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Subject: Re: Why the notches in a Presta nut?
Message-ID: <iHrJ9.53911$>
Date: Tue, 10 Dec 2002 19:58:06 GMT

David Damerell writes:

>> (*) Botts Dots:

> Botts Dots, nothing. These devices "invented" by Botts in the 1950s
> are no different from cateyes, invented by Mr. Percy Shaw in the
> 1930s. But I suppose he is insufficiently American?

Had you read the item you would have noticed that these dots, although
previously used were different in that they were attached to the road
with a special tough but pliable epoxy and that they were white
porcelain, Mr Bott's contribution to their usefulness and wide spread
use.  Subsequently reflective colored plastic lane markers became
practical.  Metal (aluminum) ones have been used in Europe for a long
time and frequently come loose exposing the spike that holds them.

I assume Mr. Percy's contribution was to put reflectors in the nailed
metal ones.

There is progress.

Jobst Brandt  <>  Palo Alto CA

Subject: Re: Accurate Odometer
Message-ID: <5YWPd.6703$>
Date: Mon, 14 Feb 2005 05:47:45 GMT

Carl Fogel writes:

>>>>> As a cross-check, my $15 Nashbar odometer varies perhaps 0.03
>>>>> miles on either side of 15.25 miles on my daily ride, which may
>>>>> say more about how much I swerve and how tight I cut my corners
>>>>> than it says about the accuracy of the speedometer.

>>>> Or variation in tire pressure

>>> Possibly tire pressure is involved, but unlikely, since the tiny
>>> odometer variation doesn't seem to go in one direction.

>>> That is, I don't see my distance slowly increasing (or decreasing)
>>> until I remember to pump my tires up again.

>>> The variation could also be due to weight changes, since the
>>> standard Fogel often varies by several chocolate doughnuts.

>> Don't rely on others reports if you don't believe them.  Just measure
>> the rollout distance with different inflation pressures on your own
>> bicycle.  I have done it and it isn't just a millimeter.  I'm
>> satisfied that 2093mm is good enough for my Avocet 700-25 tires at
>> average inflation.  I don't care if it changes a little with inflation
>> because the tires hold air to my satisfaction for more than a month.

>>> Many posters here on warn of the dangerous
>>> inaccuracy of measuring an unloaded wheel, but I've never seen a
>>> post that mentioned any measured difference in tire circumference
>>> between a loaded and an unloaded bike.  (Indeed, the warnings often
>>> fail to mention which way they think the loading affects the
>>> outcome.)

>> What dangers have been reported?  As inflation pressure decreases, so
>> does the rollout distance for one revolution.  As I pointed out, when
>> driving a car over Botts Dots on roads you'll notice the slamming
>> effect get harsher with increasing speed.  That is because the change
>> in rolling radius causes a momentary acceleration of the wheel that
>> through inertia cannot occur at higher speeds as easily.  Therefore,
>> the slamming effect bends wheel suspension.  The bumps do not get
>> larger nor does wheel bounce but the the rolling radius changes almost
>> instantaneously.  Since most car tires are radials (with a constant
>> circumference belt), I find that a dramatic demonstration of rolling
>> radius.

>>> I wouldn't be surprised if the difference was more theoretical than
>>> measurable, but it would fun if someone posted the results of some
>>> careful loaded and unload tire measurements.

>> Be surprised!

> Er, you need to read more carefully.  Your unreported "dangers" are
> not the same as my rather obviously tongue-in-cheek "dangerous
> inaccuracy."

> I'd be more surprised if you were to include the figures that you
> say are dramatic.  I can't even tell from your post whether you are
> saying that the loaded tire produces a larger or smaller
> circumference.  I'd be willing to believe your figures if you'd
> simply post them.

> You find 2093mm a good average figure for your tires, presumably
> measured loaded.  What was the unloaded measurement?  It "isn't just
> a millimeter."

As I corrected in a followup.  That was a typo.  It is 2096mm.

> If you reply with a 4-character post, it will be the first time that
> I know of an actual difference appearing in this newsgroup.

> I hope it's not a secret.

As I said, you should be aware of this difference if you measure
rollout distance.  The difference per psi varies with weight of rider,
riding position and tire cross section.  With my tires in my most
common position, hands on the bar tops (with drop bars), the
difference is 20mm reducing inflation pressure from my usual 100psi to
80psi.  I took those pressures because they represent the limit with
which I ride and because it gives a repeatable and easily measured

The Botts Dots experiment should be obvious the next time you are on a
road that allows speeds up to 65mph.  That these accelerations are
large are shown by the tire rubber that leaves skid marks in the
process.  It is also why Elbert Botts invented the significant part of
these lane markers, the adhesive.  Previously any glued devices were
readily knocked loose.  It was his research in the adhesive that made
them possible.

The first significant application of these lane markers was on
"Hospital Curve" on HWY101 in San Francisco, a long relatively sharp
curve for an 8-lane freeway around San Francisco General Hospital that
in wet weather, especially at night, was a challenge to not drift into
other lanes, the road stripes being invisible in the wet glare.  There
were many serious crashes at that curve that did not have a median nor
a dividing crash-wall.  Today, it is hard to visualize how drives
managed before Botts Dots.

Jobst Brandt

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