Cdales stem cap is just an alu sleeve that braces the steerer under clamping force. A 3mm spacer on top won't kill you but I'm pretty sure for that tiny amount I'd just install as instructed. Mind you, I'm riding a 2005 Caad with a full carbon fork, star nut and cannondale bung/topcap combo as it left the factory. I'm not sure what's going to kill me first - the paper thin frame exploding or the forks...
Cdales stem cap is just an alu sleeve that braces the steerer under clamping force. A 3mm spacer on top won't kill you but I'm pretty sure for that tiny amount I'd just install as instructed. Mind you, I'm riding a 2005 Caad with a full carbon fork, star nut and cannondale bung/topcap combo as it left the factory. I'm not sure what's going to kill me first - the paper thin frame exploding or the forks...