Swapping Ultegra Chainrings?

[Don49]

On my Atlanta I've got an 9 speed Ultegra 6503 triple crankset with a 42T inner ring. I don't like the gear ratios with the 42T and want to swap it out to a 39T.

The existing chainrings are Shimano "A" series, and an A-39 chainring was never available to my knowledge. So my options are to use a B-39 from an Ultegra double, or a 39T from a 6603 10 speed crank. The differences seem to be the ramps (or lack of ramps) on the different series chainrings, with the 39T chainring from a double not having any ramps.

So I'd appreciate any advice on which chainring to get. Thanks.

[Pete Serotta]

either or go to Peter White site and read what he says (additionally TA will work.)

[cp43]

I made a similar swap on my Tiagra triple. I am now using an FSA 39T middle ring. It was designed as a middle ring, so it has the ramps/pins. It shifts just as well as the 42T Shimano one that I removed.

Chris

[Brian Smith]

On my Atlanta I've got an 9 speed Ultegra 6503 triple crankset with a 42T inner ring. I don't like the gear ratios with the 42T and want to swap it out to a 39T.

The existing chainrings are Shimano "A" series, and an A-39 chainring was never available to my knowledge. So my options are to use a B-39 from an Ultegra double, or a 39T from a 6603 10 speed crank. The differences seem to be the ramps (or lack of ramps) on the different series chainrings, with the 39T chainring from a double not having any ramps.

So I'd appreciate any advice on which chainring to get. Thanks.

Tough call, good luck with that.

[Peter P.]

Having a triple complicates things, particularly with Shimano's integration.

Supposedly, the Shimano triple front derailleur is made specifically for the 30-42-52T combination, and the ramps and pins are in certain spots for a reason. If you deviate, your shifting will suffer but how much and whether you can tolerate it, you'll just have to find out.

As far as double ring setups go, I've combined 39T Shimano with 48T TA rings from Peter White Cycles and my STI shifts just fine in the front.

[RPS]

I have a couple of bikes with the 52/42/30 cranks and absolutely love the gear ratios so I’ve never contemplated replacing the middle with a 39T. The opposite is true for me – I’ve avoided the new 10-speed Shimano triples due to the 39T middle. Having said that and admitted my bias, I can only suggest the following, which is not exactly what you asked:

The difference between 39T and 42 T is generally one cog. That is, a 39T running the 13T cog is the same as a 42T running the 14T. Normal riding won’t be affected that much other than having the chainline off one cog over. If you don’t like the 42T how different is the 39T really going to be?

If you end up riding the middle ring most of the time as I do, and you feel the 42T is a bit too large, another option you have is to increase the size of your cassette by one cog across the range. As an example, I run an 11-21 with the 42T, but if I wanted similar gearing to that of a 39T without making the chainring modification, I could just as easily go to a 12-23 cassette and leave the 42T alone. The main differences are you’ll lose a little top end and gain a little at the bottom.

Lastly, the front derailleur for the 9-speed Ultegra is optimized for a 42 to 52T shift (10-tooth jump). If you change to a 39T the middle-to-large shift will likely suffer some (as noted above by Peter P).

[Don49]

Thanks guys, all good advice. I think I see the situation more clearly now and am just going to change out the cassette instead of messing with the chainring. The effect will be nearly the same, as was suggested, and with much less hassle.