Problems with location for cadence sensor on Sigma BC1909 HR

[keith brown]

I have just received my Sigma BC1909 HR and as normal immediately rush out to fit and test my new "toy". However after fitting the various major elements I tried to fit the cadence magnet on the crank. Firstly I had thought the sensor was close when fitted on the chainstay (non chain side) and so did not need the additional spacer for the magnet. However the crank is so close to the chainstay that I can't even fit the magnet without it fouling on the chainstay on each rotation, in fact it won't even go beyond the start of the magnet as it is too big for the gap available.

The question is can I fit the magnet on the front of the crank where the magnet face will not cross the sense unit at 90 degrees, only the edge of the magnet will be presented, and I am not sure how effective that will be. I don't want to start filing the magnet plastic surround away if there is another method that others have identified. I haven't gone through the whole programming arrangement on the basis that if there is no practical solution then it will be a waste of time.

Any help, guidance or suggestions (sensible!!!!) would be appreciated.

Keith

 

[T.M.H.N.E.T]

Perhaps it came with a manual that suggests you can also mount it at the bottom of the seat tube?

 

[keith brown]

This still doesn't overcome the magnet rotating on the crank as it still has to pass the chainstay. Yes the reader unit can go there but it is the magnet that is the problem and I can't see anyway other than being on the crank that will give pedal cadence. 32 separate pictures of how to fit things, a 243 page book, true it is in ten languages, but never a mention that the crank magnet can be fitted anywhere else.

Thanks for idea though.

 

[T.M.H.N.E.T]

First you say the magnet is fouling the chainstay on each rotation, and now the magnet is rotating on the crank. Which is it?

Move the sensor to the seat tube(wasn't this bit obvious?) - thus moving the magnet to a place that may have more clearance

 

[keith brown]

Perhaps my terminology is incorrect, sorry if that is the case.
Both statements are accurate as far as I can see but this may be due to my understanding of chainstay. Basically the magnet fits on the crank and is fouling on the tubing which goes from the bottom bracket to the rear hub, this I thought was the chainstay, or so several cycling books term it so. Hence moving anything other than the magnet will not cure the problem.

Hope that clarifies my problem.
Cheers

 

[T.M.H.N.E.T]

Why can't you mount the sensor on the seat tube and move the magnet up the crank closer to the bottom bracket?

There is bound to be clearance somewhere. Post a pic!

 

[keith brown]

Hope this helps.

As I see it I can either file off the sigma logo off the front or file away the plastic which currently moves it away from the crank. The only problem with the latter is that this would mean I couldn't fit it to any bike that needed the extension piece to move the magnet closer to the sensor where the chainstay to crank gap is large because the piece I would be filing off is the location lugs for the extension.

 

[tnr319]

Why don't you use a cadence magnet? Here's one listed on eBay 121182732705 I put one on my crank and it is rock solid. Remove the clearance issue in one go and they are really powerful.

 

[T.M.H.N.E.T]

Move it round to the other narrow edge of the crank. Magnet should be plenty strong

 

[Dusty Bin]

It's usually the magnet which mounts to the crank arm - not the sensor. Are you sure you've got that the right way round ?

 

[keith brown]

Why don't you use a cadence magnet? Here's one listed on eBay 121182732705 I put one on my crank and it is rock solid. Remove the clearance issue in one go and they are really powerful.

Sounds like a solution as even if I shave the provided magnet down to fit the gap the sensor fixing requires some space between crank and chainstay. If I move the sensor to the seat tube then the gap is too large and I need the extension to the magnet, which will then not go through the space. I could pack the sensor out but then the issue of rigidity and solidity raises its head.

Seems big old lump of iron may work, will check ebay.

Cheers

 

[keith brown]

Move it round to the other narrow edge of the crank. Magnet should be plenty strong

This may be a way forward and I think I can try this prior to buying a big magnet to fit to the crank.

Cheers

 

[keith brown]

It's usually the magnet which mounts to the crank arm - not the sensor. Are you sure you've got that the right way round ?

Yes, that is what the problem is, the magnet is too big. Sorry if I confused the issue but I am talking magnet to crank and sensor to chainstay or seat downtube.

Cheers

 

[Edge705]

Rip the magnet out of the plastic housing and use strong clear/black tape to wrap it around the crank alternatively buy another magnet fairly cheap and do the same.

 

[keith brown]

Rip the magnet out of the plastic housing and use strong clear/black tape to wrap it around the crank alternatively buy another magnet fairly cheap and do the same.

Yes I can see that is the way forward. However it is a shame that when you pay £88 (normal price about £130) you may be forgiven for expecting it to be designed to fit a "normal" bike.

Cheers for response