I've got four years experience particpating in spin classes and two
years experience maintaining the spin bikes.

From a user perspective, I have some suggestions for improvement:

1. The bikes are used by a wide range of particpants. Some are Iron
Man Hawaii qualifiers, others are cardiac rehab graduates. Some
participants are over six feet tall, others are only four-foot-six.
Some folks want an upright position, other need full aero. Pins that
fit into holes on one inch centers are horrible. You need very wide
range of adjustment and infinitely adjustable within the range.

2. It would be great to have a way that we could all use our own
pedals. The mountain bikers are happy with the SPD pedals, but the
triathletes and century riders want their Look and Time kit. The
rehabbers seem to be happy with toe clips.

3. How about some cool electronics? I want to be able to record
cadence, heart rate and watts onto my usb memory chip so I can load it
into my training log at home. Most of us bikers vanish from the spin
classes when the temperature gets over 4C and the sun rises before
0600. I would come back more often if I could get the training data.
If you're designing from scratch what's a couple of strain gages and
prox sensors.

4. One water bottle holder is not enough for the 90+ minute classes.

5. Seat angle should be user adjustable. The ladies seem like the
seats tipped up a little. The full aero guys claim fertility problems.

Maintenance issues:

1. Material selection and product design should be predicated on the
machines being used in the salt water pool. The stronger athletes
DRENCH the machines in sweat. It goes everywhe bearings, fasteners
and inside the tubing where it can't be dried.

2. The chain lines in any models can not be adjusted and the machines
clatter horribly. If your bike sounded that bad and vibrated that
much, you would throw it in the ditch.

3. The component quality supplied by the manufacturers is very low.
Bottom brackets, pedals and seats are consumed at alarming rates.

4. Brakes should be consistent from machine to machine. Many brakes
rely on a foam rubber backer that comes in a dizzying array of
thicknesses and durometers.

Have fun with your project.