Real bike differences

I see a lot of analysis about the Zwift virtual bikes, and what is more aero, etc., but how about the real bike on the trainer? I’m fairly new to Zwift, though I am not new to competitive cycling by about 4 decades. I’ve used two different frames on my brand-new Kickr, an older aluminum frame well known in its day for being the ultimate criterium bike, and a newer full carbon frame, which is my current backup road bike. I started with the aluminum, switched to the carbon while I did some maintenance on the aluminum, then put the aluminum back. The bikes are very similar in terms of components, and are set up so that I really can’t tell the difference in fit.

It is very clear to me that the aluminum frame give me about 150-175 more watts at the top end. I simply cannot reach the same levels with the carbon frame. I’ve been at this a long time, so I am quite confident that despite variables like how I’m feeling on a particular day, the power transmission is far more efficient with the aluminum frame. Given this, I’m surprised that this topic does not appear more, given the huge interest in power in general and the uber-analysis of the various frames and wheels available in the game.

I’m interested if others have had the same experience. Thanks.

This is really strange. The way I see how this could happen is if the carbon frame would be fatigued and wouldn’t be able to transfer the power well.

Do you notice any bends on the carbon frame?

makes sense to me, carbon frames should have more flex than a more stiff aluminum frame so power will transfer better on aluminum when fixed to a trainer.

I was under the impression that carbon bikes are stiffer… Although it depends greatly on the quality of both carbon and aluminium that is used for each frame.

The difference still seems unreal. Perhaps you should check the carbon bike for cracks?

You should compare which gear combo you use at that point where you see 150-175 more watts “at the top end”, which trainer you use, and how you calibrate it. There are no frame differences that can explain that sort of difference. But there are many trainers capable of generating large differences in measured power vs wheel speed.

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Do you have the same fit on each bike? Sounds like an impossible amount of difference but maybe if you are in a great position on one bike and a terrible position on your other bike that also has a seized up BB then maybe it’s reasonable

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I’m currently using a hardtail mountain bike on my neo trainer and I have just bought a road bike and I’m waiting on a thru axle adapter which should come this week to try it out on Zwift.

I’m not expecting any difference in power in most cycling, maybe a few watts from a more efficient drivetrain and a stiffer frame, and maybe some more when out of the saddle on climbs since I do bounce the front forks a bit now.

I am hoping (not expecting though) for a noticeable gain on the short flat sprints since on the mountain bike I would like a higher gear which I just don’t have on the mountain bike.

I’d suggest he get a tape out and confirm

An inch difference here or there could be seen as similar to an inexperienced cyclist

The power discrepancy is so big there has to be something weird going on, maybe extremely worn components?