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Old 02-11-2006, 09:47 AM   #1
Aondor
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Rear gears.

ok I hear alot of statements about rear gears. Such as I am running 9:3 or 4:11.What do those numbers mean exactly what do they stand for? I never realy understood this. So I basic explanation of them would help me out greatly.
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Old 02-11-2006, 10:04 AM   #2
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well you see when you have your first gear set at 20mph (you need a speed dialometer) you can move your second gear at 40 giving you that extra boost then you take the previous gear and divide by the difference so it would be 20 divide by 2 gears =10 so now you have a 10:2 ratio














JUST KIDDING!!! I actually wanted to know about this also just never decided to post on it.
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Old 02-11-2006, 10:13 AM   #3
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Thanks sal

Thanks. That makes sense now so whats the optimal acceleration gear configuration?
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Old 02-11-2006, 10:15 AM   #4
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Oh wait. Wow I thought the just kidding was part of your sig now I feel like a retard and am more confused then when I asked.
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Old 02-11-2006, 02:58 PM   #5
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Quote:
Originally Posted by Aondor
ok I hear alot of statements about rear gears. Such as I am running 9:3 or 4:11.What do those numbers mean exactly what do they stand for? I never realy understood this. So I basic explanation of them would help me out greatly.
The number is derived from simple math based on the ratio of the ring and pinion gears in your differential. Most often people only use the first part of the ratio (ie 4.11) because it's generally a given that the second part of the ratio is 1 (ie 4.11:1, 4.11/1 or 4.11 to 1). Don't get hung up on what they look like now, these pics are just to help you understand what you're looking at and aid explanation. The first one is for a FWD car and the second one is for a RWD car.

. . . .

Very basically, the pinion gear (small one) is driven by the transmission either internally (FWD/transaxle) or a driveshaft (conventional RWD/front of conventional 4WD). The pinion gear then drives the ring gear (crown wheel to our UK friends). As you can see, the pinion gear is smaller than the ring gear. So let's say the pinion has 10 teeth and the ring has 30. You have a gear ratio of 3.00:1. If you change the ring to 40 teeth, you now have a gear ratio of 4.00:1. Simple math. All this is is a way to gain a superior mechanical advantage to move the car down the road.

Generally speaking, a lower ratio (bigger number, say 4.56:1) is better for acceleration because it has a superior mechanical advantage while a higher ratio (smaller number, say 3.23:1) is better for top end because you'll have more axle RPM for every transmission output RPM. Of course power, weight, aerodynamics, max engine RPM, etc will limit the advantages either way.
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Old 02-11-2006, 04:09 PM   #6
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Quote:
Originally Posted by vwhobo
The number is derived from simple math based on the ratio of the ring and pinion gears in your differential. Most often people only use the first part of the ratio (ie 4.11) because it's generally a given that the second part of the ratio is 1 (ie 4.11:1, 4.11/1 or 4.11 to 1). Don't get hung up on what they look like now, these pics are just to help you understand what you're looking at and aid explanation. The first one is for a FWD car and the second one is for a RWD car.

. . . .

Very basically, the pinion gear (small one) is driven by the transmission either internally (FWD/transaxle) or a driveshaft (conventional RWD/front of conventional 4WD). The pinion gear then drives the ring gear (crown wheel to our UK friends). As you can see, the pinion gear is smaller than the ring gear. So let's say the pinion has 10 teeth and the ring has 30. You have a gear ratio of 3.00:1. If you change the ring to 40 teeth, you now have a gear ratio of 4.00:1. Simple math. All this is is a way to gain a superior mechanical advantage to move the car down the road.

Generally speaking, a lower ratio (bigger number, say 4.56:1) is better for acceleration because it has a superior mechanical advantage while a higher ratio (smaller number, say 3.23:1) is better for top end because you'll have more axle RPM for every transmission output RPM. Of course power, weight, aerodynamics, max engine RPM, etc will limit the advantages either way.

god, you're good
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Old 02-11-2006, 06:10 PM   #7
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Quote:
Originally Posted by vwhobo
The number is derived from simple math based on the ratio of the ring and pinion gears in your differential. Most often people only use the first part of the ratio (ie 4.11) because it's generally a given that the second part of the ratio is 1 (ie 4.11:1, 4.11/1 or 4.11 to 1). Don't get hung up on what they look like now, these pics are just to help you understand what you're looking at and aid explanation. The first one is for a FWD car and the second one is for a RWD car.

. . . .

Very basically, the pinion gear (small one) is driven by the transmission either internally (FWD/transaxle) or a driveshaft (conventional RWD/front of conventional 4WD). The pinion gear then drives the ring gear (crown wheel to our UK friends). As you can see, the pinion gear is smaller than the ring gear. So let's say the pinion has 10 teeth and the ring has 30. You have a gear ratio of 3.00:1. If you change the ring to 40 teeth, you now have a gear ratio of 4.00:1. Simple math. All this is is a way to gain a superior mechanical advantage to move the car down the road.

Generally speaking, a lower ratio (bigger number, say 4.56:1) is better for acceleration because it has a superior mechanical advantage while a higher ratio (smaller number, say 3.23:1) is better for top end because you'll have more axle RPM for every transmission output RPM. Of course power, weight, aerodynamics, max engine RPM, etc will limit the advantages either way.

Thank you I think its a question alot of people have.
Thanks now that I know the basic Idea I don't fel so dumb anymore
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Old 02-11-2006, 06:35 PM   #8
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Quote:
Originally Posted by Aondor
Thank you I think its a question alot of people have.
Thanks now that I know the basic Idea I don't fel so dumb anymore

Being dumb has nothing to do with how much you know. Being dumb is actually having limited brain power. Just because you don't know something, it doesn't make you dumb. So don't sweat it
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Old 02-11-2006, 06:39 PM   #9
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Quote:
Originally Posted by Mathew
Being dumb has nothing to do with how much you know. Being dumb is actually having limited brain power. Just because you don't know something, it doesn't make you dumb. So don't sweat it
Or to quote my old signature on this forum, "Ignorance is not knowing, stupidity is not caring". There's nothing wrong with being ignorant as long as you have the willingness to learn and realize that somewhere there's ALWAYS somebody who knows more than you do.

Besides, about 99% of the peole who toss around numbers like gear ratios have no idea what they're talking about. It just sounds good and they think it makes them look smart.
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Thanks for the pic, jedimario.

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Old 02-11-2006, 07:18 PM   #10
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Ok so take 4.56:1 gear ratio, would the ring gear be 45? and if so, where do you get the extra 6 from?
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Old 02-11-2006, 07:28 PM   #11
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Quote:
Originally Posted by Benson
Ok so take 4.56:1 gear ratio, would the ring gear be 45? and if so, where do you get the extra 6 from?
I think another way to look at that is like for every rotation made by the big gear, the pinion gear makes 4.56...

BTW Thanks for that hobo, I've been confused by those for a while too
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Old 02-11-2006, 07:39 PM   #12
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Originally Posted by Benson
Ok so take 4.56:1 gear ratio, would the ring gear be 45? and if so, where do you get the extra 6 from?
You're locked in and not thinking with an open mind. All pinion gears are not created equal. My 10 tooth count was just an example to make the math simple. Most (all?) 4.56:1 gear sets have a 9 tooth pinion and a 41 tooth ring. 41/9=4.5555555. Rounded that is 4.56. Using the other gear I mentioned, most (all?) 3.23:1 gear sets use a 13 tooth pinion and a 42 tooth ring. 42/13=3.2307692, which rounds to 3.23. See, more simple math. it works the same way as the gear ratios in a transmission.
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Old 02-11-2006, 08:43 PM   #13
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Oh alright I understand. I guess I wasn't thinking out of the box. Thanks for clearing that up for me.
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Old 02-12-2006, 11:03 PM   #14
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another way to look at it would. gear ratio is technically defined as

Driven or Output
------- --------
Drive input

so the amount of times the drive gear turns to make the driven gear do one full revolution. gear ratios in the transmission before the final drive of the differential go kinda like this depending on make and model and type of transmission. for a 4 speed 4L60 in many chevy trucks first gear reduction is 3.06:1 second gear reduction 1.62:1 3rd is your direct drive or 1:1 ratio and 4th speed is your overdrive gear of 0.70:1 to lower rpm speeds of the motor and give you better gas milage. im finishing last year off my training so i thought i would throw in my 2 cents on the gear ratio stuff
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