User

Joined: Nov 2000

Posts: 25

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Gear Ratio

Think of it like your old 10 speed bike...you pedaling the crank equates to the drive shaft. The bike's rear wheel (axle) equates to your truck's rear wheel (axle). 1st gear on your bike equals a high gear ratio number; you can climb a steep hill but pedal like a mad man to go fast down the road. 10th gear equals a low ratio rear end; pedal lazily to go fast, but you'll conk out trying to climb a big hill.
As Jim mentioned, other things come into play also...tall tires has same effect as reducing your rear end ratio (plus added stress to the drive line) Shorter tires has same effect as increasing your rear end ratio.
The bottom line: How many time does my drive shaft have to turn to get one turn of the axle ??? That is your rear end ratio.

Oh, and don't forget the gear ratios in your transmission. For example overdrive will have your drive shaft spinning faster than the engine (about .7 RPM will give you 1 revolution of the crankshaft with today's transmissions)

Clear as mud now ?????