So I’m an oft-too-injured runner turned triathlete. I made great improvements this season on the bike to the point that I was a back-of-the-front-of-the-pack rider. This fall, I went back to mostly running and trained for the Chicago Marathon. I ran a 2:59:59 - setting a PR - and reached a new level of fitness. However, I’ve hardly gotten on the bike in the past 2.5 months, and I’m worried that I’ve lost all my gains. Please tell me that I’m crazy. My triathlon training made me a stronger athlete, and I was able to increase my running volume to new levels in the lead up to Chicago. While I no doubt lost some bike-specific fitness, my hope is that my increased running fitness would have mitigated the losses and I’ll regain my bike speed in a few weeks. I’m still in marathon recovery mode (another week or so) so I haven’t been able to test myself on the bike; I’ve just gone on a couple easy spins. How long should it take for me to regain my bike-speciific fitness?
I’m no expert, but it shouldn’t take that long to regain bike fitness. It’s the least of the three disciplines that’s technique based. I won’t say that you can go out and do a 00:59:00 40k TT tomorrow, but you will probably be surprised at how much you’ve retained especially with being off only for 3 months.
Great job on the PR at Chicago. No need to worry, running translates more directly to cycling than cycling to running. Be CONFIDENT with what you just accomplished and just start riding. I think after a week or two you will be surprised.
You are not crazy, you are totally hosed. You will never be able to ride fast again. Send your bike to me immediately, you no longer have any need or use for it 
You’ll get much of your bike fitness back in the first month or 2 of consistent riding. Getting the last bit back takes longer, and of course moving beyond your previous level takes a lotta time and hard work.
What ML said. Case in point: I ran a marathon 10/1/06, having dropped all biking the last 2 1/2 months. After the post-mary break, I’ve been doing interval workouts for a couple of weeks before testing my FT Tuesday and I’m 7-10% below where I was in the height of the summer. I expect to get the rest back over the next month or so.
Dan