Steering Geometry For Handcycles
The effects of steering geometry on front wheel strength
All recumbent handcycles have a relatively shallow steering axis. This means that when steering the wheel gets leant over at a compound angle. One component of this angle is a twisting action which steers the handcycle, and the other is a leaning action.
The diagram above shows the forces that this creates for the front wheel. The force has two components; one component that goes up through the axis of the wheel and the other is a lateral force on the rim. Spoked bicycle wheels are very strong along their axis but are pretty weak structures in the lateral direction. The lateral forces on a handcycle risk collapsing the front wheel. This is why it is important to observe the weight limit and be aware of the lateral loads through the front wheel. It is also very important to use a strong front wheel on all handcycles. Several factors make a stong front wheel.
- Spoke count. Handcycles should have a 36 or 48 spoke wheels on the front.
- Spoke Lacing: Cross 3 is the preferred lacing pattern for strength.
- Spoke Tension: Even tension of approximately 50kg of tension per spoke on the drive side.
- Rim Strength: A strong rim will help with lateral strength but is not as important as spoke count, lacing and tension. A deep rim also helps by allowing the use of shorter spokes. Typically a rim with a double wall and deep section is very strong and rigid. We recommend Sun Ringle CR18 and Velocity Deep V.
- Hub: A hub with deep flanges will allow shorter spokes to be used and will therefore increase the lateral strength of the wheel. We recommend Shimano Deore hubs because they are well priced and have relatively deep flanges and we also recommend Phil Wood hubs for their quality and deep flanges.
Carbon Fiber wheels for handcycles:
The use of composites is also a great way to increase the lateral stiffness of a front handcycle wheel. Closed section tri-spoke and quint-spoke wheels offer the stiffness of closed section spokes which are more rigid than traditional wheels when it comes to lateral loads. Furthermore, while composite wheels might flex they won’t bend.
As with all composites any damage to the laminate can impair the structural integrity of the wheel. In simpler terms carbon fiber is great until you damage it, after which you are riding hair! The other drawback of carbon fiber wheels for handcycles is their immense cost.
There are many manufacturers of carbon fiber wheels including:
At Intrepid we use Aerospoke. Aerospoke make an extremely strong five spoke carbon fiber wheel with a variety of hubs for handcycles. We fit Aeropoke wheels on our Clydsdale model as standard.
Carbon fiber disk wheels do not offer the same lateral stiffness as closed section spoke wheels. Disk wheels are often lighter than spoke wheels and offer greater aerodynamics. Disk wheels are fine for the rear.