Aluminum

[sanddrag]

Not to barge in here, but I can help get a few of the above answered. Yes, they did use number 25 chain. Sprocket count was somewhere around 20 teeth. They use snap rings to hold the wheels on, and I believe the sprockets too. My team uses screws and washers which I enjoy. I imagine they use hex instead of key, because it is easier to install and remove, there is less parts, and no little parts (the key) to lose. Not to mention it is stronger.

Also, 7075 aluminum is much stronger than 6061 with only a minimal increase in density (~.003 lb/in^3 more). 7075 has a tensile yield stress of about 73ksi whereas 6061 has a tensile yield stress of about 40ksi.