crank arm length and compact rings

[vscalia]

Hey,

My new team bikes are coming with compact crank sets on them. I am used to riding a standard but am interested in trying out the compact. an 11-25 cassete will have more of a range than a 12-15 with a standard crank. According to gear ratios charts. Heres the thing though. I am not a physicist. but if the chain rings are smalled than doesnt that change the amount of force made and thus change power output. I know that I will have more gears when climbing so thats fine. Also I am around 6'2" i ride a 172.5 crank arm length and have been reading about crank arm length recently. Most things I have seen say that it comes down to preference, and that there is no decisive studies to suggest anything. But do any of you out there have an opinon on what size cranks i should use. And what longer arms might or might not help.

 

[daveryanwyoming]

.... I am not a physicist. but if the chain rings are smalled than doesnt that change the amount of force made and thus change power output. ....

Well yes, but only in the same way that riding different gear ratios changes force/cadence requirements for a given power. Gear ratio is all that matters, the actual size of the chainring doesn't matter if you pair it up with the appropriate rear cog.

For example, a 53/15 gives you 89.4 gear inches on a road bike, a 50/15 gives you 90 gear inches on the same bike. Those two gear combinations are all but identical, it doesn't matter that you achieved the same gearing with a smaller front ring and different rear cog, the gearing ratio is all that matters in terms of force/cadence requirements for a given power output.

Hope that makes sense,
-Dave

 

[vscalia]

Well yes, but only in the same way that riding different gear ratios changes force/cadence requirements for a given power. Gear ratio is all that matters, the actual size of the chainring doesn't matter if you pair it up with the appropriate rear cog.

For example, a 53/15 gives you 89.4 gear inches on a road bike, a 50/15 gives you 90 gear inches on the same bike. Those two gear combinations are all but identical, it doesn't matter that you achieved the same gearing with a smaller front ring and different rear cog, the gearing ratio is all that matters in terms of force/cadence requirements for a given power output.

Hope that makes sense,
-Dave

definetly makes sense, thanks dave

 

[dkrenik]

Also I am around 6'2" i ride a 172.5 crank arm length and have been reading about crank arm length recently. Most things I have seen say that it comes down to preference, and that there is no decisive studies to suggest anything. But do any of you out there have an opinon on what size cranks i should use. And what longer arms might or might not help.

I would recommend keeping crankarm length a separate issue from compact/standard. CL is about fit and compact/standard is, well - gearing. You'll probably end up using about the same gear/inches (most of the time) on the compact cranks. If 172.5's have been working for you - stay with them.

Welcome to the compact world. I've a compact SRM and love it. I use an 11-25 cassette and have all the gears I need.

Dave

 

[Alex Simmons]

For example, a 53/15 gives you 89.4 gear inches on a road bike, a 50/15 gives you 90 gear inches on the same bike. Those two gear combinations are all but identical...

Err, what my client meant to say was that a 53x16 (89.4") gear is almost equivalent to 50x15 (90") gear.

 

[daveryanwyoming]

Err, what my client meant to say was that a 53x16 (89.4") gear is almost equivalent to 50x15 (90") gear.

Ooops

Yeah, what he said... gotta write slower and think faster I guess.

-Dave

 

[Alex Simmons]

Ooops

Yeah, what he said... gotta write slower and think faster I guess.

-Dave

I've been using speech recognition software over the last week or so. It is seriously dangerous with respect to thinking speed.

It's pretty cool to use though.

 

[swampy1970]

Hey,

My new team bikes are coming with compact crank sets on them. I am used to riding a standard but am interested in trying out the compact. an 11-25 cassete will have more of a range than a 12-15 with a standard crank. According to gear ratios charts. Heres the thing though. I am not a physicist. but if the chain rings are smalled than doesnt that change the amount of force made and thus change power output. I know that I will have more gears when climbing so thats fine. Also I am around 6'2" i ride a 172.5 crank arm length and have been reading about crank arm length recently. Most things I have seen say that it comes down to preference, and that there is no decisive studies to suggest anything. But do any of you out there have an opinon on what size cranks i should use. And what longer arms might or might not help.

If you're going uphill the longer cranks help. On the flat it's not as straight forward. If you're the type of dude that likes to do yoga then you might be able to deal with 180+mm cranks whilst riding on the drops with your back perfectly flat... most people can't though.