Optimal Rim Width for Tire Size

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:

http://tandem-fahren.de/Technik/Reifentips/index.html

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.

HKEK wrote:
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:

http://tandem-fahren.de/Technik/Reifentips/index.html

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.

Mountain bikes aren't really "optimised" for anything in particular.
They're necessarily a compromise because they're going to be roughly
treated, but they can't get too heavy. A big air volume and the ability
to keep the rim away from rocks are the important factors here.