Wheel Circumference Setting for Computer?

Hi,

I've just bought a Halfords 6-function wireless cycle compurter but
don't know what value to select for my tyre circumference value.

My tyre says its "26x190" (and I've no reason to disbelieve it) but
the values given for me to select from a

26x1.40
26x1.50
26x1.75
26 inch (650A)
26x20 (650B)

There are other non-26 values in the table.

For the moment I've chosen 26x20 (ATB) - can anyone tell me if this is
the 'nearest match' that I can hope for please? (and whether this
makes much of a difference to actual speeds/distances travelled etc.).

Thankyou in advance,

--

John Latter

Model of an Internal Evolutionary Mechanism (based on an extension to homeostasis) linking Stationary-Phase Mutations to the Baldwin Effect.
http://members.aol.com/jorolat/TEM.html

'Where Darwin meets Lamarck?' Discussion Egroup
http://groups.yahoo.com/group/evomech

John Latter typed


Hi,

I've just bought a Halfords 6-function wireless cycle compurter but
don't know what value to select for my tyre circumference value.

My tyre says its "26x190" (and I've no reason to disbelieve it) but
the values given for me to select from a

26x1.40
26x1.50
26x1.75
26 inch (650A)
26x20 (650B)

There are other non-26 values in the table.

For the moment I've chosen 26x20 (ATB) - can anyone tell me if this is
the 'nearest match' that I can hope for please? (and whether this
makes much of a difference to actual speeds/distances travelled etc.).

Thankyou in advance,

Are the calibration numbers the tyre circumference in millimetres (or
cm)? I'm not familiar with the Halford's computer, but this is the case
for many.

If this is the case, you can measure the circumference yourself by doing
a roll-out test on the bicycle.

Otherwise, you can calculate it approximately by adding the bead seat
diameter to twice the tyre width and mutiplying by pi.

Sheldon Brown's website might be able to help...

--
Helen D. Vecht:
Edgware.

"John Latter" wrote

I've just bought a Halfords 6-function wireless cycle compurter but
don't know what value to select for my tyre circumference value.

My tyre says its "26x190" (and I've no reason to disbelieve it) but
the values given for me to select from a

26x1.40
26x1.50
26x1.75
26 inch (650A)
26x20 (650B)

There are other non-26 values in the table.

For the moment I've chosen 26x20 (ATB) - can anyone tell me if this is
the 'nearest match' that I can hope for please? (and whether this
makes much of a difference to actual speeds/distances travelled etc.).

I think each make of tyre will be very slightly different. The most accurate
way will be to measure the circumference of the wheel by rolling the bike
along the floor and measuring the distance travelled for one tyre
revolution. (Assuming the value you are supposed to input is actually the
circumference of the tyre in millimetres. Then if possible check it for
accuracy against what you know to be a mile (I noted mine from the local
half marathon mile markers) and adjust by whatever percentage it might be
out. The value given for 26x2.00 tyres on the instructions that came with
mine was 2114. I measured it as 2070 which is a difference of about 2
percent. It says the input value for 26x1.9 is 2089.

In article , AndyP
wrote:
Then if possible check it for accuracy against what you know to be
a mile

The mile markers on the Motorways are supposed to be pretty accurate
:-) Suppose you could so it in the dark.

--
A T (Sandy) Morton
on the Bicycle Island
In the Global Village
http://www.sandymillport.fsnet.co.uk

On Mon, 19 Jan 2004 17:44:02 +0000, John Latter
wrote:

Hi,

I've just bought a Halfords 6-function wireless cycle compurter but
don't know what value to select for my tyre circumference value.

My tyre says its "26x190" (and I've no reason to disbelieve it) but
the values given for me to select from a

26x1.40
26x1.50
26x1.75
26 inch (650A)
26x20 (650B)

There are other non-26 values in the table.

For the moment I've chosen 26x20 (ATB) - can anyone tell me if this is
the 'nearest match' that I can hope for please? (and whether this
makes much of a difference to actual speeds/distances travelled etc.).

Thankyou in advance,

Thankyou for the help Helen, Andy, and Sandy!

It didn't occur to me that I could program in my own values (Isorta
resumed the unit had a 'look-up rom') so I'll do the roll-out thing.

'Course, I'm bound to get the maths wrong - bet I end up going faster
than sound

--

John Latter

Model of an Internal Evolutionary Mechanism (based on an extension to homeostasis) linking Stationary-Phase Mutations to the Baldwin Effect.
http://members.aol.com/jorolat/TEM.html

'Where Darwin meets Lamarck?' Discussion Egroup
http://groups.yahoo.com/group/evomech

Is there a function for entering your own wheel circumference

if so. Get a tape measure, and measure the difference from the centre o
the hub to the outermost edge of the tire. (if the unit the want th
circumference in is millimeters then measure in millimteres, if it is i
centimeters then use that unit, but i suspect it is mm

Got the value for the radius?

Now multiply that value by 2 and then by Pi

so the calculation looks like

3.1416 x 2 x your measured value = circumferenc

Simple

Of course if there is no way of entering your own circumference then iv
just wasted my time. ;-

hope it help

dav


-

"Sandy Morton" wrote in message
...
In article , AndyP
wrote:
Then if possible check it for accuracy against what you know to be
a mile

The mile markers on the Motorways are supposed to be pretty accurate
:-) Suppose you could so it in the dark.


There are accurately marked mile/half miles all over the place, there's one
within a mile of my house. Traffic police need them to calibrate their
speeding detection equipment. Phone your local police traffic department,
they may well tell you where to go...one way or another.

--
Duncan Gray

homepage - www.duncolm.co.uk
also www.mountaineering-scotland.org.uk
The Mountaineering Council of Scotland

"Duncan Gray" wrote

There are accurately marked mile/half miles all over the place, there's
one
within a mile of my house. Traffic police need them to calibrate their
speeding detection equipment. Phone your local police traffic department,
they may well tell you where to go...one way or another.

Are they denoted by some kind of standard marker that anyone can recognise
them by?

"AndyP" wrote in message
...
"Duncan Gray" wrote

There are accurately marked mile/half miles all over the place, there's
one
within a mile of my house. Traffic police need them to calibrate their
speeding detection equipment. Phone your local police traffic
department,
they may well tell you where to go...one way or another.

Are they denoted by some kind of standard marker that anyone can recognise
them by?


No, the one near me is just marked by yellow vertical stripes painted on the
wall.