Zero-dish wheels...is there a down side?

Fred Clydesdale said:

after recently trashing a MA2 after only 4K miles, i started
thinking about building my next rear wheel with one of the
bontrager or velocity asymmetrical alternatives. seems to
me that they should be easier to true and wouldn't require
the kind of tension needed on a dishful wheel.

dish does not mean more tension - it means /less/ tension on the left
side, not more on the right.

Quoted message said:

but is there a downside? what about weaknesses in the rim's
internal structure with all the spokes over on one side?
if they really work, i don't understand why EVERYBODY isn't
building with these!

because it's harder to make them with eyelets and generally speaking, a
rim with eyelets should be more reliable as they spread the point
contact load.

another point about offset rims is that, despite frequent claims to the
contrary, they do /not/ create a zero dish wheel. if a dished rear hub
is set say 15mm off center, the 3-5mm offset in a rim is not going to
bring that back to zero!

so, do offset rims reduce tension differential? yes. does a more even
tension left-to-right create a more stable wheel? yes. does this stop
you trashing rims? not necessarily. whether you decide to go offset
rim or standard rim, you're going to get much more reliability from a
wheel built to the rim manufacturer's spoke tension spec than one that's
built with excess.

check damon rinard's latest spoke calculation spreadsheet. it has the
dish tension differential math in it so you can experiment with the
effects that different rim/hub combinations have.

Quoted message said:

another point about offset rims is that, despite frequent claims to
the contrary, they do /not/ create a zero dish wheel. if a dished
rear hub is set say 15mm off center, the 3-5mm offset in a rim is not
going to bring that back to zero!

The zero figure is in conjunction with the offset hub the rim is supposed to
be used with.

--
Phil, Squid-in-Training

fred-<< i started
thinking about building my next rear wheel with one of the
bontrager or velocity asymmetrical alternatives. seems to
me that they should be easier to true and wouldn't require
the kind of tension needed on a dishful wheel. >><BR><BR>

No easier to true(but not hard) and the tension on the right side is the same
as a more typical rim, the left side tension is higher is all, a good thing.

fred<< if they really work, i don't understand why EVERYBODY isn't
building with these! >><BR><BR>

They really do but it is expensive to make rear and front rims, rather than
just one for both.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

jim beam said:

Fred Clydesdale said:

after recently trashing a MA2 after only 4K miles, i started
thinking about building my next rear wheel with one of the
bontrager or velocity asymmetrical alternatives. seems to
me that they should be easier to true and wouldn't require
the kind of tension needed on a dishful wheel.

dish does not mean more tension - it means /less/ tension on the left
side, not more on the right.

As a practical matter, increasing dish _does_ mean more
tension on the right spokes, to prevent the left tension
from becoming too low. As shown in Damon Rinard's
deflection testing, if the spokes on one side become too
low, the wheel becomes unstable and prone to failure:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

The increased dish (and increased right spoke tensions) is
one of the primary reasons for the demise of light weight
rims. Years ago, the 360 gram Mavic GL350 rim was a common
rim used in everyday rear wheels, and the 290 gram Mavic
GL280 rim could be used in a racing rear wheel. These rims
were designed to handle the tension differentials for 5spd &
6spd rear wheels. However, rims these light do not stand up
well to the tension differentials of 8spd, 9spd & 10spd rear
wheels. These lightweight rims have been replaced by
heavier rims, built to withstand the higher tensions
required by the right spokes of 8/9/10spd rear wheels. The
lightest rims of similar construction available today are
closer to the 400-450 gram range.

Mark McMaster
[email hidden]

Mark McMaster said:

jim beam said:

Fred Clydesdale said:

after recently trashing a MA2 after only 4K miles, i started
thinking about building my next rear wheel with one of the
bontrager or velocity asymmetrical alternatives. seems to
me that they should be easier to true and wouldn't require
the kind of tension needed on a dishful wheel.

dish does not mean more tension - it means /less/ tension on the left
side, not more on the right.

As a practical matter, increasing dish _does_ mean more tension on the
right spokes, to prevent the left tension from becoming too low. As
shown in Damon Rinard's deflection testing, if the spokes on one side
become too low, the wheel becomes unstable and prone to failure:

http://www.sheldonbrown.com/rinard/wheel/tension.gif

original page:
http://www.sheldonbrown.com/rinard/wheel/index.htm

The increased dish (and increased right spoke tensions) is one of the
primary reasons for the demise of light weight rims. Years ago, the 360
gram Mavic GL350 rim was a common rim used in everyday rear wheels, and
the 290 gram Mavic GL280 rim could be used in a racing rear wheel.
These rims were designed to handle the tension differentials for 5spd &
6spd rear wheels. However, rims these light do not stand up well to the
tension differentials of 8spd, 9spd & 10spd rear wheels. These
lightweight rims have been replaced by heavier rims, built to withstand
the higher tensions required by the right spokes of 8/9/10spd rear
wheels. The lightest rims of similar construction available today are
closer to the 400-450 gram range.

Mark McMaster
[email hidden]

mark, you're absolutely on target here. it comes down to the
substantially increased loads that a really shallow dish angle can
create under lateral load.

as an example, the increased tension in a drive side spoke is a function
of the dish angle. zero angle = infinite load. kinda like the
cantilever brake math sheldon executes on this page:
http://www.sheldonbrown.com/cantilever-geometry.html - scroll down to
"mechanical advantage".

so, yes, more dish > more lateral loading > greater fatigue loading >
stronger rims are needed to cope.

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

after recently trashing a MA2 after only 4K miles, i started
thinking about building my next rear wheel with one of the
bontrager or velocity asymmetrical alternatives. seems to
me that they should be easier to true and wouldn't require
the kind of tension needed on a dishful wheel.

How did you trash the wheel? It is important to understand why your
wheel failed before you start working on your next wheel.

-----------------
Alex