1. The cyclometers I installed on bikes have a magnet attached on a spoke and a sensor to the bikeframe. What the meter detects, meassures or calculates has nothing to do with the speed of the bike. This shows when the wheel is lifted from the floor and rotates freely...The meter gives a speed as always corresponding to the wheels frequency.

Once the wheelsize is part of the calculationprogram where the sensor or magnet are on the wheel also makes no difference. So if the cyclometer sensor detects the speed of the magnet it apparently detects the same speed for any magnet on the wheel no matter the distance to the axis of rotation or where the sensor is on the bike. If it doesn,t detect speed what does it detect for one wheelcycle ?

I suppose the connection between the sensor and the magnet is somewhat comparable to the connection between a hand and a stopwatchbutton but then...? If it does 1/T then what is 1 unitwise. Just a number n=1 or 2 pi radials or 1 rev as a time unit of the wheel ? Is the registration just a matter of counting : (1+1)-1=1 then 1 is also a unity of the wheeltime I suppose (be aware registration, observing is not equal to measuring ; measuring results in equivalants and correspondency,s but is not observing things as the same things).

And does the sensor just count passages (1+1)-1 or does it register a cycle of the magnet (the magnet also makes a spin with the wheel but does not move or spin to the wheel and the wheel doesn,t move to the further parts of the bike (if this happens there is a problem within the bike).

I use (1+1)-1 here because the wheel often starts before the first passage of the magnet. The sensor has to count to passages to be able to derive a T for the wheel (as a measurement).

Be welcome to elaborate on this freely if possible with analyzing unity,s (without "just numbers").

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• try here ,this might tell you what you want to know Cyclocomputer - Wikipedia, the free encyclopedia

• For one thing counting wheelcycles is wrong there I think (not sure). It counts passings of what is attached to one of the spokes.

Two passings suffices for the meter to funktion and give a value on the screen (even though it pops up later maybe) that,s counting 1,2 (or 0, 1) that,s 2 passings but 1 for wheelcycle. Is that counting wheelcycles ?

Then there are seconds correspondingly to one cycle from the clock. Unitywise [rev/sec] comes out as the measurement and from that the meter calculates. If angle change where a dimension and cycle or revolution as unity it would be cycle /sec for unities. [/sec] if it,s not. Using n here for counting further for a frequency is not necessary for the working principle because the meter funktions to one cycle allready.

/sec frequency if sec is not one second. For instance 0,5 seconds / 1 cycle is 1 cycle / 0,5 seconds but not 2 cycles to 1 second.

If it where I could drive 0,5 seconds at that speed and travel as far as when I travel 1 second with same intensity.

It gives a conflikt between vector and scalar for velocity in newton fysics when the euclidean space has it,s referencepoint for instance at home or a cycleshop where you by a new bike.

If the euclidean space that is reference would be attached to the bike there is no speak of speed for a bike offcourse (or it has a speed to itself) and also not a speed of the wheel or a spoke to the bike because a wheel is part of the bike.

• It counts the revolutions,on the controller the wheel size is input(possibly the computer can determine by sensor),and then its a simple maths problem..
speed=distance/time

• Originally Posted by Ghrasp
For one thing counting wheelcycles is wrong there I think (not sure). It counts passings of what is attached to one of the spokes.

Two passings suffices for the meter to funktion and give a value on the screen (even though it pops up later maybe) that,s counting 1,2 (or 0, 1) that,s 2 passings but 1 for wheelcycle. Is that counting wheelcycles ?

Then there are seconds correspondingly to one cycle from the clock. Unitywise [rev/sec] comes out as the measurement and from that the meter calculates. If angle change where a dimension and cycle or revolution as unity it would be cycle /sec for unities. [/sec] if it,s not. Using n here for counting further for a frequency is not necessary for the working principle because the meter funktions to one cycle allready.

/sec frequency if sec is not one second. For instance 0,5 seconds / 1 cycle is 1 cycle / 0,5 seconds but not 2 cycles to 1 second.

If it where I could drive 0,5 seconds at that speed and travel as far as when I travel 1 second with same intensity.

It gives a conflikt between vector and scalar for velocity in newton fysics when the euclidean space has it,s referencepoint for instance at home or a cycleshop where you by a new bike.

If the euclidean space that is reference would be attached to the bike there is no speak of speed for a bike offcourse (or it has a speed to itself) and also not a speed of the wheel or a spoke to the bike because a wheel is part of the bike.
You are making this way more complicated than it really is. Sure, there will be an error in the distance calculated, but it will be no more than the circumference of the wheel, a couple of meters maybe. And how would you expect it to calculate a vector velocity? It is just a dumb counting machine, counting the revolutions of the wheel.

• Originally Posted by brane wave
It counts the revolutions
Why you use the term counting revolutions. It takes only one revolution for these things to funktion and give a value on the display. If that,s all for the instrument then how can an adequate explanation need the multiple form or n if 1 allready suffices.
There is no need for an n then.
I,m not asking to go for a bikeride ...

• im not sure what you want to know? if you mean why use n,then its easily explain as a continuous input (n) is needed to update the speed ,which is a variable..hope this helps

• Ok but an update is not needed for the funktioning of the device. N=1 then stop you have a value. Using N is not usage for that in math (simply because it,s not necessary ; 1 is 1).

N has a funktion for distance but that,s a different compartiment of the cyclometer I mean the velocity meter or speedmeter and questioning if it meassures speed in the newtonian sense.

For instance the updating you refer to is done for the next cycle and the value on the screen can be different then. But the position for the euclidean space used as reference has changed then. That may be logic and obvious for you and me also but for |newton fysics it,s highly unusual. Most Newtonian expressions have a static euclidean space as reference.

So the cyclometer seems to be a strange (or popular ?) mixture of moving (euclidean) referenceframes mixed with newtonian expressions for speed.

I programmed such a meter a few times with making a marking A on the floor and the valve down. Then drive the bike by hand and when the valve is down again make a next marking B. Then use this distance as imput.

What you mention is driving this distance and use T for one cycle for time. C/T is circumference to time and when the wheel is on the floor and doesn,t slip c/T=dS/T. The speedmeter scratches the result with every cycle and then uses marking B as referencepoint for the next cycle aso...

That implies making up a new reference space with each cycle. For a vector this means the head is the tail for the next meassurement. Velocity in Newton fysics the vector tail is tied at the referencepoint for the euclidean space. Scalar not but then the velocity meter gives a pure scalar value. That on itself is ok but it does this with a varying T ; C/T and the further part is calculating not measuring.

I can calculate myself and asking what the device technically measures for one cycle. Units, dimensions aso.

• Thats correct,each revolution is a new reference space.

• So if you drive a bike a new space is born each wheelcycle, expands to 2 pi r then the next space comes in and so on. T is the variabel time between two spaces (the former and next)
and dS (the same for all speeds 2 pi r) for the calculation is a constant interval for distance between the former and next space not a movement within the last space or towards the next (that doesn,t exist yet) but a constant expansion.

And what,s an accelleration or deceleration to that then, using a constant time interval (second) for the changing rate of speed (dS/dT)/dt ? :-)

• Originally Posted by Ghrasp
So if you drive a bike a new space is born each wheelcycle, expands to 2 pi r then the next space comes in and so on. T is the variabel time between two spaces (the former and next)
and dS (the same for all speeds 2 pi r) for the calculation is a constant interval for distance between the former and next space not a movement within the last space or towards the next (that doesn,t exist yet) but a constant expansion.

And what,s an accelleration or deceleration to that then, using a constant time interval (second) for the changing rate of speed (dS/dT)/dt ? :-)
The calculus notation you are using is not appropriate to the equipment being used. It is digital. The indicated velocity is simply the wheel circumference divided by delta-t between the last two pulses. Or possibly it may be an average over the last so many intervals, which would tend to smooth out the indicated reading so the reading doesn't jump around with every rotation of the wheel. It all depends on how the computer is programmed.

• Originally Posted by Harold14370
Originally Posted by Ghrasp
So if you drive a bike a new space is born each wheelcycle, expands to 2 pi r then the next space comes in and so on. T is the variabel time between two spaces (the former and next)
and dS (the same for all speeds 2 pi r) for the calculation is a constant interval for distance between the former and next space not a movement within the last space or towards the next (that doesn,t exist yet) but a constant expansion.

And what,s an accelleration or deceleration to that then, using a constant time interval (second) for the changing rate of speed (dS/dT)/dt ? :-)
The calculus notation you are using is not appropriate to the equipment being used. It is digital. The indicated velocity is simply the wheel circumference divided by delta-t between the last two pulses. Or possibly it may be an average over the last so many intervals, which would tend to smooth out the indicated reading so the reading doesn't jump around with every rotation of the wheel. It all depends on how the computer is programmed.

Ok thanks, I always get confused with the notations d is for derivate and delta I don,t have on the computer or don,t know where to find it. I,m a noob with computers. We didn,t use them during my technical education as today. So I often use d for delta also. I do know the difference but it,s a bit part of the problem as how I see it in that these meters can confuse this. If the cyclometer can work based on one T (or 2 or three but distinct) it allready shows there is no delta T for that one meassurement possible. How is a derivate possible without a delta T to begin with.

You mention the wheel circumference divided by T. But the repeat is for a whole cycle, 1, 2, 3 or more (if they want to avoid constant jumping) This is very well possible because it always takes a while before it gives a value.

But this needs a corresponding cycletime for a distinct amount of cycles as well then. For instance T for five wheelcycles and calculate with 5*C instead of C. The principle stays the same because of that it,s not n / T then but n* 1/ n* T (and 1/T would be the mediation from that not vice versa).

The frequency on a bike is seldomly a whole number for a second. I suppose these things can only observe collect numbers for passings of the magnet on the spoke 1, 2, 3 or 5 whatever it uses for n. Not 2,5 cycle. It would be very inaccurate at low speeds for translating to m/sec or even miles/hour.

5 * circumference and corresponding 3,25 sec then make (5 * 2pi r /3,25) / sec for the display or even the more usual km/hours gives a very high inaccuracy.
I can,t imagine it works that way because of that especially not with bikes with relative big wheels and low speeds.

Apart from that inaccuracy the 2 pi angle in C=2 pi r is not usual for a speedmeassurement but for calculating.

Remember the device including the programm is totally blind for if there is a real trajektory or not. Once it is installed and programmed any wheel can be attached to the bike and with the same T the display shows the same value.
I still think these things observes a cycle by two passings (comparable to starting and stopping a stopwatch for a random event) and meassure T with that.

That data enters the programming part and the meassuring part stops with it. That,s why it,s blind for a different wheelsize when the wheels don,t touch the floor.

But the programm uses a constant for distance S (C) then : 2 pi r (or n * (2 pi r) if its programmed to work with more then one wheelcycle).
T is variabel between meassurements instead of S and that is highly unusual for Newton fysics ; a speed that has no relation to a dS to a euclid space.

• You could program your computer to do it either way. The computer will have a clock circuit that generates pulses. The computer can also receive pulses from the sensor on the wheel. The pulses could be stored in a register, then on some trigger, you simply divide the contents of the "distance" register by the contents of the "time" register. The result would be displayed as speed. The instruction to perform the division could be triggered either by the accumulated time or the accumulated distance, however you wanted to do it. As you point out, triggering the calculation upon the lapse of time could cause more error at slow speeds than triggering it upon the completion of some fixed numbers of revolutions, as you may miss a fraction of a revolution.

• I don,t know what you mean with time register if the instrurment only needs one T (two pulses). Using a stopwatch for timing it,s not usage or necessary to use a second clock for timing the stopwatchtime. I see the measuring part more as comparing two clockunits with the wheel as an old fashioned hands clock. T is a fluctuating unit for that clock and with a linear speed T is constant. But comparing to clocks (or a clock and a semi clock if you want) is not meassuring speed in the sense of Newton fysics offcourse. Seconds used to be a unit for angle also if I,m not mistaken.

• I can't understand what you are saying. The device is a computer. It has an internal clock that generates digital pulses. It is not an old fashioned clock with hands. A register is a computer device used for storing digital numbers. The computer clock will typically generate many pulses per second, not two pulses. Units of angle are measured in degrees, minutes, and seconds. This has nothing whatsoever to do with the measurement of time, unless you are using a sundial.

• The whole devise for the cyclometers I installed and programmed consists of two parts. one part is mounted on one of the spokes and is not a computer. I suspect this to be a magnet but never really tested this (haven,t got one around to test for magnetism at the moment).
I don,t suspect the computer to send random pulses at regular times but the pulse comes from (or is?) the passage at close distance.

It first needs one passage, then the next..t1-t0=T is the corresponding clocktime then to a wheelcycle 1.

1/T or T/1 is how they relate just as a drummer and a bassplayer in a band relate with different rhytm.
The spoke with the magnet on more or less resembles the hand of an old fashioned hands clock and the computer has a more modern clock. The computer compares the two in a way.

The problem is that the scalar for Newton fysics is never variable but always a distinct time. Mostly a second. The scalar-time can be different. An hour trip on a bike you can use an hour as scalar time unit with no idea what happens between the meassurements taken with an hour distance. Someone can drive very fast then take a lunch and a short nap and arrive same time with someone driving a more regular speed for shorter scalar times (using a scalartime of a second would show this).

For an hour as scalar time it,s the same. Here T seems to funktion as scalartime in the sense of newton fysics but a unity that can fluctuate. If the screen says velocity or speed then what does it mean if it can,t be for speed or velocity in the newtonian sense ?

T is not the wheelcycle imput but the clock imput correspondent to the wheelimput. Just as pushing the buttons on a stopwatch correspondent to an event.
In this case each wheelcycle is 1, a mathematical unit. Or two or three and then 2 or three wheelcycles could be 1 cycle for the instrument to work with and use as mathematical unit.

• Originally Posted by Ghrasp
If the screen says velocity or speed then what does it mean if it can,t be for speed or velocity in the newtonian sense ?
It's an average speed.

• If I go for a bike ride for five minutes with speed the meter saying 20 miles an hour is twenty miles an hour the mediated or average speed then ? I drove only ten minutes so where is the hour to mediate for ?
Mediating is when you have a serie of measurements for consequtive interfalls as a second.

10/1, 5/1, 2/1, 3/1....mediated 20/4 and average 5/1 can be the scalar value derived from that but if the trip is shorter then what the screen mediates for...it would mediate and with that predict for the future.

The programm manipulates the imput by calculation to make it fit to the desired unity of time mostly an hour.

But the programm repeats itself every cycle T and refreshes the screen value.

• Do you understand that if you go 10 miles in half an hour, you have averaged 20 miles per hour? And if you go 5 miles in a quarter of an hour, you have also averaged 20 miles per hour? Well, interpolate that down to a few seconds or a few revolutions of the wheel, and you will understand what the computer display is telling you.

• You have incredible patience Harold

• Originally Posted by Harold14370
Do you understand that if you go 10 miles in half an hour, you have averaged 20 miles per hour?
To be honest no and you don,t either. You think you do but you only explain a certain type of calculation. I cán calculate but that,s not saying I think it is always appropriate or meaningfull.

I understand when I drive 8 miles in "half an hour" and 12 in the next or other "half hour" that,s 20 for an hour . ..average 2*10 miles for two half hours. Or 10+10 with the same average (2*) as result for that hour. "An average half hour" or "an average 10 miles" is meaningless. It needs information about that other half hour. Is it a pausing half hour or drive backwards or what ? In case of a pause average is 5 miles for both half hours and mediated 10m/h.

• I wasn,t aware I was asking for someones patience or any other favor.

A cyclometer on a bike cóuld funktion different. When every spoke had a magnet it could meassure a delta angle / sec with some accuracy even at low speed. That value meassured for five seconds could be multiplied 3600/5* .......
An extrapolation to km/h could come out with some accuracy then. Not because of mediation but because measuring faults are in both directions and will cancel each other out. That has nothing to do with mediating or meassuring but could be how the programm "works".

The eventuell distance is a case of throwing dice then. 4 cycles measured are interpreted as 4,5 then.

That can be 4,00001 or 4,999999 and 4,5 is the mediation. 1 cycle for a given period to the calculator is interpreted as 1,5....But cycletime for the wheel less then the clocktime is impossible to calculate with then. The installed clockperiod would have to be bigger then the cycletime for the wheel otherwise it falls back to zero because it can,t meassure a half cycle or 0,99 cycle.
It keeps waiting for the second pulse then not knowing if the wheel rotates or not.

• Originally Posted by Ghrasp
Originally Posted by Harold14370
Do you understand that if you go 10 miles in half an hour, you have averaged 20 miles per hour?
To be honest no and you don,t either.
Wow. You have no hope of understanding how a cyclometer works if you cant understand that. My one uses the time per revolution of the wheel to calculate speed. So it would be v=(wheel circumfrence) / (time per revolution). The cyclometer will perform this calculation every time it detects a revolution, then update the screen display at a readable rate. Note that this gives you your average speed for every circumference of the wheel you move. That is about as close to your instantaneous speed as you can get from a cyclometer.

All the cyclometer does is measure the time since the magnet last passed, and then when it detects the next pass it performs a simple calculation using the time measured and the wheel circumference.

Most cyclometers I've seen, mine included, allow you to set wheel diameter for better accuracy. Cheaper ones use a default wheel size, which will induce an error, the percentage of which corresponds to the defaults deviance from the actual wheel size.

• It calculates for an hour with the information about half an hour. The device doesn,t have the possibillity to measure for anything else then T=n seconds. If T=3 it can,t measure for t=1 steps.

The ones I have seen did measure medium speed but I doubt they use the T,s and corresponding clocktimes for that.
Counting cycles of the wheel, seconds for time after the clock was put to zero and using the installed circumference (the computer calculates only one time during installation : pi*D) is far easier then using all different T,s for that. That gives nicely distinct time intervals (seconds I suppose). One given distance (circumference) and counting cyclii ; total cyclii, total triptime then give the ratio comes out 20 in this case but from when the clock was set to zero it can never be for both an hour and a half hour trip (or something in between). Reversed is possible : If the question from Harold had been : "do you understand that for a twenty miles one hour trip the average speed is ten miles for two half hours...I can understand that as averaging to two half hours. Fourty miles distance in two hours gives an average 20m/h I also understand that. But not as how Harold puts it.

For how the device does this (with the wheel as part of the measuring device) : before the trip strarts there is not another half hour if the clock was set at zero at the start of the trip (as usual). If this is forgotten during a stop the mediated speed for the triptime is much lower value. The part of the trip that lies in the future is unknown and also can,t be used to make up for an hour ...where would the other half hour have to come from then to make up an average for an hour with only information that corresponds with half an hour clocktime ?

• When your bike speedometer is reading 20 mph, what it is telling you is this: "If you continue for 20 miles at the same average speed as you have been traveling for the last several rotations of the wheel, it will take you 1 hour to get to your destination. Furthermore, it would require 1/2 hour to go 10 miles at the same rate. However, should you decide to stop for lunch on the way, I have no way of determining how long it will take." Or maybe the speedometer would just say "Arrrrgggghhh."

• I often take the bike for much shorter trips then an hour. The time before and after are not involved then. And for these bike meters, people who use these things will mostly stop/reset the clock after a trip and start it with the trip. It,s a stopwatch more then a clock. That means a distinct total triptime with - thus (classic fysics) - a distinct total distance. So no reason for the Arrrrghhh from the meterside. The reading (you do) on the meter has the value and the km/h at seperate layers. The m/h can be written on the device beside the screen (or in the manual) and n*m/h would be the more general notation I suppose (?).

n can be 1 or less or more. If it,s less then one there is no hour involved and then the Arrrghhhh applies for "Do you understand that if you go 10 miles in half an hour, you have averaged 20 miles per hour?". If the total time is half an hour. And if the total time is an hour I don,t understand either.

Asking this to a meter that has only a registered clocktime of half an hour it won,t understand the question.

I understand averaging if the trip has a set goal before departure at an allready known distance 20 miles (that was measured earlier)....The first half hour is 10 miles the next also... then...ten/half hour could be the average value for the distance/time half an hour later but 20 m/h the total tripdistance/total time. Just as when the first half hour would correspond with 2 m/half hour and the second 18 m/half hour. That has same total 20 m/h and same average for both half hours.

What will be or what is planned is not a subjekt or concern for the topic.

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