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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 07-07-07, 04:45 PM   #1
cdkassner
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Wireless Computer with Cadence

I am looking for a wireless computer with cadence to mount on a Co-Motion Speedster Co-Pilot. I purchased a Sigma, but when I read the directions, it stated I couldn't mount the sensor more then thirty inches from the computer. In my mind, the best place to mount the sensor is on the stoker's back left crank arm, but this exceeds the recommended distance from the computer. Any ideas on a computer or place to mount this particular one? Thanks in advance for all replies. Also, we just took delivery of this Speedster after 20+ years on an old Gitane. We are totally impressed with the new bike.
Cheers!
Dave
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Old 07-07-07, 05:39 PM   #2
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Quote:
Originally Posted by cdkassner
...when I read the directions, it stated I couldn't mount the sensor more then thirty inches from the computer.
Put it on your cranks with the magnet attached to the crankarm or the backside of the chainring/spider.

Last edited by TandemGeek; 07-09-07 at 09:06 AM.
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Old 07-07-07, 06:37 PM   #3
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Having ridden the flexy Gitane years ago an also the Speedster, can imagine the grins on your faces . . .
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Old 07-07-07, 07:33 PM   #4
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The proplem with attaching to the captain chainring or crank arm is that the distance to the frame is greater then the recommended 20mm.
Dave
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Old 07-07-07, 08:23 PM   #5
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Quote:
Originally Posted by cdkassner
The proplem with attaching to the captain chainring or crank arm is that the distance to the frame is greater then the recommended 20mm.
You've got to think outside the box Dave....

Two alternatives exist here: move the sensor closer to the stock magnet or use a more powerful rare-earth magnet. I elected to go with the former for my HAC4's wired cadence pick-ups.

Since a picture is worth a thousand words, I've included 3k words worth of pictures below that illustrate:

1. A home-made cadence sensor mount I fabricated from scrap metal that screws into a pre-existing hole in my eccentric that I tapped for the 5m screw. The one in the photo is a spare off of our '98 Erickson: the joggle off-sets the sensor towards the frame, the two holes are for the small zip-ties that run through the sensor, and the cove simply follows the contour of the sensor. The single screw mount allows the mount to be pivoted independent of the eccentric's position... which is kinda important.

2. A side view of our '02 Erickson travel tandem's left-front crank to show where the sensor and mount are located in relationship to the eccentric and cranks.

3. A bottom view that shows the relationship of the sensor and the small magnet (that would be the square thing next to the sensor) that is JB Welded to the inside of my 34t timing ring just below the point where the chain plates come to rest on the ring's teeth.

These mounts have been in use for 4 years or so. I elected to make a mount because I don't like to zip-tie things to my frames, but it would be just as easy to make a small spacer out of hard foam, wood, or solid nylon that could be zip-tied around the boom tube just behind the eccentric shell. Again, a rare-earth magnet would also probably do the trick vs. the spacer but I'd be inclined to install it inboard of the chain on the chainrings so that the crankarm-mounted magnet didn't perturbate the chain.
Attached Images
File Type: jpg sensormount.jpg (5.5 KB, 71 views)
File Type: jpg sensor2.jpg (25.9 KB, 129 views)
File Type: jpg sensor1.jpg (20.0 KB, 257 views)

Last edited by TandemGeek; 07-07-07 at 08:38 PM.
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Old 07-07-07, 10:10 PM   #6
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VDO C3 DS Wireless Computer w/ Wireless Cadence has the longest range I know of I have 2 on my tandem running from single senders. The range is no problem with the VDO C3 DS.
I can walk 10ft from the senders and get readings so the short distance from stoker or Capt. bars is no problem it will get signal for either.
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Old 07-07-07, 10:19 PM   #7
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Originally Posted by JTGraphics
VDO C3 DS Wireless Computer w/ Wireless Cadence has the longest range I know of....
+1 if those are working well: very reasonable on cost and VDO has always produced a quality product.

Options for dual wireless a few years ago were far and few between. I ended up getting Debbie a Polar S720i (or something like that) for the tandems and, while they work well and have no problem sending both the wheel sensor and cadence signals to the computer head, the cost of this solution was, well, costly. Still works like a champ with only one trip back to Polar for a battery change and "tune-up" on the actual computer per the owners manual.

Last edited by TandemGeek; 07-08-07 at 07:32 AM.
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Old 07-08-07, 06:23 AM   #8
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We use a Garmin Edge 305 that includes cadence and HRM. No problems with range or cross signals... we love it.
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Old 07-08-07, 08:46 AM   #9
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Tandem Geek,
Thanks for the advice. I was looking for a way to make my own bracket and seeing the one you fabricated has sent me in a better direction.
Dave
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Old 07-08-07, 08:14 PM   #10
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If you are looking for a computer with cadence for the captain and you are using STI Flight Deck compatible levers, the best computer for a captain on a tandem is the Shimano Flight Deck computer, because of the graphic gear display that shows where you are on the cassette and the chainrings, and because of the virtual cadence that is superior to actual cadence--not only does the computer show what your cadence is when you are pedaling, it also shows what your cadence would have to be to match the speed you are going in the gear you are using (edit, oops) when you are coasting.

And there is no magnet or cadence sensor, because the computer calculates cadence from the gear selected (obtained from the STI shifter) and the speed sensor, usually on the fork with a magnet on the front wheel. There is a wireless mount too.

Last edited by SDS; 07-09-07 at 08:14 PM.
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Old 07-09-07, 07:58 AM   #11
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Originally Posted by SDS
If you are looking for a computer with cadence for the captain and you are using STI Flight Deck compatible levers, the best computer for a captain on a tandem is the Shimano Flight Deck computer, because of the graphic gear display that shows where you are on the cassette and the chainrings, and because of the virtual cadence that is superior to actual cadence--not only does the computer show what your cadence is when you are pedaling, it also shows what your cadence would have to be to match the speed you are going in the gear you are using.
+100

I think I'd be lost on our tandem without the Flight Deck.

I can see the issues you're having with the Sigma since it's designed to go on the chainstay. As another poster mentioned, you should be able to rig something to reduce the distance from the magnet to the sensor.

-murray
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Old 07-16-07, 10:32 AM   #12
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I finally got the cadence set up on the captain's chainring. We did two sixty mile rides over the week-end and I noticed the cadence seems to be doubled, i.e. instead of reading 80 or 90, it reads 160 or 180. Is this something anyone else has experienced or is this a fluke with my computer.
Thanks,
Dave
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Old 09-10-07, 12:09 AM   #13
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Originally Posted by TandemGeek View Post
You've got to think outside the box Dave....

Two alternatives exist here: move the sensor closer to the stock magnet or use a more powerful rare-earth magnet. I elected to go with the former for my HAC4's wired cadence pick-ups.
. . . . .
Again, a rare-earth magnet would also probably do the trick vs. the spacer but I'd be inclined to install it inboard of the chain on the chainrings so that the crankarm-mounted magnet didn't perturbate the chain.
I took the magnet approach.

First (false) try, bought a small package of them at the local, well-stocked full service hardware store. Was pleased that they stuck to the end of the chaninring bolt, but worried about them getting knocked off. I had 6 in the package, so decided to drill a hole through one. Took a long time, and just as the bit was finally coming through, magnet burst into flame and broke into several pieces.

So I read up on the rare earth magnets, and learned that "machining" them by drilling was not a good idea.

Trolled eBay, found 10-packs of ones with holes for about $10 and another $5+ shipping. Found an on-line seller who does single magnets, or bulk, and for $0.65 each bought 2. Shipping was still $5, but at least I didn't have 9 spares.

Went back to LHS, with magnet, chainring bolt, and chainring "nut". Tried out various capscrews until I found the one that fit through the hole in the bolt and the hole in the magnet.

Photo 1 shows the parts, laid out in a line. It took a few tries to keep the magnet from sucking everything over to it. (might need to click on the image to see it bigger)

Photo 2 is a view showing the cadence pickup unit, mounted at the very bottom of the down tube, and the magnet on the inside of the left-side crank. I used the chainring bolt opposite of the crank arm.
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File Type: jpg IMG_0563.JPG (51.6 KB, 52 views)
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Old 09-10-07, 03:53 AM   #14
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I had similar issues with where to fit a magnet on my Record crankset on my single bike for my Polar cadence sensor.

Strapping a magnet to the crank arm won't work as it hits the front deraileur as there is no clearence so I ended up mimicking what Campag does and put a small magnet into the pedal spindle. I borrowed one from an old cateye computer, chopped off the corners until it fitted then secured it with a small piece of tape.

The tape is definitely needed as I ran it without tape for a short while. After shifting into top gear down a hill the magnet jumped out of the pedal spindle and attached itself to the chain. This could have jammed the rear deraileur and caused a lot of damage, but I was lucky and it didn't. Here tape is better than glue as for my pedals you need to use an allen key rather than a pedal spanner to take them off.

I will have a look at fitting the magnet to a crank bolt - I didn't think of that at the time.
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Old 09-10-07, 08:08 AM   #15
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Originally Posted by cornucopia72 View Post
We use a Garmin Edge 305 that includes cadence and HRM. No problems with range or cross signals... we love it.
D'u have the Garmin cadence/speed pickup on the rear crank/wheel with the GPS unit on the front handlebars?
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Old 09-10-07, 08:44 AM   #16
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Quote:
Originally Posted by cdkassner View Post
I am looking for a wireless computer with cadence to mount on a Co-Motion Speedster Co-Pilot. I purchased a Sigma, but when I read the directions, it stated I couldn't mount the sensor more then thirty inches from the computer. In my mind, the best place to mount the sensor is on the stoker's back left crank arm, but this exceeds the recommended distance from the computer. Any ideas on a computer or place to mount this particular one? Thanks in advance for all replies. Also, we just took delivery of this Speedster after 20+ years on an old Gitane. We are totally impressed with the new bike.
Cheers!
Dave
Hi Dave

We also moved to a speedster from a 25 year old Motobecane this year. Congratulations. I'm curious about tandem folks and cadence. I ride a single with cadence, but I don't bother on the tandem, since we spin at vastly different rates and run a cadence that suits her best. I judge this by how much power I feel from the stoker and I get a tap on the back if I start spinning too fast for her. It seems to me that tandems just naturally run a slower cadence, perhaps it's just me. What do others do?

Frank
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Old 09-10-07, 05:56 PM   #17
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D'u have the Garmin cadence/speed pickup on the rear crank/wheel with the GPS unit on the front handlebars?
I have an Edge 305 mounted on the captains bars of our Cannondale RT3000 with the cadence/speed sensor MOUNTED on the stokers left crank arm. No problems whatsoever. These units have such a long range that I have to go to the other side of my house to get the Edge to recognise the sensor on my half bike without interference from the sensor on the tandem.
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Old 09-11-07, 12:16 AM   #18
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D'u have the Garmin cadence/speed pickup on the rear crank/wheel with the GPS unit on the front handlebars?
Yes, and it works fine on the tandem and even on the triplet
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Old 09-11-07, 07:44 AM   #19
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D'u have the Garmin cadence/speed pickup on the rear crank/wheel with the GPS unit on the front handlebars?
If you're thinking of buying one, there is a new version of the Garmin Edge coming out next month with mapping and color. It will be expensive but the 305 version may drop further as a result.
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Old 09-11-07, 08:23 AM   #20
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We recently installed a VDO C3 DS for the stoker position. We were both accustomed to the Cateye user interface. The VDO manual is small to fit in the package but it's about 3/8" thick. They tout the user friendliness of the interface & I recall a statement something like "once you get to this point, you can toss the manual because the interface is so intuitive". Not to us. Every time we want to for instance, reset the computer, we have to either get out the manual or consult each other on how this is supposed to work. Quite frustrating.

The other thing we notice about the VDO is that the transmission between the pickup & head unit seems to get interrrupted occasionally. I seem to recall that the manual states something about this (having to do with the fact that it is a digital signal). This too is frustrating. She would often say "were going 2 mph". Once it said we were going 194 mph. At the end of a ride, the distances covered agreed pretty closely between the Cateye on the front & the VDO on the back but we got to where we didn't trust the VDO.

Anyone else have positive/negative experience w/VDO computers?
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Old 09-11-07, 08:36 AM   #21
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If you're thinking of buying one, there is a new version of the Garmin Edge coming out next month with mapping and color. It will be expensive but the 305 version may drop further as a result.
We wonder if the battery life issues are going to get worse with the new models???
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Old 09-11-07, 09:26 AM   #22
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We wonder if the battery life issues are going to get worse with the new models???
It's a bit larger so the battery is probably larger. However, I think the rated life for the battery decreases from 12 hours to 8 hours. Long rides would really need a supplemental battery now.
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Old 09-25-07, 12:11 PM   #23
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My wife and I use Polar 720's with both cadence and speed. Magnet is on the timing chain side crank arms as are the sensors. I have separate sensors for captain and stoker. No crossed signals - both work flawlessly. The ability to download all the info from the Polar - for a ride is invaluable for training - not to mention pretty cool. I've had to replace the batteries in the units once in 3 years of use.
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Old 09-25-07, 02:29 PM   #24
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We use a Garmin Edge 305 that includes cadence and HRM. No problems with range or cross signals... we love it.
Cornucopia: Do both of you run the 305 without cross signals on the tandem? We have not tried 2 - 305s in close proximity yet. Perhaps if you sink the units to the heart rate monitor straps before getting close to each other...

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Old 09-25-07, 02:42 PM   #25
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We use a Garmin Edge 305 that includes cadence and HRM. No problems with range or cross signals... we love it.
Can both of you run the 305 without cross signals? We have not tried 2 - 305s in close proximity yet. Perhaps if you sink the units to the heart rate monitor straps before getting close to each other...

Here is the link to the new garmin 705:

https://buy.garmin.com/shop/shop.do?cID=160&pID=10885#
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