Speedo

Dave writtificated

Quoted message said:

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

Even the cheapest cycle computers that I've used let you enter your own
wheel diameter. Pump tyres up to your usual pressure, make a mark on tyre
and ground then sit on bike and roll 3 wheel revolutions forwards. Measure
distance and divide by three. This gives a pretty accurate diameter to
enter. I do it three times and take the average.

Mark T said:

Even the cheapest cycle computers that I've used let you enter your own
wheel diameter. Pump tyres up to your usual pressure, make a mark on tyre
and ground then sit on bike and roll 3 wheel revolutions forwards. Measure
distance and divide by three. This gives a pretty accurate diameter to
enter. I do it three times and take the average.

Circumference.

Otherwise I agree - far better than trusting the computer-maker's
estimates.

Colin McKenzie

--
No-one has ever proved that cycle helmets make cycling any safer at
the population level, and anyway cycling is about as safe per mile as
walking.
Make an informed choice - visit www.cyclehelmets.org.

Dave said:

Can anyone either recommend or give examples of faily basic cycle computers.

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and speed. You
can load the last known distance when you change the battery.

The problem I have with it appears to be that when I use my normal tyres
(700 35c - 37-622) it gives me a pretty accurate reading but when I put 700
38c it appears to be out - I lost 15% on a long ride at the weekend.

Unfortunately the manual that comes with it gives an option to set at 700
35c of 221 then the next one is 700 40c (40-622) at 222.

It appears to use a "it's near enough" principle. I would like to set it
better when I use these tyres.

Thanks
Dave

15% means about 100mm error on diameter. Are you sure it's not 1.5% ?

Roger Thorpe

On Wed, 25 Jun 2008 10:37:24 +0100

Dave said:

Can anyone either recommend or give examples of faily basic cycle
computers.

I am possibly after a new one to replace my Sigma 400 that is a
little restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and
speed. You can load the last known distance when you change the
battery.

The problem I have with it appears to be that when I use my normal
tyres (700 35c - 37-622) it gives me a pretty accurate reading but
when I put 700 38c it appears to be out - I lost 15% on a long ride
at the weekend.

There's something else going on - did you knock the sensor away from
the magnet when you changed the wheel, is there a poor contact in the
computer mount, if it's wireless is the sensor battery OK?

Quoted message said:

Unfortunately the manual that comes with it gives an option to set at
700 35c of 221 then the next one is 700 40c (40-622) at 222.

35-622 is nominally 692mm diameter, 40-622 is 702mm, a difference of
only 1.4%

Dave said:

Can anyone either recommend or give examples of faily basic cycle
computers.
I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and
speed. You can load the last known distance when you change the
battery.
The problem I have with it appears to be that when I use my normal
tyres (700 35c - 37-622) it gives me a pretty accurate reading but
when I put 700 38c it appears to be out - I lost 15% on a long ride
at the weekend.
Unfortunately the manual that comes with it gives an option to set at
700 35c of 221 then the next one is 700 40c (40-622) at 222.

It appears to use a "it's near enough" principle. I would like to set
it better when I use these tyres.

That'll be 221 and 222 cm circumference, so there can be nothing in between
if the computer's units are cm. Even some decent Cateye computers only
allow cm rather than mm. That is precise enough for most people.

I don't /think/ it could be responsible for 15% error. Cue the
mathmaticians. Please can you do the sums for us?

~PB

I scribbled:

Quoted message said:

I don't /think/ it could be responsible for 15% error. Cue the
mathmaticians. Please can you do the sums for us?

^ Ignore that. Done already by Riger & Rob.

~PB

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

Quoted message said:

Dave said:

Can anyone either recommend or give examples of faily basic cycle
computers.

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and speed.
You can load the last known distance when you change the battery.

The problem I have with it appears to be that when I use my normal tyres
(700 35c - 37-622) it gives me a pretty accurate reading but when I put
700 38c it appears to be out - I lost 15% on a long ride at the weekend.

Unfortunately the manual that comes with it gives an option to set at 700
35c of 221 then the next one is 700 40c (40-622) at 222.

It appears to use a "it's near enough" principle. I would like to set it
better when I use these tyres.

Thanks
Dave

15% means about 100mm error on diameter. Are you sure it's not 1.5% ?

I guess that there could have been other problems but I'm not sure what but
on a 127 mile ride I registered about 112 - so yes it is less than 15% now I
have taken the time to work it out but still more than 1.5%.

Dave

"Rob Morley" <[email hidden]> wrote in message
news:20080625125012.78dab28d@bluemoon...

Quoted message said:

On Wed, 25 Jun 2008 10:37:24 +0100

Dave said:

Can anyone either recommend or give examples of faily basic cycle
computers.

I am possibly after a new one to replace my Sigma 400 that is a
little restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and
speed. You can load the last known distance when you change the
battery.

The problem I have with it appears to be that when I use my normal
tyres (700 35c - 37-622) it gives me a pretty accurate reading but
when I put 700 38c it appears to be out - I lost 15% on a long ride
at the weekend.

There's something else going on - did you knock the sensor away from
the magnet when you changed the wheel, is there a poor contact in the
computer mount, if it's wireless is the sensor battery OK?

Quoted message said:

I guess that there could be something else adrift too.

I didn't change the wheel en-route and I know the sesor was fine before I
set off. It could have moved I guess whilst riding as it is not one of those
that is overtight.

Battery and holder I believe to be fine.

The weather was really bad but I'm not sure whether water between computer
and mount could cause problems.

Quoted message said:

Quoted message said:

Unfortunately the manual that comes with it gives an option to set at
700 35c of 221 then the next one is 700 40c (40-622) at 222.

35-622 is nominally 692mm diameter, 40-622 is 702mm, a difference of
only 1.4%

I guessed that there could not be much difference with there not been a
setting between 35 and 40. Imust admit though there doesn't appear to be
much reference to 38c tyres.

Dave

Dave said:

I guess that there could have been other problems but I'm not sure what but
on a 127 mile ride I registered about 112 - so yes it is less than 15% now I
have taken the time to work it out but still more than 1.5%.

Dave

Assuming that there are no other problems, and that what goes into the
computer is a circumference then, if your first test was with it set at
221mm then you need to use (127miles/112miles) *221 = 250mm

Roger Thorpe

Dave said:

The weather was really bad but I'm not sure whether water between computer
and mount could cause problems.

It could. There are various reports to be found via Google of cycle
computers not working in heavy rain, and I remember Mark Beaumont
(round the world by bike record holder) saying in the documentary of
his trip that somewhere in the southern US the rain was so bad that
his computer stopped working. He said that the official solution was
to apply silicone grease to the contacts to keep the water off, so he
used some saddle cream / gel that had silicone in it and it seemed to
do the job.

So it could be that you had enough rain that the terminals on the
computer shorted out periodically and reduced the recorded distance.
You might have noticed the computer reading 0 mph were it not for the
rain you had to keep wiping off your face.

Colin

Dave said:

Can anyone either recommend or give examples of faily basic cycle computers.

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and speed. You
can load the last known distance when you change the battery.

I've got a Cateye Enduro 8, and it does pretty much that, plus one or two
bells and whistles. You can configure the tyre size directly, telling it
the circumference, basically, and it can remember two sizes and switch
between them. I've had it for a couple of years, and have no complaints,
really.

The one annoying thing is that the choices between miles and km, and 12-
and 24-hour time are linked, so you can be imperial and 12-hour, or metric
and 24-hour, which is not a big practical problem, but is still
infuriating!

tom

--
Yesterday's research projects are today's utilities and tomorrow's
historical footnotes. -- Roy Smith

Dave said:

Can anyone either recommend or give examples of faily basic cycle computers.

Just bought a Cateye Strada wireless one yesterday, as it happens.
Have several old (>10 years) ones at home and/or on various bikes, but
none of them work any more (probably batteries in some cases, wlthough
I know at least one went through the washing machine.

Quoted message said:

It appears to use a "it's near enough" principle. I would like to set it
better when I use these tyres.

This one allows tyre circumferences in mm, as did, I think, all the
ones I've had before. Most actual tyre sizes are listed in a table,
and the setup is simple. Also very simple is the miles/km selection
and all other settings. Took me less than 5 mins from a stading start,
as it were.

Fitting was very straightforward too, also took me only about 5 mins.
In operation - well, I just did the trip home (25km) and it seemed
fine, but I remember in the past having frustrations about
auto-starting, which would probably be true here too, making it
difficult to get a true average speed or total time if you want to
include times when you're stationary. All the ones I saw were
auto-starting though.

--
Ace in Alsace - brucedotrogers a.t rochedotcom

In message <[email hidden]>, Ace
<[email hidden]> writes

Quoted message said:

Dave said:

Can anyone either recommend or give examples of faily basic cycle computers.

Just bought a Cateye Strada wireless one yesterday,

Fitting was very straightforward too, also took me only about 5 mins.
In operation - well, I just did the trip home (25km) and it seemed
fine, but I remember in the past having frustrations about
auto-starting, which would probably be true here too, making it
difficult to get a true average speed or total time if you want to
include times when you're stationary. All the ones I saw were
auto-starting though.

The Cateye Mity 8 has the option of auto stop/start or manual
stop/start, one of the reasons i like them.
--
Chris French

Tom Anderson said:

Dave said:

Can anyone either recommend or give examples of faily basic cycle computers.

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and speed. You
can load the last known distance when you change the battery.

I've got a Cateye Enduro 8, and it does pretty much that, plus one or two
bells and whistles.

Quoted message said:

The one annoying thing is that the choices between miles and km, and 12-
and 24-hour time are linked, so you can be imperial and 12-hour, or metric
and 24-hour, which is not a big practical problem, but is still
infuriating!

I should say so! My Cateye Strada has them independent.

One thing I find anoying though is that it only gives me total time
based on time travelling which is next to useless with the stop start
nature of riding in London. I'd like to know how long it took me to
ride a route without having to remember when I set off and looking at
my watch when I got to my destination. Other than that it does the
basics well. It's just a shame I haven't had much chance to use it on
my road bike of late. It hasn't been taken off the folding touring
comuting Birdy in over a year. :-(
--
Phil Cook looking north over the park to the "Westminster Gasworks"

Phil Cook said:

Tom Anderson said:

Dave said:

Can anyone either recommend or give examples of faily basic cycle computers.

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

It is a basic function thing with time, trip, total distance and speed. You
can load the last known distance when you change the battery.

I've got a Cateye Enduro 8, and it does pretty much that, plus one or two
bells and whistles.

The one annoying thing is that the choices between miles and km, and 12-
and 24-hour time are linked, so you can be imperial and 12-hour, or metric
and 24-hour, which is not a big practical problem, but is still
infuriating!

I should say so! My Cateye Strada has them independent.

One thing I find anoying though is that it only gives me total time
based on time travelling which is next to useless with the stop start
nature of riding in London. I'd like to know how long it took me to ride
a route without having to remember when I set off and looking at my
watch when I got to my destination.

Ah, right, you have auto stop/start, so it only counts the time you're
moving. Mr French says the Mity 8 has the ability to switch that off; i
think the Enduro 8 does too (in fact, i think the Enduro 8 is a Mity 8
with a different, more MTB-styled casing).

tom

--
Yesterday's research projects are today's utilities and tomorrow's
historical footnotes. -- Roy Smith

Colin McKenzie writtificated

Quoted message said:

Quoted message said:

diameter

Quoted message said:

Circumference.

🙂

On 25 Jun 2008 09:58:29 GMT, Mark T
<pleasegivegenerously@warmail*turn_up_the_heat_to_reply*.com.invalid>

Quoted message said:

Quoted message said:

I am possibly after a new one to replace my Sigma 400 that is a little
restrictive on tyre sizes.

Even the cheapest cycle computers that I've used let you enter your own
wheel diameter. Pump tyres up to your usual pressure, make a mark on tyre
and ground then sit on bike and roll 3 wheel revolutions forwards. Measure
distance and divide by three. This gives a pretty accurate diameter to
enter. I do it three times and take the average.

That should give the best results, of course, but if you're in a
hurry, I've found that Sheldon's "quick" method:

<http://sheldonbrown.com/cyclecomputer-calibration.html#iso>

is accurate to within 1%.

Quoting Dave <[email hidden]>:

Quoted message said:

The problem I have with it appears to be that when I use my normal tyres
(700 35c - 37-622) it gives me a pretty accurate reading but when I put 700
38c it appears to be out - I lost 15% on a long ride at the weekend.
Unfortunately the manual that comes with it gives an option to set at 700
35c of 221 then the next one is 700 40c (40-622) at 222.

This is a 0.5% difference. Your problem is not with the cycle computer
itself, which can be set to an accuracy of 1cm in 2 metres of
circumference, but with the conversion chart between nominal sizes and
circumferences and/or with the way tyres are often not the same size they
claim to be.

Do a rollout test for an accurate reading.
--
David Damerell <[email hidden]> Kill the tomato!
Today is First Wednesday, Presuary.