Originally Posted by
katsup
I'd say it varies more by brand / model more than category. Some examples:
Sold as Touring Bikes
2010 Trek 520 = 45cm
1990 Trek 520 = 42.5cm
Long Haul Trucker = 46cm
Sold as Allroad / Gravel
Salsa Vaya = 45cm
Salsa Journeyman = 44cm
Jamis Renegade = 43cm (58cm size)
Giant Anyroad = 43cm
Trek Checkpoint = 43mm
It does seem like the bikes sold as allroad / gravel seem to have chainstay lengths in the middle of road and touring bikes. Basically where touring bikes were in the 90s. However, I wouldn't consider 1-2cm extra "monstrously long".
The example of the 1990 520 is why I said "touring bikes in the modern sense." 1990 is trending toward modern, but it wasn't long after the age when many "touring bikes" were basically road racing bikes with clinchers and some lower gears. My '79 Fuji America is supposedly a touring bike, but I enjoy it as much on spirited rides as I do my Emonda, and it severely loses its composure with a big rear load.
I think the Vaya's marketing straddles both categories. Salsa calls it both "gravel" and "light touring."
I'd agree that the extra couple centimeters isn't that huge of a deal from a functional perspective, but chainstay lengths are usually close to as short as the manufacturer can get away with. And mountain bikes try harder in this regard than road bikes do; when your tire is 30mm taller and you've got suspension, having a chainstay that's only 20mm longer is tough.
Road bikes are typically around 400-420mm, gravel and mountain bikes typically around 420-440mm. In that sense, the extra few centimeters on heavy road tourers is off the charts.