Changing a chainring, anything I should know?

Triathlon Forum
1

I’ve been thinking about switching my inner chainring from 39t to 42t or even 44t for training/racing on the flats (with a 12-21 in the back and without crossgearing too much it’d give me a range of speeds between 14 and 23mph at 90-95 cadence which is just about perfect).

Given that this is definitely not all I do (there are hills and mountains around here as well) I’d probably be changing it back and forth with the 39t quite a bit (and the cassette as well, to my mountain-friendly 12-25) so I’d prefer to do it myself vs having to take it to the shop all the time.

Besides having a torque wrench, a crank puller and the ring bolt tool, do I need anything else? Is there any gotcha that I should be aware of? (the excellent parktool website has instructions on how to change the cogset, but not the chainrings)

2

Go to the Shimano web site and pull down the pdf file describing the chainring and installation. Not much to know anyway but may as well get it straight from the horse’s mouth

3

thanks for the tip, the shimano site doesn’t say anything about 44t rings and it also says that I’d have to switch my 53t chainring from A to B when going between 42t and 39t, grrr, I didn’t think things would be so complicated!

4

I recently went from the 52/42/30(standard triple) to 53/39/30(double chainrings), then changed it all back again. With the exception of having to make adjustments to the derailleur, I had no problems with shifting or anything else. I also briefly had the 53/42 on there. The main difference between the double and triple is the offset and the shift ramps. The only thing I noticed was that shifting up to the 53 was a little slower than the 52 because it has no shift ramps.

5

Besides having a torque wrench, a crank puller and the ring bolt tool, do I need anything else? Is there any gotcha that I should be aware of? (the excellent parktool website has instructions on how to change the cogset, but not the chainrings)
Dude, to change the chainrings all you need is an Allen and possibly that little tool to keep the backside of the chainring bolts from turning(a flathead screwdriver works sometimes too). No need for a torque wrench or crank puller unless you plan on taking off your crank arms as well. There honestly is nothing to changing the chainrings. Just take off and replace.

6

You don’t have to change big ring from ‘A’ to ‘B’ when changing the size of the inner ring. Unless you want to give Shimano more money! I went from 42 to 39 and shifting was not degraded at all.

7

checklist:

  1. Series of small ring matches series of large ring (“a” series vs. “B” series).
  2. Rings are appropriately oriented relative to crank, if a “drop rivet” is in the big ring, it is located behind the crank arm.
  3. Chainrings bolts are torqued in a star pattern (like the head of an engine block).
  4. Crank bolts are tight.
  5. Chain is correct length.
  6. Front derailleur clears teeth of large ring.
  7. Shifting is fast and precise.
  8. Double check everything.
8

Tom, would you use copper grease or similar on the chain ring bolt threads when re-assembling to assist in holding the rings?

By the way, the requested info has been pm’ed to you.

9

I’d add a couple of things to the list:
Grease the threads of the ring bolts, especially if they are aluminum. FSA cranks and their aluminum bolts are nearly impossible to remove without a drill if they are installed with no grease. Not sure about Shimano. I’d recommend using a cordless drill with the appropriate bit if you have one with enough power to remove the bolts (NOT for installation). You are much less likely to strip or damage a bolt when using a drill compared to an allen wrench.
BTW- I use an 11-23 10sp rearend and 42 front and it works great up to about 30mph. I spend almost all my time in 14-15-16, right in the middle of the cassette. I rarely use the larger chainring. With a 12-21 I think you’ll be happy with a 42T riding 18-25mph