Wireless computer question
 

I decided to hit supergo saturday and pick up thier wireless model. I just happened upon it after formerly deciding on another brand. But the SG is wireless and only 29 bucks with all the features i wanted including a display that shows 4 things at once.

But i have a question after downloading the PDF manual. It makes sense that the magnet and sensor should be close to the hub so that the amount of time they have to register each passing would be longer and therefore more accurate because it would be less likely to miss registering a revolution. I have read this too. But the manual shows it mounted up near the rim instead. The maximum distance they can be from the computer is 24" , so after measuring my bike it can be close to the hub without being over the max.

So the question is, am i and all the things i've read about this correct, or is it possible that some models may work better or as well near the rim? Or maybe i should meet them 1/2 way and put it in the middle? The model is supergo's WL9 wireless. It's got the supergo brand on it, tho i have no idea who makes it for them. I have no experience with ANY bike computer let alone a wireless, so any thoughts you have will help.

Thanks.....

For me the deciding factor was getting the distance between the magnet and the sensor right. Had I put the pair closer to the hub, the magnet would have hit the sensor. Much closer to the rim, and the sensor would have been too far from the magnet to get a reading. So I did not have much choice, maybe 5 cms or so. Depending on your fork and sensor you may have more margin.

--J

I've always installed the magnet close the rim and never had any problems with the readings.

Hmm...i see now. It depends on how far the sensor sticks out towards the spokes. And this one is pretty big, so i supposed near the hub it would be hitting the spokes. Well, i guess it's made to work up high. Better for transmitter/computer connection anyway....

Thanks

It doesn't make any difference where on the fork/spokes the transmitter/magnet are, as long as the distance from the transmitter to the receiver is correct. The magnet passing the transmitter just 'trips' it, like a light switch, on/off. The transmitter doesn't know how long the magnet is in front of it, it's either there or it's not.

What i meant is that if the magnet is at the rim, it will pass the sensor so fast, especially at high speeds, that it may not register every revolution. Thats what i've read, and made sense to me. I could see how that would be possible. But then again, i of course don't know this for a fact so i thought i'd ask and see how it works for y'all. Seems from the responses so far i don't have to worry about it tho.

Of all the various computers that I've had on bikes, I don't recall ever reading instructions regarding placing the magnet closer to the hub.The max distance from the transmitter to the receiver is specified because the tranmitter is low power. If you think about it, at any given wheel rotation speed, the magnet spends the same time in front of the transmitter. The speed you're referring to I believe has to do with centrifical force, not elapsed time in front of a stationary object.

I never saw this said from the manufacturer, just from some reviews i read. While researching them i read a few reviews that said they had problems with the sensor reading the magnet when they positioned it near the rim. But in hindsight that may be because at that point it's too far from the sensor, while at the hub it would be closer because the spokes are closer there. It may have been that which caused thier problems and not the speed at which the magnet passes at the rim. Who knows. But in any case thats where i heard it. I read a mountain of reviews.

The transmitters (pickup sensors) have a very short range, so closer to the rim will also be closer to the "computer". I'd experiment with the position, but realize that as the battery runs weaker, the "transmitter" range will be shorter and you'll be buying your battery more often. Before it all goes really dead, the operation will be intermittent and you'll most likely wonder what is going on. The sensor is just an encapsulated reed relay that gets operated by the passing magnet mounted on the spoke, in all the systems I've seen. There could be other methods, but this is best for low electrical interference sensitivity and low cost. The distance between the pickup and the magnet mounted on the wheel is more critical than the time to engage. If the time to engage the magnet by being at the magnetic field longer is so sensitive, they are either using inapropriate relay or the system is so marginal, it'll be unreliable and intermittent anyway 9sometimes not engaging, sometimes chattering). I'd primarily concentrate on reducing the distance between the magnet and the pickup. Some of the magnets maybe pretty big and heavy, and depending on how light and well balanced your wheels are, having the magnet towards the rim will exhibit much higher inertia and therefore inballance of the wheel. That would be much bigger argument against being by the rim with the sensor, than the time for the magnet to be engaging the reed relay. So I'd get as tight between the sensor and the magnet as possible and then as close as possible to the hub while still having a reliable operation with weaker batteries.

Wow ! I can't imagine how thin and delicate that reed must be in order for that little magnet to close or open it. Are they suseptable to damage over time because of what i would assume is a very delicate construction? I'm thinking it must be like tin foil as far as lightness and strength go.

Don't worry about the ruggedness of bicycle computers. Any of the 'brand' names are well made and probably will outlive your desire to have the bike it's mounted on. Tens of thousands of miles is very typical. I bought one three years ago and have mounted it on a half a dozen different bikes. Replaced the battery once, and it's still going strong. "Thin and delicate" are not words to be put to a decent bike computer.

Buy the one that suits your needs, strap it on your bike and ride.

A little tidbit from Sheldon Brown's invaluable website:

In practice: I have some computer sensors mounted near the hub and others mounted near the rim. Both set-ups seem to work just fine. The main factor for me as been the clearance between the magnet and the sensor.

My mountain bike has a wireless computer with the sensor mounted very near the hub. There is no issue with the distance from the sensor to the computer.

The sensors on most computers seem to be less fragile than the wires. Through the years I have had plenty of wires short out, but never had a sensor fail.

As a measure of my experience, I have 4 bikes with computers, and at least five magnets from old computers stuck to the refrigerator.

"Wow ! I can't imagine how thin and delicate that reed must be in order for that little magnet to close or open it. Are they suseptable to damage over time because of what i would assume is a very delicate construction? I'm thinking it must be like tin foil as far as lightness and strength go."

The reeds are encapsulated in glass, specially gold or iridium plated contacts, and are very, very fast, (I've observed them operating in microseconds) sensitive and rugged. Of course there are many different types and I obviously don't know them all. Good ones will outlive all our bikes.
These were used in phone switching equipment with millions of relays and millions of operations - extremely dependable. They were/are also used in airspace equipment as sensors, in redundant mode of course. My experience with them is that they may more likely develop residual magnetism and "stick", rather than not operating - in a good design. On a "shaking" bicycle there should be zero problem with "sticking" so they are extremely reliable in this application. My only problems involve either getting the distance between it and the magnet too large (fix both the magnet and the sensor really well) or weak battery, effecting the "transmitting" range. With wireless system you'll not have the fragile wire hassle, but it requires battery is havier and does have minor interference and range issues. Mine are rarely unreliable near power transformers and traffic signal controllers, if I stop in their proximity.