Chainring Contact with frame - Please Help
 

I bought an old GT frame the other day and found an extra chainring lying around and I figure I'll put it on the frame but for some reason the bigger cog rubs agains the frame. I dont have the brand or the model of the chainring. It is just a regular 48 tooth 3 ring cog. So, Im wondering is there different sizes mtb chainrings and what would my options be.

Your frame might be designed for a 44 or 42T biggest chainring. You would need a longer bottom bracket spindle to move the crank further away to let a larger ring clear.

How old? If it's an old mtb 48 was the standard big ring size. You probably need a longer BB.

Read This and adjust accordingly.

Either the frame isn't designed for that big of a chainring or you need a longer bottom bracket. Standard MTB cranksets have a 42 or 44 tooth big ring so you are going larger than typical but 48 tooth big rings aren't unheard of for MTBs either (I use one though it's on the road with a MTB frame).

There are several sizes available, in one to two tooth increments. A smaller tooth count ring would likely fit, and if you have the original ring you won't have to guess. Make sure you get the right size bolt circle diameter.

Depending on how much additional clearance you need, a spacer like these might work. Your LBS should have them-
http://www.loosescrews.com/index.cgi...id=70323611650