Originally Posted by
dave1959
So, My question is.... How interchangeable are these cranksets..?? I can find a few with the same tooth configuration, but a lot more that are very close...
You can replace the crankset, but there's a little more to it than that.
The part/mechanism that connects a crankset to a frame is called the bottom bracket. Your crankset uses a square taper bottom bracket, the upside of which is that they're very common. The downside is that they were made with LOTS of different spindle (axle) lengths and you need to match a crankset to a bottom bracket with the right spindle length. So if you remove your crankset and throw a new one on there, it might not work even if your new crankset was designed for a square taper bottom bracket. Your new crankset might require a different spindle length.
To make it even more complicated, many older cranksets required asymmetric spindles that are longer on one side. Those generally aren't made anymore, so finding the right one for a given crankset can be problematic. (You can sometimes use a symmetric bottom bracket, with or without spacers to offset it.) There are even different taper sizes/types that can present compatibility issues.
So anyway, to make a long story short... Yes, you can replace the crankset, but if you want it to work, you've got lots of variables to sort out.
Some other alternatives: (1) You can buy a new crankset with the proper chainring combinations, along with a new bottom bracket that's properly sized for your new crankset. (2) If your current crankset's chainrings are bolted on and not riveted in place, you may be able to replace chainrings without replacing the whole crankset.
Originally Posted by
dave1959
What happens if I change the tooth count..??? Does this just change gear ratio's ??
It depends on how different the tooth counts are. If they're within a couple of teeth and similar in range from big to small, it can likely work. You may need to reposition the derailleur on the seat tube, change your chain length, but those aren't a big deal. If your new crankset has significantly different chainring sizes, though, your front may not be able to handle the new gearing. If the difference in size between your new crankset's big and small rings is larger, you could potentially even exceed your
rear derailleur's capacity.
...and yes, as you suggested, you'll likely feel the difference in gearing as well.