Someone explain GEARS to me
03-10-2012, 11:21 PM
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Someone explain GEARS to me I've just never fully understood the gears or gearing in a car and how it affects the car, makes it slower, faster, better MPG's, idle, etc.
I know my car has 2.73's. People say the higher the gear, the better, right?
But if you go too high, you will lose MPG's. Someone recently told me higher gears also take away from your top end. So does that mean my car with 2.73's can hit 140MPH, but with 4.10's it can't hit 140MPH?
Please just explain all of it to me if you can. I would like to get some 3.42's some day.
I know my car has 2.73's. People say the higher the gear, the better, right?
But if you go too high, you will lose MPG's. Someone recently told me higher gears also take away from your top end. So does that mean my car with 2.73's can hit 140MPH, but with 4.10's it can't hit 140MPH?
Please just explain all of it to me if you can. I would like to get some 3.42's some day.
03-10-2012, 11:42 PM
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You can probably hit 140 with 4.10's, but you RPMs would be really high.
When you think of gears think of it like this. Let's say you have 4.10's. The small pinion gear has 10 teeth and the big ring gear has 41. That means the small pinion gear attached to the drive shaft will have to spin about 4 times to make the big ring gear (attached to the wheels) spin once. That lets your engine rev up higher and quicker before delivering the full power to the wheels.
If you have a 2.73 gear set, your small pinion gear now has 15 teeth and the big gear still has 41, but now it only takes 2.73 rotations of the pinion to get the ring gear to make a full rotation. That means the engine can't rev up as high before it gets into the power-band.
That's about as clear as mud, I know.
When you think of gears think of it like this. Let's say you have 4.10's. The small pinion gear has 10 teeth and the big ring gear has 41. That means the small pinion gear attached to the drive shaft will have to spin about 4 times to make the big ring gear (attached to the wheels) spin once. That lets your engine rev up higher and quicker before delivering the full power to the wheels.
If you have a 2.73 gear set, your small pinion gear now has 15 teeth and the big gear still has 41, but now it only takes 2.73 rotations of the pinion to get the ring gear to make a full rotation. That means the engine can't rev up as high before it gets into the power-band.
That's about as clear as mud, I know.
03-10-2012, 11:48 PM
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Shorter gear ratio (i.e. 4.10)=Quicker acceleration, lower top speed and less MPGs.
Taller gear ratio (i.e. 2.73)= Slower acceleration, higher top speed and more MPGs.
As for how gearing numbers are derived, 4.10s would actually be described as a 4.1:1 drive ratio. Meaning the input (4.1) rotates 4.1x the speed of the output (1). When gear ratios are altered, you also alter the torque output. For example, let's say you have a direct drive unit to a rear axle, and an engine or motor making 300 lb/ft of torque. With a 2:1 gear ratio, you're doubling your torque output to 600 lb/ft. At 4:1, you're quadrupling the torque output to 1,200 lb/ft.
It's exactly the opposite for gear ratios as they become "taller". The same engine making 300 lb/ft of torque through the input shaft will only make 150 lb/ft of torque through a .5:1 final drive ratio.
As for vehicle speed, engine speed and MPGs, increasing the final drive ratio from a direct drive situation (1:1) where the vehicle is traveling at (for example) 50 mph and the engine is rotating at 2,000 rpms, doubling the final drive ratio (2:1) would cause the engine to rotate at 4,000 rpms to maintain the same 50 mph speed.The exact opposite would happen if the final drive ratio is decreased; a final drive ratio of .5:1 would make the engine spin at 1,000 rpms to maintain the 50 mph speed. More rpms=less fuel mileage.
Taller gear ratio (i.e. 2.73)= Slower acceleration, higher top speed and more MPGs.
As for how gearing numbers are derived, 4.10s would actually be described as a 4.1:1 drive ratio. Meaning the input (4.1) rotates 4.1x the speed of the output (1). When gear ratios are altered, you also alter the torque output. For example, let's say you have a direct drive unit to a rear axle, and an engine or motor making 300 lb/ft of torque. With a 2:1 gear ratio, you're doubling your torque output to 600 lb/ft. At 4:1, you're quadrupling the torque output to 1,200 lb/ft.
It's exactly the opposite for gear ratios as they become "taller". The same engine making 300 lb/ft of torque through the input shaft will only make 150 lb/ft of torque through a .5:1 final drive ratio.
As for vehicle speed, engine speed and MPGs, increasing the final drive ratio from a direct drive situation (1:1) where the vehicle is traveling at (for example) 50 mph and the engine is rotating at 2,000 rpms, doubling the final drive ratio (2:1) would cause the engine to rotate at 4,000 rpms to maintain the same 50 mph speed.The exact opposite would happen if the final drive ratio is decreased; a final drive ratio of .5:1 would make the engine spin at 1,000 rpms to maintain the 50 mph speed. More rpms=less fuel mileage.
Last edited by why87; 03-11-2012 at 12:58 PM.
03-11-2012, 12:01 AM
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You can probably hit 140 with 4.10's, but you RPMs would be really high.
When you think of gears think of it like this. Let's say you have 4.10's. The small pinion gear has 10 teeth and the big ring gear has 41. That means the small pinion gear attached to the drive shaft will have to spin about 4 times to make the big ring gear (attached to the wheels) spin once. That lets your engine rev up higher and quicker before delivering the full power to the wheels.
If you have a 2.73 gear set, your small pinion gear now has 15 teeth and the big gear still has 41, but now it only takes 2.73 rotations of the pinion to get the ring gear to make a full rotation. That means the engine can't rev up as high before it gets into the power-band.
That's about as clear as mud, I know.
When you think of gears think of it like this. Let's say you have 4.10's. The small pinion gear has 10 teeth and the big ring gear has 41. That means the small pinion gear attached to the drive shaft will have to spin about 4 times to make the big ring gear (attached to the wheels) spin once. That lets your engine rev up higher and quicker before delivering the full power to the wheels.
If you have a 2.73 gear set, your small pinion gear now has 15 teeth and the big gear still has 41, but now it only takes 2.73 rotations of the pinion to get the ring gear to make a full rotation. That means the engine can't rev up as high before it gets into the power-band.
That's about as clear as mud, I know.
What's a good DD gear? 3.23's? 3.42's? 3.73's?
03-11-2012, 12:07 AM
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That's a matter of opinion. Some people are content with their stock 2.43's while others have no problem DD'ing 4.10's.
Probably 3.73 is good for daily use and some track duty. This is just my opinion, but if you mostly DD your car and rarely go to the track, 3.73 will wake the car up a bit but still be reasonable on fuel consumption. Opinions will vary though.
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03-11-2012, 12:13 AM
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That's a matter of opinion. Some people are content with their stock 2.43's while others have no problem DD'ing 4.10's.
Probably 3.73 is good for daily use and some track duty. This is just my opinion, but if you mostly DD your car and rarely go to the track, 3.73 will wake the car up a bit but still be reasonable on fuel consumption. Opinions will vary though.
Probably 3.73 is good for daily use and some track duty. This is just my opinion, but if you mostly DD your car and rarely go to the track, 3.73 will wake the car up a bit but still be reasonable on fuel consumption. Opinions will vary though.
03-11-2012, 08:01 AM
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If you have 2.73s your gonna love 3.73s.No more 3rd gear lag. Revs up nice through out the whole rpm range comparably to 2.73s. It will "Feel" 2x as fast, especially from a dig. Track gains are very minimal but it does "Feel" like you picked up a second.
With 2.73s at 70mph I was at about 1900rmp. With 3.73s at 55mph, I run 1900rpm.
So you lose about 1mpg maybe a tad more. It's worth it imao and I dd everyday. Matched with a frost tune to increase line pressure really made me enjoy the gears.
A shift kit is also a plus for a gear swap.
With 2.73s at 70mph I was at about 1900rmp. With 3.73s at 55mph, I run 1900rpm.
So you lose about 1mpg maybe a tad more. It's worth it imao and I dd everyday. Matched with a frost tune to increase line pressure really made me enjoy the gears.
A shift kit is also a plus for a gear swap.
03-12-2012, 10:42 AM
#13
imagine your on a mountain bike with gears. if you put it in 1st gear that is like a 4.10 where you (engine) spin the pedal fast and have a lot of torque and can accelerate faster but you hit your redline at a low speed (but we have 6 gears in a manual so thats fine).
Imagine you put it in 10th gear that is like a 2.73 you (engine) spin the pedals very slow and have to push pedals really hard. there is slow acceleration and low torque output and low rpm but the gear lasts for a much higher speed before you hit redline.
the point is you want the torqiest gear with the most acceleration that is practical. for my car with 6 gears in the transmission i will go with 4.10s from the chart i got online with stock tire height thats 160mph at like 4300rpm in 6th. doubt car can pass that anyway due to aero drag forces.
Will 1st gear be too steep, maybe i'll start in second sometimes but i still think it's worth it to have a good launch gear, able to break tires loose whenever, more acceleration, more fun, still have enough gears with my manual.
Auto may have same torque with 3.73's because remember the diff transmissions gears are different. 1st gear in M6 is not the same as 1st gear in A4 trans. they are different. thats why when i put my m6 into my car after i pulled the automatic and the rear is 2.73 car is SLOWER than before. i need 4.10's bad. the true torque you have to multiply engine torque times trans gear ratio (for whatever gear your in) and that times rear diff. ratio to get output torque. Hope that helps to show how diff trans may mean diff ideal ratio. only compare others with same trans and torque converter for that matter if an auto.
Imagine you put it in 10th gear that is like a 2.73 you (engine) spin the pedals very slow and have to push pedals really hard. there is slow acceleration and low torque output and low rpm but the gear lasts for a much higher speed before you hit redline.
the point is you want the torqiest gear with the most acceleration that is practical. for my car with 6 gears in the transmission i will go with 4.10s from the chart i got online with stock tire height thats 160mph at like 4300rpm in 6th. doubt car can pass that anyway due to aero drag forces.
Will 1st gear be too steep, maybe i'll start in second sometimes but i still think it's worth it to have a good launch gear, able to break tires loose whenever, more acceleration, more fun, still have enough gears with my manual.
Auto may have same torque with 3.73's because remember the diff transmissions gears are different. 1st gear in M6 is not the same as 1st gear in A4 trans. they are different. thats why when i put my m6 into my car after i pulled the automatic and the rear is 2.73 car is SLOWER than before. i need 4.10's bad. the true torque you have to multiply engine torque times trans gear ratio (for whatever gear your in) and that times rear diff. ratio to get output torque. Hope that helps to show how diff trans may mean diff ideal ratio. only compare others with same trans and torque converter for that matter if an auto.
03-12-2012, 01:06 PM
#14
You can probably hit 140 with 4.10's, but you RPMs would be really high.
When you think of gears think of it like this. Let's say you have 4.10's. The small pinion gear has 10 teeth and the big ring gear has 41. That means the small pinion gear attached to the drive shaft will have to spin about 4 times to make the big ring gear (attached to the wheels) spin once. That lets your engine rev up higher and quicker before delivering the full power to the wheels.
If you have a 2.73 gear set, your small pinion gear now has 15 teeth and the big gear still has 41, but now it only takes 2.73 rotations of the pinion to get the ring gear to make a full rotation. That means the engine can't rev up as high before it gets into the power-band.
That's about as clear as mud, I know.
When you think of gears think of it like this. Let's say you have 4.10's. The small pinion gear has 10 teeth and the big ring gear has 41. That means the small pinion gear attached to the drive shaft will have to spin about 4 times to make the big ring gear (attached to the wheels) spin once. That lets your engine rev up higher and quicker before delivering the full power to the wheels.
If you have a 2.73 gear set, your small pinion gear now has 15 teeth and the big gear still has 41, but now it only takes 2.73 rotations of the pinion to get the ring gear to make a full rotation. That means the engine can't rev up as high before it gets into the power-band.
That's about as clear as mud, I know.
03-12-2012, 06:04 PM
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imagine your on a mountain bike with gears. if you put it in 1st gear that is like a 4.10 where you (engine) spin the pedal fast and have a lot of torque and can accelerate faster but you hit your redline at a low speed (but we have 6 gears in a manual so thats fine).
Imagine you put it in 10th gear that is like a 2.73 you (engine) spin the pedals very slow and have to push pedals really hard. there is slow acceleration and low torque output and low rpm but the gear lasts for a much higher speed before you hit redline.
the point is you want the torqiest gear with the most acceleration that is practical. for my car with 6 gears in the transmission i will go with 4.10s from the chart i got online with stock tire height thats 160mph at like 4300rpm in 6th. doubt car can pass that anyway due to aero drag forces.
Will 1st gear be too steep, maybe i'll start in second sometimes but i still think it's worth it to have a good launch gear, able to break tires loose whenever, more acceleration, more fun, still have enough gears with my manual.
Auto may have same torque with 3.73's because remember the diff transmissions gears are different. 1st gear in M6 is not the same as 1st gear in A4 trans. they are different. thats why when i put my m6 into my car after i pulled the automatic and the rear is 2.73 car is SLOWER than before. i need 4.10's bad. the true torque you have to multiply engine torque times trans gear ratio (for whatever gear your in) and that times rear diff. ratio to get output torque. Hope that helps to show how diff trans may mean diff ideal ratio. only compare others with same trans and torque converter for that matter if an auto.
Imagine you put it in 10th gear that is like a 2.73 you (engine) spin the pedals very slow and have to push pedals really hard. there is slow acceleration and low torque output and low rpm but the gear lasts for a much higher speed before you hit redline.
the point is you want the torqiest gear with the most acceleration that is practical. for my car with 6 gears in the transmission i will go with 4.10s from the chart i got online with stock tire height thats 160mph at like 4300rpm in 6th. doubt car can pass that anyway due to aero drag forces.
Will 1st gear be too steep, maybe i'll start in second sometimes but i still think it's worth it to have a good launch gear, able to break tires loose whenever, more acceleration, more fun, still have enough gears with my manual.
Auto may have same torque with 3.73's because remember the diff transmissions gears are different. 1st gear in M6 is not the same as 1st gear in A4 trans. they are different. thats why when i put my m6 into my car after i pulled the automatic and the rear is 2.73 car is SLOWER than before. i need 4.10's bad. the true torque you have to multiply engine torque times trans gear ratio (for whatever gear your in) and that times rear diff. ratio to get output torque. Hope that helps to show how diff trans may mean diff ideal ratio. only compare others with same trans and torque converter for that matter if an auto.
The idea I'm getting from all these posts is that 2.73's really really suck. Would my car feel all that much different from upgrading to 3.23's or 3.42's?
Never thought my car felt that sluggish, but it also doesn't exactly feel like 350HP either. What do gears run in cost anyways?
03-12-2012, 06:05 PM
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A couple times a year I make an 800 mile commute to go visit family, and my Camaro is my DD. With my 2.73's I can get up to 27MPG on the interstate, with 3.73's what do you think I'd be looking at, 24?
03-12-2012, 06:21 PM
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With an M6 you will get pretty good MPG's, I'm sure. But with my 2.73's I'm at 1,800 RPM at 70MPH. If I went up to 3.73's I'd probably be close to 2,500 RPM, and with 4.11's, who knows?
03-12-2012, 07:29 PM
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If you have 2.73s your gonna love 3.73s.No more 3rd gear lag. Revs up nice through out the whole rpm range comparably to 2.73s. It will "Feel" 2x as fast, especially from a dig. Track gains are very minimal but it does "Feel" like you picked up a second.
With 2.73s at 70mph I was at about 1900rmp. With 3.73s at 55mph, I run 1900rpm.
So you lose about 1mpg maybe a tad more. It's worth it imao and I dd everyday. Matched with a frost tune to increase line pressure really made me enjoy the gears.
A shift kit is also a plus for a gear swap.
With 2.73s at 70mph I was at about 1900rmp. With 3.73s at 55mph, I run 1900rpm.
So you lose about 1mpg maybe a tad more. It's worth it imao and I dd everyday. Matched with a frost tune to increase line pressure really made me enjoy the gears.
A shift kit is also a plus for a gear swap.
And one thing too is that when you go to a 3.73 or 3.90-whatever gear ratio (different than stock) it actually takes stress off of the transmission too.
03-12-2012, 07:37 PM
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Gear ratios are definitely a bit of an opinion thing, and truth be told should be calculated by tire height and what rpm you want to go through the traps if your game is drag racing....
Otherwise the general consensus will likely be 3:73s in an A4 and 4:10s in an M6
Ive ran 2:73s, 3.23s, 3.73s, 4.10s, and 4.30s..... My vote is 3.73s...
Otherwise the general consensus will likely be 3:73s in an A4 and 4:10s in an M6
Ive ran 2:73s, 3.23s, 3.73s, 4.10s, and 4.30s..... My vote is 3.73s...