Please Explain Gearing (Rear End)

[Vito]

i am pretty much clueless when it comes to rear diffs and what gearing fits for faster track times and what turns a car into a highway monster.


Can some one please explain in depth about the different ratios out there and the benefits you gain from them. on the track and on the street,

also pricing and links would be appreciated too.

look forward to hearing some feedback

thanks

[CHARGERTREV]

The specifics? I feel I know them but would have a hard time putting into words. More or less the higher the gear the faster you will get 0-whatever, my 3.73's are a VISIOUS gear on the street from a 40 roll, I kick it down into 2nd, pedal the car slam 3rd and spin and hook mid-way through. Now if I went with 4.10s I could bring it up too 3800 and drop the clutch and roll out harder in the 1/4. Im not sure if this helps in the least..

[PlumCrazyDaytona]

Our cars came stock with 2.82 gears, monster highway cruising gear that will provide a top speed of 170 or so....Stomp the peddle at 40 and as you know its a little flat

Now move up to my 3.92 gears and stomp the peddle at 40 it downshifts and grabs second gear at 3500 rpms or so and just screams!!! NOw my top end is reduced to 130 or so, I shift out of first right around 34mph.

For flat our acceleration the bigger the number the better it will accelerate, think torque multiplication, but there is a limit

[Ddaddy]

Originally Posted by PlumCrazyDaytona

Our cars came stock with 2.82 gears, monster highway cruising gear that will provide a top speed of 170 or so....Stomp the peddle at 40 and as you know its a little flat

Now move up to my 3.92 gears and stomp the peddle at 40 it downshifts and grabs second gear at 3500 rpms or so and just screams!!! NOw my top end is reduced to 130 or so, I shift out of first right around 34mph.

For flat our acceleration the bigger the number the better it will accelerate, think torque multiplication, but there is a limit

The stock SRT gears are 3.06 on mine and Vito's car. But the rest of what you stated is right. Taller gears means grabbing higher RPM at any given speed and it means moving up in the HP and torque curve faster than stock. That means more power at any given speed. A 3.92 onthe street is a monster and hard to keep traction with the power of an SRT...but I suspect that's what Vito wants.

Add a 3000 RPM stall converter and you can power brake the snot out of it and melt the tires to the rims from a stop.

[PlumCrazyDaytona]

Originally Posted by Ddaddy

The stock SRT gears are 3.06 on mine and Vito's car. But the rest of what you stated is right. Taller gears means grabbing higher RPM at any given speed and it means moving up in the HP and torque curve faster than stock. That means more power at any given speed. A 3.92 onthe street is a monster and hard to keep traction with the power of an SRT...but I suspect that's what Vito wants.

Add a 3000 RPM stall converter and you can power brake the snot out of it and melt the tires to the rims from a stop.

LOL!! The addition of the stall convertor and 3.73 or 3.92 gears makes traction....well you really need to learn how to launch the car with a shoulder roll technique.

But if you have some sticky shoes and the above gears with a convertor that flashes to 3000 or better....hang on!!!

SRT power levels go from feeling on the edge of control to downright violent and brutal

[ozzypriest]

let me google that for you...also, the current chargers have 2.65 gears. The AWD, SRTs and Road and Track models (29r package) have 3.06 gears. The Mopar 11s have 3.91 gears.

Question

What is the rear end gear ratio and how does it affect performance?
Ive heard alot of people talk about rear end gear ratios and gears like 4.10 and 3.70 I really want to know exactly how they work. How can you change them?

----------------------
Answer

It's the ratio of how many times the drive shaft turns to how many times the axle turns and is set up by choosing how many teeth are on the ring and pinion gears.

Bottom line, the higher the ratio, the more power (Torque actually) at the rear wheels, also the higher your engine runs (RPM's) and the poorer your gas mileage.

btw - higher ratio is referred to as lower gearing (geared down) and lower ratio is refereed to as higher gearing ... nice and confusing eh?

example, with a 4.10 gear set, the ratio is 4.10 to 1 so for every 4.1turns of the driveshaft, the rear axle will be turned one time and you will have a torque advantage of 4.1x
On the flip side for every say 10 turns of the wheels, your drive shaft will turn 41 times & your engine has to turn 41 times in high gear (not overdrive).
With a 3.70 gear, your Torque advantage is 3.7 times but now if your wheels turn 10 times, your drive shaft and engine will only turn 37 times. As with everything auto, always a trade off.

see also: http://www.howstuffworks.com/gears.htm

[sector 2]

wow....great info, great thread

[Vito]

so 3.92 gears is more of a highway car. so whats a good track gear ?

[ozzypriest]

Originally Posted by Vito

so 3.92 gears is more of a highway car. so whats a good track gear ?

No, the opposite. Generally, the higher the gear ratio (which is referred to as low gearing, nice and confusing), and depending on the the transmission ratios, the faster the car will be accelerating over a specific distance/time, like the 1/4 mile or 0-100 kmh. The chargers with, say, 2.65 gears are great highway cruisers because the engine is not working as hard (and using less gas) to keep the car at 70 or 80 mph. And the car will have a higher top speed.

The chargers with 3.92 gears, but same HP/Torque, should be significantly faster to 60, or over a 1/4 mile because of the torque multiplication of lower/shorter gears. And get worse MPGs at all speeds.

Cars with short gearing benefit from having an overdrive in the top gear, significantly lower than a 1:1, like a 1:.73 or even lower. Our cars don't really have enough gears to have an overdrive. But we are geared pretty tall through all 5 gear points. It's the trade-off between mpg and speed and usability because of our crappy 5-speed tranny. Well, not crappy, but old and way past its time. Our engine's sweet spot for torque is high, around 3800 rpm- almost redline, which is pretty high for pushrod american big liter v-8, and the 8-speed coming in 2013/14 will give us closer ratios and an overdrive top gear, and will be an awesome, speed-inducing and mileage-appropriating beast for our cars. Will be very, very beneficial. Cars with the 8-speed will be significantly faster imo, (and mathematically) than cars with the 5-speed, given the same output and torque curve.

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29

[TK Charger]

Originally Posted by ozzypriest

No, the opposite. Generally, the higher the gear ratio (which is referred to as low gearing, nice and confusing), and depending on the the transmission ratios, the faster the car will be accelerating over a specific distance/time, like the 1/4 mile or 0-100 kmh. The chargers with, say, 2.65 gears are great highway cruisers because the engine is not working as hard (and using less gas) to keep the car at 70 or 80 mph. And the car will have a higher top speed.

The chargers with 3.92 gears, but same HP/Torque, should be significantly faster to 60, or over a 1/4 mile because of the torque multiplication of lower/shorter gears. And get worse MPGs at all speeds.

Cars with short gearing benefit from having an overdrive in the top gear, significantly lower than a 1:1, like a 1:.73 or even lower. Our cars don't really have enough gears to have an overdrive. But we are geared pretty tall through all 5 gear points. It's the trade-off between mpg and speed and usability because of our crappy 5-speed tranny. Well, not crappy, but old and way past its time. Our engine's sweet spot for torque is high, around 3800 rpm- almost redline, which is pretty high for pushrod american big liter v-8, and the 8-speed coming in 2013/14 will give us closer ratios and an overdrive top gear, and will be an awesome, speed-inducing and mileage-appropriating beast for our cars. Will be very, very beneficial. Cars with the 8-speed will be significantly faster imo, (and mathematically) than cars with the 5-speed, given the same output and torque curve.

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29

all good info, except the fifth gear in our NAG1s actually is an overdrive gear