Vespa Largeframe Clutches: W1R Proto | TECH

White One Racing’s Proto clutch (right) compared to a banded Cosa 2 clutch (left)

Does W1R’s lightweight largeframe clutch offer any advantages?

I can remember back to a time when the best option for a tuned PX was stronger springs for the original 7-spring clutch; fitted with a reinforcement band to stop the basket stretching at high revs. The problem with that set-up was the difficulty of pulling in the lever and consequently the amount of wear you’d get on the mechanism and pressure plate.

VIDEO: Comparing the W1R Proto to other Cosa-derived clutches

The heavy, heavy Cosa sound

The Cosa 2 clutch was a revelation. It could handle a bit more power but the actuation was much easier on the hand. While the Cosa clutch was a definite upgrade; there are still things that go wrong with them. The internal toothed splines are prone to wear and the clutch itself, with a much stronger basket, is very heavy. 

A Cosa-style clutch acts like a second flywheel. It is a high inertial mass that rotates with the crankshaft. If you fit a lightweight flywheel then you can end up with a situation where the heavy clutch acts as the main flywheel. Compare this to the later (and far superior) Vespa smallframe engine design, where the only thing on that end of the crankshaft is a tiny, lightweight drive cog.

Over time the Cosa-style clutch has been improved and upgraded to improve its power-handling capability. In many of the ‘…strong’ designs, the original toothed connection between the bell and the centre sprocket is changed to a wave-form pattern. This improves stability and reduces wear, but the penalty of increasing the strength and durability of the Cosa design is that the clutches became even heavier.

The waveform connection between basket and centre is much more durable than the original splines

More plates please!

The primary factors that dictate where a clutch can handle the power – or rather torque – that you are throwing at it without slipping are: friction surface area and spring pressure. One balances against the other.

• If you have fewer friction plates (e.g. 2.5 plates in a PX200 clutch for instance) then you need a lot of spring pressure to stop it slipping.
• If you add more plates – increasing the frictional area – then you can use weaker spring pressure and the clutch will still resist slipping. This is one of the reasons the Cosa design, with 3.5 frictional plates, but lower overall spring pressure, feels lighter on the hand.

There is much more to clutch design than that, because the material of the friction plates – how grippy it is – along with the design and diameter of the plates, also has an effect.

Sadly, you can’t just add more plates if there isn’t room to let them separate when you pull the clutch lever. As anyone who has tried a 1980s 4-plate conversion for Vespa (or 5-plate for Lambretta) will know, making the plates slightly thinner to get more of them in is not a great solution. What usually happened was the clutch dragged so badly (did not release fully when the lever was pulled) that the plates quickly overheated and warped; causing even more clutch drag until you ended up with an Aggressive O. Sorry, I mean a vicious circle.

As you’ll find on all the competent clutch solutions that followed; in order to successfully use more clutch plates you must redesign the entire clutch to make more space for them. All the really successful clutches for both Vespa and Lambretta, don’t just use thinner-than-standard plates; they use clever engineering tricks to make more space.

The W1R clutch has 10 spring positions and a special overlapping bottom plain plate

Limits

The clutch state not mentioned yet is perhaps the most important: engagement. This defines how smoothly the scooter pulls away as you let out the clutch lever.

Here, adding too many plates or too grippy a friction material can lead to snatchy engagement which makes for lurchy pull-away and uncomfortable city riding.

As with everything else in life, there needs to be a balance.

This clutch uses a total of 4.5 Honda CR80-stlye clutch plates

White One Racing – Vespa Large Proto

At the upper end of the many Cosa-based clutch designs for the Vespa Largeframe is the Proto from White One Racing (W1R); which is available from 10Pollici.com. 

The W1R clutch is a strange concept because it is largely a ‘kit’ of many commercially available parts from other manufacturers that they have assembled together with their own basket and special pressure plate. W1R claim to make no profit from the sale of these clutches – they just wanted to promote what they considered an optimised system.

The clutch uses a waveform centre design and the basket accepts 4.5 friction plates. The half-plate being the last one to go in the basket with friction material on only one side. The plates for the Proto version are slim and based on Honda CR80 design. This plate has a different number of ‘ears’ compared to a Vespa one, so it requires a special basket. Over the years, many other Vespa clutches have used this plate format.

One major advantage of the motorcycle-style clutch plate is the thickness of these ‘ears’ compared to the plate. On these aluminium plates the ears are cast to be the full thickness of the plate – including the fiction material – so they have a much larger surface area where they contact the basket. This is very important as it reduces the ‘sawing’ effect where the plates gradually create grooves in the basket.

The clutch has 10 spring positions with an option of hard or medium springs in each, giving a wealth of different possible combinations.

What’s in your basket?

The W1R clutch basket is made of an aluminium alloy called Titanal (no laughing at the back) which has been anodised after production. This makes it much lighter than most other largeframe clutches.

For example:

• Banded Piaggio Cosa clutch: 1,360g
• BGM Superstrong: 1,400g
• W1R Proto: 1,100g

The actuator rod must be ground, where the shaft is marked, to provide clearance for the oversized clutch basket

Verdict

This clutch is adaptable to many situations, but may be overkill for moderate engine tunes (W1R also offer cheaper clutch systems). At the moment we have it on test in an engine that is unlikely to ever stress this clutch to the limits.

Given that there are new clutch systems on the market that can handle as much as 70hp, selecting a clutch is now a case of picking one at a price point that you can afford. Where previously it was difficult to find a good largeframe clutch, now the W1R Proto is one of many options that will do the job.

In the end we also had to grind the cover a little for clearance. The black marker pen marks are to check if the clutch will touch.

PROS:

• Relatively lightweight
• Variable spring pressure with 2 sets of 10 springs
• Uses reliable CR80 style plates with thick alloy ears to not cut the basket
• Uses 4.5 friction plate
• Very low drag when the lever is pulled

CONS:

• You must modify the clutch cover and actuator shaft for additional clearance of the basket
• Not necessary for engines producing less than 20hp
• The clutch is sold without a drive gear so you must order the correct type (straight or helical) and tooth profile to match your transmission
• At €330 + the cost of a drive cog it’s relatively expensive