Author Topic: Tandem crank legth  (Read 9329 times)

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Offline mu2flyer

Tandem crank legth
« on: April 30, 2011, 12:56:03 pm »
I recently purchased a Co-Motion Tandem Mocho because of its short standover height. I’m 5’6” and my wife is 5’5”. The dealer set us up with a 175mm front crank and 170mm rear.  The difference in size is to keep the captain from spinning too fast for the stoker. After doing some research I find I should be using a 165mm. Co-Motion factory sets them up with 170 front and rear only. I purchase a small bike and I get a big crank. If I want a smaller crank, only a very few companies offer it and it’s not cheap. Any advice?

Offline whittierider

Re: Tandem crank legth
« Reply #1 on: April 30, 2011, 03:13:35 pm »
Unfortunately the range of crank lengths available is super narrow, like making shoes only in size 9.5, 10, and 10.5, and dictating that everyone should be fit into those, even if you need a size 8.  Ridiculous.  And it's worse for tandems because look who rides them-- often a husband and wife and she's too short for 170mm, even when she was young, and they often can afford the tandem only after the kinds are grown and gone meaning they're older and knees aren't as good and they need shorter crankarms to avoid re-injury.  Fit systems usually neglect to address age and past injuries, things that affect ideal crankarm length probably more than anything else in bike fitting.

There are a few choices for shorter ones-- very few, and they're expensive, but not as expensive as knee surgery.  da Vinci is one of them, going down to 130mm.  TA is another, going down to 150mm, and known for having the highest quality you'll find anywhere.  Both these companies have them for tandems.

Offline DaveB

Re: Tandem crank legth
« Reply #2 on: May 01, 2011, 08:38:53 am »
As noted there are custom crank makers that offer a great range of arm length.  Lennard Zinn is one.  I don't know if he offers tandem cranks but it's worth asking.   None of these are cheap as you've discovered.

I would also question the value of your "research" that said you NEED a 165 mm crank as there is much folklore and little real evidence for these recommendations.

Several years ago Lennard Zinn did a fairly comprehensive study on "proper" crank length based on rider height, leg length, etc. and (unfortunately for him) concluded there is no correlation.  He studied riders of a wide range of heights using cranks of a great range of arm lengths (IIRC, 130 to 220 mm) and found no relationship between them for power output, comfort or anything that would justify a custom crank.  He wasn't happy with the outcome since, as mentioned above he sells custom cranks, but he was honest enough to report the actual results.   

Offline staehpj1

Re: Tandem crank legth
« Reply #3 on: May 01, 2011, 10:12:21 am »
Everyone is different so take this as just one opinion, but...

There is a reason that even custom shops typically don't offer different lengths and that is because it doesn't matter much to most cyclists.

Back in my racing days I experimented with different crank lengths and found that:
  • A 10mm difference was barely noticeable.
  • I quickly adapted to what ever length I tried.
  • Performance was not noticeably impacted.

I figure it is kind of a non issue in most cases, but as I said YMMV.

Offline danacf

Re: Tandem crank legth
« Reply #4 on: May 01, 2011, 12:12:02 pm »
My advice would be to ride the bike, have fun and forget about it.  I experienced the same anxiety after my wife and I bought a Santana tandem a few years ago.  A tandem is a totally different animal from a single bike.  Due to their weight and length, they handle and feel much different from a single bike.  When first riding the tandem the pedal stroke felt slightly different from my single, but it took a month before I discovered the cranks were 175s.  I'm 5'7" and have always ridden 170s.  I've always wondered what 170s on a tandem would feel like, but after riding the bike for a few years I have come to the conclusion that 170s wouldn't make any difference and that  the 175s might be better on the tandem anyway.  I'm sure there are some trade offs.  I believe the longer cranks give you a slightly longer, smoother power stroke that more than compensates for any loss of rpm.  The most comfortable cadence for me on the tandem is around 83-85, but there is no difficulty pushing it up to the low to mid 90s on the flats.  Switching back and forth between my single and the tandem has not caused any knee/leg problems and no adjustment period is needed.  Again, tandems are different.  The bike came with 46cm handlebars for stability and control.  I have 42s on my road bike.  I can't imagine riding with the 46s on my road bike or the 42s on the tandem, but they feel fine on the bike they're on.  The cranks are probably the same story.

Offline csykes

Re: Tandem crank legth
« Reply #5 on: May 01, 2011, 12:33:13 pm »
I agree with getting out and riding the tandem.  I have a Santana from the mid 80s which is very different from my road bike; but I also ride it very differently.  You don't mention having ridden the bike yet.  Ride it for a while and make a change only if you really fee the need to do so, not just based on your research.  Enjoy!

Offline whittierider

Re: Tandem crank legth
« Reply #6 on: May 01, 2011, 03:32:18 pm »
Quote
He studied riders of a wide range of heights using cranks of a great range of arm lengths (IIRC, 130 to 220 mm) and found no relationship between them for power output, comfort or anything that would justify a custom crank.
This is the same outcome I've seen from a few different studies where they used a lot of subjects and tried a wide range of crankarms on them, but I have not seen the one you mention.  If you have a URL, I'd like to add it to my bookmarks.

It is a common misconception that longer crankarms will give you more power, for a couple of reasons.  All it will do is move your shift points down a bit.  The only thing I would comment about 5 or 10mm making a big difference is in knee injury.  One of my knees has had many minor injuries starting in childhood, and even though I'm 6' tall, 165mm is much, much better for avoiding pain and re-injury than 175 or even 170mm.  A nice side benefit with the shorter crankarms is that you don't have to keep the inside crankarm up in turns.  Another one is that you can have a lower torso position on the bike without your legs hitting your chest.  (My wife appreciates that.)

Offline Tourista829

Re: Tandem crank length
« Reply #7 on: May 01, 2011, 05:18:44 pm »
Here are two excellent resources, both sell Comotion Tandems & they have been in business for more than 20+ yrs. They know their stuff & may give you better info than Comotion. You will be glad you did.

TANDEMS EAST | contact@tandemseast.com | 856-451-5104 | 86 Gwynwood Drive Pittsgrove, NJ 08318
Mel Kornbluh www.tandemseast.com   

TANDEMS LIMITED 2220 Vanessa Drive Birmingham, AL 35242-4430 (205) 991-5519
Jack Goetz info@tandemsltd.com  www.tandemsltd.com

Offline cgarch

Re: Tandem crank legth
« Reply #8 on: May 01, 2011, 06:03:15 pm »
snip>  Lennard Zinn is one.  I don't know if he offers tandem cranks but it's worth asking.   None of these are cheap as you've discovered.  

I'm a big guy and even own two road Zinns. I have 180 cranks on those, but when our tandem came it too had 175s. Seems that's the standard available crank set. It seemed to me that the 175's exaggerated some knee problems, so last year I ordered a set of 190s from Zinn for the captain spot - I had a nice little gift show up one day. So yes, Lennard does indeed make tandem sets. I like my 190s even though the cornering clearance isn't what it used to be, not to mention breaking some conventions about how the captain crank is set up in the eccentric. In retrospect, I should have gone for either 180s or 185s. Being 6'-5" I like the opened up leg motion that comes from longer cranks. I for one do notice a slight power improvement as well and since we tow a trailer I find that it works better. I used Sheldon Brown's gain ratio calculator before I committed to this and I came up with anywhere from 4 to 10% increase.

As for mu2flyer's question, I join the others in saying stick with the 175s unless you're got some extra cash around for the custom cranks.

Craig

Offline paddleboy17

Re: Tandem crank legth
« Reply #9 on: May 02, 2011, 12:16:45 pm »
I am going to disagree on your position that a 165mm is the right size for you.  I am about the same height as you, and my first serious road bike came with a 165mm crank.  Small frames are built around the assumption that the rider is either an adult female or an adolescent (of either gender).  165mm cranks were designed with adolescents in mind.  The crank lenght is shortened because of a concern that an adolescent might due orthopedic damage to themselves.  As an adult male, the correct crank length for you is probably 170mm.  You could try the 17fmm crank and see how it works out for you.  If you are unhappy with it, then you could pursue a 170mm crank, and that should be readily available.  If you have problems with arthritis, then a shorter crank makes sense for you. 

What crank length is on your other bikes?

If you are still convinced that you want a 165mm crank, I have a 9 speed Ultegra tripple (32/42/52) that I would be happy to sell you, as I don't use it anymore.  You can contact me off list, if you are interested.
Danno

Offline DaveB

Re: Tandem crank legth
« Reply #10 on: May 02, 2011, 04:36:53 pm »
Quote
He studied riders of a wide range of heights using cranks of a great range of arm lengths (IIRC, 130 to 220 mm) and found no relationship between them for power output, comfort or anything that would justify a custom crank.
This is the same outcome I've seen from a few different studies where they used a lot of subjects and tried a wide range of crankarms on them, but I have not seen the one you mention.  If you have a URL, I'd like to add it to my bookmarks.
It wasn't originally posted on a web site but was published in, IIRC, a VeloNews issue several years ago.  A search of the VeloNews web site might turn it up in their archives but I don't know for sure. 

Offline mu2flyer

Re: Tandem crank legth
« Reply #11 on: May 07, 2011, 11:10:13 am »
Wow, what great info....I will give the 175's a chance to see how it works for the long run. to answere peddleboy17, my other crank sizes are MB 175, touring Surly LHT 170, road 170. these cranks all came on the bike when purchased as standard. All frames are 50CM.