Shazaam's Tech Library - Clutch OEM or Aftermarket?

A useful technical article from guest contributor Larry Kelly of San Diego CA (aka Shazaam!).

Clutches - Stock vs Aftermarket


Decisions, Decisions ...

It’s a common scenario. You’ve worn out your clutch pack and your clutch basket fingers have been deeply notched by the plates. So, do you replace them with stock parts, or do you take this as an opportunity to install an aftermarket clutch? For significantly more money, you can install a slipper clutch, but is it worth it - and are there disadvantages?

Let’s assume that you ride your bike on the street mostly, but you’ve signed-up for a riding school and some club track days. You’ve also heard that a slipper clutch will help you to go faster on the track and ride safer on the street.

So, what should you know before you decide?

Ducati Clutches

The Ducati dry clutch on most models use steel plates, hub and basket. It’s noisy and it’s heavy, compared to aftermarket units, but it’s pretty durable and the friction material lasts at least as long as aftermarket plates. The reason that they’re noisy is that each time you shift, the edges of the plates hammer the fingers of the basket, causing each to deform, causing the gap between them to get larger, causing higher impact forces, and causing more rattling noise when the clutch is disengaged. So they get louder and louder until the plates and basket are replaced.

You’ll need to replace the plates when the thickness of the friction material gets too thin to prevent slipping. You’ll notice a little slippage first when starting-off in first gear, but when it starts to slip in top gear it’s time for a new clutch pack. Depending on the mileage and the depth of notching, you will probably will want to replace the basket at the same time. A notched basket will be louder, but I’m not convinced that it makes it any more difficult to for the plates to separate when disengaging the clutch. But replacing just the plate stack, which then has to engage the basket notch pattern worn-in by the previous plates, will possibly affect your ability to shift smoothly.

The price of the Ducati original equipment manufacturer (OEM) parts varies from dealer to dealer, so shop around. In the US the cost of a clutch pack is around $180, a basket is about $140.

The 999 comes with an aluminum basket that works on the older bikes. It retails for $324, about $75 less than an alloy aftermarket part.

Aftermarket Clutches

After market clutch components are marketed as performance items with unique features that are intended to address design defficiencies in the OEM clutches. Foremost is lighter weight.

Aluminum drive and friction plates, basket, hub and pressure plates combine to reduce rotating mass as well as overall bike weight. Less rotating mass in the engine allows it to change rpm more quickly and less overall bike weight improves acceleration, braking and handling.

However, the reduced mass offered by an aftermarket clutch alone is not very significant because the clutch turns once for every four revolutions of the flywheel. Consequently, it is accelerated one quarter as quickly as the flywheel, so rotational weight reduction at the flywheel, gram-for-gram, will give you four times the effect as weight reduction at the clutch. Reducing the flywheel and clutch weight often will adversely affect drivetrain smoothness (so unlike lighter wheels, for example) this is not necessarily an overall improvement for the street.

The weight savings from an aluminum clutch basket and plates is about 3.5 pounds, less than 1% of the overall bike-plus-rider, so any improvement in performance is not really of major importance in deciding to change to an aftermarket unit.

Clutch durability is another area where aftermarket clutches are marketed as an improvement over stock clutches. Clutch life varies widely from rider to rider but all direct comparisons suggest that the Ducati OEM clutch plate friction material has outlasted the clutch plates from aftermarket manufacturers. In one case 25K vs. 16K miles. So, at roughly the same price, the OEM plates seem to be the better deal.

There has been some innovation to try to address the durability issue associated with the plates impacting and notching the basket.

For example, STM has tried to overcome this problem by increasing the number of tabs on each plate (and the number of basket fingers) from the stock 12 to 48 tabs. The intended result is to distribute the impact loads over a larger tab-basket contact area (lower psi) to reduce notching to the clutch basket fingers and mushrooming of the plate tabs. Only STM makes a 48-tab clutch pack, however.

Nichols Manufacturing designed their CNC-machined aluminum basket with wider basket fingers that results in larger finger contact area and consequently lower impact stresses, particularly when combined with their Barnett clutch pack where extra care has been taken to initially minimize gaps.

Another option is a Barnett aluminum basket with stainless steel inserts to protect the basket fingers. About $225.

Keep in mind that when you mix steel and aluminum, the softer metal deforms preferentially and clearance gaps suffer, more than for steel-to-steel. So if you have a steel basket, stick with steel plates.

Slipper Clutches

Slipper clutches are an innovation that allow your rear wheel to move freely whenever it tries to turn faster than the drivetrain. When engine braking reaches a certain reverse torque level, the clutch disengages and allows the rear wheeel to move freely, much like on a bicycle when you pedal in reverse.

Under normal circumstances, the clutch remains engaged and the engine provides a reverse torque to slow the bike when the throttle is cut. But if you downshift to a lower gear before you have reduced your speed sufficiently, the clutch disengages. Consequently, a slipper clutch will allow only a limited amount of engine braking. This is seen as a safety benefit if you accidentally downshift to too low a gear, especially while cornering on a V-twin. Not just at the track, but on the road as well. We’ve all done it.

Setting up a slipper to release properly and launch smoothly is sometimes time-consuming, and naturally the friction material will wear out more quickly depending upon the amount of times it releases. Also, unlike a standard design, the slipper release mechanism need to be cleaned and lubricated periodically to prevent wear and to provide a smooth release.

Slipper clutches are being offered by more manufacturers (including Ducati on some new bikes) as original equipment these days.

 

Please note that Ducati-UpNorth.com cannot accept any liability for the accuracy or content of this section. Visitors who rely on this information do so at their own risk. If you are unsure it's worth contacting your local Ducati dealer who will be able to help. Do not attempt a repair or modification if you do not have the correct tools or knowledge to do so.