Over the years, I have frequently come across the ERTO tire width chart on Sheldon Brown's website with which most of you are undoubtedly familiar
Tire Sizing Systems
And then, just today I was looking at the specs of the Hed Jet 6 Plus
https://www.hedcycling.com/jet-6-plus/
...which lists the internal rim width as being 21 mm. So according to that chart, that would mean that the
narrowest tire I should use on a Jet 6+ would be 35 mm. But, the Hed-recommended tire size is 23 mm
That has got to be wrong (the chart, I mean, not Hed's recommendation).
Now I realize this chart is merely for
recommended widths. The note right under it says that it errs on the side of caution. but these two width numbers are so far apart that I feel certain I must be missing something obvious.
Could someone with a clearer understanding (or better eyes) tell me what I am missing?