ChevyLuva3

Hey all, I can't seem to get my head straight. I'm so lost of the know how of gears. For argument sake, I'm using the comparison (and difference) between 2.73s and 3.73s. This is what I thought the purpose of 3.73s were:
>To get better acceleration, by making the engine work harder, so the rpms would reach PEAK torque and horsepower.
>But the problem was that since the 3.73s kept the engine running harder, and the fact that the rear is turning slower (compared to 2.73s), you would have less top end speed.

I thought the purpose of 2.73s were:
>To get better top end, by making engine work less, so the rpms would not reach there limit, and you still had more top end go.
>But the problem was that since the 2.73s kept the engine running less fast, and the fact that the rear is turning faster (compared to 3.73s), you would lose low end speed.

I am really lost in the mumbo jumbo, I can't find which way is up. Are 3.73s bigger/taller gears? Or are 2.73s the bigger/taller gears? I always thought 2.73s were smaller.
And what exactly is it ratioed to, what exactly is spinning 3.73 revolutions to 1 revolution of something else? Please show the difference between the gears, some 101 would be great help, to ease my brain. Thanks.

Mark A Shields

The higher numerically the gear the lower it is.

ChevyLuva3

Lower what is? Do you mean the higher the number assigned to the gears the SMALLER it is?

AJ_92RS

Most of your thinking is correct.

A 2.73 gear ratio will spin the engine at less RPMs than a 3.73 will, at the same speed and the same size tires.

Think of it this way (how my grandpa explained it to me).

If you're riding a 10 speed bike, from a dead stop, you should start out in 1st gear. You don't have to pedal as hard to get going, and you get going quicker. That would be like a 3.73:1. But as soon as you reach the fastest that you can physically pedal (RPM), you can't accelerate anymore and you won't be going very fast.

Next start out from a dead stop in 10th gear (same as 2.73). You can't get going as quick, but you can go faster overall. It just takes a lot longer to get going as fast as 1st gear.

Now for ratios. A 3.73:1 ratio means that the pinion gear (the one that's hooked to the driveshaft) turns 3.73 times for every 1 time the the ring gear turns (the one that's hooked to the axle). Well that's like the 1st gear on a 10 spd. bike. Your feet go around almost 4 times for every time the back tire turns only once. (not really but it gives you an idea )

When we talk about higher or lower gears, there are actually two meanings. A "higher" gear (like a 2.73) came from the fact that most cars used them for highway driving, or higher speeds. But if you are talking numbers, a 2.73:1 is "numerically" lower than a 3.73:1.

A "lower" gear came from meaning that it was made for lower speeds, and also from "lower" gears in the transmissions. People called 1st gear lower because it was lower than 2nd, according to what the shifter said. But again, a 3.73:1 is a "lower" gear using the "slang" term, but higher numerically.

Hell, the slang terms are even different for 4x4 guys. A 3.73 is a "deeper" gear than a 2.73. I guess because you can drive through deeper mud easier with it? I dunno. But you may hear that term also.

As you see, it gets a little confusing. So when someone says they're gonna get lower gears, ask them if they mean numerically lower, or lower speed. You might just confuse the hell outta them.

AJ

ChevyLuva3

Thanks for the responce... Wow, these gears are tough to understand... its like I start explaining them, and then I question myself if I'm correct, and then I feel like I'm not correct... and then arrrgh d@mn gears who knows.
I try to justify it as someone who is tippytoeing (3.73s) they are moving fast continuously. But then theres taking large steps (2.73s)you don't move fast, but when the next foot comes down you traveled a lot already, so it gets me thinking isnt 2.73s better?? Aaaahhh, I'm so lost I guess I'll never know.

Jay 727

3.73's are for those who want to accelerate fast and have a limited top end, 2.73's are for those who want fuel efficiency and/or slower take offs and higher top speeds.

Think of 3.73's as a a 5 speed manual transmission starting off in first gear and going only to third-you get good acceleration but no top end.
Now 2.73's would be like starting out in third and shfting through to fifth. not much acceleration but higher top end speed.

If you have 3.73 or even 4.11 you can enjoy the g force of accelerating hard and have a top end limited to about 110 MPH.
If you have 2.73 or even a 2.41 it'll feel slow accelerating but you'll be able to go 150 plus mph if your engine has enough power to overcome the aerodynamic drag on the vehicles body.

ChevyLuva3

Thanks again, I get it a little better, I just have to keep my brain from running a muck. For our cars, say my car (look at specs above). Whats the fastest speed I could go with 3.73s? Whats the fastest speed I could go with 2.73s?

Jay 727

Here is a formula to figure top speed. You need to guess at what RPM your engine will go up to with it's power and the wind resistance.

gear ratio x 336 x mph x overdrive ratio divided by rear tire diameter=RPM.
Here is an example of a car with 2.73's , 25" tall tires and a 700R4 (.70 OD) going 140MPH

2.73 x 336 x 140 x .70 divided by 25 = 3596 RPM at 140 mph.
336 is the common number for standard transmissions or automatics with lock up converters. For automatics with non lock up use 355.

Here is an example of a car with 4.11's, 28" tires with a turbo 350 going 140
4.11 x 355 x 140 divided by 28 = 7295 rpm.