Actually, you chain should not be very tight ... there should be
some slack. I can't tell you how much slack as I dun have the
figure on hand, so let the experts tell you that.
I can tell you why though ... actually, when the bike is not loaded
(not carrying any weight), the chain has some slack. But when you
sit on your bike, you compress the suspension and the swing arm
actually moves about it's pivot, as a result, tightening the
chain.
Furthermore, I think there is a chain tensioner in your gearbox or
something. When you kick in your gear from Neutral, the tensioner
will tension your chain making it even tighter. So you can imagine
what happens if your chain is already very tight when not carrying
any load; you'll stress the chain even further when you sit on your
bike. And imagine what happens when you cross a hump heavily ....
Your chain might break.
The chain cannot be too tight, neither must it be too slack. When
the chain is too slack, it probably jump some teeth on the
sprockets, and wear out both chain and sprockets prematurely.
Worse, the chain may even come away from the sproket and imagine
what's going to happen after that ... think the chain will jam in
the gearbox and ... you know lah ....
That much said, you must realise however that over time, chains
that were at correct tension will eventually gain more and more
free play ... this is normal wear and tear. This is why you should
tension your chain properly on a regular basis.
