Let's play with words: gear ratios

[SuperDave]

I offered to explain how the word "ratio" may be defined two different ways. Follow me. Here goes:

A ratio is an expression of the numerical relationship between two similar things. In the context of gearing and specifically differentials, ratio compares the rotational relationship between the axle and the and the pinion. Example: 3:1 means the pinion revolves three time for each revolution of the ring gear which drives the axle.

If the ratio were LOWERED to, say, 5:1, there would be a LOWER relationship between the two numbers. Conversely, a change to 2:1 would RAISE the relationship.

Confused? Remember, I'm playing with words just like the President who said: "Ah didn't have sex with that woman."

I realize that this runs contary to popular thinking. Comments?

 

[gingerbreadman]

where does the expression "tall gears" come from??? I know "tall gears"
stands for a high ratio such as 2 to 1 but where did this expression come from????



-gbm-

 

[DarkBuddha]

A ratio is an expression of the numerical relationship between two similar things. In the context of gearing and specifically differentials, ratio compares the rotational relationship between the axle and the and the pinion. Example: 3:1 means the pinion revolves three time for each revolution of the ring gear which drives the axle.

I pretty much agree SD, but I think of the ratio a bit differently. While you state the relationship of the ratio as the comparison of rotation of the pinion and ring gear, I specifically think of it as a comparison of the number of teeth between the ring gear and pinion. I realize it equates to the same thing in terms of the end result (i.e. the number of revolutions of the pinion to the number of revolutions of the axles), but maybe this is one of the things that contributes to the confusion about discussing "higher" and "lower" gear ratios.

 

[D.Hearne]

That's what's so confusing about the ratios in rearends to some beginners, what's thought of by higher or taller gears by us old timers, could be confused to be "lower gears" by newbies. A numerically higher ratio will result in a lower top speed at a given rpm than a numerically lower ratio.The numerically lower ratio results in a higher top speed for the same given rpm than a numercally higher ratio .

 

[D.Hearne]

And add into the mix a tire with a different diameter, and you could end up with the same final drive ratio after a gear swap that you had before the swap

 

[SuperDave]

Good insights! I compare this to a multi-speed bicycle. 1st gear, with more teeth on the sprocket gets you goin quicker and with less effort but has a lower "top end'. And the reciprical is likewise true.

All gearing is a COMPROMISE, wheter it is on a bicycle or in a car. If this were not true, why do we have transmissions?

 

[6Stang7]

Exactly SD. You trade off RPM for torque, and vise-a-versa. If I remember my physics correctly, it's force x distance=work. Think of a leave arm with a 2:1 ratio; one side moves 1in with 10 ft/lbs of force, so the other side will move 2in with only 5ft/lbs of force. It's a trade off. You need that low end torque to break your moment of inertia from the start, then once the car is up and moving, you can reduce your gear ratio and torque in exchange for more rpm's at the driveshaft.

-Shaun

 

[SuperDave]

And that is why you have a transmission! (To change to a different ratio) Seems simple enough to me!

But THEN, would that shift be to a higher or lower ratio? Hmmmm..?

 

[D.Hearne]

Damn, we're good , ain't we ?

 

[SuperDave]

D.Herne: Good at making the simple more complex?

 

[D.Hearne]

Possibly, yes

 

[6Stang7]

That part there really got me thinking. When someone says they have low gears, they mean they have a numerically high ratio. But why did they say they had low gears if the ratio is higher? I think this came from transmissions. 1st gear is "lower" then 2nd gear because 1 is lower then 2; even though the numerical ratio is higher for 1st then it is for 2nd. We are calling it a "lower" gear not because of its numerical ratio, but because of its location in the transmission. I think that this just stuck with people, and worked its way into society. Maybe I'm wrong/crazy, but I think that this is where it all started from. Your comments?

-Shaun

 

[kslushy]

seriously, i was better off before i started reading this.

 

[crushnut]

lol, your not the only one

 

[6Stang7]

I've though about a gear being called "taller" and have no clue where that came from. Any ideas?

 

[D.Hearne]

I'd tell you but you'd never believe it

 

[SuperDave]

I TOLD you that I was "playing with words" and that there were two (at least) ways to correctly express the ratio concept.

It boils down to where you want the best performance: on the bottom or the top end. The farther you go in either direction, the more you sacrifice the other. Selection of a proper ratio is merely an individual preference. I prefer a nice compromise because I'm in no hurry to get anywhere and I like good mileage.

Also there are a huge number of other factors. I run 3:1 in my 260 'Stang and 3.55:1 in my 460 F250 4x4. I am well pleased with their performance overall.

 

[restomod]

you guys are good!!!!! i am not confused . i am not confused .

 

[D.Hearne]

I TOLD you that I was "playing with words" and that there were two (at least) ways to correctly express the ratio concept.

It boils down to where you want the best performance: on the bottom or the top end. The farther you go in either direction, the more you sacrifice the other. Selection of a proper ratio is merely an individual preference. I prefer a nice compromise because I'm in no hurry to get anywhere and I like good mileage.

Also there are a huge number of other factors. I run 3:1 in my 260 'Stang and 3.55:1 in my 460 F250 4x4. I am well pleased with their performance overall.

But, remember this: with the taller tires Super Dave's 4X4 has, the effective final drive ratio for both vehicles is probably close to being the same. Or more likely, the final ratio on the 4X4 is probably a lower numerical ratio than the 260 Stang.

 

[D.Hearne]

I TOLD you that I was "playing with words" and that there were two (at least) ways to correctly express the ratio concept.

It boils down to where you want the best performance: on the bottom or the top end. The farther you go in either direction, the more you sacrifice the other. Selection of a proper ratio is merely an individual preference. I prefer a nice compromise because I'm in no hurry to get anywhere and I like good mileage.

Also there are a huge number of other factors. I run 3:1 in my 260 'Stang and 3.55:1 in my 460 F250 4x4. I am well pleased with their performance overall.

But, remember this: with the taller tires Super Dave's 4X4 has, the effective final drive ratio for both vehicles is probably close to being the same. Or more likely, the final ratio on the 4X4 is probably a lower numerical ratio than the 260 Stang.