...For anyone leaving from Glasgow
There’s a train from Glasgow Central at 08:34, arriving at Ardrossan at 09:20 in time for the 09:45 ferry. Check-in is at least 10 minutes before departure, it looks like the cost is £11.05 return, and the bike goes for free. Car parking is not expensive (less than £5 for the day?)
You can take the precaution of leaving a bag of dry clothes etc. in the "Left Luggage" at Brodick Ferry terminal, at a cost of £1 per bag. Walking around and climbing stairs on the ship in cycling-shoes can be tricky, and uncomfortable in wet clothes (said he, optimistically).
Return ferry time is: Brodick leave 16.40 (17.35 Ardrossan arrive) Train 18.00 for Glasgow 18.44
"Just in case" later ferry leaves
Brodick 19.20 (20.15 Ardrossan arrive) Train 20.31 for Glasgow 21.14 but hopefully we wont need this one...