question about windy conditions

[jkallo]

(still trying to make the decision on the iBike)

I live and train in Chicago, and more than half of my miles are logged our path which runs along the lake. I don't really keep track of it, but I would say an average day during the summer is 10-15 mph wind with gusts of another 5mph. Days of 20mph with gusts near 30 are a weekly occurance.

So is it the case that if I am riding with the wind, but not as fast as the wind, the power numbers will be skewed? So if I'm cruising at 20mph with the wind behind be, every time there is a 25mph gust there would be a power spike which is not actually the result of my own power output right?

If so, this would be a huge problem for me. One of my staple rides involves ~20m up the lakefront and then the same back. Almost invariably, the wind is coming from the front on one half of the ride and the back on the other half -- days where that isn't the case are really rare. We actually make jokes about which way ended up being uphill. If wind gusts from the rear are going to mess with numbers, 50% of my staple miles would be skewed.

So is the iBike suitable for a chronically windy locale like this?

[R Mc]

I ride in west Texas, home to some of the largest wind farms in the world. I suppose you could call it chronically windy here, too.

In my experience out here, the ibike does not have a problem with wind gusts--its sensors seem to be sensitive enough, and the calculation equations are run quickly enough, to register those power readings accurately. Having a record of the wind data to look at in ibike3 has been a useful tool, because you'll be able to see how power relates to those gusts.

As people have mentioned, the ibiike does under-report power in side-on winds, although this seems to be somewhat less the case with the gen3 than it was with the gen2.

The more difficult consideration, though, would be finding a relatively calm day and a traffic-free stretch of road to do your coast-downs and calibration ride, because that's where gusty conditions can cause strange results. As a side note, my g3 unit also did not flash to "turn around" directly upon turning over to 2 miles--I screwed up one calibration ride as a result. It was a lot closer to 2.1 when the messages started appearing . . .

[jkallo]

Thanks for sharing you experience using it under these kinds of conditions!

I'm still somewhat confused about how it could account for a tailwind gust, though. If the wind sensor is on the front of the meter, and the wind is coming from behind (so it's blocked by your body), then a sudden large gust would be seen by the iBike as a surge in power, right? I totally could be missing something in how the measurement process works!

[coachboyd]

If there is a gust of wind from behind you, there will be less air flowing into the wind port. If you are riding at 30 mph, and the wind is at your back at 15 mph, then there will only be 15 mph of wind going into the unit.

It makes the calculations for this very well, and you can see afterwards on your ride when you had a tailwind. And it's been pretty fun riding with people who complain about this headwind to tell them "actually, we have 3mph of tailwind right now"

[jkallo]

If you are riding at 30 mph, and the wind is at your back at 15 mph, then there will only be 15 mph of wind going into the unit.

No, I understand how things would work in that situation. My question is about the times when the wind is behind you AND it's going faster than you are. So if I'm suddenly pushed by a gust moving 10 mph faster than my bike is.

I don't want to sound like I am imagining the proverbial perfect storm -- riding with a tailwind which occasionally gusts hard (i.e. so suddenly you can hear the wind even though you're riding with it) is something that happens super frequently on rides near the lake.

[jkallo]

Just to answer my own question, it turns out that this question has been answered in a past thread:

http://www.ibikeforum.com/viewtopic.php ... ilit=windy

Unfortunately, this is really a deal breaker for me I think.

[coachboyd]

It is pretty hard to ride at 20 mph with a 20+ mph wind at your back if you're putting pressure on the pedals. Chances are if you have a 20 mph tailwind you are going well over 20 mph, or going uphill. If you are going uphill, almost all your watts come from overcoming gravity, so wind speed does not give you that much of a percentage of your watts. If you are going 30 mph with a 20 mph tailwind, your iBike will see 10 mph of wind. If there is all of a sudden a gust of wind at 40mph, then yes, you could be off for that brief second of two of the gust of wind. . .but is that second or two worth an extra 1-3 thousand dollars?

In real work conditions, in the pack and by myself, in upstate South Carolina my iBike has been reading great in these conditions. Sure, in adverse weather it can be off for a brief moment, but you have to ask yourself if that few moments of riding in a tailwind is enough to throw off your training. For me, this is definitely NOT a dealbreaker.

In fact, seeing the people here getting the same results as people spending 3500 dollars or more for a power meter would be a dealbreaker for me buying that expensive power meter.

[racerfern]

Unfortunately, this is really a deal breaker for me I think.

I live on the Pacific coast and have substantial winds riding along the coast most of the time. I have yet to see a situation where the wind was "faster" than me and the numbers got skewed because of it. Generally when weather stations report wind speeds it is some height (sorry I don't remember exactly) above the ground, maybe something like 30 ft or 30 meters. Anyway, the wind at ground level is quite a bit less. Attached is this afternoon's ride. A nasty headwind (actually more at a 45degree), but when I turned around I was up against a sand berm most of the way back and that broke the wind just a bit. So you see more headwind than tailwind even though it was an out/back.

A true ground level 30-35mph wind is so strong that it could easily knock you off the bike. At that point what are you doing riding in those conditions? More wind than this and I would have no trouble making up my mind which trainer to buy.