I have a 12-25 on my Tri-bike with a compact crank. For an exceptionally hilly course (for a triathlon, anyway) I'd like to put on a 11-28. Should I expect to need to tweak the gears, or will my Shimano Ultegra derailleurs manage it OK?
12-25 to 11-28 with Compact Crank
- Thread starter cbjesseeNH
- Start date
A short cage will wrap 33T with a min. of an 11T on the rear and a max. size cog of 28T.
You're right on the limit for low gear cog size.
34-50 = 16T plus 11-28 = 17T...that's...er...carry the seven....um...33T. Again, right on the upper limit of the short cage's capacity. The long cage GS version wraps 39T and is pretty darn cheap...any excuse to buy new gear is a good excuse to me!
I would be really, really careful when shifting off the big ring onto the little ring...especially if on the outside of the cassette stack. Bouncing the chain around if it's slack enough can also cause hilarity to ensue.
You are running a chain minder, aren't you? 34 x 28 on a tri course? If you can climb, you're going to crush a lot of them guys. Conventional bars/shifters with clip-ons?
You're right on the limit for low gear cog size.
34-50 = 16T plus 11-28 = 17T...that's...er...carry the seven....um...33T. Again, right on the upper limit of the short cage's capacity. The long cage GS version wraps 39T and is pretty darn cheap...any excuse to buy new gear is a good excuse to me!
I would be really, really careful when shifting off the big ring onto the little ring...especially if on the outside of the cassette stack. Bouncing the chain around if it's slack enough can also cause hilarity to ensue.
You are running a chain minder, aren't you? 34 x 28 on a tri course? If you can climb, you're going to crush a lot of them guys. Conventional bars/shifters with clip-ons?
Actually I've got a 50/34 crank paired with an 11-28 cassette (Campy). The only change I had to make when changing to the current cassette from an 11-25 was to adjust the B-screw slightly to provide the correct distance between the largest cassette cog and the top pulley. Without the change, I had interference. You may or may not need to make the adjustment depending on the gruppo you have.
Looks like I have a 6600 short cage on my road bike with 50/34 Rotor rings and 11-32 cassette, and 6700 short cage on my Tri-bike with 50/34 Rotor rings and 12-25 cassette. I'm not sure how my LBS got my road bike to work in that configuration. Maybe the Rotor rings? Anyway, I'll try the 11-28 on my Tri-bike and assess the chain length and B-screw settings. I have a chain-catcher on my Tri- bike but need one on my road bike too?
"Need" is a funny thing. Theoretically, if the limit screws are set just right, you can't lose the chain, but when conditions become less than ideal--bumpy roads while shifting, big shifts under power when starting a big climb--chains have been known to come off. Some will say that shouldn't happen or that they've never had it happen......but it can and does occasionally happen, even to those pro mechanics who are at least as good as any mechanics on this forum.cbjesseeNH said:
If you're careful you don't need 33T...as you will (or should) never use the largest chainrings and sprockets at the same time, nor the smallest of each due to the extreme chain cross over. These are not "usable" gears. If the second largest sprocket is 25T then you can reduce by 3...so 30T only. And if the second smallest sprocket is 12T then take off another 1....so in fact its 29T.
It's fine to use the extreme gear combinations, especially given how laterally flexible today's 10 and 11 spd chains are compared to wider chains in days of old. Cross chaining will increase wear, but it's unlikely to cause calamity, especially given that cross chaining is done for relatively short periods of time.Dr Lodge said:
I was running a compact on one of my bikes and in the big/big, and despite fiddling with the barrel, the chain would occasionally skip. During a race, and when riding over rolling hill terrain, sometimes one needs to go big/big to maintain precious momentum, especially if just about to crest a hill. I suspected it was chain length as I had no issues with my prior chain skipping which was one link longer.
When I asked my mechanic, who could not replicate the skip on his workstand, to "just add another link please",
he responded "you shouldn't run big/big, it'll increase chain wear".
I asked "would you like to ride the next race on my behalf?".
He replied "I'll add the link".
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