Training tips coming soon!
Tips from an expert who has done this ride multiple times...
Any bike that will take a tire larger than 32mm will work. The GAP portion (Pittsburgh to Cumberland) is very smooth, crushed stone & almost feels like pavement. The C&O side is much rougher - sometimes extremely rutted, muddy etc. This side is where fatter tires will be welcome - for both traction and comfort. Choices will come down to personal preference and budget.
will work great; front (and rear) suspension will be welcome on the C&O. Tires sizes are no problem but I'd recommend not going to big or anything with too many large lugs as you will be working much harder.
Cons to Mountain Bikes:
Many will not have rack mounts, so depending on how much gear you like to have on your person, you will need to look at other options. Flat MTB handlebars give only one hand position. This can get extremely uncomfortable on 50+ mile days of bumpy trail. If you are going to ride a bike with flat bars I strongly suggest getting bar ends to give at least one extra hand position. Most MTBs will not have fender mounts and the plastic fenders made for MTBs don't offer much mud protection. Fenders are very welcome on the C&O when it is muddy & wet.
Basically the same pros and cons as MTBs but they usually have rack & fender mounts and a more upright position which some will find more comfortable. Tire choices are great, most any shop and all online retailers will have good choices.
Great choice, long wheelbase, very stable and comfortable; more upright position than a "road" racing bike; tons of braze-on mounts for rack, fenders, water bottles etc. Road style handlebars which IMO are more comfortable on longer rides as they allow you to switch hand position easily and in many different positions.
Cons to Touring Bikes:
"True" touring bikes will have bar-end shifters and I'm not a fan. You can't shift as easily as with shifters that are integrated into the brake levers.
Cyclocross or Cross bikes:
A great choice to ride on the C&O but if you are looking at them be careful as most will not have fender/rack mounts and typically have a more aggressive geometry than a touring bike (more like a road bike). The head tube will be shorter and will not lend itself to a more upright position - definitely personal preference and what you are in shape to ride. Will have road handlebars and typically integrated shifter/brake levers.
1. Tires & tubes: Tons of good choices out there. I'd recommend nothing smaller than a 700 x 32 and suggest going 700 x 35 or 38. With larger tires you can run lower pressure for comfort and speed. With mountain bikes you won't want a heavily lugged tread as it will make you work harder. A semi-slick tire or one with a center tread and lugs on the corners are great. I mention tubes only because each rider will want to carry at least 2 spares and hopefully not use them.
2. Bags/panniers: Since the riders will have support carrying their gear panniers are probably not needed. You will want a handlebar bag and/or trunk bag to carry food, jacket, sunscreen, extra clothes etc. With handlebar bags I suggest a rigid mount. Many of the rear racks or post racks out there have compatible trunk bags that securely clip on. There are a ton of good choices out there. A waterproof bag is best but not 100% necessary as you could plastic bag anything that would suffer from a downpour. My preference are Ortlieb bags but they are expensive. Worth the investment if they will be used again but probably not for one trip. I've not purchased from this site but they seem to have a good selection: http://www.bikebagshop.com/. REI usually has a good selection, the LBS's are hit or miss.
3. Bike lock: Personal choice depending on how you feel about leaving bikes outside during lunch. (For 2013, bikes were left unlocked with no issue) Bikes can be secured in the support truck or inside the lodging overnight.
4. Seats/shoes/pedals: Completely personal preference but I do not suggest trying to break in a brand-new Brooks leather saddle on the trip - did that & it was painful. If you are using clipless pedals I'd stick with a mountain bike-style (like SPDs) and not a road pedal (SPD-sl, Look, Keo, Speedplay etc). The road pedal cleats and pedals will suck up the mud.
5. Clothes: Also completely personal preference but I do recommend cycling gear for comfort. Also wool socks (like DeFeet) are a great choice if it gets wet. A good rain jacket is a must, I've carried rain pants and never used them. If the weather is cooler I'm a fan of arm/knee warmers because they are more flexible than worrying about long sleeves/pants. Good gloves are a must IMO. You shouldn't need to pack a fresh set of cycling clothes for each day, cycling shorts/shirts can be washed in the hotel shower and then rung out and "squeeged" dry in a towel before sitting overnight to dry. Of course with the luxury of the support vehicle you could just pack clean clothes for each day, space permiting.
6. Water: Carry plenty - there will be long stretches without water or just with very poor tasting pump water. I tend to sweat and drink a ton so I've always carried 4 bottles. I also can't stomach the taste of the pump water. To carry extra bottles I added water bottle cages to my front fork rack mounts (using the side braze-on, zip ties and a bungee cord over the bottle because they will vibrate out of most mounts when on the fork). I've also carried electrolyte drink tabs or powder which help mask the nasty pump water if you are stuck drinking it.
7. Food/Nutrition: I definitely recommend carrying plenty of food. Obviously personal preference, everyone should try out different foods/gels/bars while training to make sure that the food agrees with their stomachs.
8. Tools: For on the bike make sure that there at least a couple of decent pumps that will inflate both Schrader and Presta valves, a good multi-tool with a chain tool, plenty of chain lube and a few patch kits. You will have too many diverse bikes to worry about chains, spokes etc. and with the luxury of a support vehicle really shouldn't have to worry about finding parts if needed.
9. Miscellaneous: Chamois creme, sunscreen, sunglasses, helmet (w/ visor), insect repellant. At least one rider should carry a basic first aid kit. Flashlights/headlights may also be welcome in case you fall behind schedule (and for the unlighted Paw Paw Tunnell). Handlebar bell or horn optional but sometimes nice to have.
Good resources, recommend bookmarking a couple on your smartphone so that you have a mileage chart handy while riding:
Official GAP website
C&O Canal / Great Allegheny Passage Guide
National Park Services - Will show trail alerts for the C&O
Crazy Guy on a Bike - TONS of bike touring information