Wheel sizes
John Heaps
asking for a size which I do not know how to work out. Size is between 60
and 300, but my wheel size is 26".
Does anyone know what this equates to in the bicycle computer world?
Many thanks in advance.
thirty-six
Wheel rollout in centimetres. Put a mark on the road and the edge of
your tyre with chalk or wax crayon. Get on the bike and roll forward
until the mark has come around. Mark the road where the mark on the
tyre join is. Measure the distance between the two marks in
centimetres. This is the value your computer requires. I guess it
will be around 200 and is dependent on tyre size, tyre pressure and
your weight.
Tosspot
It wants the circumference in some unit or other, I suspect centimeters.
See
http://www.sheldonbrown.com/cyclecomputer-calibration.html
You could do a rollout, but you'll be within a percent or two just using the chart.
Tom Anderson
> On 20 Nov, 22:17, "John Heaps" <j...@smallshopsonline.co.uk> wrote:
>> Hi, I need to put my wheel size into a new bicycle computer/odometer. It is
>> asking for a size which I do not know how to work out. �Size is between 60
>> and 300, but my wheel size is 26".
>>
>> Does anyone know what this equates to in the bicycle computer world?
>>
>> Many thanks in advance.
>
> Wheel rollout in centimetres. Put a mark on the road and the edge of
> your tyre with chalk or wax crayon. Get on the bike and roll forward
> until the mark has come around. Mark the road where the mark on the
> tyre join is. Measure the distance between the two marks in
> centimetres. This is the value your computer requires.
Instead of making a mark, you can just use the position of the valve on
the inside of the rim.
tom
--
Work alone does not suffice: the efforts must be intelligent. -- Charles
B. Rogers
Rob Morley
It depends on the particular 26" that your wheel is, but assuming it's
something like 26 x 1.95 then the rim diameter is 559mm, add the
thickness of the tyre (1.95 x 25.4 x 2 = 99mm) to get the overall
diameter of 658mm, multiply by 3.1416 for the circumference of 2067mm
so you need to put 207 in your computer. That doesn't allow for the
nominal nature of tyre widths or the fact that the tyre deforms under
load, but it's probably near enough if you can't be bothered to sit on
the bike and measure the distance travelled in exactly one wheel
revolution.
Garry from Cork
Rob Morley
Garry from Cork <gol...@gmail.com> wrote:
> Usually 210 if it's a Cateye or similar.
>
You're just guessing.
Keitht
Don't bother with any maths.
Stick a bit of tap on the front wheel and a bit on the ground.
Line up both bits of tape and wheel the bike until the tape on the tyre
has done one revolution.
Put another bit of tape on the ground next to the bit on the tyre.
Measure the distance in whatever the comp wants.
Bung it in the comp.
Sorted!
--
Its never too late to reinvent the bicycle
Mark McNeill
> Don't bother with any maths.
>
> Stick a bit of tap on the front wheel and a bit on the ground.
> Line up both bits of tape and wheel the bike until the tape on the
> tyre has done one revolution.
> Put another bit of tape on the ground next to the bit on the tyre.
> Measure the distance in whatever the comp wants.
> Bung it in the comp.
>
> Sorted!
Back in the days when I CBA with cycle computers I marked the ground at
one end of my cul-de-sac, put the valve stem next to it, put my weight
on the bike and rolled it till the valve stem had done 10 revolutions,
marked and measured the ground, did just one moderately straightforward
calculation [divide distance by 10] and put the distance in the
computer.
These days when someone asks how far I went yesterday I say "Dunno, but
it took me about three hours". :-/
--
Mark, UK.
Hbunnet
markonne...@yahoo.co.uk says...
>
>
>
> Back in the days when I CBA with cycle computers I marked the ground at
> one end of my cul-de-sac, put the valve stem next to it, put my weight
> on the bike and rolled it till the valve stem had done 10 revolutions,
> marked and measured the ground, did just one moderately straightforward
> calculation [divide distance by 10] and put the distance in the
> computer.
>
Yes thats more like it, its worth a few revolutions to reduce error.
--
Hbunnet
Adam Lea
If you want to be really rigorous, you could repeat this a hundred times,
fit a distribution to the data and then you can obtain the standard error
for the recorded speed.
Ian Jackson
Keitht <keith_...@knotmail.com> wrote:
>Stick a bit of tap on the front wheel and a bit on the ground.
>Line up both bits of tape and wheel the bike until the tape on the tyre
>has done one revolution.
This is of course a perfectly sensible and low-tech way of doing
things.
But I was lazier. When I first got my computer I just took the
value for my wheel and tyre size from Sheldon's site. When I wanted
to know how accurate it was, I cycled around 1km along a nice straight
road and compared the distance measured with that reported by my GPS -
and the results were within the measurement resolution of the cycle
computer.
--
Ian Jackson personal email: <ijac...@chiark.greenend.org.uk>
These opinions are my own. http://www.chiark.greenend.org.uk/~ijackson/
PGP2 key 1024R/0x23f5addb, fingerprint 5906F687 BD03ACAD 0D8E602E FCF37657
Keitht
> In article <PZOdnV_CttymKJrW...@bt.com>,
> Keitht <keith_...@knotmail.com> wrote:
>> Stick a bit of tap on the front wheel and a bit on the ground.
>> Line up both bits of tape and wheel the bike until the tape on the tyre
>> has done one revolution.
>
> This is of course a perfectly sensible and low-tech way of doing
> things.
>
> But I was lazier. When I first got my computer I just took the
> value for my wheel and tyre size from Sheldon's site. When I wanted
> to know how accurate it was, I cycled around 1km along a nice straight
> road and compared the distance measured with that reported by my GPS -
> and the results were within the measurement resolution of the cycle
> computer.
>
Lazy ?
My fat hairy yellow butt* it is!
My method can be done in the time it takes a mug of tea to get cool
enough to drink -- yours needs a microwave to warm the tea up later ;-p
'kin techjunkies I dunno (Muttley FX)
*Homer