Bike Friendly Hostels
This list is based on my own experience, hence no hotel recommendations.
There are plenty of hotels, and Warmshowers in Bangkok also if needed. It’s best to book on booking.com, or in person for the best rate.
Once Again Hostel & Luk Hostel – Separate hostels in different areas but owned by the same company. Both offer free egg sandwiches 24/7 – simply incredible. I think Once Again hostel is the nicer of the two and is in a more manageable location with garage-based bicycle parking adjacent to the reception, whereas Luk is right bang in the middle of China Town although does have large in-lobby parking for bicycles.
Here Hostel – Definitely the most social hostel on this list, even more so than Mad Monkey IMO. Events every night, a pool, bar, inside slide, and great food on-site. Not the best rooms and no AC during the day (11-7PM), but there is a safe place (by the pool) to keep bicycles.
Flapping Duck – Although I haven’t stayed here personally, it is one of the most commonly-cited bike-packer gaffs. Flapping Duck, offers very cheap private rooms and is also close to the popular party scene of Khao San Road or its adjacent (better) Thanon Ramm Buttri street.
Although I hear most Flapping Duck guests are flower smokers, you can also make friends at the two nearby hostels which I also stayed at and highly recommended: Jam Hostel, and Mad Monkey.
Best Bike Shop (Repairs, and Boxes)
Greenhorn Bicycle Project – A specialist bike touring shop owned and managed by Pun. The workshop is small so this means a smaller chance of getting a box, although I recommend contacting Pun directly on WhatsApp to find out if she has any boxes and if she can fit you in for servicing/boxing. +66 (0) 94 646 1795
ProBike – Good selection of bicycle parts and accessories, and very competent workshop staff. This is a large bike shop with many bikes therefore its more likely you’'ll find a bike box. It is best to contact ProBike in advance and request that they reserve a box for you. There is a great breakfast cafe around the corner called The Lazy Brunch while you wait for your bike to be fixed or boxed.
BicycleBOYS – Great workshop skill/ability, downstairs cafe, and amazing selection of specialist accessories from Knog and Salsa, however, parts are quite pricy and more suited towards fixie and single speed bikes. Space is also an issue here so it is best to call-in in-advance to check for boxes.
Anything I missed, let me know in the comments!