Shimano 105 Hollowtech II chainring compatibility

[eddief]

my f-ing quick new used bike friday pocket crusoe came with Shimano 105 Hollowtech II triple crank. Big ring installed is 50 tooth and I'd prefer 53 tooths.

Are older 9 speed rings compatible with newer 10 speed cranks? I am running 9 speed everything else; 9-26 capreo cassette, shifters, chain. Seems older version rings are less expensive; especially for 53 tooths.

[RPS]

...... capreo ...... Capreo as in Shimano 9-26 tooth cassette?

[eddief]

The BF is a Pocket Crusoe and yes it does have a 9-26 Capreo cassette.

[RPS]

In my Shimano catalogs Capreo groups are listed as having only a single FC-F700 45T chainring crankset, but I’m relatively sure any other 9-speed would work OK provided they are compatible and components are of adequate size to handle the needed capacity.

I’d be concerned with two potential capacity/size problems in making the swap you asked about. Because the 9-26 cassette requires greater capacity (17T) versus the largest 9-speed road cassette (the 12-27 which only requires 15T), combining it with a 53-39-30 triple crankset would require a total capacity of 40, which is higher than any Shimano road rear derailleur I’m familiar with. I expect that may be one reason for the 50-39-30 crankset since the total capacity would be 37T, or the same as a triple derailleur.

The other concern I’d have is that Shimano triple front derailleurs seem to be sensitive to the tooth jump between middle and large rings. As an example, on the older Ultegra triple, the jump was 10 teeth, and trying to change that significantly made shifting slower. The newer Ultegra front derailleur is designed for a 39 to 52 jump, and as far as I know is not compatible with the older 42 to 52 jump because of clearances. I’m just trying to say that if you increase the front ring to 53T and raise the derailleur accordingly, shifting may not be as smooth as you’d expect. The 105 front derailleur is rated for 50T max size and 20T max front capacity (although I’ve exceeded capacity on stuff that worked well enough for me).

Lastly, I don’t recall when Shimano offered a 9-speed 53T large ring for a triple – maybe early DA triples. :confused: Most Shimano road triples use 52T and not 53T front rings; newer 105 use 50T front rings. You could try a 53T ring from a double, but if so you’ll be exceeding the capacity of the front derailleur by that much more. And rings won’t be a matched set in most cases.

[eddief]

the Crusoe is a bit of a mongrel. Mountain rear derailleur, Dura Ace triple front. Currently with its installed 50-39-30 triple crank and bar end shifters shifting is quite surprisingly crisp. I thought with the cable routing challenges of the folder it might miss a beat. It doesn't. In the 50/9 combo I can spin it out at about 27 mph. Thought adding a bigger ring would balance things out. But your points about limits is appreciated and well taken.

[RPS]

In the 50/9 combo I can spin it out at about 27 mph. Thought adding a bigger ring would balance things out.
Seems kind of low, but I don't know the wheel size or how fast you spin.

I can tell you however that going from a 50 to 53 ring will only get you from 27 to 28.6 MPH if you hold everything else constant. That's still pretty slow for pedaling downhill if you are into that type of riding.