RE: alfa-digest V9 #522

["Jim Steck" <4sfed@xxxxxxxxx>]

I've listened to this thread for a while and feel the need to correct some
misconceptions about the strength of wire wheels.

First, wire wheel spokes do not stretch . . . the spoke is the highest
strength component of the wheel, with a yield strength three or more times
that of the rim and wheel center.  It's the design of the Dunlop wire wheel
that is mostly responsible for this myth.  When a cornering load is applied
to the typical Dunlop wire wheel, it overloads the wheel center and causes
the rear flange to plastically deform, shortening one leg of the triangle
that gives the wire wheel it's strength.  This results in loose spokes.

The other common failure mode of a wire wheel is broken spokes.  If the
wheel is properly tensioned, the spokes share the load over a large number
of spokes.  If one spoke is over tightened, it's preload stress can put the
cyclic stress about the fatigue endurance limit (resulting in failure).
Once a spoke fails, it's load is added to adjacent spokes beginning a
cascade of fatigue failure.  Loose spokes cause a similar problem.  Even if
evenly tensioned, the cornering loads will not be widely distributed, again
resulting in high cyclic loads on individual spokes.

It is possible to design a wire wheel to exceed the strength requirements
demanded by modern tires.  The wheels I designed for the Jaguar XJ-6
exceeded all of Jaguar's fatigue requirements and the German TUV
requirements for road wheels . . . they were never installed by the factory
because of cost and market timing, but are still available directly from
Dayton Wheel.  I also redesigned the wheel centers for the Dunlop wheels so
they could be used on vintage race cars.  Walk around the paddock at a
vintage race and talk to the drivers running Dunlop style wire wheels (made
by Dayton).  You may get a different impression of their durability.

Aesthetics are left up to the beholder.  Personally, I like the way they
look . . . on some cars . . . including my GTV.  Other than cleaning,
they've been maintenance-free for 60,000+ street and track miles.

Jim Steck
(former) Director of Engineering, Dayton Wheel Products, Inc.



> -----snip-----
> My point about wire wheels for automobiles (four wheelers) was precisely
> that they were inadequate from an engineering point of view. Sure
> they were lighter than the equivalent steel wheel but they were unable
> to deal with the side forces generated by really good tires. Pneumatic
> tires are slip angle devices on four wheeled vehicles. As tires got better
> this became obvious. The tire tries to punch the hub out of the wire
> wheel causing endless maintenance problems. Camber thrust vehicles
> (two wheelers) do not suffer from this but do suffer from spoke stretch,
>
> Cheers
>
> Michael Smith

--------------------------------
[This E-mail scanned for viruses]
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided