That was fast!

Don Whybrow said:

I was in our local Sainsbury's the weekend before last and saw that they
stock Tchibo stuff. Aha, thought I, there was much discussion about the
cheap cycling goodies on urc. So I bought shorts, shirt & computer. The
largest size they had in the shorts and shirt were L. Shorts are OK, but
the shirt is a bit tight.

Last weekend I managed to get to the shed for some fettling time on my
bikes and I fitted the computer to my fixie after putting in the correct
numbers for the tyres. On getting to work on Monday I checked max &
average speed and the max was at around 40mph. Something fishy I
thought, but I put it down to the fact that when I had put it on I had
spun the front wheel to confirm that it was recording and I had perhaps
been a bit zealous. Last night I reset the relevant numbers ready for
today.

Going into work my fasted bit is going down Liberton Brae and I let it
run, spinning my feet as fast as I was able. Glancing down at the
handlebars I saw that I was going just over 30mph. Considering that I go
down this on my tourer at around 35-37mph when I just let it roll, I was
chuffed. When I got to work I had a look at the max, 47mph, hmmm!

On the way home, my fastest bit is going down to Cameron Toll from the
Bridges. The road name changes too often to remember the exact bit. As
my feet frantically flapped I saw that I was over 32mph. At home I
checked the max again, 53mph, double hmmm!

If anyone has a calculation for working out cadence from the speed of a
bike, I would like to work out how fast my feet were supposed to have
been spinning at 53mph. I suppose I could go and figure it all out, but
is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to work
and 26.5mph home.

Does it say mph? The figures sound normal for km/h.

Don Whybrow said:

On the way home, my fastest bit is going down to Cameron Toll from the
Bridges. The road name changes too often to remember the exact bit. As
my feet frantically flapped I saw that I was over 32mph. At home I
checked the max again, 53mph, double hmmm!

If anyone has a calculation for working out cadence from the speed of a
bike, I would like to work out how fast my feet were supposed to have
been spinning at 53mph. I suppose I could go and figure it all out, but
is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

252rpm

Quoted message said:

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to work
and 26.5mph home.

I had a cheap Lidl computer which also gave spurious high top speed readings.
It always seemed ok when I was riding along, except when stopped at traffic
lights with buried sensor loops, when the speed would go crazy. Perhaps
riding over one of these at normal speeds gives just enough of a blip to
give a plausible seeming max speed which the computer saves.

cheers,

Finlay

Don Whybrow said:

I was in our local Sainsbury's the weekend before last and saw that
they stock Tchibo stuff. Aha, thought I, there was much discussion
about the cheap cycling goodies on urc. So I bought shorts, shirt &
computer. The largest size they had in the shorts and shirt were L.
Shorts are OK, but the shirt is a bit tight.

Last weekend I managed to get to the shed for some fettling time on my
bikes and I fitted the computer to my fixie after putting in the
correct numbers for the tyres. On getting to work on Monday I checked
max & average speed and the max was at around 40mph. Something fishy I
thought, but I put it down to the fact that when I had put it on I had
spun the front wheel to confirm that it was recording and I had
perhaps been a bit zealous. Last night I reset the relevant numbers
ready for today.
Going into work my fasted bit is going down Liberton Brae and I let it
run, spinning my feet as fast as I was able. Glancing down at the
handlebars I saw that I was going just over 30mph. Considering that I
go down this on my tourer at around 35-37mph when I just let it roll,
I was chuffed. When I got to work I had a look at the max, 47mph,
hmmm!
On the way home, my fastest bit is going down to Cameron Toll from the
Bridges. The road name changes too often to remember the exact bit. As
my feet frantically flapped I saw that I was over 32mph. At home I
checked the max again, 53mph, double hmmm!

If anyone has a calculation for working out cadence from the speed of
a bike, I would like to work out how fast my feet were supposed to
have been spinning at 53mph. I suppose I could go and figure it all out,
but is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to
work and 26.5mph home.

There's a calculator on Sheldon Brown's site. IME 40mph upwards feels very
scary on a road bike on anything but a very smooth road. The same speed on a
mountain bike on the same road seems fine...

Don Whybrow said:

If anyone has a calculation for working out cadence from the speed of a
bike, I would like to work out how fast my feet were supposed to have
been spinning at 53mph. I suppose I could go and figure it all out, but
is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

48*18 @ 80 revs is 30.3 kph
http://p_carre.club.fr/index.htm

In article <[email hidden]>, Don Whybrow
[email hidden] says...

Quoted message said:

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to work
and 26.5mph home.

If the wheel magnet is hitting the sensor it can cause a double click.
Other vibration may also rattle the reed switch. If it's wireless then
electrical interference might confuse it - my Lidl cheapo wireless thing
goes crazy near the security scanners in shop doorways.

Don Whybrow said:

I was in our local Sainsbury's the weekend before last and saw that they
stock Tchibo stuff. Aha, thought I, there was much discussion about the
cheap cycling goodies on urc. So I bought shorts, shirt & computer. The
largest size they had in the shorts and shirt were L. Shorts are OK, but
the shirt is a bit tight.

Last weekend I managed to get to the shed for some fettling time on my
bikes and I fitted the computer to my fixie after putting in the correct
numbers for the tyres. On getting to work on Monday I checked max &
average speed and the max was at around 40mph. Something fishy I
thought, but I put it down to the fact that when I had put it on I had
spun the front wheel to confirm that it was recording and I had perhaps
been a bit zealous. Last night I reset the relevant numbers ready for today.

Going into work my fasted bit is going down Liberton Brae and I let it
run, spinning my feet as fast as I was able. Glancing down at the
handlebars I saw that I was going just over 30mph. Considering that I go
down this on my tourer at around 35-37mph when I just let it roll, I was
chuffed. When I got to work I had a look at the max, 47mph, hmmm!

On the way home, my fastest bit is going down to Cameron Toll from the
Bridges. The road name changes too often to remember the exact bit. As
my feet frantically flapped I saw that I was over 32mph. At home I
checked the max again, 53mph, double hmmm!

If anyone has a calculation for working out cadence from the speed of a
bike, I would like to work out how fast my feet were supposed to have
been spinning at 53mph. I suppose I could go and figure it all out, but
is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

I also have a Touche with the same gearing and by my reckoning 20mph =
93 rpm, 30mph = 140 rpm. I don't often get to 30!

Dave

Don Whybrow said:

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to work
and 26.5mph home.

--
Don Whybrow

Here's a calculator for you:

http://www.kreuzotter.de/english/ecadence.htm

Not so long ago I got a new personal best of 185rpm and 58.6km/hour.
Not that impressive when I know a couple of people who've beaten the
magic 200.

In article said:

Don Whybrow said:

If anyone has a calculation for working out cadence from the speed of a
bike, I would like to work out how fast my feet were supposed to have
been spinning at 53mph. I suppose I could go and figure it all out, but
is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

48*18 @ 80 revs is 30.3 kph
http://p_carre.club.fr/index.htm

And http://home.earthlink.net/~mike.sherman/shift.html will give you a table of
speeds in each of your gears for a given cadence (among other formats).

LSMike said:

Don Whybrow said:

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to work
  and 26.5mph home.

Sounds likely- probably not enough "debounce" on the contacts

Quoted message said:

Here's a calculator for you:

http://www.kreuzotter.de/english/ecadence.htm

I like this one:

http://software.bareknucklebrigade.com/rabbit.applet.html

Which does gear equivalents and stuff, too.

Quoted message said:

Not so long ago I got a new personal best of 185rpm and 58.6km/hour.
Not that impressive when I know a couple of people who've beaten the
magic 200.

Well, I'm impressed...! I think my PB is about 170, though I'm
usually watching the road, rather than the clock, so I'm not sure!

There's a piece on the 63xc website about how to adapt a computer to
read cadence, but it misses the point that there's a direct
relationship between wheel rpm and cadence, so you don't need to
measure pedal rpm, just work out a calibration that maps your wheel
rpm to cadence via your preferred gear ratio.

e.g. Computer calibrated by wheel circumference in millimetres, set
to read out in Km/h:

Using the online calculator, my gear ratio of 52x22 and wheel
circumference at 2105mm (700x25c): at (say) 30 km/h, the cadence is
100rpm, so to get the display to read cadence, divide the calibration
figure by 100/30 (2105/(100/30)=631). Not all computers will accept a
value this low, apparantly, but for those that will you now have a
cadence display.
I'm not sure about some of the number, here (it's been a while since
I set this up) but I hope you get the idea.

Cheers,
W.

Don Whybrow said:

max &
average speed and the max was at around 40mph. Something fishy I
thought

What type of cycle computer do you have?

My Cateye Velo 5, used with my old-fashioned Raleigh Sports, regularly
registers over 180mph (I wish, though the effort in moving the bike
makes it seem like that *should* have been the speed!). Whatever
causes a silly top speed is never enough to make a visible difference
to the distance travelled.

My lad's Velo 5 never messes about with silly figures, and nor do any
of our Velo 8s.

PhilD

--
<><

Nick said:

Does it say mph? The figures sound normal for km/h.

They do, but all the other numbers are in mph, so unless the max alone
is shown as kph ...

--
Don Whybrow

Sequi Bonum Non Time

Give your child mental blocks for Christmas.

PhilD said:

Don Whybrow said:

max &
average speed and the max was at around 40mph. Something fishy I
thought

What type of cycle computer do you have?

Tchibo cheapo, probably the root cause.

--
Don Whybrow

Sequi Bonum Non Time

Give your child mental blocks for Christmas.

Don Whybrow said:

If anyone has a calculation for working out cadence from the speed of a
bike, I would like to work out how fast my feet were supposed to have
been spinning at 53mph. I suppose I could go and figure it all out, but
is has been a long day. Tyres are 25-622, gearing 48x18, crank 170mm.

Either that or there must be "feature" with this calculator to double
count the clicks under given conditions when I was going 23.5mph to work
and 26.5mph home.

Thanks for all the calculators & stuff.

Considering the cost/quality of this piece of kit I can live with the
false readings now that I know they occur. As suggested on the thread
these could be due to induction loops or bounce. I do not think the
magnet is striking the detector.

--
Don Whybrow

Sequi Bonum Non Time

Give your child mental blocks for Christmas.