I noticed that my road bike flexes a lot when I am doing interval work on the computrainer. It moves noticeably from side to side at the junction of the crank and the seatstays and makes a fairly loud squeaking noise. I was actually worried a couple of times that the darn thing was going to snap. It is an entry level carbon frame. Will this translate into less power when I am outside riding or is it because I am stationary and suspended? Gracias.
This is a long debated subject on both the saftey of frames in trainers and the stiffness=better power transfer.
IMHO the trainer is a very artificial situation that subjects your frame to unnatural forces that do not translate to the road.
IMHO BB stiffness (what people are usually talking about when they talk about frame stiffnes) does not measurably affect power transfer from the leg to the rear hub.
I’m sure someone will have a different (perhaps more educated) opinion than me though.
I agree that the trainer puts un-natural forces on the rear end of a bicycle frame. I would not worry about the frame appearing to flex while on the trainer (some of the movement might actually be the trainer flexing).
Without knowing exactly what frame you have, or any FEA type data (or even what to do with said data!), I would say that most frames are stiff enough for most riders. If you are a field sprinter then you are putting out enough wattage to flex frames to an extreme (1500-2000 watts). When we are racing triathlon we are putting out what, 400 watts at the pointy end of the race? Many times when a frame feels flexy it is actually the cranks or wheels or even the stem/bars that are being felt.
I would be less concerned with any sort of performance loss than I would with the fact that I don’t really like it if a frame (or wheels/cranks/etc.) feel flexy.
Just about any decent frame is going to be stiff enough for triathlons. It is not like we are track sprinters. I suspect that the “flexing” you see is sort of an illusion. Your bottom bracket is indeed moving from side to side but your tires are doing the flexing.