High Temperature Reading

[Ferg]

My original iBike did a fairly good job of showing an accurate temperature reading. It was replaced last year. The new iBike is always 5-12 degrees high, even in cloudy conditions.

Any ideas?

Ferg

[Site_Admin]

When we moved the factory to Montana, that could have changed the temperature calibration slightly. I think we can fix it, or you can send it in. Let me know off list.

[travispape]

My original iBike did a fairly good job of showing an accurate temperature reading. It was replaced last year. The new iBike is always 5-12 degrees high, even in cloudy conditions.

Any ideas?

Ferg

I've had several iBike units in my hands and found a couple that were consistantly low, one by 4 degF and another by 6 degF; however they were consistant. If you are trying to compare to airport weather data, it would be harder to get the offset. The best thing to do would be compare the average ride temperature from the iBike unit to another device mounted on the bike if you have one.

Once you pin down the offset, you can enter it into iBike 2 under Edit->Preferences and then iBike 2 will always correct temperature reading from the unit. The temperature offset correction was added in 2.0.5, so download the latest version if you are using something older.

Travis

[schroed15]

I’ve been riding with my new black iAero for a couple weeks now, and I have noticed that the temperature displayed while riding is consistently high. I read in the manual that the black model does in fact reflect higher temps due to direct sunlight. However, some of the temps reported by my iAero seem really high. For example, actual temps on my ride today ranged from the mid-50s to the upper 60s (weather.com reported 68 degrees immediately after my ride at around noon). However, the iAero displayed temps as high as 95 degrees. The temp in the ride file summary was 79 degrees--I assume that is average temp. Anyway, knowing the exact temp during my ride isn’t all that important to me, but I’m concerned as to what impact this might have on the power and other data reported by the iAero. Is there anything to worry about? Also, if the iAero is registering 95 degrees on a 68 degree day in May, should I be concerned about any implication of riding in what is routinely 85-90 degree heat during the summer?

Incidentally, I’m confident my iAero can pick up the correct temp, so I'm not sure an offset is necessary. I checked it yesterday against my digital outdoor thermometer and my Polar S625X HRM by setting all three outside in the shade for about 20 minutes. At the end of the 20 minutes, all three were within +/- 1 degree (57 degrees). I also checked the temp reported by weather.com for my zip code and it, too, was right on.

Cheers,
Jason

[travispape]

Jason,

Your experience is different than mine. I did a 66 mi ride on Saturday with 3 units, 1 white and 2 black. It was mostly sunny. I rode from roughly 9 am to 1 pm and the temperature range as reported at the local weather station was 68 degF -> 78 degF. Average speed was a little over 18 mi/h.

The average temperature recorded by my 3 units were:

white: 79 degF
black #1: 82 degF
black #2: 80 degF

I didn't make a note of the max temperature during the ride and that information is not recorded in ride files. These average temperatures are after applying the 4 & 6 degree cal offsets I mentioned earlier in the thread.

Note that the temperature 3 or 4 feet above black asphalt on a sunny is in fact hotter than airport temperatures, measured 10 m above the ground.

black #2 is on a stem mount a little close to me and may have spent more time in my shade explaining its lower reading than #1. So there is some evidence of solar loading affecting the black units more, but not by much. Any solar loading was much too small to cause any problems with the power calculations. The key is the good air flow over the units, which does a really good job keeping the units tied to the air temperature.

Here are some ideas of what could have gone wrong in your data for that ride:

* Several long stops in the sun. When you are not moving, the black unit could bake in the sun. I'm sure that is what caused your 95 degF reading. It takes a 3 or 4 miles of riding to get the internal temperature of the iBike unit back down to air temperature, so this can affect the average temperature too if have several long stops in the sun.

* Make sure your unit is mounted to get good wind exposure. This shouldn't be a problem with a normal road bike with either the handlebar or stem mounts.

* I guess it is possible if you rode at a leisurely pace with a tail wind in the sun that solar loading can be a bigger factor.

[schroed15]

Travis,

Thanks for the reply...I did indeed stop to refill on water with about an hour left in my ride. However, that left an hour of riding until home and it was within the last several miles that I noticed the 90+ temp readings, topping out at 95 by the time I reached home. As for the mounting, my unit is mounted out in front of my bars on a Topeak Barxtender, so good airflow shouldn't be a problem. However, this also ensures that it gets virtually no time in my body's shadow on a ride. Cloud cover is hard to come by here along the Colorado Front Range on most days, too. Incidentally, the last 45 minutes or so of my ride was heading southwest into a headwind.

Anyway, like I said, knowing the exact temp is not really a big deal to me. My main concern is whether the iAero becoming too heated will cause distortions in power and other data, especially as the summer heat begins to crank up (the sun seems a little more intense at higher altitude, too). I'll keep an eye on the data and see if I notice anything suspicious, especially where it might correspond to rides in hot, sunny weather.

Thanks again...I really appreciate this forum.

Jason

[travispape]

Jason,

I'm still not sure why you would see such a large temperature difference between your unit's temperature and the air temperature; however, that issue aside for the moment, I don't think the temperature delta you reported would have much impact on your power readings. Temperature goes into the air density calculation in iBike2, but it is not that sensitive to temperature. On my ride file, adding 20 degF to the recorded temperature only made a 2.3 W difference in the average power.

The other concern is the wind offset calibration; however, the temperature variation of the wind offset is mainly a problem in the winter with cooling temperatures. Doing your wind offset with the internal temperature of the iBike at 70 degF and then riding at 40 degF causes a large error in the reported wind speed and a large under-reporting of power. Doing your wind offset at 60 degF and then riding with your unit reporting 90 degF results in much smaller errors. It is the colder temperatures the throw off the wind offset cal.

So, don't worry too much about summer-time temperature deltas, but still, it would be interesting to figure out what is so different about your riding than mine. We do have more trees providing road shade in NC; however, I don't think trees blocked the sun much on the route that I took on Saturday.

[travispape]

This post is really in response to another thread, but it best fits here. Again, I have 3 iBike units mounted on my bike, 1 black one on the stem and a black and white on each side on the bars. Here is some data from several of my recent rides showing the average measured temperature on each unit compared to the average airport temperature at the time of the ride. There are varying amounts of sun exposure.

Code: Select all

Time               Duration  Airport  White   Black   Black   Speed
                             degF     (bars)  (bars)  (stem)   mi/h
5/3/2008 9:03      3:46:06   71        79      81      80      18.1
5/6/2008 11:51     1:02:35   75        83      85      84      19.4
5/7/2008 9:02      0:20:59   67        71      71      71      19.9
5/7/2008 18:45     0:19:44   78        78      77      78      21.0
5/9/2008 9:02      0:20:10   70        71      70      70      20.5
5/9/2008 18:54     0:20:18   78        77      76      76      20.4
5/10/2008 9:05     3:37:21   73        79      82      80      18.2
5/12/2008 8:50     0:20:46   56        60      60      60      20.1
5/12/2008 18:43    0:21:17   56        61      61      61      19.5
5/13/2008 12:03    0:41:51   65        76      80      78      18.6
5/17/2008 14:20    1:41:43   73        84      86      86      18.7
5/18/2008 9:26     0:29:16   67        70      71      71      19.5

The ride on 5/13 is a good one to focus on in particular. It was a bright, noontime, sunny day on roads with high sun exposure (that is, hardly any shade from trees) and there was one 10 min stop in the middle of the ride where the black units could have shot up in temperature without airflow.

Observations:

* The maximum difference between a white and black unit was only 4 degF, so there is a slight effect due to the color of the iBike unit, but not much. The fact that the black unit on the stem had smaller deltas than the one on the bars bears out this trend since the one on the stem spends more time in my shadow.
* Early morning rides or rides on overcast days result in riding temperatures that match the airport data.
* Mid-day rides on sunny days result in the largest difference between the airport data and the iBike average temperature: up to 11 degF difference for the white model and 15 degF for the black. Note that most of that temperature difference is in fact real--the temperature riding on the black asphalt is actually several degrees warmer than the airport temperature.

The reason I put the speed in is because the faster you ride, the easier it is for the airflow to keep your unit locked in to air temperature. In general I seem to be riding fast enough and getting enough air flow on the units that units are doing a good job of measuring the air temperature--the slower you ride the bigger affect the sun will have on the temperature of the black iBike.

Conclusion: If you are primarily concerned with getting that last bit of data accuracy, get the white unit. If you are primarily concerned with the unit color, the temperature measurement of the black unit is good enough for most riders. A 5 degF temperature error is not going to have a significant effect on your power readings--usually less than 1 Watt.

Travis