Replacing a chainring - is my part compatible?

[galfeh]

Hi all,

My chainrings were are really worn, and I've recently replaced the upper and lower chainrings with lightly worn used parts at one of those DIY non-profits in my neighborhood. They didn't have a middle chainring, so I've had to buy one to put on. I'm not sure that the part I've got will fit, because the packet shows it's a 2x10 speed chainring, and I have a 3x9 bike. The site I bought it from didn't show this information and I don't know enough about bikes to look for that.

I have this Shimano Sora 50-39-30 and am replacing the 39 chainring (hopefully) with a Shimano Ultegra 39 2x10.

I can't find replacement chainrings for the Sora, and I can't afford to buy a whole new crankset, nor can I afford a bicycle mechanic right now.

What I want to ask you all is whether this chainring will fit and function (that you know of). I will send it back, if not and try something else.

Thank you all for your help.

[DaveM]

I dont think there's any inherint issue with replacing the chainring with one from a double crank, except that it won't have the extra little teeth on the inner surface that help the chain climp up from the small chainring. You might get slightly slower shifting because of this.

Other than that though, the two issues are BCD (bolt circle diameter) and offset. If the bolt holes line up, good. If the chainring you have now flares in or out a little from where it bolts on to where the teeth are and the new chainring is straight (or vice versa) you may have a problem. Other than that, I think you're good.

[galfeh]

Hi Dave,

Thanks very much. I think I should be ok, then. I really appreciate your opinion!