Road or Tri Bike on Trainer

I absolutely think you should put your P2C in the trainer and use it train for your race. Forget the old road bike unless you're riding in really bad weather outdoors, and then maybe considering just skipping that day.

I haven't seen any convincing data that says a trainer puts weird loads on the frame or undo stress. I've read an article or two that talk about this as if it were fact, and the occasional post, but everyone seems to repeating what they've heard rather than producing convincing hard data. If there were a source article from someone who has done a credible engineering analysis Slowtwitch-style, I'd love to read it.

So I don't think trainers are bad for bikes. That bottom bracket on your road bike is moving around on the street the same it's moving around on the trainer - you just can't see it move as easily. The trainer isn't making it do anything it wasn't doing already...

The muscle thing makes a big difference. If you recall when you first bought that tri bike, it probably wasn't as easy as your road bike to ride hard - different muscle groups. Mine took a few hundred miles before I felt strong on it. Plus you should be training in the aero position so you can ride in the aero position. And of course the principle of specificity says you should be training the same way you will be racing (well, more or less).

Not sure about A but I have a cervelo dual and ride it on the trainer all the time. Just make sure you use the steel/metal skewer instead of the light weight ones that come with most wheels.

I have been using my P2SL on the trainer and have not have the difficulties you mention.  It is what I race with so I might as well train on it, eh.  As for the skewer, it should come with the trainer when you buy it ... or at least, I did get on with my Cycle Ops 2.

The bike IS doing somethign different than it is doing outside, it is especially noticable if you stand and pedal. Remember, your trainer does not allow your bike to swing from side to side. When you push down on a pedal, instead of the entire bike rocking to one side, the frame must flex absorbing that load. I do however believe that there is a trainer that exists that allows the rear wheel to swing back and forth, mimincing more of a realistic road feel.

You are actually better off putting that carbon bike in the trainer than if it were Aluminum or steel though. One of the most significant benefits of carbon is that it doesnt have a fatigue life like Al or Steel.

So yeah... it is putting different loads on your bike, but it isnt going to matter with Carbon.

Yes, I have heard that before and it does seem reasonable standing is going to be a different thing on a trainer, causing much more significant side forces due to the rocking.

Note that even in that case, it's not really the trainer that's adding the load so much as the trainer forcing the bike to carry the side forces that it wouldn't normally have to bear.

I'd love to know what difference that really makes, though. I don't massively rock my bike side to side even when standing. I'm not wearing the polka dot jersey on the mountain, after all - the rocking I do is fairly small compared to the pros.

So the question is: are the side forces created by a "typical rider" on a trainer within the normal range the bike can handle or not? I would say "yes" but I have no data, just opinion.