With so many modern clutch baskets now available for the large frame Vespa engines running a Cosa 2 clutch, there’s pretty much a setup to suit every level of tune. Whether you’re building a fast road tourer or something pushing beyond the 40bhp mark, today’s clutch options are more than capable of coping. Heavy-duty CNC-machined one-piece baskets, such as the SIP ultrastrong and MMW superstrong, have largely dealt with the traditional weak points in the assembly. In many cases, that leaves the clutch plates themselves as the next area worth improving.
Key features
At first glance, clutch plates can seem much of a muchness. There are plenty of options on the market, made from different materials and all claiming improved performance. But the real issue often lies not with the friction material, but with the backing plate itself. Standard items use fairly basic steel plates, which means they are relatively thin, soft and heavy for the job they’re being asked to do. They also have a habit of chattering around in the basket at idle, gradually wearing away at the tabs and basket. If the basket is harder than the plates, which is often the case with modern upgraded items, the plates can quickly take a hammering.
That’s where better-quality alternatives come in. By using aluminium as the main backing material, weight is reduced, and heat dissipation is improved. Reinforced tabs also help the plates stand up better to the repeated loading and unloading that takes place in use. Some tuners have previously turned to modified motorcycle plates, while others have gone down the route of using clutch baskets specifically designed for those plates.
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That approach can work, but it is not without compromise. Motorcycle-derived plates do not always bed in as cleanly as you’d like, and they can make the clutch feel more sudden or grabby in operation. They sometimes tend to be less durable than the original Vespa Cosa 2-type plate. In truth, the original Cosa 2 dimensions are already capable of handling serious power, comfortably enough for engines producing well over 40bhp.
SIP’s answer is to keep the proven Cosa 2 format, but improve the materials used. The SIP Performance clutch plates use aluminium backing plates with reinforced tabs, giving you the best of both worlds. They retain the original dimensions, so clutch feel remains progressive and predictable, but they offer a worthwhile improvement in durability and thermal stability.
Because the load is spread more effectively through the reinforced tab area, the plates are less prone to the kind of wear that can occur at idle and during repeated engagement. The reduced weight of the aluminium backing also helps the clutch respond more cleanly, while its improved ability to shed heat makes the whole setup less vulnerable to thermal fade and heat-related abuse.
Friction material options
The SIP Performance Race Cosa 2 plates are offered in two friction materials: sintered and black carbon.
The sintered version is the better all-rounder for most fast road and high-performance road engines. It offers a very good balance between grip, durability and sensible bedding-in behaviour, making it a strong choice for powerful everyday use.
The black carbon option is aimed more squarely at race and track applications. It offers greater resistance to heat and remains controllable even under sustained hard use. The trade-off is that it needs more spring pressure to transmit the same torque as the sintered version, so it is a little more specialised in its intended use.
For anyone running a modern clutch basket in a tuned Vespa large frame motor, these make a lot of sense. They keep the proven Cosa 2 format, improve the materials where it matters, and help extend plate life without introducing the harsher engagement often associated with motorcycle conversions. A smart upgrade, particularly for higher-output engines where reliability matters just as much as outright grip.
More info: www.sip-scootershop.com
