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John Cobb Discussion on Shorter Cranks
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Hello,

I was at the Slowtwitch Road Show in Dallas this past weekend and listened to John's presentation on using shorter cranks. In the presentation he was talking about cadence increasing with shorter cranks and that a person might need to move to a larger chain ring to make things feel right. He mentioned possibly a 53 to 55 big ring. I'm ready to buy a new crank with 150mm arms but trying to decide if I should go 110 BCD as I would normally run a 52/36 set (at 170mm arms) or should I go 130 BCD with a 53/39.

Any of you have experience with this? Interested to hear experience with shorter arms and chain ring choice.

Thank You,
Ron
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Re: John Cobb Discussion on Shorter Cranks [WaterRat] [ In reply to ]
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This is a complicated subject..and that may be an understatement. In my experience...For some people it works...for others it doesn't.
I tried it...for a good two years...unsuccessfully. I went from 175 all the way to 165.
175mm cranks for me...highest overall power...highest overall speed.
Again...it works for some...for others it doesn't.
I respect Cobb's work...that's why I tried it....maybe I needed more than two years...unsure.
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Re: John Cobb Discussion on Shorter Cranks [WaterRat] [ In reply to ]
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WaterRat wrote:
He mentioned possibly a 53 to 55 big ring
You sure you got this right? Seems to me a person would need to go to a smaller chainring since he/she loses some torque when going to shorter cranks. This topic has come up several times in the past, and usually a person would need to go one cog up on the cassette when climbing hills after switching to shorter cranks. For example, if you usually use the 28T when climbing a hill, now you would need to use the 30T or even the 32T.
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Re: John Cobb Discussion on Shorter Cranks [RichardL] [ In reply to ]
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The cobb research is that oxygen consumption decreases on the shorter cranks, so you actually need to go up in the front to be just as intense as before.
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Re: John Cobb Discussion on Shorter Cranks [WaterRat] [ In reply to ]
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I would most definitely NOT run a compact ring with a 150mm crank. Not sure if there is a calculator out there, but a 52 probably becomes a 46 with a lever that small. For some, that's OK, but I really want that extra speed going down hills. This is coming from a former 165mm user (now at 170).
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Re: John Cobb Discussion on Shorter Cranks [nickwhite] [ In reply to ]
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nickwhite wrote:
I would most definitely NOT run a compact ring with a 150mm crank. Not sure if there is a calculator out there, but a 52 probably becomes a 46 with a lever that small. For some, that's OK, but I really want that extra speed going down hills. This is coming from a former 165mm user (now at 170).

Incorrect, you have you math backwards.
Shorter cranks require smaller chain rings to maintain the same gear ratios.

http://www.slowtwitch.com/...nd_Gearing_4095.html

Alex Arman

Strava
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Re: John Cobb Discussion on Shorter Cranks [doublea334] [ In reply to ]
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doublea334 wrote:
nickwhite wrote:
I would most definitely NOT run a compact ring with a 150mm crank. Not sure if there is a calculator out there, but a 52 probably becomes a 46 with a lever that small. For some, that's OK, but I really want that extra speed going down hills. This is coming from a former 165mm user (now at 170).


Incorrect, you have you math backwards.
Shorter cranks require smaller chain rings to maintain the same gear ratios.

http://www.slowtwitch.com/...nd_Gearing_4095.html

Yes, you're exactly right, slightly smaller chainrings and/or larger cogs to obtain the same gearing when going to shorter cranks. This is why some people have felt longer cranks helped for climbing; simply because they give a lower effective gear ratio at the same cog/chainring size.

I really don't know why John Cobb is advocating larger chainrings with short cranks, if that is actually what he said. If oxygen requirement is lower the most likely explanation to me is that shorter cranks open up the hip angle in the aero position, enabling some increased efficiency, not that the shorter cranks impart some innately more efficient way of cycling. Anyway, optimum cadence and foot speed varies from person to person and it's likely that some people will find they like the feel of short cranks better than others.
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Re: John Cobb Discussion on Shorter Cranks [WaterRat] [ In reply to ]
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WaterRat wrote:
Hello,

I was at the Slowtwitch Road Show in Dallas this past weekend and listened to John's presentation on using shorter cranks. In the presentation he was talking about cadence increasing with shorter cranks and that a person might need to move to a larger chain ring to make things feel right. He mentioned possibly a 53 to 55 big ring. I'm ready to buy a new crank with 150mm arms but trying to decide if I should go 110 BCD as I would normally run a 52/36 set (at 170mm arms) or should I go 130 BCD with a 53/39.

Any of you have experience with this? Interested to hear experience with shorter arms and chain ring choice.

Thank You,
Ron

I think this is one of those things that John has backwards...It's not about cadence, it's about tangential foot speed.

http://bikeblather.blogspot.com/
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Re: John Cobb Discussion on Shorter Cranks [WaterRat] [ In reply to ]
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I wouldn't go higher than a 53/39 with a 150mm arms! I went from 172.35 to 165 arms and switched to rotor QXL and it has been a learning curve to be quite honest... most times I find myself pedaling in the 16-18t as opposed to back 8 months ago when I was on a compact riding on the 11-14t.

I did feel pedaling the QXL with the smaller crank arms was very challenging initially and I think I am just now getting just enough power to maintain the speed I'd like when hammering! keep it a 110 bcd as you have more options of going bigger if you need to for ex: I'd start at compact with 11-25 cassette and work my way up to a 52/36 and whenever you feel that the semi-compact is not enough, then you can join the QXL team and really hammer away IMHO

Speed kills unless you have speed skills!!!
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Re: John Cobb Discussion on Shorter Cranks [playero] [ In reply to ]
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Appreciate all the info. I'm going to go with the 110 BCD and probably the 52/36 combo. I'll ride it for a while and can make changes to the ring size if need be. I did see at least one option for a 53 or 54 tooth in a 110 BCD but based on all the comments I will probably be good at the 52 or if I do find that I need a change it will be to a 50 tooth.

Thank You,
Ron
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