Different bikes on same trainer - much different results

I setup my old classic (1973 Schwinn Varsity) road bike on my Tacx Vortex trainer so I could spin when the weather’s bad.  I’m used to averaging 3.2 w/kg during the winter with my Felt Z5 and I struggled to get half that power with the Schwinn setup on the trainer.  I calibrated the bike on the trainer and not sure what else could effect it that much.  I doubt the Schwinn is 1/2 as efficient as the Felt especially on the trainer where the weight of the bike is not a factor (granted the Schwinn is a tank).  I’m not using a trainer tire on the Schwinn and did smell a slight burning rubber smell but don’t think that was really an issue.  I’ll also note I had to modify things on the rear axle nuts/bolts to get the rear wheel to align with the trainer.

So in short, have other people had similar issues where different bikes on the same trainer yield significantly different performance readings (in particular power)??




I would expect some losses in the older bike, but not 50%. 


I also have a older 1980’s bike on my trainer, and found that I have less power due to differences in gearing. I upgraded my crank, derailleurs and rear wheel.  Now i have better comparison between bikes. 


Also make sure you don’t have slip between the trainer and wheel. I usually tighten the knob (3-4 quarter turns) then I rotate the wheel by hand forward and reverse to see if there is any slip. 


i would think a lo of the power difference will be with your tires on the vortex being a wheel on trainer. 

simply adjusting pressure to match wont exactly fix it either, as tires can be wildly different. 

can you change your back wheel and try that between them and see if its closer?

Alan, I wonder it perhaps the way the bike attaches to the trainer could be causing some binding and friction.  Try mounting the bike on the trainer but don’t engage the trainer “drum” against the tire.  Can you easily spin the rear wheel?