Crank Arm Length

In a previous post, a writer suggested that the crank arm length for a recumbent should be shorter
than the normal calculation for an upright bike. I can't find any published info on this subject. In
my case I have a 33" inseam and most conventional sizing charts for uprights would indicate a 170mm
crank arm length. I have two goals (which may be conflicting): 1. More spinning than pushing to
protect a couple of ancient knees. 2. Maximize hill climbing ability - but this does not mean going
up hills fast, it just means getting up steep hills at any speed I can balance and avoid walking
hills (we climb a lot of hills now at 3.8 mph on our daVinci upright tandem, and 5-6mph on my
upright single).

I realize that gearing plays into this heavily and our recumbent tandem will have 24/42/48 11-34. My
recumbent single will have 30/42/52 11-32.

We're in the final stages of getting delivery on our new recumbents. Maybe this crank arm length
stuff is not all that important. Any thoughts on this crank arm length business?

 

In article <[email protected]>, [email protected] says...
> My recumbent single will have 30/42/52 11-32.
>
> We're in the final stages of getting delivery on our new recumbents. Maybe this crank arm length
> stuff is not all that important. Any thoughts on this crank arm length business?

I've never played with crank arm lengths (too $$$), but I have put a lot of thought into gearing for
hills. And spinning those lower gears.

If hills are a concern, I would replace the 30T on your chain ring with a 26T or 28T. Even though
the capacity of the front derailleur is 22T, you can usually go to a 26T with no difficulty. I would
also like a 34T on the rear for an even lower 'granny' Your rear derailleur will probably support a
11-34 cluster and your knees will appreciated it.

--

Cletus D. Lee Bacchetta Giro Lightning Voyager http://www.clee.org
- Bellaire, TX USA -

 

I have a 34" inseam and switched from 180mm cranks to 165mm several years ago and they seem to work
really well for me.

Hope this helps you.

Lewis.

...........

"Dave Harney" <[email protected]> wrote in message
news:<[email protected]>...
> In a previous post, a writer suggested that the crank arm length for a recumbent should be shorter
> than the normal calculation for an upright bike. I can't find any published info on this subject.
> In my case I have a 33" inseam and most conventional sizing charts for uprights would indicate a
> 170mm crank arm length. I have two goals (which may be conflicting): 1. More spinning than pushing
> to protect a couple of ancient knees. 2. Maximize hill climbing ability - but this does not mean
> going up hills fast, it just means getting up steep hills at any speed I can balance and avoid
> walking hills (we climb a lot of hills now at 3.8 mph on our daVinci upright tandem, and 5-6mph on
> my upright single).
>
> I realize that gearing plays into this heavily and our recumbent tandem will have 24/42/48 11-34.
> My recumbent single will have 30/42/52 11-32.
>
> We're in the final stages of getting delivery on our new recumbents. Maybe this crank arm length
> stuff is not all that important. Any thoughts on this crank arm length business?

 

> We're in the final stages of getting delivery on our new recumbents. Maybe this crank arm length
> stuff is not all that important. Any thoughts on this crank arm length business?

Dave,

I am a shorter guy (5'7", 28" inseam), and I rode with 170mm's for a while. I always tolerated some
degree of knee soreness, until I switched to a bike with 150mm's. IMO, that was one of the most
signifigant equipment upgrades I have experienced on a bike. My spinning form immediately improved.
My hill climbing efficiency increase, less of a "mashing" experience. My avg. cadence increased and
my speed endurance increased noticeably as well. Post ride, my knees felt great. On the same rolling
to hilly course with 170mm's, my knees would ache in proportion to the amount of effort exerted.

I would give crank arm length some thought. It is one of the more costly components of the
drivetrain, but in my experience I believe proper crank length is critical to your overall riding
performance.

-Windy City Keith

 

My experience is completely anecdotal, with no scientific facts or method.

When I began riding bents, the differences became immediately obvious. They were harder to start
up. Acceleration was harder. In general, I tended to shift like I had on my DF road bike. My
first bents had 170 mm cranks.

The net result was that I developed tender knees. If I pushed much, they ached.

Reading about knee problems on this forum, I learned about the spin approach and read that
shorter cranks had helped others. Since I had a set of Dotek 155mm, from a 24" MTB, I changed to
them. If I remember correctly, there was no miracle, but it seemed that I could push a bit
harder. Remember, I was also concentrating on pedaling at a faster cadence. Anyways, the knee
problems went away over time.

I could notice no particular difference in effort with the shorter cranks. This is counter
intuitive, but that is how it was for me.

Reading the research in HPV Journal, their criterion was top speed in an all out sprint. The
longest cranks were best according to their study.That didn't apply to my world very well.

That's my story and I'm sticking to it. Hope it helps you decide.

--
Miles of Smiles,

Tom Blum Winter Haven, Florida Homebuilts: SWB Tour Easy Clone Speed Machine Clone

www.gate.net/~teblum

 

Windy City Rider wrote:
> I am a shorter guy (5'7", 28" inseam), and I rode with 170mm's for a while. I always tolerated
> some degree of knee soreness, until I switched to a bike with 150mm's. IMO, that was one of the
> most signifigant equipment upgrades I have experienced on a bike. My spinning form immediately
> improved. My hill climbing efficiency increase, less of a "mashing" experience. My avg. cadence
> increased and my speed endurance increased noticeably as well. Post ride, my knees felt great. On
> the same rolling to hilly course with 170mm's, my knees would ache in proportion to the amount of
> effort exerted.

What was your typical cadence before changing and now after changing? Could you not have obtained
this difference in cadence just by training on high cadence?

> I would give crank arm length some thought. It is one of the more costly components of the
> drivetrain, but in my experience I believe proper crank length is critical to your overall riding
> performance.
>
> -Windy City Keith

I thought most people compensated change of crank length by a change of chain ring too, resulting in
effectively a simelare gear set.

Kees, used 170 to 175 on DF and hurricane, but didn't feel much difference between them, van Malssen

 

More spinning than pushing to
protect a couple of ancient knees.

.

Maybe this crank arm length
stuff is not all that important. Any thoughts on this crank arm length business? [/B][/QUOTE]I have a 31" inseam and went from 170mm to 152mm and no longer have pain in my left knee (30 yr. old injury). I also spin automatically it seems, and my legs stay inline better as I pedal. My legs don't get near as fatigued or sore, and I go a tad faster and am much quicker to react to turns or road obstacles. I ride smoother and more mechanically efficient. I had a local df frame builder modify some 175mm 105 hollowtechs, as they are solid down to at least the 140mm mark, I tested them first with a 1/16 drillbit. I'll be doing another set to 157mm soon just to try that length. Crank arm length is important, and shorter ones are making my bent riding far better. Don

 

More length means more torque strength, but I needed less stroke lengths for retaining faster
speeds. I found a great solution for me was a shortener from Hostelshoppe. It just bolted into the
existing pedal holes and clamps onto the arms giving me 4 choices to put the pedals.

Not cheap - $92. - but worth the high price to me by adding lower gears I never used.

Chris Jordan Santa Cruz, CA.

>
> We're in the final stages of getting delivery on our new recumbents. Maybe this crank arm length
> stuff is not all that important. Any thoughts on this crank arm length business?

 

[email protected] (Christopher Jordan) wrote in message
news:<[email protected]>...
> More length means more torque strength, but I needed less stroke lengths for retaining faster
> speeds. I found a great solution for me was a shortener from Hostelshoppe. It just bolted into the
> existing pedal holes and clamps onto the arms giving me 4 choices to put the pedals.
>
> Not cheap - $92. - but worth the high price to me by adding lower gears I never used.
>
> Chris Jordan Santa Cruz, CA.
>
> >
> > We're in the final stages of getting delivery on our new recumbents. Maybe this crank arm length
> > stuff is not all that important. Any thoughts on this crank arm length business?

Does this also give a little more distance from the centerline? Like pedal extenders? I need some
extenders, and if the length adapters also give me a few extra MM out from the centerline maybe
that's my solution then.

Thanks Bryan

 

[email protected] (azqaz) wrote in message
news:<[email protected]>... ?
>
> Does this also give a little more distance from the centerline? Like pedal extenders? I need some
> extenders, and if the length adapters also give me a few extra MM out from the centerline maybe
> that's my solution then.
>
> Thanks Bryan

Yes; it does widen the pedals about an inch. I also have Kneesavers, which add another inch. This
combination works beautifully for me by equalling hip/leg/pedal spacing. After riding that Thebis, I
missed that wide crank. Thebis goes through the middle of the front wheel, so is wider than normal.

Chris Jordan (not a physical therapist- just play one on this newsgroup) ;-) Santa Cruz, CA.

 

Christopher Jordan wrote:
>
> Yes; it does widen the pedals about an inch. I also have Kneesavers, which add another inch. This
> combination works beautifully for me by equalling hip/leg/pedal spacing. After riding that
> Thebis, I missed that wide crank. Thebis goes through the middle of the front wheel, so is wider
> than normal.

For those who have never seen a Thebis: < http://home.mindspring.com/~kb7mxu/images/thebis.jpg >.

Tom Sherman - Various HPV's Quad Cities USA (Illinois side)

 

I'm thinking about the shortener also, but am concerned about two things: 1. the first shortening
increment is 24 mm, so that's a pretty big jump if one is starting with 170 mm. 2. it adds nearly
50% more to the weight of the pedal - which is part of the critical "rotating weight" we all tend to
worry about.

What length were you starting with? Did you notice the pedal weight?

"Christopher Jordan" <[email protected]> wrote in message
news:[email protected]...
> More length means more torque strength, but I needed less stroke lengths for retaining faster
> speeds. I found a great solution for me was a shortener from Hostelshoppe. It just bolted into the
> existing pedal holes and clamps onto the arms giving me 4 choices to put the pedals.
>
> Not cheap - $92. - but worth the high price to me by adding lower gears I never used.
>
> Chris Jordan Santa Cruz, CA.
>
> >
> > We're in the final stages of getting delivery on our new recumbents.
Maybe
> > this crank arm length stuff is not all that important. Any thoughts on
this
> > crank arm length business?

 

"Dave Harney" <[email protected]> wrote in message
news:<[email protected]>...
> I'm thinking about the shortener also, but am concerned about two things: 1. the first shortening
> increment is 24 mm, so that's a pretty big jump if one is starting with 170 mm. 2. it adds nearly
> 50% more to the weight of the pedal - which is part of the critical "rotating weight" we all tend
> to worry about.
>
> What length were you starting with? Did you notice the pedal weight?
>
>
Starting with about 170mm (standard?) arms, the shorteners go about 40mm or so. I dislike missing
pedals, or slipping off small ones - yet I do not want to lock up my feet. I have been using those
big BMX horseshoe pedals, and I wear cowboy boots to make weight problems worse. I do not notice
extra weight from the Kneesaver extensions or the crank arm shorteners.

It did quell my interest in huge chain rings, since it is a high "enough" top gear in the real short
adjustment.

Chris