Shimano Compact Crankset

[frusso]

I understand that begining in January 2006 Shimano will be introdcting their road bike compact crankset. The gearing will be 50/34 and is intended to be used for 10 speed with 10 speed chain and front derailler. Does anyone know why I would not be ablw to use the new crankset with my currrent (new) 9 speed chain and front derailler?

www.terrybicycles.com/weblog/2005/10/compact_chainsets.html[/url]

Thank you

 

[John M]

I understand that begining in January 2006 Shimano will be introdcting their road bike compact crankset. The gearing will be 50/34 and is intended to be used for 10 speed with 10 speed chain and front derailler. Does anyone know why I would not be ablw to use the new crankset with my currrent (new) 9 speed chain and front derailler?

www.terrybicycles.com/weblog/2005/10/compact_chainsets.html[/url]

Thank you

Should work fine. The FSA compacts work with both 9s and 10s drivetrains and the Shimano 53/39 integrated BB cranks work with 9s chains.

 

[herman stiphout]

I would like to understand the difference (except lenght) of cranksets. How would one decide between a 175/172.5/170 or even a compact?

 

[Insight Driver]

I would like to understand the difference (except lenght) of cranksets. How would one decide between a 175/172.5/170 or even a compact?

You apparently misunderstand the specs. 175, 172.5 and 170 are the differences in crank lengths which allow riders with different leg length to have the optimum pedal angular rotation. A compact crank refers to having two chain-rings that are wider range than a typical road double which gives a wider gear ratio approaching a typical triple setup. Traditional front cranks are something like 52/42. A compact crank might be 50/39.

 

[Ozark Bicycle]

You apparently misunderstand the specs. 175, 172.5 and 170 are the differences in crank lengths which allow riders with different leg length to have the optimum pedal angular rotation. A compact crank refers to having two chain-rings that are wider range than a typical road double which gives a wider gear ratio approaching a typical triple setup. Traditional front cranks are something like 52/42. A compact crank might be 50/39.

Actually, the term "compact crank" refers to the Bolt Circle Diameter (BCD) of the crank. In this context, a traditional, modern road crank has a BCD (130mm for Shimano, 135mm for Campy) that accepts an inner ring no smaller than 38T (for 130mm BCD). A "compact", using a BCD of 110mm, accepts a small ring down to 34T. A typical compact crank, with 50/34 chainrings, offers somewhat wider range gearing at the expense of a less convienient shift pattern. IMHO, a properly set up triple (proper BB length, proper FD, etc.) is a better choice, giving wider range gearing and a better shift pattern.

 

[bbattle]

using Sheldon Brown's gear calculator,

A compact crank(50/34) with a 12-25 cassette will give you a calculated gear inches of 112.5 for 50-12 gear and 36.7 gear inches in 34-25 gear. (27in tire, 175mm crank)

A 53-39 crank with 12-25 will give you 119.3 gear inches for 53-12 and 39 gear inches for 39-25 gear.

A 52-42-30 triple with 12-25 cassette will give you 117 gear inches for 52-12 and 32.4 gear inches for 30-25 gear.

The compact crank 50-12 gear @ 90rpm will give you theoretically 30.1 mph

Double crank 53-12 will give you 31.9 mph

triple crank 52-12 will give you 31.3 mph.

I've been very happy with my compact crank; I give up a little bit on the high end which doesn't bother me as I'd never be able to crank 90 rpm in 53-12 anyways(or 50-12 for that matter) on level ground. I can swap my cassette for the 12-27 and get a gear inch number the same as a 30-24 gear on the triple.

I believe what Ozark means by better shifting is that you can use a "narrow" cassette like the shimano 11-21 and not have any big jumps in between gears. Or, if you have lots of hills and don't care about blasting down the flats, get a 15-25 cassette. Cross-chaining is less of an issue then.

 

[Ozark Bicycle]

using Sheldon Brown's gear calculator,

A compact crank(50/34) with a 12-25 cassette will give you a calculated gear inches of 112.5 for 50-12 gear and 36.7 gear inches in 34-25 gear. (27in tire, 175mm crank)

A 53-39 crank with 12-25 will give you 119.3 gear inches for 53-12 and 39 gear inches for 39-25 gear.

A 52-42-30 triple with 12-25 cassette will give you 117 gear inches for 52-12 and 32.4 gear inches for 30-25 gear.

The compact crank 50-12 gear @ 90rpm will give you theoretically 30.1 mph

Double crank 53-12 will give you 31.9 mph

triple crank 52-12 will give you 31.3 mph.

I've been very happy with my compact crank; I give up a little bit on the high end which doesn't bother me as I'd never be able to crank 90 rpm in 53-12 anyways(or 50-12 for that matter) on level ground. I can swap my cassette for the 12-27 and get a gear inch number the same as a 30-24 gear on the triple.

I believe what Ozark means by better shifting is that you can use a "narrow" cassette like the shimano 11-21 and not have any big jumps in between gears. Or, if you have lots of hills and don't care about blasting down the flats, get a 15-25 cassette. Cross-chaining is less of an issue then.

Yes, an absence of big jumps is part of it. So is the idea of less shifting on the front. Just stay in the middle ring most of the time and enjoy nice small steps between rear shifts. Hit the big ring for cruising the long flats and the downhills. Hit the inner ring for the big hills and mountains.

IMHO, a 30T inner ring on a triple doesn't give a really useful low gear, which is why a compact double with a 34T inner comes off looking pretty close. A 28T or 26T (or even a 24T, which is the limit of the 74mm BCD, if you are not hampered by the limitations of indexed front shifting) is a much more sensible choice.

 

[nbfman]

using Sheldon Brown's gear calculator,
I've been very happy with my compact crank; I give up a little bit on the high end which doesn't bother me as I'd never be able to crank 90 rpm in 53-12 anyways(or 50-12 for that matter) on level ground.

I find this to be the best rationale behind the compact crank i.e. combinations like 53-12 or 52-12 are outside the ability range of many road bike riders who want to have some rpm's in their pedaling. In that case, you may as well shift everything down to get more usable gears. One of my bikes is a triple with a 48 on top, and, at my level, it would not be such a bad large front ring on a double, either. The obvious weight reduction that comes for free with going compact is certainly another point that some may get excited about.

 

[casey mcvicars]

I understand that begining in January 2006 Shimano will be introdcting their road bike compact crankset. The gearing will be 50/34 and is intended to be used for 10 speed with 10 speed chain and front derailler. Does anyone know why I would not be ablw to use the new crankset with my currrent (new) 9 speed chain and front derailler?

www.terrybicycles.com/weblog/2005/10/compact_chainsets.html[/url]

Thank you

I am currently looking for a setup for my 8-speed Shimano, does anyone know if I need to change the crankset?

Casey