Weird Speed Measurements Lately

[smokey26_02]

Lately in my last 2 rides my Ibike has been incosistent in terms of speed readouts.

No one near me is using an ibike thats for sure.

Today I was in a break and it was showing 50km which was probably what we where doing, but then it will go to like 68km, 60, then 40km, all over the place. While it doesnt really bother me that much I am not expecting this to happen all that often regularly. When riding in a break you just keep the tempo and follow the wheel, speed is not that important.

However for when I train solo I do need a consistant power output. While the speed may be all over the place the power reading is pretty much what I would expect, however once in a while it does vary greatly. For example today at one point going down probably a 2% descent, if you can call that a descend, coasting I maxed out at over 2300 watts.

Over the weekend I raced and during the race towards the end it started pouring buckets. It got nasty. I have attached the picture of me in the front when it was really coming down. Since that day the speed problem has surfaced. I havent had time to check the tutorials and see what I should do if the ibike gets wet, but i would expect it to mess with the power measurement and not with the speed since its being sent from a sensor!

Does anyone have any suggestions on what may be going on with my Ibike.

Thanks for any advice in advance.

Freddy

[iodaniell]

I'd check your magnet's placing on the spoke compared to the mark on the sensor; the magnet distance from the sensor (0.5 millimeter is the usual recommendation); the security of the magnet--it should not move on the spoke.

If using wired sensors, I'd contemplate going wireless. I went thru about 4 wires with my Pro. The wireless mount fixes all of the bad things associated with the wired mount (i.e., better battery life, no more cracked or broken sensor bodies and wires).

[howard]

I have a wireless mount. Suddenly got speed readouts all over the place. Changed battery in transmitter, redid the pairing----- no more problems with the speed readouts.
Perhaps this will help.
Regards,
Howard

[klaus]

I have the same problem here I did just receive a new pair of Wheels (Mavic R-Sys) and since the speed readings have been very strange.

Sometime they are very high 100km/h 250km/h or it will drop to 0. The magnet seems to be inline with the wireless sensor. I will try to change the battery in the sensor to see if it does make a difference.
Power for the most part is pretty accurate.

Just waiting for a dry day to get out there and ride. Will have to do the 4miles and coast down but lately it has either been very wet or windy.

[klaus]

I did change the battery in the Speed sensor. The great news was that I had not to go through the pairing process.

Speed is absolutely normal, no more strange readings or other.

[klaus]

I am having some very strange speed readings again despite the new battery.

I was riding in the Ardeche yesterday and a 130km ride shows up as 210 on the IBIKE (This is friends bike computers and 2 gps sources). I accept some difference but this is way off.

Very strange is that downhill the speed was correct most of the time not always but most. There was not flat section so I can't judge there.

On the climbs it was particularly big difference. We where going up at 8km/h (I know it is slow but the slope was 6% and that for 4km) the ibike did show 24km/h which I was not doing.

Does anybody have any explanation on the source of this problem and how to fix it ?
Since I have my new Mavic R-Sys wheels (with their integrated magnet) I seem to be getting so strange readings. (I can not use other magnets as they would not fit and could actually damage the spokes which are made of Carbon "straws".

[racerfern]

Try moving the sensor closer or further away. You can also accomplish this by sliding it forward or backward on the stay depending on your setup. It sounds like you are getting double hits as the magnet passes.

[travispape]

I am having some very strange speed readings again despite the new battery.

Be sure that you have plenty of separation if you have more than one magnet on the wheel for other devices. Note that it is only the wireless transmission that is coded--a magnet is a magnet and if you have 2 on your wheel that are close enough for the iBike detector, the detector will pick up too many magnet ticks. Same story for wired mounts too.

Also, people tend to have more problems if the magnet is too close to the hub. You might try sliding both the magnet and the sensor closer to the rim.

If you have a wireless speed sensor, make sure it is not mounted backwards. The battery cover should be out and the words facing in. There is a little mark where the magnet should pass.

One interesting thing that happened to me a while back is that I was having trouble with my cadence data. I check everything and it seemed like everything lined up, but what I eventually noticed is that my left crank was starting to get a little loose. There was just enough play that the gap was too large when I was actually pedaling. I guess the moral of the story is to make sure your wheel skewer is clamped tight.

Travis

[klaus]

Travis following your advice I did check everything.

I have only 1 magnet and it is 2/3 out from the center of the wheel.
The wheel is thight. The sensor is mounted the right way.

The magnet was not in front of the marking about 1cm of from the mark. I did adjust the settings and will let you know after the next ride if that did resolve the issue.

Klaus

[klaus]

After a long cycling break I am finally back on the bike.

I am still experiencing some strange readings. The Ibike will report the correct speed for about 2hours then it will have very strange recordings for 15-30minutes and then it will return to normal readings.

Any suggestions on why this could be happening.

Yesterday I did only ride for 1h40 and the readings for speed where fine but suddenly in the middle of the ride the slope and power numbers where all over the place. First I thought I was related to the bad state of the road but I got on a new section in perfect conditions and the Ibike would read 6% grade when it was actually slightly descending. And again after 5 minutes all the number returned to normal.

Any ideas on where to look for causes ?

[travispape]

After a long cycling break I am finally back on the bike.

I am still experiencing some strange readings. The Ibike will report the correct speed for about 2hours then it will have very strange recordings for 15-30minutes and then it will return to normal readings.

Any suggestions on why this could be happening.

Yesterday I did only ride for 1h40 and the readings for speed where fine but suddenly in the middle of the ride the slope and power numbers where all over the place. First I thought I was related to the bad state of the road but I got on a new section in perfect conditions and the Ibike would read 6% grade when it was actually slightly descending. And again after 5 minutes all the number returned to normal.

Any ideas on where to look for causes ?

A bad speed signal will mess up everything else including power and slope, so that is the thing to address first. These sensors are pretty forgiving, so I'm not sure why you are having trouble. I just want to make sure that there are not two magnets, the trouble might be that the iBike sensor is able to pick up both.

If the one integrated magnet isn't enough to do the job, you might try getting a small rare-earth magnet and tape it to your spoke--just for a test. If that fixes the problem then you know the integrated magnet is too wimpy.

Travis

Travis

[klaus]

Ok I will try that I will tape a magnet to the spokes and move the other one out of the way. I can't remove it as that would mean removing the spokes, ..

I am sure there are no other magnets and actually nothing metal as the spokes as full carbon.

I will let you know how it goes at some point next week probably.

[coachboyd]

I wonder if there could be a small chance that the carbon spokes are throwing off the wireless signal. I know I have set up Polar sensors before on an all carbon bike and they had to be on the same side of the handlebars as the watch computer. There was something about the signal crossing over the carbon frame that would make the Polar lose signal. Now, I know the iBike sensors are a lot better and I have never seen a dropout on my bike so I am not inclined to believe this could be the case. Try the stronger magnet, but if that doesn't work. . .try a different wheel for a day and see if that's the case, or maybe switch sides that the speed sensor is on.

Is the magnet on the front or rear wheel?

[coachboyd]

And while we're on the subject or R-Sys Wheels, and this the iBike is a great aero measuring tool, you may want to look at how much extra work you are doing with those wheels that with any other wheelset. They are great for pure climbing when aerodynamics doesn't matter that much, but even in a hilly road race, think about the extra kilojoules you'll be expending just by getting to the climb.

http://accel95.mettre-put-idata.over-bl ... nglish.jpg

If these are just a training/wheel pit wheel then you are fine, and your race wheels will feel mighty sweet when you switch over.

[scotty]

I wonder if there could be a small chance that the carbon spokes are throwing off the wireless signal. I know I have set up Polar sensors before on an all carbon bike and they had to be on the same side of the handlebars as the watch computer. There was something about the signal crossing over the carbon frame that would make the Polar lose signal. Now, I know the iBike sensors are a lot better and I have never seen a dropout on my bike so I am not inclined to believe this could be the case. Try the stronger magnet, but if that doesn't work. . .try a different wheel for a day and see if that's the case, or maybe switch sides that the speed sensor is on.

Is the magnet on the front or rear wheel?

I'm not sure carbon spokes are the problem, I have Topolino wheels that utilize carbon/kevlar spokes. I have never had any problem with the Polar or the iAero. Both units have worked great.

[howard]

I had a problem with the speed data last week. Turned out to be caused by the magnet not being tight on the spoke. If you have a "covered" magnet and it's tight on the spoke, perhaps the magnet is loose in the case.

[gregh3285]

I have Mavic R-Sys wheels. They have a magnet that wraps around the carbon fiber spokes. Lately, I've had a series of bad clumps of data when the speed is almost exactly double the speed I'm actually going. It jumps from normal to double and then (a couple miles later) back to normal. Playing with the bike on a stand, I think I can hear the magnet double clicking (as it where). Initially, I thought it was a bad speed sensor magnet. I changed that. Sill, I had problems. Then, I moved the magnet (and the sensor) further out on the wheel (closer to the rim than the hub). The reason I did that is that when the magnet is closer to the hub, the magnet (on my bike) crosses the sensor diagonally rather than top to bottom. This didn't help either. What finally seems to help is to offset the magnet so that one end of the magnet passes the line on the sensor rather than centering the magnet on the line on the center on the sensor. This is probably a very Mavic R-Sys-specific problem.

To Coach Boyd's 9/2/08 post, I'm feeling doubly depressed. Not only are the wheels a bad aero bet, they've also been somewhat unreliable. My wheels have been out of commission for two separate spoke repairs amounting to 5 or 6 weeks of down time. I feel even better about my trusty Rolf Vector Comps. A bit off topic, but I need to vent.

[R Mc]

Well, imo, the r-sys wheels are an accident waiting to happen.

Check out Graham Watson's images of last year's Tour Down Under for a photo: http://grahamwatson.com/gw/imagedocs.ns ... m&08tduSt1 (you might have to scroll down the frames a bit . . .)

Also, in February of this past year, in a cat 4/5 race in Texas, I witnessed something similar happen in the final sprint: a spoke broke in the front wheel. Unable to withstand the extra load, all of the rest of the spokes proceeded to snap. It was an ugly crash. (There was a photo sequence of this that went around at the time, but I'm not sure I can find it).

[Russ]

Sorry about the wheel problems.

As to the magnet and extra sensing, I have a similar problem, I think due to using a higher strength magnet than is stock. To solve the problem, I have to open a wider that normal gap between the magnet and the sensor. This brings 100% reliable operation. I like the catseye extra strength magnet because it fits my flat spoke better and because, actually, I like the extra wide gap as insurance against fowling.

Russ

[gregh3285]

Russ, your theory about stronger magnets being more than what the sensor expect seems to agree with what I'm seeing. I'll have to try the wide gap technique. I do like the idea of giving a little extra space between the magnet and the sensor. One of the R-Sys spoke failures I had this year was due to my bad bike handling skills. I brushed a traffic cone during a race. This pushed the sensor into a spoke -- cracking it. In the process, the speed sensor was ripped off the bike never to be seen again. In addition to the wheel repair, I had to order a spare speed sensor.

[iodaniell]

Pace Bend Crash Photo Series (Cat 4 / 5 Race) showing what happens when you lose a front spoke on an R-Sys wheel:

(Slide show)
http://www.flickr.com/photos/dcmphotogr ... 3668/show/

And an observation by a local DC area racer regarding an exploding R-Sys wheel during a Cat 4 race:

http://www.bikeforums.net/showthread.php?t=424301

[gregh3285]

This evening I took my bike into the basement, put it on a stand, and did some experiments with the factory R-Sys magnet communicating with my iBike wireless speed sensor. I learned some interesting things. The position of the magnet up and down the spoke relative to the sensor can cause zero, one or two magnetic pickups per revolution. My most interesting finding of the evening is that a magnet centered on the sensor can result in no pickup at all. It also seemed that the results are repeatable fairly independent of the spacing between the magnet and the sensor. In the final analysis, I wonder if the configuration of the R-Sys factory magnets is such that the speed sensor can see two magnetic changes North to South to North to South. I'm not going any further with this. I'm changing to a magnet taped to a position near the hub. That works. While I like the elegance of the R-Sys magnet, I can suffer unreliable speed measurements no more!