"the bike

general

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"Whether you'll be comfortable touring on a ""racing"" frame with a seatpost rack depends on several factors: how long is the tour; how much stuff will you need to carry; how many miles a day will you do; and last, but certainly not least, what is the condition of the road surface.

A touring specific frame has a more relaxed geometry that's more comfortable for riding lots of miles day after day. It will also accommodate wider tires which adds to comfort, especially if the road is rough or the surface is chip seal. If you're only touring for 4 or 5 days, these may not be serious issues for you. If you're going for a couple of weeks, they need to be considered.

If you plan to carry more than about 10 pounds of gear (including the weight of the rack & panniers) and there will be any climbing, you may want lower gears than are typically found on a road bike. Touring bikes generally have lower gears.

A seatpost rack works fine if you aren't carrying much stuff. They're generally limited to 20-25 pounds. The weight sits higher on a seatpost rack than on a fully mounted rack, which can be make the bike feel less stable, especially when you stand. The other issue is the shorter chainstays on a road bike - with panniers on a seatpost rack, you may encounter heel interference at the back of the pedal stroke. If the panniers are small enough and/or your cranks aren't too long, this may not be a problem."

There was a thread last week on accomodating a road bike for touring that you should check out:

http://www.nycc.org/mb/thread.aspx?b=1&t=8606&tp=1#msg38870.