What's likely to be flexing?

Plastik

I've a wireless computer, and both the magnet on the spoke and the transmitter on the fork need to be very close together in order for a reading to register - somewhere in the region of 1/2mm max it seems. On the flat or putting the power down while holding the bike in a stable upright position there's no problem, but if I'm pumping the pedals and the bike moving left/right the magnet & transmitter start to come into contact.

Is it likely to be the wheel, the spokes or the carbon fork that's flexing slightly?

Thanks ..

niceonetom

Most likely it's the wheel.

Maybe moving both the magnet and the sensor closer to the hub might reduce the amount of relative movement due to flex... ?

Plastik

Certainly an option, wouldn't that then throw the distance & speeds out of sorts though? Though in saying that I'll then be fooling myself that I'm going both further and faster than I previously was ! :P

niceonetom

Plastik wrote: »

Certainly an option, wouldn't that then throw the distance & speeds out of sorts though? Though in saying that I'll then be fooling myself that I'm going both further and faster than I previously was ! :P

Um, no. How close the magnet is to the hub won't effect your speed reading - it will still pass the sensor precisely once per wheel revolution.

petethedrummer

niceonetom wrote: »

Um, no. How close the magnet is to the hub won't effect your speed reading - it will still pass the sensor precisely once per wheel revolution.

It will also pass slower so maaaaybe it will get picked up better and won't need to be so close.

DirkVoodoo

Further from hub = magnet passes sensor faster, but it's closer to the computer.

Sounds like your wheel is flexing alright, I think Tom is right and moving the sensor closer to the hub is the way to go. I did this before with no issue, just doesn't look very "clean" on the bike, if you follow.

ROK ON

I destroyed a rear wheel earlier in the year with a cadence sensor arm jamming in the spokes as I was taking a roundabout at speed.
Either the wheel or frame flexed. Given that wheels were a cheap Shimano pair. Am choosing to belove it was them.

TBH. It turned me off cadence sensors and I have removed them from my bikes for fear of a repeat.

cdaly_

Interesting. I've seen most wireless cadence setups appear to be part of the wheel sensor and are typically mounted on top of the chainstay in the jam-if-it-touches-a-spoke-at-all position. Is there any reason it couldn't be mounted below the chainstay such that it would be pushed out if it touched?

Plastik

OK, cheers folks, will move everything a little closer to the hub this weekend and see what difference it makes. I have them located about 2/3's distance to the rim at the moment.

niceonetom

cdaly_ wrote: »

Interesting. I've seen most wireless cadence setups appear to be part of the wheel sensor and are typically mounted on top of the chainstay in the jam-if-it-touches-a-spoke-at-all position. Is there any reason it couldn't be mounted below the chainstay such that it would be pushed out if it touched?

Can't see any reason why that wouldn't work for a wired unit. My old polar wireless cad sensor (the non-WIND type) didn't have the range to be mounted on the stay at all - it had to go on the seattube - so there could be range/directionality issues with some wireless units.

Was it a garmin sensor ROK?

ROK ON

niceonetom wrote: »

Can't see any reason why that wouldn't work for a wired unit. My old polar wireless cad sensor (the non-WIND type) didn't have the range to be mounted on the stay at all - it had to go on the seattube - so there could be range/directionality issues with some wireless units.

Was it a garmin sensor ROK?

Yep. It remained tightly fastened to chainstay. The arm took out three spokes.
I don't use the wheels any longer - but as precaution took the sensor off also.
Not too worried in that I often spin an easy gear, only dropping to fact gears on a descent or with a tailwind.
When climbing I spin as fast as I am able (not that fast at all).
I don't miss it.
Always struck me as ugly. I saw a pic of the new Madone last week and the chainstay has a built in cadence sensor. The future methinks.

doozerie

Plastik wrote: »

I've a wireless computer, and both the magnet on the spoke and the transmitter on the fork need to be very close together in order for a reading to register - somewhere in the region of 1/2mm max it seems. On the flat or putting the power down while holding the bike in a stable upright position there's no problem, but if I'm pumping the pedals and the bike moving left/right the magnet & transmitter start to come into contact.

Is it likely to be the wheel, the spokes or the carbon fork that's flexing slightly?

Thanks ..

If you are having to put the sensor that close to the magnet then one possibility is that the battery in the sensor is running low. If so, then replacing the battery should allow you to move the sensor further away and eliminate the rubbing problem entirely.