I have a Felt tri bike with 650 wheels, a 55-42 chain ring and 11/23 cassette. I live and race in Georgia and have been debating switching out my cassette to better handle uphill riding. Can anyone offer me some advice on what cassette I might want to go to that would allow easier hill climbing but not completely ruin my speed on flatter courses?
12-27?
I ride a 650 Felt. I put a 39 on the front and have no shifting problems to and from the 55. Hilly rides I use a 12-27, everyday riding I use a 12-23. I’m not strong enough to pull an 11 tooth that much.
It’s tough to ride in second gear of the 27 (the 24) while on the 55 cuz my chain is a little short but everything else is fine.
jaretj
Leave the cassette alone and switch out the front to a 53/39. You’ll save weight and pick up better climbing ratios. If you can spin out the 53-11 on the flats you can go with a 54 and still keep the 39, but the 53 should be good for 40+mph.
I use a 12/25 dura ace and climbed a hill of 12% grade with a total elevation of 1150 feet. So, I like the 12/25 and it was enough for me.
I use a 12/25 dura ace and climbed a hill of 12% grade with a total elevation of 1150 feet. So, I like the 12/25 and it was enough for me.
With a 55/42 crank? Depending on the OP’s leg strength and cardiovascular ability, the 42-25 combo may not provide enough of a “granny gear.” I dunno. Never run a 27-tooth cog and I don’t run a 55/42 crank, so I don’t know how much harder it is than a standard 53/39.
I ride a 650 Felt. I put a 39 on the front and have no shifting problems to and from the 55. Hilly rides I use a 12-27, everyday riding I use a 12-23. I’m not strong enough to pull an 11 tooth that much.
…then why the 55? Use a 53/39 with an 11-23 or 11-25 and get closer gearing, better shifting, less weight, and not lose anything at either the high or low end.
No…I did it on a 53/39 good point, though.
a 55/42 on a 650c bike is equivalent to a 53/39 on a 700c bike.
a 55/42 on a 650c bike is equivalent to a 53/39 on a 700c bike.
I’ll admit I didn’t know that. Never dealt with a 650c bike. Thanks for the info. In that case, maybe a 12-25 would be just fine.
Try replacing the 42 with a 39. If that doesn’t take care of it, try a 12-25 cassette. If the hills are monstrous, try a 12-27. The 55/39 combo will require good alignment of the FD, but it’s doable and gives you more usable gears as there’s less overlap. I run 56/39 and don’t have much trouble shifting, although I have to feather the downshift to keep from dropping the chain. I’ve practiced it enough that it’s no problem.
Actually, a 55 on a 650C bike is equivalent to a 51 on a 700C bike.
jaretj
Yes you’re right.
'Course you have to consider the increased Crr of 650c wheels so it will feel like a 53 hahah…
Sometimes i wonder if it’s worth going to 650c just so i can use a 56/44 up front. 
If I had a choice I would use 700’s like everyone else.
My height makes my tri-bike fit options limited.
That giant 55 tooth FSA ring I have gets people wondering though.
jaretj
Let me preface my response with a quick story from the World’s Toughest Half a couple of weeks back. That course is brutally hilly and I came with 40x25 low. Once I saw the hills I asked my friend to use his 12-27 cassette. Even that was not enough for me in some places. On the day’s long, steep climb I left a big group of riders behind (including the race winner, Platta) by being able to sit and spin for the most part. They were all overgeared. They passed me later, so they were either stronger riders or riding too hard. Even more important, my legs were good for the run.
Having said that, most triathletes are way overgeared. If you have to run after the ride, then you should be spinning and if you are going to spin then you have to have a pretty low gear for hills. I am averaging between 23-24 mph for hilly courses and time trial bricks this year and 40x25 seems to work for me. If your race speeds are lower, or you are racing half IM or longer, then you really need something to let you spin which means you should consider the smallest ring you can put on in the front, a 38, and probably going to a 27 in the back. For the high end, you could probably go with a 48x12 and be fine. My shorter race I did with a 48x38 and averaged better than 24 mph. These are relatively decent speeds and anything bigger than 48x12 is a waste of energy if you are pedaling hard on the downhills. I soft-pedal the downhills or if I spin out then I just tuck and rest.
If your average speed on hilly courses is better then 25 mph then keep the gearing you have.
Chad
I have the new Felt B2(650) that came with a 54/42, 11-23. I swapped everything out for a 53-39, 12-25. We have a lot of rolling hills here in central PA and being 56 years old I wanted to be able to spin up the hills. Now I can almost do that 
Hey Andrew!
Based on what cdw said, I definitely need to switch out something, because I’ve never seen a 25 mph average on a race. I’m lucky if I have an average around 19 mph. Most of the local races I do have the female winners and female age group winners riding with an average in the low 20s. I am relatively new to biking and racing (started last year) and know just putting in more miles on the bike and training for hills would help, but I’m thinking a change to my gearing would be a boost too, but I can’t seem to get a definitive answer from people on exactly how I should change my gearing.
Those that recommended changing the front to a 53-39 or other, are you recommending that with the 650s in mind? The issue always seems to get a little cloudy when 650s are involved because a good portion of riders and mechanics seem to have 700 recommendations but get less confident when talking 650s.
With that new information in mind, you should try swapping out both the chainrings and the cassette…
Bingo.
Leave the cassette alone and switch out the front to a 53/39. You’ll save weight and pick up better climbing ratios. If you can spin out the 53-11 on the flats you can go with a 54 and still keep the 39, but the 53 should be good for 40+mph.
I have the new Felt B2(650) that came with a 54/42, 11-23. I swapped everything out for a 53-39, 12-25. We have a lot of rolling hills here in central PA and being 56 years old I wanted to be able to spin up the hills. Now I can almost do that
Hey Andrew!
Did you see any reduction in speed (on flats and downhills) going to that set-up on the 650 wheels?