Originally Posted by
raqball
You should be able to fit anything from a 25c up to your current 42c tire with no issues on a 21mm internal width wheel.
If you are not convinced then call Trek or a local LBS and ask them
It was never about being convinced, it was about arming myself with as much information as possible.
And after a convo at my LBS, I had them replace both tires with new 35c width tires.
I appreciate your help, friend!