Transmission vs differential

[dmw16]

My friend and I are having this debate about the trasmission vs the differential. He insists that when you set gear ratios(that is to say setting the gearing)in a car you are setting the ratio in the differential. To my knowlege the differential is a fixed ratio(atleast until you yank one out and change in) - meaning that when you are driving the ratio in your differential is fixed. So could anyone tell me if Im right or wrong? And either way, explain this more clearly.
thanks,
-doug

 

[notfred]

When you shift gears, it's the trasmission. If you're referring to modifying your gears "Hey, I'm gonna put 3.73 gears in my car" then it's the differential

 

[Halogen]

the differencial is a fixed setting and when you change gear ratios you are not changing the differencial

 

[Heisenberg]

Yes, the differential is a fixed ratio. The transmission has several different gears (each gear is a different ratio), so the final drive ratio is a combination of the diff ratio and whatever gear you're in.

 

[silverpig]

Short answer: you are right.


The differential can be set to different ratios, but it involves taking the ass-end of the car apart. For 99.9999% of cars, the differential never changes. What the differential does (afaik anyways) is to turn one wheel faster than another when making turns. When you turn left, the right wheel has to travel a greater distance than the left wheel, so the differential spins it more quickly to aid in turning.

The transmission is where you change from 1st to 2nd to 3rd etc.

 

[boyRacer]

Time to bust out your Gran Turismo manual...lol...

From howstuffworks.com

The differential has three jobs:

To aim the engine power at the wheels
To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)

 

[Soybomb]

Yes the diff is a fixed ratio, IE:3.73:1

 

[BoberFett]

<< To transmit the power to the wheels while allowing them to rotate at different speeds >>

At which point engineering is thrown out the window and your wheels spin completely by magic.

 

[Pacfanweb]

<< To transmit the power to the wheels while allowing them to rotate at different speeds >>

<<At which point engineering is thrown out the window and your wheels spin completely by magic. >>

That's how the differential works, hence its name. It allows the wheels to rotate at different speeds when necessary, like when turning a corner.

I think you and your friend are partially right, if I understand your question.

The term "setting the gear ratio" generally refers to the gears in the rear end. The final gear ratio generally refers to the rear end gearing.
You can change gear ratios in the transmission, but not many people outside of racing do this.

The differential is a "fixed ratio", unless you disassemble the rear end and change it. The only gears that can "change" while driving are in the transmission.

 

[Demon-Xanth]

It sounds like a difference in what you two are thinking. When he's referrring to gearing a car it's the differential because changing that gear affects all gears. A 3.92 will be lower geared than a 3.55. However if you're on the road shifting, that is done in the transmission.

When it comes to modification it's almost always the differential, the internals of the transmission are rarely modified to change the ratios in street cars.

 

[dmw16]

Lets use the example of Grand Tourismo 3. When you go into the settings and chage your gearing...so you have 1st, 2nd, 3rd, ect...and they each have a number next to them. What does that number refer to? And what is being changed?
thanks,
-doug

 

[flot]

Uh, I haven't played GT3 but if you have more than one choice - it's the transmission gearing. If you have one choice, it's the differential gearing.

You said 1st, 2nd, 3rd so I presume you are changing the ratio of each gear in the transmission. For instance, you could choose a high 1st gear ratio to get you off the line quicker...

In reality *both* make up the final drive ratio of the car, so both play a part. In real life, though - it's usually "easier" to change the gears in your rear end, so you swap out your differential gears. For instance, let's say you have a "race car" and you notice that when you have it floored your top speed is limited by your redline - you are at 6000 rpm and the car is going 160 mph. You could lower your rear end ratio from 4.11 to 3.07 - now your top speed would be 190 mph (I'm making these #s up) at 6000 rpm. The reason you wouldn't just keep lowering the ratio is that eventually your engine won't have enough *power* to make the car go that fast. You'll sometimes see top speeds listed as "rpm limited" which means just that - the car hit redline before the engine ran out of balls.

In some cases you'll see road tests where the drivers were determined to see just how fast a car could go - you could also put bigger rear tires on, which will have the same effect as changing your rear end ratio.

 

[notfred]

<< Lets use the example of Grand Tourismo 3. When you go into the settings and chage your gearing...so you have 1st, 2nd, 3rd, ect...and they each have a number next to them. What does that number refer to? And what is being changed?
thanks,
-doug >>



And next time someone starts a thread on firearms, we'll use counterstrike as the practical example.

 

[Perknose]

Actually, not all differentials are fixed. Most semi's (trucks) have at least dual range differentials, which multiply by a factor of two the number of gear selections you can have. As an analogy, think of multi-speed bicycles -- that 18 speed? It has a set of six gears that operate off a primary hub with three selectable ratios. (No differential on a bike, this is just an analogy).

Various autos down through the years have also had driver selectable multi range differentials. The last one that comes to mind for me was the Dodge Colt (Mitsubishi built) from, if I recall correctly, the 1970's, which came with a four speed transmission and a dual range differential, giving the enterprising driver a choice of eight gear ranges.