Boxerworks.com

vanzen@rockerboxer.com wrote:

robert wrote:The difference in stiffness between a cast wheel and a wire spoke wheel on an airhead, unless the frame has been seriously modified and forks replaced with something more substantial, would not be noticed.

Your subjective and personal evaluation, then -
And so,
not to be confused
with any valid and verifiable experience of others, eh ?

Pretty much it.

Once cast wheels became mainstream they were probably fitted because they were cheaper to make Than spoked wheels. The punters would have been told that it was for performance reasons! Not many airheads are raced like Arter Matchlesses.

The punters who do use their GSs off road seem to prefer spoked wheels because they don't break like the cast ones can.

Cost can always modify a manufacturer's choices.
However, cost rarely, if ever, determines the components used
on the (roadracing) track at the upper levels.
If the performance of cast wheels
did not surpass that of spoked wheels on the track,
factory road race teams would still be wearing spokes.

Conversely, spoked wheels are, without a doubt,
the preferred choice for off-road.
I, for one, cringe at the thought
of encountering a hole as Chas described earlier
on my R12S - with it's well designed cast road ONLY wheels !
But then, knowing the limitations,
I would be rolling at a speed somewhat slower than 60 mph
if the terrain demanded.

Desirable performance characteristics of any wheel type
cannot be judged without contextual consideration.
Context defines both the forces acting upon the wheel
and the desired responses of that wheel.

And still - unsprung mass cannot be the sole determining factor
used to judge the performance value of a wheel.

I would think that many of the forces that acted to "outdate" spoked wheels were (are) market driven forces. That statement does not address any performance gain or loss or compromise. What I'm getting at is that I wouldn't go along with the fact that there are no spoked wheels on performance bikes as pointing to cast wheels being superior for performance applications.

The competition world would be a better place to look for that evidence. The problem with that is that if you really get down to a well prepared competition bike, it would likely not have stock wheels. So, that returns the issue to one of the marketplace (perceived racy look, cost to manufacture).

My guess is that the Butler & Smith bike(s) had mag Morris wheels primarily because of their weight. Those must be some light wheels.

At one point, I weighed snowflakes, spoked and Lesters and the weight was very close. I suspect tire choice could sway the results. For example, a heavy tire/tube on the lighter wheel may make it heavier than a light tire/tube on the heavier wheel.

Chuey

Chuey wrote:

...
The competition world would be a better place to look for that evidence. The problem with that is that if you really get down to a well prepared competition bike, it would likely not have stockwheels. So, that returns the issue to one of the marketplace (perceived racy look, cost to manufacture)...

2013 WERA Superbike rulebook requires stock wheels
unless the production machine is fitted with spokes.
Then, the spoked wheels can be replaced with cast wheels
provided the cast wheel is the same diameter and width as the stock spoked wheel
and the weight of the cast wheel is the same or greater than that of the stock spoked wheel.


AMA Pro World Superbike rules :
WHEELS/BRAKES A. Original equipment wheels must be used, except where a TIF provides for substitutes. Substitutes must appear on the Eligible Equipment List.

Then, there is Moto-GP,
the "no holds barred" realm of pure prototype roadracing MCs.
That place where performance is paramount,
money is no object,
and the best of the best unobtanium / exotic components used ...

I have not seen spoke #1 there ... ever.

I know where Chuey is coming from, as some pretty incredible things are done with tension spoked wheels in the bicycle world. I wonder, and I bet he does, too, what would be the result if MC spoked wheels were developed to the extent that we see in a bicycle.

Even 20 years ago, using what was even then old parts, I could build wheels that I would best describe as "papier mache" regarding their perceived weight, yet they held up for several seasons on the velodrome under me and likely would still be in use if I still raced.

That said, I think if I were to cut the five AL or MG spokes out of a modern Marchesini wheel, they would weigh less than 36 or 40 SS spokes, and the Marchesini (or other cast) rim and hub have advantages in that they do not have to be designed to interface with 36 or 40 point loads from the spokes.

I was shocked at how light a rim was for a 250cc dirt bike. It made me wonder what the limits would be for reliable motorcycle wheels.

With the fairly long view I have of what the marketplace effects (fads, perceived performance enhancers that aren't really that, hype, misunderstood "technology" brought over from other disciplines, cost cutting that is sold as technological advances, and more that I can't think of right now), I admit to seeing things through a filter.

I really would think that the main reasons for cast or forged wheels being popular now is mostly due to ease (cost) of manufacture, with the genesis being originally, lightness for racing. That wouldn't have crossed over without being muddied by the fact that factories couldn't afford to put real magnesium wheels on production bikes but aluminum ones would look the part. Also, magnesium wouldn't be so practical even if it was cheaper from what I understand about mag wheels.

Heck, this could get nasty. I even run tubes in my snowflakes!

Chuey

No question about it. Production costs can always be a factor
After all, the consumer price of a front spoked wheel for a Hex GS
is @ $200 more than a cast wheel for a Hex R1200S.

However, in terms of motorcycle chassis dynamics
the principle advantage of a cast or forged wheel remains increased lateral stiffness.
Lateral flexation in a motorcycle, whether frame, forks, or wheel induced
will be a primary cause of chassis instability.
Even as too little lateral flexation will be the source of rear wheel chatter
in certain (very demanding) situations.

I have seen racing bicycles with laced wheels that use as few as 8 spokes.
Bearing in mind that a bicycle does not weigh 500 lbs,
does not produce 120hp,
and does not travel at speeds approaching 150mph,
I would be very cautious about making simplistic wheel comparisons.
The magnitude of forces acting upon the respective wheels are not comparable.
There is good reason why a bicycle wheel can be lighter
than that used on a 250cc motorcycle,
or that wheel lighter than the one appropriate to a 1000cc motorcycle.

The term "magnesium" and "aluminum" are, at best, generic terms.
Any discussion of the performance or characteristics of these
without reference to the specific composition of the alloy in question
is simply pissing into the wind.
However,"Magnesium" is a popular choice for a track bike wheel
due to it's lesser mass AND
the predictable uniformity of the road / track surface.
Magnesium alloy wheels are often considered too brittle
for general street use.

Cast and forged wheels have been the preferred choice in roadracing
since long before technology caught up, allowing them to be lighter
than a comparably sized spoked wheel.
Again, lateral flexation is a primary source of chassis instability -
Cast and forged wheels were instrumental in controlling that flexation.
In view of that one factor, the unsprung mass of a wheel
became a secondary consideration
even as metalurgists and engineers scrambled
to design and build even lighter cast (forged) wheels
without sacrificing designed performance criteria.


I own exactly 1 motorcycle that is fitted with tubes.
It is a 1952 R68. :)

vanzen@rockerboxer.com wrote: There is good reason why a bicycle wheel can be lighter
than that used on a 250cc motorcycle,
or that wheel lighter than the one appropriate to a 1000cc motorcycle.

More than one, and rim brakes is a big one.