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Someone want to explain rear end gearing to me?

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GasX

Lifer
Feb 8, 2001
29,033
6
81


<< Some newer cars with overdrive transmissions can handle 4.10 gears in the back.

There is also more to the equation. The height of your rear tires can effectively change the ratio of your rear end gears. For example, if a guy has a big four wheeler and gets maybe 35-38&quot; mud tires on it, he may have to drop to a 4.56 gear or lower to maintain the proper final drive ratio of his vehicle. The motor may not have the torque to turn the taller tires without the assistance of the lower gears.

If you put shorter (heightwise) tires on a car, you will be effectively lowering...(higher numerically) your rear end gears.
>>


How can that be? A turn is a turn is a turn.

You will screw up your odometer readins, but the gearing will not change.
 

Sluggo

Lifer
Jun 12, 2000
15,488
5
81


<< but the gearing will not change >>



The gearing itself does not change, but the final drive ratio will change, making it feel like the gear ratio has changed.

Also do lots of checking before you let any ole' idiot start tearing into your rear end gears. There are lots of shops that specialize in rear-end set-up, and doing it wrong will cost you a fortune in the long run. There are lots of clearance, backlash and other specs that must be strictly adhered to or failure of the new gears, and ultimately the entire differential carrier will be a common and recurring problem.
 

GasX

Lifer
Feb 8, 2001
29,033
6
81
What happens is that the bigger tire radius makes the circumference of the tire higher. Therefore, in order to spin the wheel once, more power is needed to move the weight of the car the additional distance.

Nevertheless, you still have the same number of turns in the drive shaft to turn the wheel once. The gear ratio is not changed, but the performance characteristics of the car are.
 

Sluggo

Lifer
Jun 12, 2000
15,488
5
81


<< you still have the same number of turns in the drive shaft to turn the wheel once >>



But, the actual turn of the wheel is what is changed. A taller tire has a much longer &quot;turn&quot; than a shorter tire. The taller tire has a much larger circumference. It takes the same number of turns of the driveshaft to turn the hub of the wheel, but the vehicle travels more distance for the same turn of the hub

Its not the gearing, but the taller tire changes the effective gearing.

I think we are saying the same thing, just using different terms.
 

Colt45

Lifer
Apr 18, 2001
19,721
0
0
fubak

i have a 9&quot; rear end too.. its in my vega.. i still need an engine for it though, havent decided on what yet though.. im thinking 350..
 

GasX

Lifer
Feb 8, 2001
29,033
6
81


<<

<< you still have the same number of turns in the drive shaft to turn the wheel once >>



But, the actual turn of the wheel is what is changed. A taller tire has a much longer &quot;turn&quot; than a shorter tire. The taller tire has a much larger circumference. It takes the same number of turns of the driveshaft to turn the hub of the wheel, but the vehicle travels more distance for the same turn of the hub

Its not the gearing, but the taller tire changes the effective gearing.

I think we are saying the same thing, just using different terms.
>>


Yup, same number of turns, different distance covered.
 

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