Originally Posted by
newbert
From your reply, can I assume that it's possible to change only one of the three chainrings, and that there's no need to change them as a complete 3-ring set? IOW, I could theoretically change from 30-39-52 to, say, 39-52-62 by keeping the original 39 and 52 and adding a new 62? Not saying that's a good idea in my case necessarily, but is that how it would work? ie - could I re-use 2 out the 3 existing chainrings?
Thanks!
It's not quite as easy as it sounds. The large chainrings have one bolt circle diameter (BCD) - the circle defined by the 5 attachment bolts. Most road cranks use 130mm. You can probably swap around rings if they're the right BCD. Inner rings typically have a different BCD - often 74mm, and sometimes 58. Mountain bike 4-arm cranks use something else entirely. The limit of a 130mm BCD is about 38 teeth; after that the bolt circle is too big for the number of teeth. And cheapie cranksets use riveted rings, which are not replaceable. Rings have indents meant to hold the attachment bolts, and you have to put those on the correct side or the ring won't sit solidly on the spyder.
There are other complications, too. The front shifter has a ramp that lets you shift from 2nd to granny. If you add a bigger outer ring without changing the middle ring, the ramp may no longer align properly, making it very difficult to shift to granny.
So I guess what I'm saying is that you can make changes of a few teeth either way yourself, but if you're going to rework the whole crankset, you're going to need help from someone who knows what they're doing. But yes, it can be done.