You should do it. In North Africa, English doesn't get you very far, as people already study Modern Standard Arabic (quite different from street Arabic) and French as foreign languages. If they studied English, it was probably their third foreign language and hence didn't get much time.
German and French sound very distinct, so you should have little trouble keeping them apart. As far as time goes, see if you can use some of that bike-riding time for learning or review, for example with podcasts. I developed a lot of (but not all) podcasts for GermanPod101, so I can recommend e. g. the progression from Absolute Beginner Series 1, then graduating to Upper Beginner Series 1 and from there to Intermediate Season 4. They are made for easy transition. (Note that I stopped working for GermanPod101 two years ago and am not getting royalties or any payment for recommending them; I just like seeing my work get used)
For French, try Michel Thomas as a quick introduction that teaches you the most important stuff right away. I also like Teach Yourself French or Colloquial French.
Since you already have the basics of German and German is spelled regularly, I'd probably spend biking time listening to 75% German and 25% French, and sit-down study time 75% French and 25% German.
Good luck and have fun!
Duolingo is a great beginning start, especially when you're on-the-go. Also, language pod 101 is a site I found on one of those "top sites to use" things. I've yet to give it a try, but maybe it'll help you out. Plus the two links primus454 commented are great as well.
As for books, I currently just have a basic German dictionary. Also, changing the language to German on websites and video games, your electronics, etc. can really help you grasp the language as well (once you've got the basics down, of course).
http://www.germanpod101.com/ Start learning for free? I use some of the podcasts from their other site to get a bit of a leg up in french and japanese, for free! You can pay for a subscription, but I found it wasn't necessary.
I'm currently trying to use the materials found at GermanPod101.com. So far I've found them quite useful.
Another tip I've found useful is to use some sort of Spaced Repetition or flash card software to drill vocabulary. Anki is a particularly good one.
Viel Glück!