Looking for a primer on gears
Thread Starter
Instructor
Joined: Dec 2002
Posts: 109
Likes: 0
From: Mountain View CA
Looking for a primer on gears
Okay, so sue me... I never took an automotive mechanics course. I've been having a great time reading jillions of archived posts on here about modifying the C5 and I've been starting to add those that look easy enough, safe enough, and practical enough for a non-mechanic.
Now I'm into the archives about different gear ratios. All right, I know the function of gears and I know the basic mechanics (heck, I once owned a 10-speed bike... you can't get much more basic on the concept of gearing!).
But I don't have a clear understanding of how to interpret specific ratio numbers, what their effects (positive and negative) will be on low-end/high-end performance, side-effect considerations, and so on.
Can anyone point me at a good background basics link that helps clear up the concepts as applied to automobile performance?
Thanks much!
--Ken the Newbie
Now I'm into the archives about different gear ratios. All right, I know the function of gears and I know the basic mechanics (heck, I once owned a 10-speed bike... you can't get much more basic on the concept of gearing!).
But I don't have a clear understanding of how to interpret specific ratio numbers, what their effects (positive and negative) will be on low-end/high-end performance, side-effect considerations, and so on.
Can anyone point me at a good background basics link that helps clear up the concepts as applied to automobile performance?
Thanks much!
--Ken the Newbie
Le Mans Master
Joined: Jun 2000
Posts: 5,555
Likes: 9
From: Indiana
Re: Looking for a primer on gears (KLMonline)
There's really no magic to it. A gear ratio is expressed in two parts, like 3.42:1. Frequently, the :1 is simply removed and assumed. This number represents the number of turns of the input shaft to get 1 turn on the output shaft. This is true whether you're referring to the gear ratio in the differential, or to any particular gear in the transmission. The product of the transmission ratio and the differential ratio represents the number of revs the engine has to turn in order to turn the rear wheels once.
That said, higher numbers (like 3.73, which is actually a LOWER gear ratio) mean the engine has to turn faster to achieve the same number of turns at the output .. therefore at any given speed and gear, the engine will be turning a little faster. Obviously at higher gears, the engine has to turn LESS fast.
There are a number of gear ratio calculators available on the internet .. the best way to determine the effects of a gear swap is to play with different combinations.
That said, higher numbers (like 3.73, which is actually a LOWER gear ratio) mean the engine has to turn faster to achieve the same number of turns at the output .. therefore at any given speed and gear, the engine will be turning a little faster. Obviously at higher gears, the engine has to turn LESS fast.
There are a number of gear ratio calculators available on the internet .. the best way to determine the effects of a gear swap is to play with different combinations.
Burning Brakes
Joined: Aug 2001
Posts: 1,206
Likes: 21
From: Roswell GA
Re: Looking for a primer on gears (Jerry Velders)
You do not indicate A4 or MN6. To experience it first hand mearly do the following:
In A4 use D first and go 70 mph then push the pedal half way. Now put the shifter in 3rd and again go 70 mph and push again. Same thing can be done with a MN6 Use 5th as D and 4th as 3rd.
D lower rpm, better gas milage, less acceleration, less engine noise.
3rd higher rpm, less gas mileage, more acceleration, more engine noise.
Top end is not really a practical consideration as even 4.10's in an A4 can give you 162 at 6000 rpm. I back off at 100 mph.
In an A4 - 3.42's are a nice middle ground, 3.73's are real fun around town but a little closer to the edge on the hghway. I can lay rubber for 60' just by punching the pedal, and I have a Cadilac for the road trips. So I'm thrilled with 3.73's.
If I had an MN6 I would have 4.10's because 6th can cover you highway needs.
It is always give and take.
[Modified by KingTut, 12:25 AM 12/18/2002]
In A4 use D first and go 70 mph then push the pedal half way. Now put the shifter in 3rd and again go 70 mph and push again. Same thing can be done with a MN6 Use 5th as D and 4th as 3rd.
D lower rpm, better gas milage, less acceleration, less engine noise.
3rd higher rpm, less gas mileage, more acceleration, more engine noise.
Top end is not really a practical consideration as even 4.10's in an A4 can give you 162 at 6000 rpm. I back off at 100 mph.
In an A4 - 3.42's are a nice middle ground, 3.73's are real fun around town but a little closer to the edge on the hghway. I can lay rubber for 60' just by punching the pedal, and I have a Cadilac for the road trips. So I'm thrilled with 3.73's.
If I had an MN6 I would have 4.10's because 6th can cover you highway needs.
It is always give and take.
[Modified by KingTut, 12:25 AM 12/18/2002]
Racer
Joined: Mar 2002
Posts: 397
Likes: 2
From: Marstons Mills MA
Re: Looking for a primer on gears (KingTut)
Eckler's advertizes 3.90 (thiswould be for MN6 tranny). What do you think about these? Can this be done without a huge investment in specialty tools?
:flag
:flag
Burning Brakes
Joined: Aug 2001
Posts: 1,206
Likes: 21
From: Roswell GA
Re: Looking for a primer on gears (CapeCodCoupe)
As can be found in several other posts on gears, the general concensis is if you do not have a specific reason for not getting 4.10's then they are the best choice. A little more of the good stuff for the same price as the 3.90's.
As for the install question - spend $400-$500 for the install by a profesional and you will not need any tools. It is only for the very deturmined do it your-self-er
As for the install question - spend $400-$500 for the install by a profesional and you will not need any tools. It is only for the very deturmined do it your-self-er
