I have read threads concerning gears. They seem to only apply to those that have larger tires and lifts. How would they help my stock 20 rims? How could they hurt?

 

If you were to go up from stock (either 3.55s or 3.73s generally) to 4.10s, you notice a bit more throttle-response and probably a little better city gas mileage. Most people who do this are very happy with it.

 

A higher axle gear ratio means your final drive ratio will be higher. (and every gear for that matter) When I say that I mean it literally as in 3.55:1 is a lower ratio than 4.10:1.* This means more revolutions of the crank per one revolution of the tire.

For practical purposes the result of a higher axle ratio are typically;
Increased towing capacity
Greater torque throughout the RPM range
Decreased zero to 60 times
Decreased fuel mileage (this is assuming no change in tire size from stock as it very often means increased fuel mileage on trucks with larger than stock tires)

*(I have to clarify as it is common to refer to them backwards, possibly because of manual transmissions where the lower the gear your in the higher the numeric ratio)

 

No, it's just like transmissions. A higher numeric ratio is LOWER gearing and the engine turns FASTER for the same road speed.

 

You are one of the poeple I was talking about. You refer to the higher gear ratio as a lower gear. Regardless the fact is that 4:1 is a HIGHER ratio than 2:1 is. That is why I went to the trouble of explaining it.

 

And I maintain that I'm correct, sir. A higher numerical ratio is a lower gear. 4.10's are lower gears than 3.55's. Your RPM's in high gear at a given road speed are higher with a lower gear.

Why is 1st gear in a transmission (typically around 3:1) called LOW gear while direct 3rd (1:1) called HIGH gear?

 

Glc, you are absolutely right. Think about it this way, a ratio is really a fraction. A 4.56:1 gear ratio is LOWER (1/4.56=0.2193) than a 3.55:1
(1/3.55=0.2817) gear ratio.

The entire off road and racing community accepts this as fact. The higher the number, the lower the gears.

 

Thank you. I know I'm older than dirt but I'm not senile - yet!

At least gearing terminology is still the same as it was 40 years ago.

 

I agree with GLC. Lower gears = a higher # ratio.

For the original post. Gears help with acceleration and towing. ESP with factory 20 inch rims it can make a big difference.

The F150 Heavy Duty can tow 10+k. It has the 4.10 gears in the 10.75 rear. Same motor, same tranny. If you were to put 4.10 gears in your truck, it wouldnt legally allow you to tow more than you were rated, but if you were near your limit, it would take load off of the transmission and give better acceleration for merging and passing.

There are formulas to calculate this, but if you have a 32.1 inch tire and 3.55's you will go from 2000 rpm to right around 2300 at 75. The OD on these trucks is deep enought that I wonder why they dont have 4.10's from the factory, at least an option.

I want them, but the install cost is got me stalled.

Also if you put a bigger tire on your truck, you can go back to a stock overall drive ratio since a taller tire has more rollout. You travel further per tire revolution and the gears can put your engine back in the stock rpm range.

The gears available for the 9.75 rear (5.4) are 3.55, 3.73, 4.10, 4.56, 4.88. For the 8.8 there is the same plus 3.90 & 4.30. There may be more ratio's above 4.88 but you are in big tire only territory. Anything bigger than 4.56's are going to be pushing it for a stock or 1+ tire size.

If you want to know how they will affect your truck's rpm range on the highwy, do this simple calculation.

(New RatioXOLD RPM)/old ratio=new RPM at same speed.

Or use one of the web calculators. 4lo.com has a good calc to tell you what ratio will bring your big tires back to stock.

 

I'm sorry but I don't agree with that statement. A ratio is defined as the indicated quotient of two mathematical expressions or the relationship in quantity, amount, or size between two or more things.

While I will grant that it is considered a LOWER gear, the fact remains that the ratio between 4.56:1 is higher (or greater) than the ratio between 3.55:1.

This is demonstrated logically by saying that if my current ratio is 3:1 then my crank rotates 3 times for every 1 rotation of the axle. If the ratio is INCREASED to 4:1, then my crank turns 4 times for every 1 rotation of the axle. However, the HIGHER ratio is called a LOWER gear.

Some peoples may ask "why is that?" The only answer I know is tha it's just what's accepted among the existing racing/off-roading community.

The whole reason I went to the trouble of explaining it was that not everyone that comes along understands that 4:1 is a lower gear than 3:1, so I thought I'd spell it out. However if you look at what I said, nothing that was given in response (with the exception of what I quoted here) is actually in conflict with it.

 

I know that what I said wasn't entirely correct, but I thought it may make it a little easier to understand.