BB visibly flexing while on the trainer?

Quoted post said:

Originally posted by Aztec
Yesterday I did some intervals on my Cervelo Soloist, on a Cycleops II trainer. When I was on the 38-15 or so, and maybe 100 rpm, I looked down and could see that the chainrings looked bent. Of course, they weren't, because as I eased up, they appeared straight again.

Could this be the frame at the BB flexing? The Soloist is supposedly REAL stiff in the BB, though. Plus, I wasn't exactly 53-13ing it. Everything appears tight and with no slack.

If it matters, I run Campy Veloce 10speed.

There's no way to verify that you saw BB flexing, but lateral torquing while on a rear-wheel trainer makes everyone a little edgy. When it's locked in, there's really not much else the frame can do with the pressures but twist at the BB a bit.

It's probably nothing to be concerned about, but I suppose it would be discouraging to see a nice frame like a Soloist bend and turn... I'm sure it's stiff as hell on the road, and not to worry.

Difficult to judge specially since you're on the trainer briskly spinning at 100 rpm and maybe your head/torso wobbling a little bit with the effort, so on and so forth. Everything would seem flexing. A soloist is a relatively stiff frame. Better to ask someone else to do the observing while you're on the trainer. Or maybe take a video.

I'm sure what you see is the frame flexing about the two fixed points....the rear axle and the front wheel.

Quoted post said:

Originally posted by Aztec
Yesterday I did some intervals on my Cervelo Soloist, on a Cycleops II trainer. When I was on the 38-15 or so, and maybe 100 rpm, I looked down and could see that the chainrings looked bent. Of course, they weren't, because as I eased up, they appeared straight again.

Could this be the frame at the BB flexing? The Soloist is supposedly REAL stiff in the BB, though. Plus, I wasn't exactly 53-13ing it. Everything appears tight and with no slack.

If it matters, I run Campy Veloce 10speed.

Chain rings do flex a little when the chain line isn't perfectly straight. The Bottom bracket will also move, especially when the rear axle is clamped into a "fixed" position.
"for each action, there is an equal an oposite reaction"

The flex, when viewed from above, occurs when my right foot gets to about the point of max leverage (3 o'clock position viewed from the side of the crank). The flex goes inward (i.e., to the left from above). If I pedal easily, no flex. If I hammer with the left foot, and ease off a bit with the left, it flexes less.

I don't think this is my head moving around because I have flawless cadence. OK, more seriously, it's because I can sight down the top tube to the floor and see that it ain't me that's movin'.

Another point... in the big fella up front, and say a 14 or so on the cassetts, if I stand and sprint on the road, I can rub the FD a bit. I cannot do this on my C40. Of course, it could well be that the clearance is tighter on the Cervelo due to adjustment.

Quoted post said:

Originally posted by Aztec
The flex, when viewed from above, occurs when my right foot gets to about the point of max leverage (3 o'clock position viewed from the side of the crank). The flex goes inward (i.e., to the left from above). If I pedal easily, no flex. If I hammer with the left foot, and ease off a bit with the left, it flexes less.

I don't think this is my head moving around because I have flawless cadence. OK, more seriously, it's because I can sight down the top tube to the floor and see that it ain't me that's movin'.

Another point... in the big fella up front, and say a 14 or so on the cassetts, if I stand and sprint on the road, I can rub the FD a bit. I cannot do this on my C40. Of course, it could well be that the clearance is tighter on the Cervelo due to adjustment.

Yes, I think that clearance adjustment difference has something to do with is, and it is possible the your chainrings are not exactly the same... like maybe a little less precision or shape such that when they are put under side load they are closer to start with and move in response to the load. Not all cranks and chain rings have the same lateral stiffness.
What are the chain stay lengths of the 2 frames?
The chain angles on the Cervelo may be more pronounced, and/or the chain on the Cervelo might have less side flex.

Good points, and for prospective buyers, may be a good test in checking for bottom bracket flex. Pick a high gear combo with the straightest chainline (to rule out what daveornee describes as chainring flex); and instead of centering, position/trim FD cage so it's not quite touching the chain, and then start hammering away (on the road).

Even the most rigid frames will have lateral movement when used on a trainer. What you are experiencing is very common. Simulate the same criteria on the road and you will see no abnormal chainring flex. It would benefit your Cervelo to have limited use on the trainer.