Jan 24

Light flywheels: pros and cons

Often times during a clutch swap, the car owner will decide to use a lighter flywheel than stock. In this article, we will take a look at the pros and cons of doing so, to help you decide if this is something you want to do in the future.

First, before we dive into it, we should answer what the flywheel does in the first place. On a car specifically, the flywheel rests at the end of the crankshaft on the outside of the crankcase. The reason for this is so that as the engine’s crankshaft turns, the flywheel is also turning at the same speed. This, in turn, is a source of stored energy, so that when you are taking off from a stop, there is instant torque applied once the clutch is engaged. The heavier the flywheel, the more angular momentum it will be allowed to store. Thus the more torque it will be able to apply when the clutch is engaged, without increasing RPMs.

So should you buy a lightweight flywheel for your car? The advantages of a light weight flywheel are the same as reducing the weight of any part of your drive train, you are going to get a quicker revving engine. This is fantastic once you are moving, because it means you will get to the higher RPMs, where the power is, much quicker. The down side of this is drivability.

A lightweight flywheel means you are going to have to get really good at clutch control really fast. The stock, heavier flywheel (usually 20+ lbs) means you can be pretty liberal with clutch engagement and still not stall. However, the lighter flywheel (sometimes 11 lbs or less!) means as soon as the clutch engages, the clutch, driveshaft, rear end, axles, etc that are at a dead stop can overcome the lower angular momentum of the light flywheel, thus causing a stall. The solution, of course, is very easy, you add more throttle while engaging the clutch. This can, however, cause added wear to your clutch and replacing clutches gets old after a bit and can be costly.

The other downside of the lightened flywheel comes between shifts. Once the clutch is disengaged it means the engine is going to rotate slower, because the heavy flywheel is not there to keep the momentum going. This means a greater RPM drop between shifts if you shift at the same speed that you did with the heavier flywheel. This could mean your engine falls out of the power band between shifts. There is also extra stress on drivetrain components when the clutch is re-engaged.

Now, finally, we can answer the age old question of “should I put a lighter flywheel on?” The answer of course is not straight forward. If your car is just a daily driver, then I say no. There are probably better, easier, and less expensive ways to make up the performance difference without the added headache of driving with a light flywheel. However, if your car is a racer only, then yes, it’s kind of a no brainer.

As always happy modding!