Crank length?

[cooljaysquat]

I just bought 16" rims with Michelin M29s 16x2.75 tires. My bike has a 26" frame (EW-400). I was wondering what size cranks most people use to conpensate for ground clearance? I want to be pedaling a little as well when I am using the electric motor. I know the difference between 170mm and 115mm is only 2.24 inches. I know a lot of people have put 16x2.75 tires on their 26" bikes. What size cranks is everyone using to have pedaling ground clearance?

 

[chisixer6]

I have a 24" bike with twin 406 tires(20" bmx) and am using 140mm cranks, still scraps sometimes.

 

[ddk]

serendipitously I just received two cranks to test on my trike
-one on the right is 3.5" or 88mm
-the one on the left is 4.5" or 114mm
The 5.5" (140mm) crank scrapes the ground at times and I don't like catching my heel
the chain ring is 28-tooth
schmaller is schmaller

 

[skeetab5780]

im too tall to be pedaling those things.. that would just feel goofy and slightly useless

 

[ddk]

im too tall to be pedaling those things.. that would just feel goofy and slightly useless

useless as in?
In the past year I've gradually reduced my crank lengths (from 170mm) so I -can- continue to pedal
But my most recent build is a bit too low to the ground. (crank-forward lowrider)
I'd rather use a shorter crank than have to modify the suspension system at this moment in time.

 

[dogman dan]

Others have reported significant improvement in knee pain from shortening the crank.

It will feel goofy at first if you are used to long cranks, but if you ever hurt your knee, a shorter crank will help the healing process. You want to heal it moving, but not rip it again pushing hard and over stretching the range of movement. Stretch it long some of course, but not while out pedaling and concentrating on other things.

Not on topic, but yet another reason not to resist swapping to a short crank if clearance is an issue as well. You will get used to the funny feel of the short crank if you aren't switching back to other bikes with long cranks all the time. Soon the short crank will feel right to you.

 

[docnjoj]

Not on topic, but yet another reason not to resist swapping to a short crank if clearance is an issue as well. You will get used to the funny feel of the short crank if you aren't switching back to other bikes with long cranks all the time. Soon the short crank will feel right to you.

Definitely on topic for me. The shorter crank, and gearing down to spin saved me from knee surgery. I highly recommentd it, particularly on recumbents. I went from 175 mm down to 150mm and learned to keep my cadence higher and my gears lower. Knee pain went away in about a month.
otherDoc

 

[cooljaysquat]

Thanks for the feed back cuz I asked the question about crank length becuase I thought there might be a standard crank length that people were using on a 26" frame with 21" tires. I guess I can measure the the ground clearance when I finish putting the bike together. I was hoping that there was a standard legnth that I should use.

 

[Jeremy Harris]

I'll add a vote for short cranks being a blessing as you get older.

I've just built a bike with 172.5mm cranks and it definitely feels harder on my joints than the bike with 165mm cranks, so much so that I'll probably swap them out before too long.

 

[docnjoj]

You know, Jeremy, it seems counter-intuitive that shorter cramks are better for knees than long ones which have a longer lever arm. The thing is that you must gear down and spin so you are then restraining knee motion and pressure. Every once in a while I forget to shift down and get caught having to start on a hill. That can hurt if one is not able/willing to shift down! Then the electric is worth it's salt.
otherDoc

 

[amberwolf]

http://sheldonbrown.com/cranks.html

 

[docnjoj]

Thanks AW. He pretty much confirms what I was thinking.
otherDoc

 

[Jeremy Harris]

You know, Jeremy, it seems counter-intuitive that shorter cramks are better for knees than long ones which have a longer lever arm. The thing is that you must gear down and spin so you are then restraining knee motion and pressure. Every once in a while I forget to shift down and get caught having to start on a hill. That can hurt if one is not able/willing to shift down! Then the electric is worth it's salt.
otherDoc

Thanks AW. He pretty much confirms what I was thinking.
otherDoc

Not sure if we have our wires crossed here or not. My observation was that shorter cranks feel more comfortable for me, i.e. the 165mm cranks on my old bike feel better than the 172.5mm cranks on the new bike. This seems to agree with Sheldon Brown, quote:

"Too long cranks cause excessive knee flex, and can cause pain/injury if it causes your knee to flex more than it is used to.

I learned this the hard way when I bought a used mountain bike that came with 180 mm cranks. I found that it made my knees hurt every time I rode it.

On the other hand, there doesn't seem to be any deleterious effect from shorter cranks."

 

[docnjoj]

Yeah Jeremy, sorry to be jabbering and thinking out loud.
Well the shorter ones work well for me too. The only difficult spot I have encountered is when I ran out of battery on an uphill situation, there is that moment when you are tempted to really push on the short crank, and that puts more pressure on knees due to the shorter "lever arm" compared to long cranks. It really means getting off the trike and turning it around and going downhill a bit to shift into a lower gear. Other than that they are really much better than long crank arms, at least for my knees. As an added bonus the short cranks give me more ground clearance for my big feet in the clipless pedals.
otherDoc

 

[Jeremy Harris]

Yeah Jeremy, sorry to be jabbering and thinking out loud.
Well the shorter ones work well for me too. The only difficult spot I have encountered is when I ran out of battery on an uphill situation, there is that moment when you are tempted to really push on the short crank, and that puts more pressure on knees due to the shorter "lever arm" compared to long cranks. It really means getting off the trike and turning it around and going downhill a bit to shift into a lower gear. Other than that they are really much better than long crank arms, at least for my knees. As an added bonus the short cranks give me more ground clearance for my big feet in the clipless pedals.
otherDoc

Makes sense to me, although in my case it's my left hip rather than my knees that gives me a small problem (onset of arthritis, apparently, the doc has already warned me I'll need a new hip at some point.......). I've found there's a critical angle when lifting my left leg up at the hip joint, beyond which it hurts, and the longer cranks are just starting to hit that angle if I have the seat set so that I can comfortably put my left foot down when stopped. I'm going to play around a bit and see if moving the saddle fore and aft eases it, as getting the special shorter cranks to fit the Speed Drive will probably be expensive.

 

[docnjoj]

Jeremy wrote:

I'm going to play around a bit and see if moving the saddle fore and aft eases it, as getting the special shorter cranks to fit the Speed Drive will probably be expensive.

You coould probably drill and tap a hole 20-30mm up on the cranks and save some money. There is a guy in the states that does this service for about $60 but it is not hard for a person like yourself with mucho skills.
otherDoc

 

[motomech]

Jeremy wrote:

I'm going to play around a bit and see if moving the saddle fore and aft eases it, as getting the special shorter cranks to fit the Speed Drive will probably be expensive.

You coould probably drill and tap a hole 20-30mm up on the cranks and save some money. There is a guy in the states that does this service for about $60 but it is not hard for a person like yourself with mucho skills.
otherDoc

I was thinking about doing this, but isn't one of the pedals screwed in with reverse threads?
Left-hand taps cost $20 to $30 ea. I guess unless one already has one, it would be more cost effective to just buy new crank arms.

 

[docnjoj]

Probably for Jeremy's Speed Drive I'll bet the cranks are expensive. He may very well have a reverse threaded tap in his shop.
otherDoc

 

[ddk]

I might add:
I hadn't gotten around to changing the 5.5" crank on mt2 to the smaller 4.5" crank and after only two days of use my knees were giving me fits.
To the point of difficulty climbing stairs, sitting and standing (old age sux)
Changed the crank to 3.5" and the pains and fits almost immediately stopped (test-this is only a test)
I'll likely fit the 4.5" crank today.

 

[docnjoj]

I might add:
I hadn't gotten around to changing the 5.5" crank on mt2 to the smaller 4.5" crank and after only two days of use my knees were giving me fits.
To the point of difficulty climbing stairs, sitting and standing (old age sux)
Changed the crank to 3.5" and the pains and fits almost immediately stopped (test-this is only a test)
I'll likely fit the 4.5" crank today.

Don't forget DDK that your new trike probably has 170 or 175 mm cranks. You will probably have to change 'em or drill and tap 'em.
otherDoc

 

[Jeremy Harris]

Doc, you're right, cranks for the speed drive are pricey. As it happens I don't have the right tap for pedal threads (either right or left), because being in metric-land I've never had the need for a good collection of old imperial thread taps and dies............

What I have found is a set of cranks that I took off my old folder when I fitted a crankset with a bigger chainring. They have a riveted on steel chainring that looks like it can be machined off and it also looks as if I could make them fit the speed drive OK. They are pretty short, at 152mm, but may well be worth a try.

 

[docnjoj]

Mine are 150 but 2mm is really no difference at all. The tap thing is a problem andI too can't find anything for less that 50+USD. You could almost buy a new crankset/chainrings for that amount of money. Great idea to reuse an old one.
otherDoc

 

[ddk]

Don't forget DDK that your new trike probably has 170 or 175 mm cranks. You will probably have to change 'em or drill and tap 'em.
otherDoc

here's a concept I wish bike manufacturers would use:
"optional accessories" that includes important things like crank length instead of pom-pom choices.
Of course LBS owners and operators would have to be edumacated on wut's actually required and why, as opposed to their personal idiotic opinions.
(I know I know... a lost cause)

 

[docnjoj]

Don't forget DDK that your new trike probably has 170 or 175 mm cranks. You will probably have to change 'em or drill and tap 'em.
otherDoc

here's a concept I wish bike manufacturers would use:
"optional accessories" that includes important things like crank length instead of pom-pom choices.
Of course LBS owners and operators would have to be edumacated on wut's actually required and why, as opposed to their personal idiotic opinions.
(I know I know... a lost cause)

Our LBS in Daphne, AL has the ability to order various crank lengths in a few days. One guy who works there has has experience with short cranks and reduced knee problems. They can be educated and some actually know stuff. Not all though. These guys build bikes for some of the older Senior Class riders.
otherDoc

 

[ddk]

Our LBS in Daphne, AL has the ability to order various crank lengths in a few days. One guy who works there has has experience with short cranks and reduced knee problems. They can be educated and some actually know stuff. Not all though. These guys build bikes for some of the older Senior Class riders.
otherDoc

my experience with the local is like "opposites day"
In a conversation about knee pain and hip pain, lbs gave the considered opinion that I needed longer crank arms, not shorter.
Needless to say, I didn't agree with that assessment.
For sure, they'll immediately take your order for special parts but they'll actually order said part whenever they feel like it.