On 2017-01-19 19:00, John B. wrote:
On Thu, 19 Jan 2017 14:57:42 -0800, Joerg
wrote:

On 2017-01-19 14:39, Doug Landau wrote:

On road bikes it usually happens when hitting a rock "just so". Like
when the rock gets under the tire off center and flies off to the side
with gusto.

Haha and makes a loud CRACK as it hits the passenger door or window of the car to your left :-)


No kidding, that has happend. Also, drivers give me extra wide margin
when I just came off a dirt path in bad weather and all sorts of gunk
flies off my rear wheel.

I am beginning to wonder.

You have repeatedly stated that your usual speed is 20 MPH. Now, a 26
x 3.0 tire will be spinning at about 250 RPM at that speed..... But
this speeding tire accumulates "all kind of gunk"?


As explained many times 20mph is the speed on flat sections of trail or
slightly higher when downsloping a little. My average trail speed is
more around 10-12mph depending on turf unless I want to push it. Meaning
there are murky or gnarly stretches in the low single digit mph. There
are people on this NG who do not understand the difference between top
speed and average speed.

On such trails I often slow down to enjoy the scenery, animals, and so
on. Something that the "bicycles belong on road" people will likely
never understand.

Then I ride on 29" wheels. A usual scenario is that I come back on
singletrack from Placerville and the last section before entering a
regular road is this:

http://www.analogconsultants.com/ng/bike/Chapparal2.jpg

Imagine that after three days of rain. Also, on rainy days my average
speed on the "real" trail can drop substantially because the rear wheel
becomes stuck several times. Big clump of mud caked up near the BB,
wheel will hardly turn even in granny gear, have to stop, look around
for a sturdy branch piece of manzanita, poke the mud out of there,
continue the ride. Until it gets stuck again a few miles later.
Sometimes it's so bad that I strap that piece of manzanita onto the rack.


I ask as my road bike, who's wheels are spinning at only about 157 RPM
don't seem to accumulate any junk at all.


Well, do your road bike tires have knobbies? BTW, my road bike does
fling dirt off the wheels after a muddy stretch of "bush road" and I
have caked up its BB area with mud. Usually purposely rolling through
some water puddles washes the mud off the tires, something that does not
work for the MTB tires.

--
Regards, Joerg

http://www.analogconsultants.com/