Originally Posted by
chasm54
No, not really. The issue for training is not how fast the bike moves, but how much power you generate. You can train just as hard on a light bike as a heavy one, you just go faster for the same power output. And your maximum power, functional threshold etc. don't change because you get on a different bike. Or to put it another way, if you train at 400watts on a light bike you are working just as hard as if you train at 400 watts on a heavy one.
There is certainly a difference in feel. If you ride a heavy bike for a while, you feel as if you're flying when you go back to the light one. But that's just in your head, it doesn't mean that training on the heavier bike has given you any physical adaptations that you wouldn't have got otherwise.
There is definately a degree of resistance that adds into this though I'm not wanting to train on my 32lb mountain bike to get what's needed. To rule out
any benefit of putting a heavy bike into one day per week would be an inadequate assessment. How it applies to the lighter road bike usage is dependant on the user as is the significance of such training.
My serious bike is the Trek in my sig line, the fun bike is the Moto. After riding a century last month I laid off the Trek for a week and just did more casual, shorter distance rides (but did generate some speed). When I grabbed the Trek it was bliss.
I'd train with what I'd be riding competively or what you are training for. Another bike is fun but it really isnt serious training.