using PT without the hub

[doctorSpoc]

is there something special that i need to do other than change the mode to km - HR and add a magnet to the back wheel to use my PT as a regular cyclo-HR computer? i have added the magnet and changed the mode but i get completely screwy speed/distance readings... looking at the unit i generally too low readings but with are few super high speed readings so the distance usually ends up being way too high. do i need to use a special magnet? i am just using the one that comes with Ksyriums (plastic with metal sleeve)

 

[acoggan]

is there something special that i need to do other than change the mode to km - HR and add a magnet to the back wheel to use my PT as a regular cyclo-HR computer? i have added the magnet and changed the mode but i get completely screwy speed/distance readings... looking at the unit i generally too low readings but with are few super high speed readings so the distance usually ends up being way too high. do i need to use a special magnet? i am just using the one that comes with Ksyriums (plastic with metal sleeve)

No, it sounds like you should be good to go. Thus, I'm guessing that the magnet you're using just isn't strong enough to reliably trip the reed switch in the sensor, at least at the present distance between them. The solution is, well, obvious: use a stronger magnet and/or move the sensor close to the magnet (and make sure that they are aligned properly).

If that doesn't solve the problem, I'd next try replacing the wiring harness/sensor...

 

[Krazyderek]

my ksyrium magnet works fine, i think mine's setup for 3 or 4 mm from the sensor. How old is the battery in the CPU? i'd try replacing that first. Also make sure you're on the latest firmware, the earlier versions were kinda buggy with the cyclo computer mode.

 

[kennethn]

Do you have any other sensors on your bike? I got the wild readings in no-hub mode at first before I removed my old Polar sensors.

 

[palewin]

my ksyrium magnet works fine, i think mine's setup for 3 or 4 mm from the sensor. How old is the battery in the CPU? i'd try replacing that first. Also make sure you're on the latest firmware, the earlier versions were kinda buggy with the cyclo computer mode.

This sounds like good advice. I've been using my PT in cyclocomputer mode for a couple of weeks (wheel is back in Wisconsin for repairs) and the main issue is the distance of the pickup to the magnet. I just pushed the pickup in towards the wheel (the pickup should be parallel to the PT hub in normal "power mode" but in cyclocomputer mode can be as "unparallel" as you want - I push mine so that it just clears the magnet). If you look at your speed graph (cyclingpeaks to the rescue!) the only time I sometimes get fluky readings is standing still at stoplights (I bet there is an issue if the magnet comes to rest just at the pickup) so that I'm doing 50mph when I know I'm standing still... The only time I got a "low" distance was when a pothole moved the receiver too far away from the magnet (and that became obvious when I looked at the supposed speed while riding, so I stopped an repositioned the pickup.)

 

[doctorSpoc]

thanks... i'll try it with a stronger magnet... works flawlessly with the hub so i'm not sure if it would be the harness... the reciever is very close to the magnet (3mm probably).. no other sensors either.. i had that polar problem sensor conflict at first too so took all the other sensors off.

 

[WarrenG]

thanks... i'll try it with a stronger magnet... works flawlessly with the hub so i'm not sure if it would be the harness... the reciever is very close to the magnet (3mm probably).. no other sensors either.. i had that polar problem sensor conflict at first too so took all the other sensors off.

The manual says to position the magnet near the lower edge of the sensor. Reed switches are more sensitive near their ends and just beyond their ends than they are in their middles.

The neodynium ("rare earth") magnets sold at Radio Shack are about the strongest magnets you can get for their size. ~2mm thick, 4mm in diameter.

 

[doctorSpoc]

just an update... stronger magnet worked like a charm... thanks guys.