Index Cranksets & Bottom Brackets

Home Rider Specifications Trike Stuff Drivetrain Rolling Stuff Accessories Places to Ride Cool Trike Links

 

Cranksets = Crankshaft

There is enough detailed information about Cranksets to fill a book. Fortunately we've taken those details put them in a crucible and boiled away the impurities. Your legs are the engine that powers the trike; every mile will add somewhere between 500 and 2000 stroke repetitions depending on gearing. When the cranks are sized correctly its about the best therapy for legs and knees. When the cranks are the wrong size it can lead to joint pains, particularly with knees.

With a long enough lever you could move the world.

Most trikes come with a standard crank size of 165-175mm in length, while a few may offer optional sizes. Trike OEM's get much better pricing on volume sales and for a trike to be ready-to-ride cranks must be installed. Just not always with the crank thats right for you. It is not unsual for someone to buy a trike and later decide they need to replace the Crankset with one better suited to their needs.

Replacing cranksets generally costs at least $100, and can quickly go up from there. Most Cranksets will take special tools to remove & replace, and often requires replacement of the Bottom Bracket. The Bottom Bracket is basically the axle the Cranksets mount on, with a set of bearings and endcaps to mount the Bottom Bracket to the bike frame.

Sizing the length before you buy is dependent on the length of your legs and the condition of your knees. Weaker knee joints that have experienced meniscus tears or osteo-arhtritus will prefer a shorter crank as it reduces the bend angles at the knee. On the Rider Measurements page we provided a Crank Length Sizing Table which is repeated here.

Recommended Crankset Lengths
Strong Knee X-Seam
Weak Knee X-Seam
Crank Length
Cadence
47"
49"
180mm
84 RPM
44"
46"
170mm
90 RPM
41"
43"
160mm
97 RPM
38"
38"
150mm
105 RPM
35"
37"
140mm
112 RPM

Longer cranks increase leverage to the chain; some will prefer the added leverage if they have healthy knees and stocky leg muscles. Typically their pedaling style is known as a "Stroker". While longer cranks may add leverage, the circle they rotate through is larger so the distance traveled for a revolution is longer. They pedal slower, and use lower ratio gears. In effect they don't really put more force to the drive wheel then a shorter crank so long as the gear ratios are adjusted to the shorter crank.

Conversely, shorter cranks decrease leverage but have a shorter distance to travel through a revolution. As a result the pedals spin faster. With a faster spin the short rider shifts to a higher gear ratio so they effectively apply as much force to the drive wheel just in a different gear. Their style of pedaling is refered to as a "Spinner".

Don't let the fact that Spinners have to pedal faster then Strokers seem like Spinners are working harder. What it comes down to is the distance your feet are moving which is generally the same.

Smaller orbits take more orbits then larger orbits do to travel the same distance. And smaller legs prefer to spin faster then larger legs. Take a look at the animation below and click through the buttons to learn the basics about cranks.

   

Recapping the Components you'll need to consider:

  • Crankset
  • Bottom Bracket - don't forget the A/B/C dimesnions shown in the animation
  • Optional - Chain Rings
  • Chainring Bolts; 8-12mm with nuts, & 8mm without nuts
  • Chainring Shims; usually 2 sets @2.2mm thick

Cheatsheet Links:

If you're considering changing Chainrings to accomodate different gear ratios we'll cover ratio selections in Derailleurs, Chains & Shifters.