Quick bike Q- 12/25 and 34/50 compact- good?

[kb1dqh]

Wrong forum, but it's late and this won't last long. Got a new S-Work Tarmac carbon frame. Need to get ultegra components. Like hills, lots in bay area. Think the above component setup is a good idea of the classic double 12-27?

[cj001f]

no. will spin to damn much at the high end.

[mghwk]

I think its a good choice. If you are worried about the top end, then get an 11. I spin out in a 53-12 around 40-42, and in a 50-12 around 36. A 50-11 is higher than the 53-12, but you need to accept the 11-13 jump on the back. If I'm going fast downhill anyway, I am usually better off working on the tuck than pedaling that 36-40mph range. Also, you can almost pull stumps with a 34-27, so don't overlook that possibility if its really steep for a while. YMMV, and I suck anyway.

[upallnight]

i'm using that very setup out here and i do hit some hills. it's been great in 95% of situations.

my ideal setup would be 50/34 & 11-25. i like having the 34-25 for some big hills (and sometimes even want for a 50-27), but maybe others don't mind the 39-x if they're in better shape than me or not rehabbing their knee.

so far, i've never been unhappy with the lower gears (34-23,25), and it's only a few times i want something bigger.

i've been told that if you go 11-25 (i think you have to do that custom for the ultegra), then you should eliminate the 13 and keep the 12.

caveat: i am able to go up to 40mph and not spin out, and i don't really ever go more than 45, max. i think if i (you) were regularly going above 45, the 53 front ring would be more important, although the additional of an 11T cog in the rear would make up for most of that difference.

good luck!

[upallnight]

If I'm going fast downhill anyway, I am usually better off working on the tuck than pedaling that 36-40mph range.

a friend told me the very same thing, and i was amazed at what a difference it made. i had been in the mindset that i should always be pedaling, but mghwk speaks the truth.

think about how often you will be pedlaing hard while going downhill >40mph.

[Cornholio]

It's a fine option. Get another cassette after a few months of riding if you want, or if you're doing a race that demands it, or...

Enjoy your tarmac.

[Viva]

Don't know what kind of shape you're in. What do you mean you "like hills"? You talking mountain passes?

I'm completely with cj001f here, 50/34 with a 12-27 rear just screams GAPER. Little kids will point and laugh as you ride by. So, unless you've got wet noodles for legs, get a tighter rear cluster or go with the 53/39 rings.

[kb1dqh]

Thx all. By hills I mean lots of 1k to 2k hills (vert) i the bay area from 3-6 miles long.

So, the shop ran out of the compact and I got a regular double and a 12-27. I think that's as good as you can get w/ out a compact. -kb

P.S. The new frame is a S-Works Tarmac 2006- all carbon. Got the frame, fork, headset, seatpost for 1/3 of retail- so stoked.

[ski_faster]

I have 53/39 up front and 12/25 and find that its just about perfect. There are several climbs that I do that are hard but it just gets me in better shape.

[The Suit]

no. will spin to damn much at the high end.

I don't get the obsession with big gears for recreational riders. With a 50x12 and a 700c wheel, you'll be pedalling about 124 rpm at 40 mph. At 124 rpm, you shouldn't be any where near spun out. If you're going downhill, you'll probably do better tucking at that speed, anyway. If you're applying power at 40 mph on the flats, I guess you're on Alessandro Petacchi's wheel, and yes, you need a bigger gear.

[Viva]

With a 50x12 and a 700c wheel, you'll be pedalling about 124 rpm at 40 mph.

Is this realistic? I think not...

[The Suit]

Is this realistic? I think not...

What's unrealistic? The math? You're welcome to double check it for me.

At 40 mph you are traveling 40 x 5280 *12 / 60 = 42,240 inches per minute.

A 700c tire has a circumference of about 82". With a 50x12 you get 50 wheel revs for every 12 pedal revs. Therefore you move 82 * 50 / 12 = 341.666 inches per pedal rev.

42,240 inches/minute divided by 341.666 inches/rev gives you 123.63 revolutions/minute.

Or do you think it's unrealistic to pedal at 124 rpm? If so, you should get a set of rollers and practice spinning. Get to the point where you can spin at 120 rpm for a half hour or so. It will do wonders to smooth out your pedalling.

[Viva]

Let's put it this way, if I were to ride a 50/12 (and I don't have a compact, never have, so I may be wrong) at 120 rpm, I bet I break the chain before the 30 minutes is up.

I guess what I'm saying is that you're using a really extreme example to make a point and yet you were, at least orininally, taking recreational riders into consideration.

[The Suit]

Let's put it this way, if I were to ride a 50/12 (and I don't have a compact, never have, so I may be wrong) at 120 rpm, I bet I break the chain before the 30 minutes is up.

I guess what I'm saying is that you're using a really extreme example to make a point and yet you were, at least orininally, taking recreational riders into consideration.

Why would the chain break?

I think, based on your reply, that you think pedalling at 120+ rpm is unrealistic. Maybe it is, these days, but it didn't used to be. When I raced as a kid, the younger age classes were gear-restricted. For the "intermediate" age group - ages 12-14 - we were limited to a gearing that worked out to be a 44x14 with 700c tubulars. I trained and rode club races with national-caliber racers and was never dropped because of my gearing. The only time it was a real issue was in a sprint, or trying to follow an attack in a fast criterium. Those aren't recreational rider problems.

I'm not even suggesting that recreational riders need to pedal at 120+ rpm for any extended period of time. If you're a recreational rider doing 40 mph, you're probably going downhill, and, as upallnight noted, you'll do better tucking instead of pedalling anyway. What do you need that huge gear for?

[Viva]

Well, now I feel like a dumb, stupid, idiot. Forget the chain breaking comment, I was thinking about the chain line, but that's not an issue here. I'm not used to thinking about compact cranks since I've never used one.