On Mon, Mar 31, 2008 at 8:49 PM, Jerome & Elizabeth Moos <
jerrymoos@sbcglobal.net> wrote:
> Auto tire designers , including designers of tires for sports car
> prototypes and Formula 1, obviously believe the tread makes a difference, as
> they design rain tires with much deeper tread than dry tires, which are
> often slick, or nearly so. Maybe Jobst is arguing that motorcycle and
> bicycle tires are fundamentally different than auto tires, but I don't see
> the basis for such an argument.
So, you don't see a difference in how water may be displaced from a car tire vs a 23/25/28mm road tire? A flat rectangular footprint vs a curved (or as Jobst says 'canoe' shaped profile? It's not really Jobst's discovery. This theory is a matter of simple physics. I would agree that Jobsts' approach to the bicycle and it's function is a little too eng'y for me but in this instance, it is a proven theory.
Jobst wrote a really good how-to book on wheelbuilding, with useful
> illustrations, but I find most of his theories, even some of his theories
> about wheelbuilding, to be totally unsupported by any facts that I can
> discern.
Where did you come to this conclusion that what is in his book, is unsupported? Again, it's written from a engineers viewpoint and the book doesn't leave much for the wheelbuilders personal nuance, but it's not really supposed to. The book is about the dynamics surrounding the wheel. His building technique is his own and subject to opinion. Ask Ric Hjertberg who also disagreed with Jobst method, but the physics surrounding it are just that physics. I will agree that not all tests on paper transfer to the shop or on the road.
I remember once questioning Bob Lickton about why he built some wheels for
> me with some detail that was counter to a Jobst theory. Bob replied Jobst
> should stick to computer programming and leave wheelbuilding to those who do
> it for a living every day. The same probably applies to designing tires.
As a wheelbuilder myself who has done it for over 15 years, I would say the
same thing! In fact I used to work for Wheelsmith (RIP) Avocet and at Palo
Alto Bicycles. So, run-ins with Jobst were common and so were debates on
wheelbuilding...and tires. :)
>
>
> Regards,
>
> Jerry Moos
> Big Spring, Texas, USA
>
>
>
> John Barry <usazorro@yahoo.com> wrote:
> Sounds like another shot-from-the-hip Jobst theory.
>
> Anyone who has driven on good tires on a wet road, and
> then driven on bald ones on a wet road and not noticed
> a difference, would have to be either very distracted,
> or borderline comatose.
>
> Hydroplaning is a very real phenomenon, and to suggest
> that tread pattern could not have some bearing on how
> severely hydroplaning affected a tire just doesn't
> have their facts straight. I'll leave the posting of
> citations on the topic to the engineers here.
>
> John Barry
> Mechanicsburg (where bald tires wouldn't be a good
> idea tonight), PA, USA
>
>
>
> >
> > Anyway, here's Jobst on the subject (found on line).
> >
> > *snip from Jobst*
> >
> > * Tread patterns have no effect on surfaces in which
> > they leave no
> > impression. That is to say, if the road is harder
> > than the tire, a tread
> > pattern does not improve traction. That smooth tires
> > have better dry
> > traction is probably accepted by most bicyclists,
> > but wet pavement still
> > appears to raise doubts even though motorcycles have
> > shown that tread
> > patterns do not improve wet traction.*
> >
> > */snip Jobst*
>
>
>
>
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--
Mike Scammon
Menlo Park, Ca.