check out these other shops in Bangkok too
Shop My Comment Where ? Phone
Probike. Importer. Top-quality stuff, good selection. Organizing bike events. A bit expensive. North of Lumphini Park 253-3384, 254-1077
Saengthong Bicycles. Excellent service, honest, low prices. Best overall reputation. Prachakaj Rd, Nonthaburi 525-1789, 526-4664
Cannasia. Everything Cannondale. Rare items, cool owner. Near Nana junction 253-3454, 01-332-8687
Viwat Bike. Moderate prices, rare items Phahon Yothin Rd 552-8583, 972-3934
World Bike. Importer Huge selection, odd parts, bargains. Take their good service but not their advice. Ram Inthra Rd 946-4117-9, 510-1041
Sahapatt Bicycle. Moderate prices check GPS 447-0169, 879-4259
Lan Luang Bikeshop. Medium quality, lowest prices Worachak / Chinatown 221-3775, 221-8545
I pulled those details off this website http://www.kutu.com/thai/bike/bybike.htm
I visited World Bike recently. Good selection, but damn expensive.
Best of luck on your S.E. Asia tour!