You can also install stiffer springs.
The following is one of my company secrets.
I can tell you this, because I can not make good deals with you:
-> shipping is expensive
-> USD-EUR exchange rate is bad for you
These reasons will make for you standard parts a bit expensive.
The clutch springs from EBC are 10% stiffer, as the OEM springs.
The fitting springs for the TW does have the number CSK052.
-> This is not the secret
But I've found a other set of fitting springs.
These springs will fit perfect on the 2001 and newer models, because Yamaha has changed the pressure plate a little bit.
All other bikes will need a small modification. There must be removed a bit material from the pressure plate, because the spring diameter is a bit bigger (~0.8mm bigger, but you don't have to remove so much -> ~0.4mm).
Sorry, I not describe it better. I hope, you understand what I try to say.
I've made a small calculation to get the spring rate from the different clutch springs.
-> I don't know the exact value of "G = modulus of rigidity", but I use 81.500 N/mm² as basic value for the calculation.
13,40 N/mm² -> OEM spring
14,74 N/mm² -> CSK052 -> 10% stiffer as OEM
15,69 N/mm² -> CSK002 -> 17,1% stiffer as OEM
I've ordered some other springs from EBC and I want to check these springs too.