Originally Posted by
nelsonfung21
why sometimes the chain is tight but sometimes it's loose ?
Like, the upper chain is tightened but the lower part is loose, after rolling the crank a half circle,the situation is reversed
Is that a normal condition ? (I have chain tensioners on it.)
If your chainring isn't perfectly round (which many are not), centering it won't completely fix the problem. Also, a lot of inexpensive cogs aren't perfectly round either.
Originally Posted by
nelsonfung21
And what model or which brand of helmets do you recommend for a good deal ?
I'm not here to dress you. Go to some shops, try some on helmets and buy the one you like best.