Hi Bob

You've set the bait. Here's the bite:

On (09 Nov 98) Bob Lawrence wrote to Theo Bee...

 RM> My experiment seems to confirm this, the result was a lot
 RM> closer to my prediction than it was to dorkbrain's prediction
 RM> that The Speedo Reading Is Governed By The Distance From The
 RM> Axle To The Ground.

 TB> Going against established wisdom and it "is so simple stupid"
 TB> arguments is paramount to uphill battles and windmill
 TB> fighting.

 BL>  For Christ's sake, Theo... are you agreeing with this idiot?

Nice scientific argument. Abuse the enemy's allies as well as the
enemy.

 TB> If you are right there obviously has to be a compensating
 TB> mechanism, I.e. on the surface it seems since the radius is
 TB> obviously reduced there have to be more axle revs for a given
 TB> distance. However, the tyre is flattened over a wider area, not
 TB> just at the point of minimum radius.

 BL>  You're an engineer. You KNOW that for the speedo reading to change
 BL> (and it does)

By how much??

 BL> then the radius must change. It is totally insane to say
 BL> (as Roy does) and the height of ignorance, that the speedo can't
 BL> change because the tyre remains the same circumference. Of course it
 BL> can't! The speedo *does* change.

My argument has always been that a steel radial will *resist* this
effect, not cancel it altogether. Of course the speedo changes. But
my argument is that for a given axle rpm, the speedo reading is
*not* directly proportional to the axle to ground distance, and its
error is reduced further by the stiffness of the tread.


 TB> Simply pulling the integral over the linear distance would
 TB> solve it conclusively.

 BL>  Simple my arse... it's impossible. So measure the axle height
 BL> instead, which will reflect the speedo reading, precisely.

Go back and read my experiment description. The axle to ground
distance changed by 4.7%. The speedo reading changed by 0.7%.
Explain that. If you can.

 BL>  v = r * d0/dt as simple as that. v is the actual speed, and d0/dt is
 BL> proportional to the speedo reading. r is the radius, axle height above
 BL> ground.

 BL>  Roy is saying circumference is constant, that dl/d0 = r is constant.
 BL> If that is true, then the radius is constant! But any idiot can see
 BL> the wheel get closer to the ground with a flat tyre.

And any idiot can see that a flattish tyre is *not* a circle!!! How
can you talk about the "radius" of a non-circle?? It's easy to push
a circle out of shape while keeping its circumference constant.

 BL>  And the darling part I find incredible is that Roy tells us this
 BL> only applies when there is air in the tyre. When it's flat, it no
 BL> longer applies, so... as you add pressure, when does it start to
 BL> apply?  When does the circumference suddenly get constant? ROFL! He's
 BL> an idiot. It's sad.

When was I ever talking about a dead flat tyre? Whatever you're
smoking, I'd like some too. Stick to the point, if you can.

 BL>  I can't be bothered arguing with him, I've explained all this and he
 BL> calls me a dork, but I'm shocked that you agree with him. He keeps
 BL> saying *IF* the circumference is constant. He may as well say IF
 BL> Young's Modulus is infinite, IF God exists, or IF you can trust
 BL> politicians. It's just crap. Young's Modulus in *rubber* is infinite?
 BL> There's a novel approach to reality! I thought rubber stretched. What
 BL> a dork I am!

Rubber stretches. Rubber with a steel mat embedded in it stretches
too, but a lot more reluctantly.

 BL>  When I answered his original query a year ago, all this occurred to
 BL> me in the first minute. There seems to be a paradox.

 BL>  The tyre going past on the bottom *has* to be l = Integral (r d0)
 BL> which seems to make the tyre run slower on the bottom and slip around
 BL> the wheel. Silly Roy accepts this as true. The reality is that the
 BL> wheel does not slip, but the length passing under the car does
 BL> change,

You don't need calculus for this, simple geometry will do. See
"Polite Reply". Try to poke a decent hole in the arguments I've
given there. If you can't, please concede. You have yet to give me
one decent mathematical or experimental argument in favour of the
"radius" model better than "It's Obvious, Dork!!"

 BL> so how can that happen? The answer is the circumference must change
 BL> because the *shape* changes.. maybe it squirms, I don't know. I do
 BL> know that it gets hot, so there are big forces involved in twisting
 BL> into another shape.

True. But it's changing shape in plenty of ways, mainly by being
bent hard at the front and back of the flat bit. I'm suggesting
that the steel in a steel radial will help the tread resist being
squashed lengthwise.

Question: if the tread is squashed lengthwise, where does the force
to do this come from? Are you telling me that the thin flimsy
sidewalls are bigger and stronger than the steel reinforced tread,
and are pulling it way out of shape? Crap. Most of the force must
come from the tread just in front of and behind the flat bit, so
that tread will be squeezed too, so it will bulge out in front and
behind a bit, and *reduce* the required compression of the flat
bit, which could easily explain my experiment results (combined
with my geometry argument in "Polite Reply").

 BL> It's a three-dimensional problem I knew I couldn't
 BL> solve, but it's easy enough to measure radius and that'as all you
 BL> need.

I did. The speed difference was *not* proportional to the radius
change. Explain that. Nobody else has managed to do that yet. All
they can do is bleat "It's Obvious!" with no experimental or hard
theoretical backup.

 BL>  And then Roy did some fuckwit mini-brain techie measurements
 BL> without the knowledge or experience to realise that he has to know the
 BL> order of accuracy before he can form a conclusion.

In the whole argument, I saw not one real criticism of the accuracy
of my experiment, and no effort at criticism at all from you.
What's this? If the results don't come out the way you want, you
simply claim they're inaccurate without even looking or asking?
You're beginning to sound like an astrologer.

 BL> And if that is
 BL> not silly enough, he left the steel wheel out of the calculation!

WTF has this to do with anything???

 BL>  A 75-profile tyre on a 14" wheel is 75mm on a 180mm fixed steel rim.
 BL> OF COURSE the radius will not be directly proportional to tyre
 BL> pressure, even if it were a balloon he was pumping up!

When did I ever claim this? I measured axle to ground distances,
and only mentioned pressure as an aside. If you're going to throw
mud, get your facts right first.

 BL> I went through
 BL> this before, I even tried to solve the problem mathematically, the
 BL> way you say is simple (my arse, it is) but then I realised that I was
 BL> dealing with a persistent fool and all you can do is walk away.

 BL>  Thank Christ Roy is not doing real engineering. That takes real
 BL> engineers... dork-brains like me.

If you're so wonderful, suggest a feasible experiment that will
prove this assertion that indicated speed is directly proportional
to axle-ground distance. Then go and do it yourself, and see
reality with your own eyes.

Before you do that, kindly point out your alleged "inaccuracies" in
my experiment.

Better still, email me a phone#, so we can settle this in minutes
instead of months.

--- PPoint 1.88