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

[Fred Clydesdale]

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.

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!

[Jim Beam]

Fred Clydesdale wrote:
> 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.

>
> 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.

[Zeeexsixare]

> 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

[Qui Si Parla Ca]

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 (http://www.vecchios.com/) "Ruote convenzionali
costruite eccezionalmente bene"

[Mark McMaster]

jim beam wrote:
> Fred Clydesdale wrote:
>
>> 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 MMcMstr@ix.netcom.com

[Jim Beam]

Mark McMaster wrote:
> jim beam wrote:
>
>> Fred Clydesdale wrote:
>>
>>> 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 MMcMstr@ix.netcom.com
>

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.

[Alex Rodriguez]

In article <fred-
761501.18382509072004@news5.west.earthlink.net>,
fred@belldinger.com says...
>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