12/22/2004
By: Roger Hewson
Clutches and gear ratios are a couple of the most misunderstood aspects of tuning out there. From terminology to setup to how it works, we have not come across anything more mixed up, applied wrong or just screwed up more than these two applications. It’s why we figured we would save the best for last.
Know Yer Words
Before we get too technical we should tackle another issue when it comes to gears and gear ratios; the proper terminology. Tall gears, short gears, long gears, higher gear, lower gear, there are so many different terms for which direction you can go with a gear ratio it will make your head spin. The best thing to do is not use any slang or any terms which can get you in trouble.
When asking someone about what gear ratio you should run, ask them, “Should I run a numerically higher or numerically lower gear ratio.” By using numeric terminology you are going to eliminate any confusion caused by a difference in slang terms and prevent yourself from installing a final drive ratio which makes your Honda Civic run 80 miles per hour in first gear when you have a stock 1.6 SOHC VTEC that can barely pull fifth.
Short Is Best For Midg… err “Little People”
The most common mistake we see made with gear ratios is in the selection of ratios used. It is way too common for people to choose gear ratios which are way too short for their applications because they feel or sound faster than they actually are. Very often someone will assume a gear ratio shorter than what they have is going to be faster because the motor revs quicker and you have to shift more often because you run out of gear sooner.
You can ask five people the proper way to gear a car and get five different answers. Many people act like transmissions are some kind of black magic or lost science and they really aren’t. Figuring out the proper setup on a gearbox is fairly simple once you take a step back and understand what kind of a situation you are dealing with.
The ideal setup depends on each individual application and its purpose and needs. You really can’t say something like all normally aspirated cars should have a shorter (numerically higher) final drive ratio, or all turbo cars should have long (numerically lower) gears. There are too many variables from engine to engine and chassis to chassis.
Because we are dealing with traction, we will not get too in-depth with gears. There is enough there for a whole separate series on gearboxes. What we are concerned with is the first couple hundred feet and the first two gears. Running the longer of the available factory first gears is the way to go when it comes to running the proper gear for hooking the car up. The farther you can carry the car before the first shift, the longer and farther it’s going to have that wicked first gear acceleration. Now the acceleration in a 50 mph first gear might not be as vicious as the acceleration in a 30 mph first gear, but the longer 50 mph gear is going to be easier to hook up and the acceleration is going to last longer too. The 50 mph first gear will still be accelerating long after the person with the 30 mph first has already shifted to second gear, a much slower accelerating gear than both first gears.
Whatever advantage the shorter gear had in the beginning—if it wasn’t lost due to wheel spin problems—was given up at 30mph when the shift to second gear was made and the longer first gear still had another 20 mph of acceleration left. Remember that a 50 mph first gear isn’t all that extreme if you consider how high some engines rev, or if you have a responsive turbo car with the torque to pull a long gear. The turbo car will appreciate the load.
The slower of these two cars would still feel faster. The faster revving engine, the shift to second gear made sooner, the wheel spin from the engines torque overcoming the short first gear, all of these things make a car feel fast, but in reality it’s the smooth, drama free power delivery of the better setup which accelerates faster.
While this is an extreme example, it should give you an idea of how you shouldn’t trust the seat of your pants all of the time. It doesn’t mean if something feels fast and out of control by the seat of your pants it isn’t. It just means you need to use your head.
There’s more to gears than shifting!
The gears in the transmission are just the first part of the picture. There is what is called the overall gear ratio and it’s determined by the final drive ratio and the overall tire diameter. I know we’re backtracking a bit by mentioning tires again, but you can’t talk about gear ratio without mention tires. Tires are critical to determining what kind of gear you should run in a car, or if you can get away with a certain gear by modifying it with a smaller or larger tire. Shorter tires shorten ratios while a taller tire lengthens them.
Now like we mentioned before, you want to run the longest first gear you can get away with that will not bog the motor. Now what if you do this and your first gear is still too short? The next step is to go up with the overall gearing like the final drive ratio or the tire diameter. If it’s a street car, I say try going up with the final drive ratio first because this way you don’t need to put a tire on the car every time you want to try to put more than 40 percent of the power you are making to the ground. Don’t forget- you can mix and match final drive ratios and first gear ratios to make the perfect combination. A much taller final drive, and a slightly shorter first might be considerably taller than the previous setup and more streetable than if you were to just change final drive ratios. It’s just a numbers and a parts game.
I know this can all be a little hard to follow. Here is an example of what I did on my 1997 Volkswagen GTI VR6. The stock gear ratios (first through fifth) were as follows: 3.78, 2.12, 1.34, 1.03, and a 0.84 final drive 3.39. The gear ratios were barely too short in first gear and way too long in third, fourth and fifth. Even with the car capable of more than 150 mph it was difficult to get past 6000rpm in fifth gear. If I remember correctly, fourth in the stock box was good for almost 140mph at 7000 rpm.
I knew there was a lot of speed and acceleration choked up in the gearing of this car. In first, the big V6 would spin the tires easily because of the short first gear and once in third it was like pulling a trailer because the final drive was so tall. I did some research and found a 3.30 first gear and a 1.94 second gear available in the same gearbox offered in a different car. There were also 3.65 and 3.94 factory ring and pinions available instead of my stock 3.39.
So what I did was change the gearing in the stock gearbox to 3.30, 1.94, 1.34, 1.03, and 0.84. By looking at what the overall gear ratios would be I chose the 3.65 final drive over the 3.94 because it gave me a slightly longer first gear (even though the final drive was shorter than the stock 3.39), basically the same second gear and a much shorter, more useable third fourth and fifth gear. Now I had a longer first gear with more traction which was closer to second, and a set of lower third through fifth gears which pulled like mad all the way to 7000rpm. All of this just from shuffling around some gear ratios.
I know this was a little off topic and long in the end, but I just wanted to show how much of a difference you can make with just gear ratio changes alone. Just like running a taller tire; if you are having problems with traction, run a longer gear to help hook the car up, increase ET, and make your ET more consistent by creating a car which is easier to launch.
Why Pucks Were Meant For Hockey
One issue rarely touched when it comes to getting your car away from the starting line in a hurry is the clutch and flywheel. Most people see it as of it works, then it is fine and that’s it. They don’t think about how important the clutch is to driving the car out of the hole.
How do you expect to get a car out of the hole gently with a clutch that engages like an on/off switch? There is no better way to break the tires loose than just dropping the clutch, right? Sprung center or not, after speaking to reps at ACT and Clutch Masters they both said a puck disc is not going to be very forgiving on engagement. This means the only time you should be running a puck disc, is when you absolutely need one.
When we say need one, we mean you tried a Stage 3 ACT full face organic disc and fried it not because you drive like an ass, but because you actually have too much power. We don’t see that happening for 90 percent of most dual purpose cars. Don’t buy a puck clutch thinking it will impress your friends. All it does is make you look like an idiot, give us someone new to make fun of on Dr. Bentrod and give the clutch techs a good chuckle.
One last bit of wisdom before we bring this to a close. Lightweight flywheels might not help with traction, but they will make your car faster down the track on or off slicks and is easier to install during a clutch change. If someone is willing to buy me one I’ll prove it to them.