Help TrainerRoad users! You’re my only hope!
I know that it is the internal width between the walls of the rim. But what does that do in regards to the tire?
I want the Reynolds ATR 46mm wheelset to use for both gravel and road. It has an internal rim width of 21mm. What effect will this have on my 28m road tires? My 40m gravel tires?
The wider the internal rim width the more “true” the tire will be to its size. Meaning 28mm tires on internal rims or 21mm will ride closer to 30 or 32s. Put 25s on those rims and they will be a true 28mm tire (maybe larger actually, you’ll get away with very low pressures and great grip and feel). You get better comfort (ability to run lower pressures as well), better grip and better overall performance.
Also depending on the rim depth and aero profile of the rim with the tire you can get significant aero advantages. Most modern deep carbon rims have a recommended tire width that will maximize road feel, comfort AND aero.
Thank you so much. This was so simple and clearly laid out! This community is just pure 
!