wrote:
Mykal Crooks writes:


I'm building a bike for XC races and I'd like it to be reasonably
light. I thought of using butted spokes (my friend told me that u
can save as much as 100grams per wheel). My questions a


1) does it make any sense to use butted spokes at all?
2) is yes, is there any big difference in their durability (for
instance standard 2.0 stainless steel spokes vs 2.0 - 1.5 - 2.0
spokes) ?
3) what spokes would you recommend (thickness) and why ?


Now some data: I weight around 170 lbs, the rim I want to use is
Mavic 317 DISC, DT hubs, hydro disc brakes, the bike is a hardtail.


I found spokes swaged to as thin as 1.6 mm are recommended by
manufacturers to NOT be used in disc brake wheels; presumably this
restrictions has something to do with the forces exerted through
spokes with the use of hub disc brakes. (2.0 x 1.8 swaged spokes
are OK and may be optimal; however, there are spokes available with
ends greater than 2.0 that are marketed for some hub disc brake
applications.) Disc brake wheels I've used for road application came
with 2.0 mm x 1.8 mm "Race" spokes manufactured by Sapim.


http://www.sapim.be/

I don't understand the aversion to thin spokes with disc brakes if it
is something other than for the caliper crashing into the spokes.
Disc brake torque is no greater spoke load than peak pedaling torque
and it is distributed to both sides of the wheel, which pedaling
torque is not.

eh? disk braking torque exceeds pedalling torque by a factor of at
least two. and the torque transfer from one side of a hub to the other
is the same for drive or braking. unless the hub somehow mutates when
it finds it's being used for braking vs. drive that is... maybe you
have the math for that?

Besides, finite element analysis shows that torque is
a far lighter load on spokes than radial loads. I don't believe these
folks are aware of any of that and are guessing with the seat of their
pants, or maybe they are just impressed with the power of their brake.

so we'll just completely ignore fatigue loading shall we??? sure!!!
that makes life much more convenient!!! the jobstian way /is/ to ignore
inconvenient facts after all!!! doubtless braking increases wheel
strength too...


Jobst Brandt

evidently.