The ads are a recent addition to help generate revenue to fund CC's future development.
What's probably happening is that a lot of the sites you visit are using Google's free site statistics service - Google Analytics - which tracks visitors so site owners can see all kinds of metrics about users on their sites, where they go, number per day, etc. and view trends and results of changes.
Google then gets to share in this info and can see where you've recently visited (based on a number of factors, including your browser type, device type, IP address, ISP network, etc.). It will then use this info to select from a pool of advertisers who will be bidding on ad slots that are related to what you've been looking at - the idea being that you will likely be more interested in something you've recently looked at than a random advert for some unrelated product or service. After you've spent a bit of time on CC you'll possibly find the ads are bike related when you visit other sites.