21 Tooth Cosa Clutch for T5?

Hi all,

Wondering if anyone knows about putting a 21 tooth cosa clutch in my T5 Mk1?
What sort of a speed increase can i expect? (the bike is Malossi kitted, Simonini pipe). I want to do a bit of long distance work and am thinking it could be good for those evening summer rides (!).

Are there any downsides to the upgrade?

Also, if i go ahead … can i use the old castelated nut to fix the clutch or do i need a special ‚cosa‘ nut as listed as an item on Sip’s site?

Thanks for responses!


Thanks very much fellas! Big Help.


yes, see Anthony-Kell answer.
As far as set up he is right too. For expample if you were using your kit with a PM expansion it would not be a good idea to upgearing. With the Simonini you can if you need for this summer rides.
For the clutch you can either use the old castelated nut or put the new cosa one that is more pratical.


I’m no T5 expert but you can quite easily take ratios and work out the proportional increase in gearing between the standard setup and what you propose. I’m upgearing my LML from 21/68 to 22/68 using a 22 tooth Cosa clutch.

21/68 = 0.3088
22/68 = 0.3235

0.3235/0.3088 = 1.0475 or a near 5% increase in gearing

Theoretical top speed increase is then: top speed, say 60mph * 1.0475 = 62.85mph

However, this will depend upon the setup of the bike assuming it can pull the longer gearing in top. Maybe someone else can clarify this.

Cheers, AK