Okay, I have seen the chart on Sheldon Brown's web site. I have
followed the link on his site back to his source for the chart:
tandem-fahren.deindex.htmlOpen ↗
I am curious about the source of the data used to generate these charts. I suspect that the data was
generated from 4-wheeled vehicles where the tires are maintained normal to the road surface and
where side loads are significant.
I am revisiting this topic because I have just order a new bike. It is more of a free-ride style
frame with 5 inches (125 mm) travel front and rear. Depending on the build, it either comes with
rims that are classified as light-weight cross country or rims in the downhill class.
The width of the XC rims (the inside dimension, between the "hooks" on the rim, is about 16 mm.
According to the chart, proper tires for this rim should range in width from about 25 to 35 mm (1 to
1.4 inches); however, the bike comes with tires that are 2.25 inches wide!
As Sheldon states...
"In the interest of weight saving, most current mountain bikes have excessively narrow rims.
Unfortunately, current mountain-bike fashion pushes the edge of this. Such narrow rims work very
poorly with wide tires, unless the tires are overinflated... but that defeats the purpose of wide
tires, and puts undue stress on the rim sidewalls."
The other factory option is a downhill rim which has a width of about 33 mm. While this rim width
is off Sheldon's chart, extrapolation of the data would indicate that the rim is ideal for tires
from 2.4 to
3.1 inches wide. Seems reasonable to me.
Surely, bicycle tire manufacturers must have a rim width (or range) in mind when they design a tire.
But neither tire manufactures or rim manufactures make this data readily available.
Maybe the better wheelbuilders have the data.
For now, I will get the wheelset with the narrow rims and keep them for my commuter bike (high
pressure tires). I have a free-ride wheelset with 31mm rims that should be great for the 2.25 inch
tires, even at low pressure.