Camber: The degree to which the rear wheels are inclined inwards at the top. The idea of camber was first developed in the wheelchair industry for two reasons.
It increases the width and thus the stability of the wheelchair.
- A cambered wheel follows the natural path of ones arm as one reaches down to push the rim.
This logic was then applied to handcycles. Typically modern handcycles have anywhere from 0 to 15 degrees of camber. Unfortunately one of the drawbacks of using camber in a handcycle is that alignment of the cambered wheels needs to precisely set otherwise the handcycle will have tow-in or tow-out and the associated drag and wear characteristics on the rear tires. Furthermore the presence of camber puts a lateral stress on the rear wheels. In practice this is not normally enough to cause rear wheel failure however it is enough to introduce flex into the rear wheels.
The less the amount of camber on the wheels of a handcycle the lower the risk of misalignment and rear wheel flex.
Tow in/Tow out: Is the inwards or outwards misalignment of cambered wheels. When you have a wheel pair, both wheels in the pair need to roll in a parallel direction. If not the sideways component of the misalignment will resolve itself in the form of tires scrubbing sideways across the ground. This is a common phenomenon in the cars and recumbent trikes. The consequence of tow in or tow out is excessive drag on the handcycle and premature tire wear. In very extreme cases tire misalignment can cause vehicle wobble and a loss of control.
Tow in or tow out is often caused during abusive riding off road, or in an impact situation.
To correctly adjust tow in or tow out varies from cycle to cycle, however us usually is a fairly simple operation. With fixed camber floating axle handcycles you can rotate the axle and measure the distance between the center of the tire both in front of and behind the axle at the same height. These distances should be equal. It is often wise to check whether the wheels are true before adjusting camber.
For fixed axle floating camber plug type handcycles you can adjust camber on each wheel independently. Do this carefully until the distance the same fore and aft of the axle. It is important to always measure the distance at an equal height.
Many handcycle manufacturers use a tool to help accurately set the camber on their handcycle. It is worth contacting the manufacturer to see whether it is possible to obtain such a tool. It is much easier to set camber accurately using a tool than with a tape measure.
Is the theoretical center of the area of tire in contact with flat ground.
The distance from the line between the rear contact patches to the front contact patch of the handcycle.
Is the line about which the front steering wheel of the handcycle pivots.
This is the distance from the contact patch to the center point at which the steering axis intersects the ground. This can also be thought of as the amount of caster on the front steering wheel. This is a critical distance in determining steering characteristics. The more trail the greater the self centering forces on the front wheel while the handcycle is in motion.
One of the effects of handcycles with a lot of trail, is that the wheel does not self center at low speed. This is also known as static instability or wheel flop. To counteract wheel flop most handcycles are fitted with a centering spring or a steering spring and damper.
If trail were to go negative then you would have negative caster. The dynamic forces would cause the handcycle to turn sharper as it corners. This is a dynamically unstable condition which can be very dangerous.
One of the effects of negative trail is that at low speeds and at rest the handcycle steering will self center. This might seem like a benefit, but at high speed it is an unstable and unsafe system.
Is the external tube that houses the headset bearings. The head tube is concentric with the steering axis. Most handcycles use 1-1/8 inch threadless bicycle headsets, however some Top End and Freedom Ryder models use custom proprietary headsets. For a standard 1-1/8” threadless headset the bearing cups of the headset press into the head tube. This press fit measurement is 34mm exactly.
Is the bearing and spindle assembly about which the handcranks and crankset rotates. The bottom bracket shell is the part of the frame into which the bottom bracket screws. Some handcycles use custom machined bearing seats instead of a standard bottom bracket. The tendency, however, is for more and more handcycles to use standard bottom brackets of which there are several types:
Cartridge bottom bracket:
This is probably the most common type of bottom bracket available. It is screwed into the frame with a spline tool and rotates about sealed cartridge bearings.
Cup and cone bottom bracket:
This system uses a conventional cup and cone bearing system. The cups screw into the bottom bracket shell using the same threading system as a cartridge bottom bracket. The play has to be adjusted out of the bearings using the left cup, and then set with a lock nut.
Ashtabula Bottom bracket:
Rarely seen in handcycles this is the old American one piece crank bottom bracket system. This mostly seen in low end department store bikes, older American made bikes, and some BMX. It is also in common use throughout Latin America.
Threading and Sizing
Standard Threading Left side thread direction Right side thread direction Shell width British/ISO 1.375” x 24 tpi Right Left Standard 68mmOversized 72mm
Bottom bracket interface:
This is the method by which the bottom bracket attaches to the crankarms.
Square tapered shaft
ISIS: International Spline Interface System
Steering Axis Offset:
The perpendicular distance from the steering axis to the bottom bracket axis.
This is the circle through which the handcranks rotate. It is determined by the length of the crankams. This is one measurement that varies greatly within the handcycle industry. Handcycles that use custom crankarms can vary anywhere from 110mm to 195mm. Studies have shown that average power output varies very little with crankarm length. (reference).
Intrepid Handcycles use standard bicycle cranksets. These are typically 170mm long but are also available in a size range from 160mm to 180mm.
Distance of drop associated with the introduction of camber. One of the side effects of camber is that as well as increasing the width of the wheelbase it also drops the rear of the frame. Unless this is accounted for in the design phase it will affect the trail and the steering characteristics of the handcycle.