Remove 7- or 8-speed chainrings from Shimano/SRAM/Sunrace crankset and use on 3x9 speed Samox/Shimano drivetrain?

Question

I have 3x9 gearing on my touring bicycle. I've got a Shimano Acera friction shifting front derailleur and an Alivio rear derailleur. The rear cassette is a Shimano 11-36T. The front crankset appears to be a Samox 48/36/26T with 4 bolts at 104/64 BCD. I would like to replace the 26T with a 22T. It is my understanding (due to limit on front derailleur capacity) that I should not simply drop in a 22T but rather also change the middle and outer ring.

Unfortunately, it is hard to find reasonably priced outer chainrings that are in stock at Canadian suppliers right now (the inner and middle rings are easily available).

One reasonably-priced option I came up with was to purchase a SRAM S-600 crankset with 42/32/22T and 4 bolts at 104/64 BCD (https://www.sram.com/en/sram/models/fc-s600-a1) . The crankset is not compatible with my bottom bracket, but I would remove the chainrings and mount them on my Samox cranks. One concern I have is the S-600 description says it has “8- and 9-speed chainrings” but the specifications says 8 speeds.

I found other similar cranksets with 4 bolt 104/64 BCD but incompatible bottom bracket: the Shimano Acera FC-M361 and the Sunrace FCM600 crankset, both of which are 7/8 speed cranksets. The Sunrace is about half the price of the other two-- in fact, it would be the cheapest way to put my hands on a 42T outer ring, which I rarely use anyways.

For slightly more money, I found 9-speed Alivio cranksets (also not compatible with my bottom bracket).

QUESTIONS: Is it okay to use “8- or 9- speed” crankset chainrings or even 7/8-speed chainrings with 9 speed chain/derailleurs/cassette?

If so, are there reasons why I wouldn’t be able to remove the rings from the SRAM/Shimano/Sunrace cranksets and mount them on my Samox cranks? (And no, none of these is riveted as far as I can see).

If this would work, any thoughts on which of these would be the best quality rings? (In terms of durability, compatibility, and shifting—weight is not a concern for me). Would the cheapo Sunrace rings be okay?

Would Shimano Deore 9-speed rings (which I can find through suppliers, but they are more expensive) be significantly better and would they mount on my Samox cranks? Could I mix the Deore for the inner and middle ring with the cheaper Sunrace outer ring? (I rarely ride in my outer ring.)

Thanks very much!

Answer 1

Give BB's are pretty close to a consumable, have you considered replacing the BB to match the new cranks? Given the price points of the listed components, and equivalent square (Shimano UN300) taper BB only another $15.

If you want to keep you existing BB and swap rings, it should work fine (if not perfectly) as long as the PCD and bolt counts match. If you are worried about shift performance, you are more likely to get 'as good as it can be' by replacing the BB.

The speed of the chain rings is not really a concern. Internal width of all multispeed chains is the same. For 7-9speed, the external width of chains does not change materially with the speed of the chain, 10/11/12/13 are each a bit narrower than the preceding one. On the front of the driver train, the gears and derailleur are pretty 'agricultural' You can always get away with anything from the 7/8/9 speed stable as interchangeable, and then go up or down one without problems (e.g 9speed chain on 10speed cranks), although it may not be perfect.

Answer 2

Your actual question has been well answered - 7, 8, 9 speed cranks are compatible. However, there are some other issues you should consider. First off, a quick check shows for me (in the US) a 4 bolt 64BCD 22t steel ring can be had for under $8. (Ok shipping is probably just as much.) It would certainly be inexpensive to mount a 22t and determine if it really is too low for your current set up or not. Next, are SURE your crankset is not riveted?? Samox seems to have common 48/36/26 riveted model, and if that's what you have you will be stuck. Third, there are two reasons your BB would not be correct for a new crank - the spindle form, and the chainline distance. Since the SRAM model you cite comes in both PowerSpline and square taper, and Samox seems to be JIS square taper, this should not be too much of a problem. Chainline might be off, but this is more difficult to find using specs, and can be fudged a bit. Forth as has been suggested, you may find it economical and convenient to replace the whole front end, as sealed square taper BB are very cheap, and a complete crank is often comparable to buying individual chainrings. Finally, you already have 6x range. Some of that is in the top end, and you could use a 12-36 instead of 11-36 which would make your 48T ring the equivalent of a 44T ring with your current cluster. You have a 19.5 inch low. Only you know what you ride over and what you need, but by traditional standards those are extreme for a road touring bike.