Once upon a time, chainrings were only a little complicated. You typically had 4 or 5 holes of some common measurement apart. Teeth were approximately the same and if they fit, they were fine. But with newer cranksets and chainrings, there are more options, and I see people get confused. I am sure there are some more systems out there than I'm listing, but here are a few: Conventional Bolted Rings These have been used for decades. The chainrings use some number of bolts to mount to the spider of the crankarm. The critical dimensions are the number of holes and the diameter of a circle that passes through them all. If your old one is not labeled (or the crank isn't) you need to measure and that can be complicated. Measure BCD on 4 Bolt (Source: Wolftooth) 4-bolt patterns are easy, whether symmetrical or not. Just measure across an opposing pair. In theory, you're measuring the centers of the holes, but edges on the same side is usually easier. That distance IS your BCD. 5-...
Mechanical experience I've been messing around mechanically with bikes for decades. I learned the basics in childhood doing all the basic tuning and repair activities. But it is only in recent years that I've started to take on the full spectrum of work. Recently, I've started building bikes from the frame up ( Litespeed Road , Litespeed Gravel , Waterford ) and fully overhauling old bikes with various generations of technology. Doing this brought in new skills like replacing headsets, working press-fit bottom brackets and hub bearings, hydraulics, and more such that there isn't much I don't feel comfortable doing. But wheelbuilding is scary But there was one major component build that remained scary voodoo to me: Wheelbuilding. I'd been able to true a wheel without screwing it up since I was a kid. But the idea of starting with a hub, a rim, a stack of spokes and a pile of nipples made me very uncomfortable and I avoided it. I avoided it even when the rear ...