I've killed my Cycle computer Help !

[BADGER.BRAD]

O.k so I just fitted a new chain sprocks and cassette to my bike and decided to zero my Cycle computer to see how many miles I get out of the new equipment,I pressed the reset button but have reset every option does anyone have any idea of my wheel size on cycle computers 26X1.6 as I seem to have also lost the instructions (they are somewhere very safe I'm sure!)

Many thanks all

Brad

 

[Ticktockmy]

O.k so I just fitted a new chain sprocks and cassette to my bike and decided to zero my Cycle computer to see how many miles I get out of the new equipment,I pressed the reset button but have reset every option does anyone have any idea of my wheel size on cycle computers 26X1.6 as I seem to have also lost the instructions (they are somewhere very safe I'm sure!)

Many thanks all

Brad

Depending on the make and if it a fairly new model (last 5 years), most intructions can now be downloaded from the makers website as a pdf.

 

[Brains]

[QUOTE 1176047"]
Roll the bike along the ground with you on it and measure the distance of 1 rev.

Remember as well to place the magnet towards the outside of the wheel (towards the rim), magnets placed near the hub go around quicker then those placed near the rim thus giving an inaccurate reading.
[/quote]


Cycle computers count revolutions, so it does not matter how close to the rim or hub the magnet is, as the number of revolutions remains constant.

The setting on cycle computers is to know how many millimeters a single revolution equals as different tyres (and even how pumped up the tyres are) will give different results.

I'm not sure the best way to work out the exact circumference as a ruler around the edge may not be the same circumference as loaded with a rider. Maybe mark a line with chalk on the tyre and then ride it across the kitchen floor ?

 

[HLaB]

If you want to be lazy Brad, you could use Sheldon's table; for a 26 x 1.5, its 1985 and for 26 x 1.9 its 2055. Taking in between (26 x 1.6) its 2002.5 (round to 2003) I think.

 

[BADGER.BRAD]

Many thanks everyone much appreciated, I used a piece of string and ran that around the circumference of the tyre giving me exactly 2000 MM The tyres run pretty high pressures so should remain at least very near this with me sat on. Just shows most things are simple when you know how !

Again many thanks all.

Brad

 

[Ticktockmy]

Cycle computers count revolutions, so it does not matter how close to the rim or hub the magnet is, as the number of revolutions remains constant.

The setting on cycle computers is to know how many millimeters a single revolution equals as different tyres (and even how pumped up the tyres are) will give different results.

I'm not sure the best way to work out the exact circumference as a ruler around the edge may not be the same circumference as loaded with a rider. Maybe mark a line with chalk on the tyre and then ride it across the kitchen floor ?

Again most for most make of tyre if you go to the makers website, they provide the required details, I set my Computer for my Schwalbe marathons from the table on there site, and the results are quite accurate

 

[661-Pete]

I find that the best way, is to first of all set an approximate wheel circumference on the computer, then go for a ride on a known level route between clearly identified end-points, and see what distance your computer shows, and compare it with the actual distance (this is a fairly accurate online calculator). Then a bit of simple arithmetic:
If you entered 'c' as your approx. circumference;
Your computer showed a distance travelled of 'd';
Google (or similar) showed the true distance as 'D';
Then you need to set the correct circumference on the computer, to C = c * D/d.

Simple!

 

[chillyuk]

[QUOTE 1176047"]
Roll the bike along the ground with you on it and measure the distance of 1 rev.

Remember as well to place the magnet towards the outside of the wheel (towards the rim), magnets placed near the hub go around quicker then those placed near the rim thus giving an inaccurate reading.
[/quote]

Whilst it makes no difference where on the spoke the magnet goes, I wonder if your statement about relative speeds is correct. I haven't done the maths to give proper figures, but take a wheel with a circumference of 5 feet near the rim, and 1 foot near the hub. If the wheel is revolved at one revolution a second, then the magnet near the hub will travel approx 1 foot per second, but the one near the rim will travel 5 feet per second. Therefore the one nearest the rim travels faster than the one nearest the hub.

Now watch someone with an education come and blow my theory to bits!!

 

[Midnight]

Whilst it makes no difference where on the spoke the magnet goes, I wonder if your statement about relative speeds is correct. I haven't done the maths to give proper figures, but take a wheel with a circumference of 5 feet near the rim, and 1 foot near the hub. If the wheel is revolved at one revolution a second, then the magnet near the hub will travel approx 1 foot per second, but the one near the rim will travel 5 feet per second. Therefore the one nearest the rim travels faster than the one nearest the hub.

Now watch someone with an education come and blow my theory to bits!!

You're sort of right. In a circle the circumference is given by pi x diameter, so if distance from centre is 1ft, then distance travelled would be 3.14 x 2 = 6.28 ft per revolution, and at 5ft would be 3.14 x 10 = 31.4 ft per revolution.

Lee has got it the wrong way round.

 

[sandman77]

Whilst it makes no difference where on the spoke the magnet goes, I wonder if your statement about relative speeds is correct. I haven't done the maths to give proper figures, but take a wheel with a circumference of 5 feet near the rim, and 1 foot near the hub. If the wheel is revolved at one revolution a second, then the magnet near the hub will travel approx 1 foot per second, but the one near the rim will travel 5 feet per second. Therefore the one nearest the rim travels faster than the one nearest the hub.

Now watch someone with an education come and blow my theory to bits!!

If a wheel is revolved at at one revolution a second then any single spoke will pass the fork once every second (both ends of the spoke will pass the fork at the same time).
The computer just measures the time it takes for the magnet pass the fork sensor (and hence the wheel do a complete revolution). The computer then just does a simple calculation (S=D/T) to calculate the speed you are travelling (D being the circumference of your tyre). It makes no difference where on the spoke the magnet is placed).

 

[Midnight]

The general concensus is that it's better to have the magnet mounted as close to the hub as possible. This means that the magnet passes the sensor more slowly, and is less likely to give erratic readings at high speeds. See Sheldon Brown's advice here... Sheldon Brown

 

[sandman77]

The general concensus is that it's better to have the magnet mounted as close to the hub as possible. This means that the magnet passes the sensor more slowly, and is less likely to give erratic readings at high speeds. See Sheldon Brown's advice here... Sheldon Brown

I had never thought of that but makes perfect sense.

 

[661-Pete]

The general concensus is that it's better to have the magnet mounted as close to the hub as possible.

True, but take care that the transmitter is firmly attached to the fork and can't swivel round and foul your spokes! Sometimes the mounting cradle will only fit at a higher point where the fork is wider. Also you may not get enough clearance for the magnet if you're too close the hub.

Some types of magnet that I've seen, are designed to clamp to two spokes. This is an advantage in that it can't swivel around, and it fixes the height of the magnet from the hub, however it obviously can only used on certain types of wheel. Anyone else come across these?