Jed19

Hello, I have a bike with Shimano Ultegra FC 6603 triple 50x39x30 (10-Speed). I have always thought of having a 42t middle ring, but was always of the impression that my current shifting smoothness could get compromised. Anybody knows what 42t middle chainring (130BCD), preferably ramped, that could work seamlessly with my current set-up?

As usual,thanks for all positive inputs.

Crescent Cycle

I thought 6603 was 52/39/30? I imagine the FD doesn't like being adjusted for 50/39 and would like a 50/42 even less since Shimano calls for a minimum of 13t between big and middle rings. If I were to do this I would pick up a FD-4603 or a FD-5703 or a FD-5603 and 52/42/30 chainring set. You can get a brand new FSA 52/42/30 crankset for $35 and salvage the rings off of that.

HillRider

Yep, that's the only triple configuration Shimano's Techdoc's list for the FC-6603. If the OP really has a 50/39/30 triple I expect it's an FC-5603. The matching FD-5603 front derailleur wants an 11T minimum between the chainrings and changing to 50/42/30 will require the cage be too far above the big ring to shift well.

Funny, but I have a couple of FC-6503 (Hollowtech, Octalink) Ultegra cranks and they came 52/42/30. I never really liked the 42 and, when they got worn enough, I replaced them with FC-5703 (Hollowtech II) 50/39/30 cranks and the matching external bearing bottom brackets

bobotech

I would gladly trade you one of my Shimano 52-42-30 chainring sets off of one of my Ultegra/105 cranksets for your 50-39-30.

Jed19

Oops! The crankset is actually 52x39x30. Sorry for the misinformation.

HillRider

OK, there probably isn't a 42T chainring that is an exact match to your current 52T big chainring but any Shimano 130 mm BCD 42T chainring should shift adequately if oriented properly at installation. You do want to get a 9-speed or 10-speed chainring so the gap between the two outer rings isn't excessive. Anything from 6500/5500 cranks or newer should work.

dwmckee

With the newer Shimano derailleurs, I think they are tightly tuned to the tooth difference between the large and medium rings so if you increase the middle by 2 teeth you need to increase the large by 2 teeth to maintain optimal shifting. The difference between the small and medium rings is not as critical and you can change it by a few teeth with little difference in shifting performance.

HillRider

The real problem is that current Shimano front derailleurs have the inner cage plate depth chosen to match the factory crankset chainring tooth difference. So a 105 FD-57005703 is designed to work with 50/39 or 50/39/30 chainrings or an 11T difference.

The FD-6700/6703 is made for a 53/39 or 52/39/30 crankset or a 13 or 14T difference and it's inner plate is wider. Using it on a 105 crank will require positioning it to high for best shifting to assure the inner plate misses the small chainring.

I happen to be using an FD-5703 on an old FC-6503 crank that's 52/42/26 for a 10T difference in the two larger rings and it JUST clears the middle ring when positioned properly.

Crescent Cycle

Does the chain ever get stuck between 42/26? I've seen that combo so I though I'd try out 39/24 and the chain just keeps getting jammed between the rings so I'm hesitant to try a 26. I'm hoping the 26 is tall enough that the chain has a hard time falling onto the chainring posts.

HillRider

I've never had the chain get stuck between the granny and middle ring on any of my 8,9 or 10-speed cranks. I do use a chainwatcher on all of them to assure the chain can't spill to the inside of the granny ring.

fietsbob

FYI TA of France makes 7075T6 premium quality chainrings , in several bolt circle types .

https://www.peterwhitecycles.com/chainrings.asp

ramps and pins machined in .. Alize is said to be STI compatable , made in 40,41 & 42t

TA has long specialized in cutting both odd and even numbered tooth-counts..