We've worked with two large groups in the last week- one was 20 university students and the other was 38 highschool students, both for an hour and a half.
One activity that works well that i'd like to share:
Everyone gets in a big circle with a wheel. The facilitator then shows how to spin the wheel to check for trueness... and then asks everyone to pass the wheel to the left.
Then explain, say, a well-adjusted cone, spin the wheel, feel it, look at it, pass the wheel to the left.
Give it a spin... lean into it so it really spins... check to see if all the spokes are there... any broken? what's the nut at the end of the spoke called? Yes. Pass to the left.
Look at the axle. Is it hollow or solid? Why? Pass to the left.
Is the axle bent? How do you know if a replacement axle is straight? Hint: anyone play pool? Yes! Give it a spin. Pass to left.
Is the wheel your holding Aluminum or Steel? How do you know? What are the differences?
I think you get point fellow think tankers.
Here are other wheel issues, as you pass the wheel around:
reflectors, front or back?, rim strip, sizes, spoke tension, axle threads, weight transfer in spokes...
I always go around the circle until everyone has the wheel they started with. (a teaching point is not needed for every 'pass to the left')
And then a fun puzzle/game:
'Everyone hold onto the wheel next to you, so we have a complete circle. Now, how can we- without letting go of the wheels, and keeping a complete circle- move around so that everyone is facing outward instead of inward?'
Once they actually do it, I have them reverse to the original position, and then as a closer, 'on 3, everyone raise your wheel in the air and yell 'wheel power!''.
If the group is under, say, 7 years old, then tires work well for this activity and puzzle...