cycle computer on 28" wheel

Knowing you, it is. Also knowing you, you did that w/o any safety
equipment. I have heard others on this forum say that your brain is
your best piece of safety equipment, but if you were doing 13+mph on
your 28 with 102's in the rain after dusk... I'd say you were completly
w/o safety equipment.😄 Were was your wife? You are so in trouble if
she starts reading this forum.😉

--
bugman
------------------------------------------------------------------------
bugman's Profile: http://www.unicyclist.com/profile/3812
View this thread: http://www.unicyclist.com/thread/41143

C = (28" * 2.54) * Π = 223.43 cm

--
James_Potter - betcha can't stick it!
------------------------------------------------------------------------
James_Potter's Profile: http://www.unicyclist.com/profile/3807
View this thread: http://www.unicyclist.com/thread/41143

I measure my tire's circumference by laying a thin line of water on the
dry floor of the parking garage downstairs, riding over it, and
measuring the distance between the line of water and the damp dot
tracked by the tire. It doesn't account for wobble, but I guess it's as
accurate as any other method I've used.

--
weeble - .

======================
To avoid danger of suffocation
keep away from babies
and small children
======================

------------------------------------------------------------------------
weeble's Profile: http://www.unicyclist.com/profile/1625
View this thread: http://www.unicyclist.com/thread/41143

James_Potter said:

*C = (28" * 2.54) * Π = 223.43 cm *

Thanks JP. My next question is whence 28"? If it's supposed to be the
outer diameter of the tire, I think it's a little short - at least by my
crude measurement method. How much error is there in such a measure
anyway? And how does it affect the calculated speed? If the true
circumference is greater than the C-factor I've entered, I'm actually
going faster than the calculated speed, correct? If it's less, I'm
going slower. (Methinks.)

weeble said:

*I measure my tire's circumference by laying a thin line of water on
the dry floor of the parking garage downstairs, riding over it, and
measuring the distance between the line of water and the damp dot
tracked by the tire. It doesn't account for wobble, but I guess it's
as accurate as any other method I've used.*

I like this idea. Thanks. I'm going to try it today. Plus now we know
for certain that Weeble's wheel wobbles, but it don't fall down.

Bugman said:

*Knowing you, it is. Also knowing you, you did that w/o any safety
equipment. I have heard others on this forum say that your brain is
your best piece of safety equipment, but if you were doing 13+mph on
your 28 with 102's in the rain after dusk... I'd say you were
completly w/o safety equipment. Were was your wife? You are so in
trouble if she starts reading this forum.*

I was wearing my underwear, flipflops and fuzzy earmuffs. (I couldn't
find my aviator's cap.) What else do I need? I mean, what do you
suppose motivates a guy to ride down a $90 unicycle that way anyway?

--
munipsycho - Sometimes I fall down.

=====================
Yoopers on family: "Happy wife, happy life."

'Stories' (http://munipsycho.com/stories/)
'The UniSkills Assessment' (http://www.munipsycho.com/uniskills_2.jsp)

I can fly too. But I can only fly down.
-Little Bear

Imagine all the people
Riding on one wheel.
J. Lennon. (paraphrased)
------------------------------------------------------------------------
munipsycho's Profile: http://www.unicyclist.com/profile/9589
View this thread: http://www.unicyclist.com/thread/41143

A mile is 1609344 mm.

If I use the three C-factors I have from JP's calculations (a), the
cycle computer instructions (b) and my seamstress tape measurement (c)
to calcluate revolutions...

a) 1609344 / 2234 = 720.39 revolutions per mile
b) 1609344 / 2237 = 719.42 revolutions per mile
c) 1609344 / 2250 = 715.26 revolutions per mile

If my outer diameter measure is correct, I rode 4 extra revolutions,
making my "mile" about 11.5 meters too long.

(I'll have to figure out later how to calculate the effect on speed of
the extra 11.5 meters.)

--
munipsycho - Sometimes I fall down.

=====================
Yoopers on family: "Happy wife, happy life."

'Stories' (http://munipsycho.com/stories/)
'The UniSkills Assessment' (http://www.munipsycho.com/uniskills_2.jsp)

I can fly too. But I can only fly down.
-Little Bear

Imagine all the people
Riding on one wheel.
J. Lennon. (paraphrased)
------------------------------------------------------------------------
munipsycho's Profile: http://www.unicyclist.com/profile/9589
View this thread: http://www.unicyclist.com/thread/41143

All wheel sizes are nominal. A 700c is not exactly 700 mm across. A 20
inch tyre is not exactly 20 inches across. There is also variation
according to tyre pressure and the weight of the rider.

Take the diameter, measured between two vertical sticks (or a door post
and a spirit level). Choose your units (inches, millimetres, cubits,
hands, whatever) and multiply by 3.142.

That will give you the circumference of the tyre at normal pressure with
no weight on it.

Knock about a centimetre off the diameter for deformation of the tyre
when ridng, if you must.

1 centimetre off a 70 cm nominal tyre size will make 1.4% difference.
At speeds of around 10 mph, that's negligible unless you are
obsessive.

Most of the time, you will be measuring against your own previous
achievements anyway, and the level of inaccuracy will be exactly
constant, and therefore irrelevant.

If you are competing against someone else, variables like their route,
the wind speed and so on will make more difference than any honest error
in the setting up of your computer.

--
Mikefule - The first cuckoo of unicycling

Sumer is icomen in, loud sing Mikefule!
------------------------------------------------------------------------
Mikefule's Profile: http://www.unicyclist.com/profile/879
View this thread: http://www.unicyclist.com/thread/41143

Mikefule said:

*Most of the time, you will be measuring against your own previous
achievements anyway, and the level of inaccuracy will be exactly
constant, and therefore irrelevant.*

Well said! Thanks. (To wit: Today I hit at least 15.8 mph.)

Thanks as well for the technical detail. Very helpful.

--
munipsycho - Sometimes I fall down.

=====================
Yoopers on family: "Happy wife, happy life."

'Stories' (http://munipsycho.com/stories/)
'The UniSkills Assessment' (http://www.munipsycho.com/uniskills_2.jsp)

I can fly too. But I can only fly down.
-Little Bear

Imagine all the people
Riding on one wheel.
J. Lennon. (paraphrased)
------------------------------------------------------------------------
munipsycho's Profile: http://www.unicyclist.com/profile/9589
View this thread: http://www.unicyclist.com/thread/41143