How to get your bike back to the start
Being a linear route, if you dont want to cycle all the way back to the start, there are a few options for you.
You could try Ticket to Ride who are a "cycle taxi" firm who will transport your bike on the mainland. You can travel to and from the Outer Hebrides iwith their mainland transfer service for cyclists between Inverness, Ullapool and Oban.
The most simple option is to leave your vehicle in Oban and take the ferry to Castlebay. and use the bike transfer services who will take you (and your bike) back to Barra to catch the Oban ferry. Bespoke Bicycle Hebrides provides this service. You could also take your bike on the train to Oban, but you must make a reservation as bike spaces are limited. See www.scotrail.co.uk for details
Other options include taking the ferry from Stornoway to Ullapool and take the Citylink bus to Inverness. Citylink have introduced a new booking service which enables travellers to book their bike on the bus at the same time they make their seat reservation. A free bike space can be reserved as an "Additional Hold Item" when buying a ticket online and you get a "bike sock" to protect your wheels and chain whilst in the bus hold. This also also available on buses from Uig to Glasgow.
There are limited buses in Lewis and Haris that have space for a couple of bikes in their hold, if there is space. See bus timetables. Generally, buses in Uist and Barra will not take bikes