cruzbike crank length & bottom bracket shell

[Brennus]

Looks like all cruzbikes come with a standard BSA30 bottom bracket shell, correct? So, 68mm width, english threaded, 42mm ID...meaning if I wanted to switch my favorite cranks in there as long as they are BSA30 compliant they should work!

Also, it looks like in general folks prefer what might be considered shorter crank length on their cruzbike. Something like 165mm where 172.5mm or 175mm might be more common on a standard DF. I'm not quite sure I completely understand the nuance of this preference. It's probably not hip angle (as it might be on a tri bike)! Ha!

Does it have to do with knee clearance of the handlebars...or is it more related to how cadence affects steering? Or both? Or neither?

 

[tiltmaniac]

I'd say shorter even than 165.

Knee clearance with the handlebars is the largest part of it. In particular, it allows you to move the bars more forward (or the crank towards you, same thing different perspective), allowing you to have a wider range of fit options.

It also can make it easier to sit up while riding, with more clearance between chest and bars.

In my case I also appreciate being able to spin faster for the same level of comfort, which seems to translate to being more willing to go for it (i.e. I become faster because I'm more comfy on average).

I haven't noticed cadence affecting steering in any meaningful way.

Theoretically, a smaller crank is less frontal area, but I'd be shocked if this really turned up as a a major factor.

 

[LarryOz]

Looks like all cruzbikes come with a standard BSA30 bottom bracket shell, correct? So, 68mm width, english threaded, 42mm ID...meaning if I wanted to switch my favorite cranks in there as long as they are BSA30 compliant they should work!
Also, it looks like in general folks prefer what might be considered shorter crank length on their cruzbike. Something like 165mm where 172.5mm or 175mm might be more common on a standard DF. I'm not quite sure I completely understand the nuance of this preference. It's probably not hip angle (as it might be on a tri bike)! Ha!
Does it have to do with knee clearance of the handlebars...or is it more related to how cadence affects steering? Or both? Or neither?

There is at least one other thread on our forum dedicated to crank length - search for it and read up - so much there!
Since I started riding Cruzbike about 5 years ago - I have been a major proponent of shorted cranks and have convinced many they are the way to go!
My personal thoughts are that you can get away with longer (175mm, etc) crank lengths on upright bikes because your hip more easily oscillates up and down during your normal pedal stroke letting you use longer cranks - people were convinced they wanted more and more leverage.
On a recumbent you are less mobile in the seat so that just does not work.
There is a pretty good "recumbent calculator: out there that also helps you estimate what you need. Here is the link. http://www.recumbents.com/wisil/misc/crank_angle.asp
There are many reasons to choose a shorter crank length for recumbents, but the largest one for me is knee comfort, both now and in the future. If crank length is requiring your knee to bend beyond 90 degrees on your back-stroke it will eventually start affecting you.
The other other major advantage is power. The more your knee is bent beyond 90 degrees on your back-stroke the less power you will have whey trying to extend it. Try it just leaning against a wall with you knees bent at different angles.
Also as mentioned, you can spin up faster and there is a less frontal area. Also at higher cadenses your legs do not have to move as much and will not feel like they are flailing all over the place. I can easily spin 100-110 for hours with my short cranks,
I have regularly been riding 140-145mm cranks and do very well with them. I seem to have pretty good power for my age-group. Owner's: Jim and Maria have even recently (after I have been pestering them for years!) moved to shorter cranks (145mm I think) - and they love them.
Don't let people tell you that you will loose all this leverage because of a shorter moment arm on the crank. Yes, technically that is true, but that is what we have all those gears for. Now you have another an excuse to use them
I have tested and ridden with cranks down to 95mm. The "only" negative I have noticed with the really, really short ones is that you do have to push harder on them for a shorter time since the distance around it so much shorter. You will not notice this with them in the 140-150 range.
Best way to "get" shorter cranks is to look on ebay for used solid AL Apex cranks. Buy then and get someone local at a machine shop to shorten them and tap them where you want. (If you can't do it yourself.)
My 2-cents on the topic,
Larry

 

[super slim]

There is at least one other thread on our forum dedicated to crank length - search for it and read up - so much there!
Since I started riding Cruzbike about 5 years ago - I have been a major proponent of shorted cranks and have convinced many they are the way to go!
My personal thoughts are that you can get away with longer (175mm, etc) crank lengths on upright bikes because your hip more easily oscillates up and down during your normal pedal stroke letting you use longer cranks - people were convinced they wanted more and more leverage.
On a recumbent you are less mobile in the seat so that just does not work.
There is a pretty good "recumbent calculator: out there that also helps you estimate what you need. Here is the link. http://www.recumbents.com/wisil/misc/crank_angle.asp
There are many reasons to choose a shorter crank length for recumbents, but the largest one for me is knee comfort, both now and in the future. If crank length is requiring your knee to bend beyond 90 degrees on your back-stroke it will eventually start affecting you.
The other other major advantage is power. The more your knee is bent beyond 90 degrees on your back-stroke the less power you will have whey trying to extend it. Try it just leaning against a wall with you knees bent at different angles.
Also as mentioned, you can spin up faster and there is a less frontal area. Also at higher cadenses your legs do not have to move as much and will not feel like they are flailing all over the place. I can easily spin 100-110 for hours with my short cranks,
I have regularly been riding 140-145mm cranks and do very well with them. I seem to have pretty good power for my age-group. Owner's: Jim and Maria have even recently (after I have been pestering them for years!) moved to shorter cranks (145mm I think) - and they love them.
Don't let people tell you that you will loose all this leverage because of a shorter moment arm on the crank. Yes, technically that is true, but that is what we have all those gears for. Now you have another an excuse to use them
I have tested and ridden with cranks down to 95mm. The "only" negative I have noticed with the really, really short ones is that you do have to push harder on them for a shorter time since the distance around it so much shorter. You will not notice this with them in the 140-150 range.
Best way to "get" shorter cranks is to look on ebay for used solid AL Apex cranks. Buy then and get someone local at a machine shop to shorten them and tap them where you want. (If you can't do it yourself.)
My 2-cents on the topic,
Larry

Larry, thanks for the details about the different hip movement on a recumbent! I was wondering why most recumbent riders use shorter cranks!
I can confirm that for me, the change from 175 mm cranks on my Silvio v1.0, to 153 mm on my Quest V1.0, was an eye opener, as I could not figure out why the Quest was a better climber, and less knee pain than the Silvio! The forum informed me of the shorter Quest crank, and its advantages!