What's your thoughts?

While riding my Kickr Snap trainer my indoor bike got a flat tire. The next day when I went to ride I just put my nice carbon outdoor bike on instead of changing the tube in my indoor bike. Suddenly riding on zwift felt alot easier (i was putting out more power). I always calibrate the trainer after warming up each ride. I always have 2 full turns of the resistance knob. I always have the tires inflated the same before each ride. My indoor bike has super old drivetrain, probably 8k miles on it, I hadn’t cleaned it in a year (it doesn’t really get dirty inside though does it?), and a 23mm crappy old tire. My nice bike has very well maintenance drivetrain, 25mm continental grand prix 4000s ii, and deeper dish rims (more rotating mass/momentum). I’m just curious if changing bikes has led to this increase in power that I’m feeling in zwift. Workouts in ERG at 300 ftp were good and challenging, I did 2.5 group ride the other day then ftp tested afterwards at 314. Either I had let my indoor bike deteriorate, robbing me of watts or something is awry in my setup now. Just curious if anybody has seen different results switching between bikes on the trainer, and if clean drivetrain/deeper dish wheels, 2mm wider tire can cause me to gain 15 watts on ftp.

I would say your old bike has a lot of resistance/loss of watts within the drive train, just as you are thinking. 

My power is measured at the crank, so changing bikes would not make much of a difference in power to me. Yours is at the wheel so that is why you are seeing a difference in watts measured (you are losing less through the driver train).

Those tires are going to wear out very fast, so I would think about change it to a trainer tire ASAP or just change out the entire wheel.

Thanks for the reply! I don’t want to ride my nice bike on the trainer forever, I have just been intrigued by this sudden increase in power so continued to ride it for the sake of science and testing myself at different levels of exersion. I will put a new tube in my indoor bike in the coming days and see if my power goes back down, I suspect it will.

Outside, _ road tires _ generally are more efficient (less power loss) the wider they are and the more supple they are. A less efficient road tire might soak up an extra 10 watts or more of your power (before that power gets measured on the KICKR Snap) per https://www.bicyclerollingresistance.com/road-bike-reviews and others. The inner tube also makes a difference. Some are more supple than others.

Indoors on the wheel-on trainer might also be a good place to skip having thorn-resistant inner tubes and puncture resistant tire liners. 

I haven’t seen studies specifically addressing tire rolling resistance in the context of indoor trainers where the wheels are in use, but my first thought is the effect would be similar to that on the road. In fact, some of the tire rolling resistance tests are done on special rollers indoors.

Also, dirty and/or worn chains soak up some watts.

Thanks for the reply Steve. Good info.

I started on my wahoo kickr with my road bike and i didn’t change my tires (I assumed I would just replace them with the season started) So now 4 months in. I have watched my watts change from 300 to barely 62 as my tire gets smoother. So I assume a training tire will help achieve more consistency OR does the same thing happen over time with the training tire?