i can't comment on the bike tours in barcelona.

but i can say that i took a fat bike tour in paris and loved it.
dd and her friends (19 - 20 year olds) took the fat bike tour in barcelona and loved it.
i plan to take it in barcelona when i am there in april.

I did the Flat Tire Bike tour in Barcelona six years ago and really enjoyed it. If you're on your own, it's very sociable and a good way to meet and chat to other tourists. It's not very strenuous, because all ages take part, but it's fun and a good way of getting your bearings around the city.

For Architecture just take any old Gaudi tour (public transport is very affective). If there is another bike tour I'd take it

If the bike tour is something your friends would also like to see, then perhaps you can all go together. If you are really into history and art more than your friends you would probably be doing yourself a favor by maxxing out some of those visits before they came.

You can also just rent a city bike and leave it off in special stands here and there when going around this first day if getting on a bike sounds like the way you want to go.

Here's another company which may be abel to accommodate you.

http://www.bicicletabarcelona.com/?cl=1&lang=en

careful about where you ride. Not sure in Barcelona, but now in valencia they are strictly fining anyone outside a bike lane.. on the sidewalks , up to 400E and without a helmet and ringing bell on bike.
Unbelievable ( the sidewalk and bell part)

Have a great time.

Spanish bike rules are pretty tough (no idea why), you have to wear helmets, you have to have a bell and you are right riding on the pavement/sidewalk is illegal (actually that is true in a fair number of European countries). The helmet rule is slightly odd as you are allowed to take it off if 1) riding up hill and 2) out side of a city and 3) It is very hot (not definition provided. So do hire a bike with a helmet and wear it.

Helmet rule is also in place in Oz where the massive reduction in bike riding hid a zero improvement in bike accidents

Thanks for the advice guys. I mean I didn't check this site again until just now after my trip because at the time of my departure there were no responses. But honestly, I appreciate it!

The bike tour was great and I would wholeheartedly recommend Fat Bike Tours, especially the tour guide Buddha. I saw he was recommended in a Barcelona thread so I recognized him at the meet up spot. It was a great way to experience most pockets of the city and figure out where you wanted to spend more time. Also our guide was funny, insightful, knowledgeable and was able to provide tips and give advice. Example he told us how much time to expect to spend at Parc Guell and how long it would take there. Also, since I'm into the nightlife he was able to recommend good places to go and where to avoid tourist ripoffs.

The tour was also great for meeting people. Everyone was pretty friendly and I met 3 girls and 1 guy that we kind of formed a group after the tour and just experienced the city together. Coincidentally we all were staying in the same hostel. This was great because most of what my friends did was lazily stroll about Barcelona.

I might actually do a trip report when I have some more spare time! All in all 2.5 days in Barcelona was AMAZING but I wish I had another day (As I wish with most trips I've taken so far in my very short traveling career)

Thanks again!

So glad you came back tell us how it went! Sounds like it was the prefect solution. You'll just have to come back again!