How long will my clutch last?
The life of the clutch is completely dependent upon the driver. Some drivers can make a clutch pack last several seasons, while others can't even finish one race. In-between race maintenance goes a long way towards long clutch life. To ensure long life, use your clutch at it's performance limits, but responsibly. Avoid heat build-up through excessive slippage!
My clutch is slipping. What could be wrong?
1. Check your release bearing clearance to ensure that the release bearing is not partially releasing the clutch. This has the same effect as driving around with your foot on the clutch pedal.
2. The clutch pack may be worn out. Measure the thickness of the discs with a caliper or micrometer. Refer to the instructions that came with your clutch to determine if they are worn beyond their service limits. If they are too thin, it's time for a new clutch pack.
3. The floater plates or pressure plate could be worn. Measure the thickness of the floater plate(s) and pressure plate with a caliper or micrometer. Also check for straightness. You should NOT be able to put a .006" feeler gage underneath the straight edge.
4. The diaphragm spring(s) in the clutch cover may be down on clamp load. If the clutch was excessively slipped, it is possible that the heat generated took the temper out of the diaphragm spring(s). If the springs are overheated they will lose their spring temper. They also take a `set' as they get older. Your clutch cover will need to be checked for proper clamp load. Only the PTT factory can properly check and replace diaphragm springs. PTT will inspect and repair any PTT clutch free of charge for as long as you own the clutch. All you pay for are any parts required to put your clutch back into service.
Will PTT clutch packs and other parts interchange with other clutch manufacturer's clutches?
YES most of PTT's clutch products offer backwards compatibility with QMI's V-Drive type products. After all, PTT's head engineer originally invented the V-Drive clutch. Please call the factory for a list of complete parts compatibility. PTT's clutch packs are compatible with most AP Racing, QM, & Tilton clutches, and in most cases will improve their performance.
I want to run a 4.5" clutch. What do I need to consider before making this decision?
First consider how long you can get your current clutch to last. If the answer is almost a full season, or more, then you are a good candidate for a smaller clutch. The smaller the clutch, the less mass it has to tolerate excessive heat generated by slipping the clutch. Smaller lighter 4.5" clutches offer outstanding performance, but this performance comes at the expense of heat tolerance. You should be prepared to treat smaller clutches like the racing thoroughbreds that they are. That would mean do not drive your race car around the pits, instead push it. Do not drive the car on the trailer, instead winch it on. Most importantly, do not excessively slip the clutch. This leads to heat build-up which could damage a smaller clutch sooner.
I have a hard time driving my clutch (getting the car off the line). How do I get easier engagement from my clutch?
Racing clutches require an extremely small amount of travel to disengage the clutch. (PTT's 4.5" clutch requires less than 3/16" of travel at the release bearing for full release!) A smaller clutch master cylinder will give you more control or modulation while at the same time making the pedal easier to push. You can also substitute a small contact diameter release bearing such as PTT's part number RM001.
Will a PTT clutch work with my crate motor?
YES. If your crate motor is externally balanced you need to run an externally balanced flywheel, or flexplate. PTT offers external bob weights for its line of button flywheels that bolt on at the same time the clutch is bolted on. This allows you to use your existing PTT flywheel and saves you money by not having to buy another expensive externally balanced flywheel.
Will a lightweight clutch with aluminum pressure plate and lightweight floater plates last as long as a standard weight PTT clutch?
There are a lot of variables to take into consideration when talking about clutch life. All things being equal though, when installed and used properly, a lightweight PTT clutch will last as long as a standard weight clutch. It should be noted however that the lightweight clutch will be more susceptible to heat damage under extreme use (abuse) due to its lower thermal capacity. The decision to gain the competitive advantage that lighter parts offer should be carefully considered against the type of use the clutch will be subjected to, and how well the driver treats a clutch.
Is it more important to reduce the static weight of your racecar, or reduce the MOI of your car’s rotating parts?
It is generally recognized that there is about a ten to one advantage in favor of reducing rotating MOI over static weight reduction of the racecar. Let’s face it, if you have the chance to remove just one pound of rotating weight from your flywheel, you will see an immediate and noticeable improvement in the racecars acceleration. On the other hand if we put a ten pound brick in your racecar without your knowledge, you probably would not even realize it was there.
Moment of inertia, (MOI) or more properly called angular moment of inertia as it applies to rotating (racecar drivetrain) parts deserves important consideration. The reduction of MOI in your racecar’s drivetrain will pay big dividends in your car’s performance. First let’s consider how MOI is calculated. The MOI of rotating parts can be solved by the formula 1/2 MR² where M = mass and R = radius. This means that one half the mass of a rotating part times the radius (squared) of the rotating part will give us the MOI of the part expressed in lb./in.². Let’s solve for the MOI of a simple flywheel:
Let’s say we have a flywheel that weighs 12 pounds and is 10” in diameter.
Mass (M) = 12 lbs. and Radius (R) = 5”
½ x 12 x 5² = 150 lb./in.²
Now let’s take our 12 pound flywheel and put it on a diet. Let’s turn 4 pounds off of it to reduce its weight down to 8 pounds. (That is a full 1/3 reduction in weight!)
Now, M = 8 lbs. and R = 5”
½ x 8 x 5² = 100 lb./in.²
This shows that a 1/3 reduction in weight results in a 33% reduction in MOI. OK. Good. 1/3 lighter MOI will result in a good performance increase on the track.
To illustrate how important MOI is, let’s look at this problem a little differently. Let’s reduce the size of the flywheel to a 6” diameter but for comparison sake we will say that it still weighs 12 pounds (just as heavy as our original flywheel).
Now, M = 12 lbs. and R = 3”
½ x 12 x 3² = 54 lb./in.²
This shows that a 50% reduction in size results in a 64% reduction in MOI.
If you reduce the size of the flywheel to a 6” diameter and reduce the weight to 6 pounds you have:
½ x 6 x 3² = 27 lb./in.²
Your flywheel now has a full 82% reduction in MOI.
This example illustrates that you get a bigger reduction in MOI by reducing the rotating diameter than by reducing the rotating weight. So…the next time you are shopping for a new clutch you should not ask how much it weighs. Instead, ask how much MOI it has.
This also clearly illustrates that the MOI of a 5.5”, 3 disc clutch (39.4 lb./in.²) will be significantly lower than a 7.25”, 2 disc clutch (71.4 lb./in.²).
What are the benefits of a lower MOI clutch?
MOI shows up as a benefit in your race car in several different ways:
Low MOI Advantage #1
On acceleration the engine’s horsepower is more efficiently transmitted to the drive wheels. Due to the fact that this extra power is not being absorbed by having to spin up the excess inertia of the heavier clutch and flywheel, the racecar with the lower MOI driveline parts will out-accelerate a racecar with heavier MOI driveline parts.
Low MOI Advantage #2
On braking when approaching a turn, the racecar with the lower MOI driveline parts decelerates harder, with less stress on the braking system. This is due to the fact that the engine has much less flywheel inertia trying to carry the car deeper into the corner. This increased engine braking can result in less brake pad wear and less stress on the rest of the brake system.
Low MOI Advantage #3
Lower MOI parts take less horsepower to accelerate. This can result in lower fuel consumption. In an endurance event this can add up to a substantial fuel savings. Perhaps enough to alter your pit stop strategy.
Low MOI Advantage #4
Low MOI rotating parts usually also have lower static weight. This allows the racecar designer to reduce the car’s weight. If the class has a minimum weight and the car is already under that weight, it allows the designer to put the ballast where it will help the car’s handling the most.
Low MOI Advantage #5
Low MOI clutch disc(s) allow for quicker up-shifts and down-shifts. This will result in a measurable difference in reduced lap times on a road course.
Low MOI Advantage #6
Low MOI clutch discs allow for reduced stress on transmission synchros or dog rings. Because the low MOI clutch disc(s) change RPM quicker there is less force applied to shychros or dog rings, resulting in longer life of these critical transmission components.