Affordable "Cruzbike" Short Cranks

[LarryOz]

I can't stop thinking whether 165mm crankarms are a good compromise.. but that's for a different time.

The real key to whether 165 would be good for you is how much your knee bend is on your back-stoke. You want you knee bend to be about 90 or more. Anything less is ultimately bad for you knees, and your power making ability. When you knees are bend more than 90 degrees you cannot really make good power until they open up to that point - which will only happen as you continue pedaling - but when that point is reached you have lost a significant percentage of that "10-2" range where you make most of it. Not to mention your knees hurt if you try and push hard when compressed at more than 90 degrees. Hope this helps.

 

[ak-tux]

The real key to whether 165 would be good for you is how much your knee bend is on your back-stoke. You want you knee bend to be about 90 or more. Anything less is ultimately bad for you knees, and your power making ability. When you knees are bend more than 90 degrees you cannot really make good power until they open up to that point - which will only happen as you continue pedaling - but when that point is reached you have lost a significant percentage of that "10-2" range where you make most of it. Not to mention your knees hurt if you try and push hard when compressed at more than 90 degrees. Hope this helps.

To add to what Larry said, I came across the online calculator below, though Iam yet to try anything shorter than 165mm (which came with my S40). Iam currently using 170mm cranks becuase I got a crank based powermeter on it.

The Recumbent Bicycle and Human Powered Vehicle Information Center

Recumbent and Human Powered Vehicle Information Center

www.recumbents.com

 

[ak-tux]

I finally recieved some "Goldix" 150mm cranks from AliExpress. Costed me $40 total (inclusive of Shipping to Kenya). Quite affordable indeed.

First impression: they look strong and well built. The color is a mat finish. Just functional not flashy.
The spindle is standard 24mm for Shimano HollowTechII bottom brackets. The cranks install just like Shimano ones, with two pinch bolts at 12-14Nm.

The downside is that they are designed to fit mountain bikes and therefore the Q factor results in a slightly wider stance, about +5mm. Not a show stopper though. (When I started pedalling, I did notice this change for a few minutes then I adapted.)

They required some spindle spacers in order to fit properly and apply the necessary bearing preload. I added 3 aluminium spacers (1mmx24mm) between the left crank and the BB. (I had previously acquired these for another project from https://www.aliexpress.com/item/1005003657191586.html)


I decided to install it on my old homemade recumbent. (I don't want to change my S40 at the moment becuase it has a 170mm left crank based power meter that I have fined tuned to match my fit. )

For the chainrings, I had an old GXP/SRAM Rival 50x34 direct drive set that I bought used from a friend. It fits perfectly on the Goldix.

I first tested it on a turbo trainer to see how it feels. I was afraid 150mm will be too stubby and even comical. However, surprisingly, the 150mm felt very natural! I must admit, I even liked them! It feels like one is applying a continuous force all around the pedal stroke unlike the pulse like input feeling of the longer cranks. Hmmm, interesting.

The assesment is positive so far.
Next step, I will fine tune it further and try it outside on the road.

 

[Don1]

Just got some carbon 150mm cranks of aliexpress. Lease cs-01. 220aud. They look amazing, yet to try them thou. Unfortunately they'll go on the roadbike for an alpine grand fondo. I was able to beat several 10year old pr's on my local hills with 155's and 6kg heavier, so I'm hooked on short cranks

 

[ak-tux]

Just got some carbon 150mm cranks of aliexpress. Lease cs-01. 220aud. They look amazing, yet to try them thou. Unfortunately they'll go on the roadbike for an alpine grand fondo. I was able to beat several 10year old pr's on my local hills with 155's and 6kg heavier, so I'm hooked on short cranks

Cool! Maybe share the AliExpress link too?

 

[Rampa]

Those Goldix are the same ones I got. But I went with 140mm. My legs are kind of short for my height. But same feeling. It just rotates smoother and spins up so fast!

 

[kizarmynot]

To add to what Larry said, I came across the online calculator below, though Iam yet to try anything shorter than 165mm (which came with my S40). Iam currently using 170mm cranks becuase I got a crank based powermeter on it.

The Recumbent Bicycle and Human Powered Vehicle Information Center

Recumbent and Human Powered Vehicle Information Center

www.recumbents.com

View attachment 17756

Any idea what the high/med/low BB means? All entries are green (good?), but that's 4 different crank lengths between them.

 

[LarryOz]

Any idea what the high/med/low BB means? All entries are green (good?), but that's 4 different crank lengths between them.

This is talking about the height of the BB in relation to the ground (or your seat bottom). A "low" BB would probably have your BB below your seat and would feel rather odd compared to how most Cruzbike BB's are fit to riders. The only way you get a really low BB on Cruzbike is if you have really long legs and a really short chain stay. Usually you want the BB to be about 5-6 inches above the bottom of your seat. And you never want it so high that your boom in angled down from the BB to the handlebar.

 

[ak-tux]

Any idea what the high/med/low BB means? All entries are green (good?), but that's 4 different crank lengths between them.

Yes, basically, what @LarryOz said.

Generally, all Cruzbike S40s with the standard (450mm) chainstays that come with the bike, for an average rider (height 178-180cm), will place the bottom bracket (BB) just slightly above the level of the seat base. This would qualify as a med BB. If however you modify the bike and put longer chainstays(which cruzbike also sells) then the BB will qualify as high.

On the other hand, I think Cruzbike V20 will probably qualify as having a high BB for an average rider.

For my dimensions (for an S40 with standard chainstays), both 150mm and 145mm cranks would fit me. However according to the calculator the 150s would give me a knee angle of about 85 degrees, which is what it recommends.

 

[kizarmynot]

Thanks for the helpful explanations @LarryOz and @ak-tux.