So… I know that there are a lot of “what gears do I use???”/cry for help threads on here… so forgive me… I’m going to ask my specific “help me!” question.
I am currently running a setup on my road bike of a compact 50/34 with an 11-23 on the back. My TT bike, which I do not ride nearly as much, has a 53/39 with the lowest gear being a 23 on the back as well. Even on the road bike lately I have been wanting a lower gear climbing (probably because I’m out of shape, but also because I tend to like my cadence really high), and so I’m pretty nervous about taking the TT bike with that cassette to Wildflower. I’m trying to stay as cheap as possible and get a cassette that will work for the race and that I can use on my road bike when I want to do a lot of climbing. I was going to buy a 12-25 but someone suggested the DA 12-27 which while it sounds pretty girly to me would have been WONDERFUL on the ride I did yesterday. Especially with the 53/39. Any thoughts/comments?
“Stay as cheap as possible” and “DA” shouldnt be used in the same sentence.
You can also buy an Ultegra 6600 12-27 that will work just as good as the DA version, wont be as light, but will last significantly longer.
The cassette you can use will be limited by the capacity of the rear der. on your TT bike. This is know as “chain wrap”. I’m going to assume that both bikes have short RD cages.
Chain Wrap = (large chainring – small chainring) + (large rear cog – small rear cog) so in your case (53-39) + (27-12) = 29. I believe that a Shimano short cage RD can handle that but it is the limit. You also probably either need a new chain or links added to the current one.
For your road bike the chain wrap would be (50-34) + (27-12) = 31 so you probably wouldn’t be able to interchange the cassette between bikes. The max cassette on this bike would be 12-25 or any gear range of 13 or less.
The cassette you can use will be limited by the capacity of the rear der. on your TT bike. This is know as “chain wrap”. I’m going to assume that both bikes have short RD cages.
Chain Wrap = (large chainring – small chainring) + (large rear cog – small rear cog) so in your case (53-39) + (27-12) = 29. I believe that a Shimano short cage RD can handle that but it is the limit. You also probably either need a new chain or links added to the current one.
For your road bike the chain wrap would be (50-34) + (27-12) = 31 so you probably wouldn’t be able to interchange the cassette between bikes. The max cassette on this bike would be 12-25 or any gear range of 13 or less.
I have this set up exactly on my road bike, Ultegra short cage RD. No shifting issues to speak of, though I don't ever use big/big or small/small because that's just silly. Of course, your mileage may vary.
Shimano’s specification for this derailer is 29 teeth total with a maximum 27 tooth cassette cog. If one pushes the derailer to it’s limits, it is possible to exceed Shimano’s recommendation by a few teeth, but not a lot.
So it looks like a 12-27 will work, but pushes the limits. I have 53/39 and 12-27 on my road bike but it has a long cage, left over from when it was a triple.
There’s nothing girly about a 12-27, you can pick up an Ultegra one for pretty cheap and it’ll last for a long time.
If you get the 12-27 cassette you’ll find that the 39-27 low gear on your tri bike, would be virtually the exact same gear as the 34-23 low gear you currently have on your road bike.
You can use Sheldon Brown’s gear calculator to see what different gearing combos will do and help you make these types of decisions.
Forgive my ignorance, but from my understanding my road bike actually comes stock with a 50/34 12-27 DA setup… when I bought mine I knew even less than I know now about gearing and I trusted the guys who sold it to me, who set me up with the 11-23, which they have since explained was to make it as close to the gear ratios on my old bike as possible. With the rest of the componentry identical, why wouldn’t the 12-27 work? Other than the fact that I may get laughed at.
But you’re saying it should work for the TT bike???
According to Shimano, the 12-27 should work with the 53/39 chainrings on your TT bike. Again, assumption is a short cage since it’s a double.
Seems odd that a bike with compact chainrings would come standard with a 12-27. But, I won’t even pretend to know what the manufacturers do. The 12-27 may work but you won’t be able to go 50-27 or 34-12 (not that you would want to). You could just get a 12-25 and I’ll bet that you would never notice the difference. A 34-25 is a low gear.
Edit to add: Unless you tell them, no one will know you are on a 12-27. They would need to get down and count the teeth. Think about it, do you know what cassette they are using?
Forgive my ignorance, but from my understanding my road bike actually comes stock with a 50/34 12-27 DA setup… when I bought mine I knew even less than I know now about gearing and I trusted the guys who sold it to me, who set me up with the 11-23, which they have since explained was to make it as close to the gear ratios on my old bike as possible. With the rest of the componentry identical, why wouldn’t the 12-27 work? Other than the fact that I may get laughed at.
But you’re saying it should work for the TT bike???
A stock 12-27 x 50-34 would seem curious to me… the whole point of a compact front is to get the closer steps of an 11-23 while still having the low-end climbing gear (although I confess I do have a 50-34 x 12-28 on my rain/cross bike, but that’s specifically for tackling ridiculous logging roads without having to run a triple up front; all my regular road bikes have 53-39 and either 12-23, 12-25, or 13-26 combos).
I agree that it’s a bit crazy that that’s what came stock…it’s a women’s bike and I think that they were trying to get rid of the option of a triple. There are very few times when I would want a 34x27. However…I do think I’d want the 27 on my TT bike which doesn’t have a compact. Looks like I need to buy 2 new cassettes???
And I was a bit tongue-in-cheek about people knowing I have a 27. I frankly couldn’t care less as long as I’m going faster…