A Universal Granny(gear)

Grannies come in many forms, but they do tend to make life easier for those with them! Well, granny gears are no different – especially considering the all those damned bolt hole variations.

This is a bit of a MYOG post. At least where I live, finding reasonably priced inner chainrings through an LBS can be painful – especially 58 and 74 BCD. Given that I'm often tinkering with bicycles manufactured any time from the late 80s to present, I’m almost guaranteed to encounter different crank bolt patterns, so I’d have to have 2 or 3 different BCDs of chainring on hand. A minor inconvenience, but annoying moreso because granny chainrings are the most mechanically simple – no ramps or pins required to aid in shifting – so they should be cheap and plentiful!

Well – it bugged me enough that I went ahead an whipped up a quick-n-dirty CAD file that I could get laser cut in flat stainless, a 24T chainring that had all 3 common bolt patterns: 4bolt/64mm, 5bolt/58mm and 5bolt/74mm. Yes, there is some bolt-hole overlap given the combined bolt patterns, but this is a small unless you are a gorilla I doubt you’d be able to generate enough torque to cause issues. And as it’s an inner ring, the shifting isn’t as picky, so simply picking a thin enough plate metal lets this work all the way up to 10 speeds without requiring chamfering of the tooth pattern!

Despite being custom made and manufactured locally, these are actually cheaper for me to get than the cheapest stamped-steel granny rings I can find locally – and I only have to keep one variant on hand for all my tinkering.

Is it crude? A bit. But it’s also definitely effective.