Wheel Circumference Setting for Computer?

John Latter <[email hidden]>typed

Quoted message said:

Hi,

Quoted message said:

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

Quoted message said:

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

Quoted message said:

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

Quoted message said:

There are other non-26 values in the table.

Quoted message said:

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.).

Quoted message said:

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: [email hidden] Edgware.

"John Latter" <[email hidden]> wrote

Quoted message said:

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 are:

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.

On Mon, 19 Jan 2004 17:44:02 +0000, John Latter <[email hidden]>

Quoted message said:

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 are:

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. members.aol.comTEM.htmlOpen ↗

'Where Darwin meets Lamarck?' Discussion Egroup groups.yahoo.comevomechOpen ↗

In article <[email hidden]>, AndyP

Quoted message said:

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 sandymillport.fsnet.co.uksandymillport.fsnet.co.ukOpen ↗

Is there a function for entering your own wheel circumference?

if so. Get a tape measure, and measure the difference from the centre of the hub to the outermost edge of the tire. (if the unit the want the circumference in is millimeters then measure in millimteres, if it is in 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 = circumference

Simple.

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

hope it helps

dave

"Sandy Morton" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

In article <[email hidden]>, AndyP <[email hidden]-

spam.co.uk said:

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" <[email hidden]> wrote

Quoted message said:

There are accurately marked mile/half miles all over the place, there's

one

Quoted message said:

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?

Helen Deborah Vecht said:

John Latter <[email hidden]>typed

Quoted message said:

Quoted message said:

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

Quoted message said:

Quoted message said:

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

Quoted message said:

Quoted message said:

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

Quoted message said:

Quoted message said:

There are other non-26 values in the table.

Quoted message said:

Quoted message said:

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.).

Quoted message said:

Quoted message said:

Thankyou in advance,

Quoted message said:

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.

Quoted message said:

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

Quoted message said:

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

To do this properly you must take into account your typical tyre pressure, which is half way between
how hard you pump it up to and how soft you let it get before you pump up again, and how much your
weight squashes it. You do this by getting it to that average pressure (e.g half the usual number of
pump strokes from soft), and then rolling it under your normally distrib weight (usual lean) one
exact cirumf. Use a chalk mark on the tyre.

You ought to be able to calibrate to within at least 1% accuracy like this.

--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
["]http://www.dai.ed.ac.uk/homes/cam/]

"AndyP" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

"Duncan Gray" <[email hidden]> wrote

Quoted message said:

There are accurately marked mile/half miles all over the place, there's

one

Quoted message said:

within a mile of my house. Traffic police need them to calibrate their speeding detection
equipment. Phone your local police traffic

department,

Quoted message said:

Quoted message said:

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.