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Help with chain ring sizing... I'm lost

2K views 12 replies 6 participants last post by  osmarandsara 
#1 ·
I bought my bike from someone who took one of the chain rings off, changing it from 18 speed to 9 speed. I would like to add another one to bring it back to 18 speed. The one currently on the bike has "Shimano M9 T36" stamped on it. I've been looking for chain rings but there are so many different styles I don't know where to start. Any suggestions?
 
#2 ·
Well, first you gotta figure out how many teeth you want (ie. 28T)
then, make sure you have the right bolt pattern (ie, 4 or 5)
and finally, the spider diameter - or the radius of the bolting pattern and the corresponding radius of the spider's flange if applicable (some spiders are flat @ the granny gear location - so you might just have to worry about the pattern/ radius).

sorry if my 'help' is of no help yet, but some more info would help ;)

what kind of cranks do you have?
Any chance of getting ahold of the person you bought the bike from to possibly get that chain-ring??
 
#4 ·
Well, less teeth up front means 'easier' gearing up front - opposite of what happens in the rear.
I cant really tell you how many you'd want... do you want an easier gear up front? (I assumed you did because a 36T (which you already have) is pretty stout for MTB. A 'granny' gear is most likely IMO - a common one is 28T for instance
Are you running a bash-ring? outermost ( likely a plastic composite) on the crank arm's spider (the arms off of the crank that the chain-ring bolts too)? or is it just the one chain-ring - I ask because most MTB cranks allow for a triple ring setup - ie 4x, 3x, 2x ( I'm researching your crank right now - so bear w/ me) and you could add a bigger (harder) ring and a smaller (easier) ring if you wanted.
Are you spinning out too much, and/ or do you find it too hard to climb in the setup you have now?
 
#5 ·
OK, first off, here's PDF for your cranks http://www.raceface.com/comp/inst/FR-DH_Crankset_web.pdf
Save it for parts and installation reference.
It looks like to me, that the 'granny-ring' spider is removable, so hopefully the previous owner did not remove it - An easy way to tell...is there a blank spider inboard of the current chain-ring? (ie 4 open holes on an 'X' shaped armature?)
If not, (ie - no way to mount anything, you'll need to order one to install a granny) If you wanted a bigger ring, the same mounts are used as the 36T ( but if you have a bash...I'd leave it personally ;))
So check out if you have a 'granny' spider and we'll go from there.

BTW according to 'RaceFace' your triple setup (stock) would be a 24T, 36T, Bash.
 
#6 ·
Thanks for the info - it's a great help.
I want to add another chain ring on because I'm topped out on my hardest gear. I can't go any faster - I need a harder range of gears so I can get some top end speed. The 9 gears I have now are great to start out with, it's just that I run out of gear on the hardest one when I'm trying to go fast. Hopefully that makes sense.
I do have that plastic ring you mentioned (see pic). There are holes on the back of the existing chain ring that look like something should be screwed into them. Perhaps that's where the 24 goes?


 
#9 ·
Bashguard is to protect the chainrings from things you bash into with that part of the bike (crossing logs, getting over some rocks, that sort of thing). If you don't bash you don't need a bashguard, replace it with a chainring.
 
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