mdbrown

I'm looking to swap out some 175 FSA SLK cranks I have for 172.5 FSA cranks that I found a good deal on. My 175 is 46/36 and the 172.5 cranks have 52/38. Both have a BCD of 110 so are the two chainrings interchangeable? I'm looking to keep the 38 on the 172.5 cranks, but swap over the 46 from the 175 cranks to the 172.5 cranks so in the end I'd have 46/38. I feel like swapping over shouldn't be an issue, but I'm not 100% so I figured I'd ask.

ScottNotBombs

It'll be fine, just move your derailleur down so there's a 1mm gap between the cage and new chain ring.

mdbrown

Awesome, thanks for the quick reply.

FastJake

It'll be fine. Any reason why you want such a close ratio up front? Just curious..

Chris_W

Agreed that the chainring swap will be fine. Plus, there may be no need to move the front derailleur. If I understood you correctly, the large ring is going to stay the same (46 teeth), and it is that normally determines the front derailleur position. Try it as it is, and only if the inner cage of the FD contacts the inner chainring when you try to shift to the big ring, then move it up, but if it doesn't then leave it.

Burton

An easy switch and no reason to change the position of the front derailleur. Correct installation requires a 2mm clearance between the large chainring and the ouside face of the front derailleur as it passes over it.

Since your large chainring will remain unchanged the front derailleur calibration should be unaffected.

ScottNotBombs

Oops. I didn't realize he was changing the smaller chainring.. On the park website it says 1-2mm or about the thickness of a penny

Kevinative

ok so I did the search function to avoid starting a new thread. I've got a slightly different angle on this same question. My new carbon bike (CR1) came with a CD, 50/34. I recently purchased an older 105 octalink crankset that has a 53/43. I want to simply put the 53/43 rings on the new crankset. both are 105, don't see any fit issue, may have to slightly raise fr der. question is, what about chain length? are 3 extra teeth going to require an extra link?

fietsbob

Probably.. may be time to put on a fresh chain anyhow..

mdbrown

Just an update, everything worked out well on my end. But for you, I feel like you're in the same position I was in. 53 tooth rings only fit on BCD 130 spacing cranks so they wouldn't fit on a BCD 110, which is compact.