Friday, April 13, 2007

ibike - part 5 - the fun begins

OK, so now I'm getting into it. It's addictive. I'm a data junkie and it's making me get out on the bike and ride, just to see what it looks like when I sprint, chase a car or climb a hill. Then I want to compare sprints, compare hills... goddamn it, I wish I had one 20 years ago! (But they didn't exist at this price, of course.)

That's the good side of the ibike - real data that makes sense. You've got to set it up right and do the coast-down test properly, as per spec, and make sure the battery is delivering the goods. But once done it's great. Of course today I punctured and swapped front wheels, but because it's just a magnetic pickup there was no sweat. I could even swap bikes as I've got a spare mount and pickup already on bike number 2. So I think ibike is still looking like a pretty good thing.

Bad news? It goes a bit screwy if you watch the Wattage display too much (it seems to jump around constantly, especially on the flat, only settling down when efforts are made, in a sprint or in a climb) - but when you download to the PC the odd figures seem to have disappeared and clarity returns. And the peak figures on the LCD don't always match the data logged. The battery seems to play a part in this, as does road surface - bumps and corners definitely throw it off.

So on to the fun.. the screenshot on the left shows power in blue and bike speed in green. You can see steady state on the left, then I accelerate to catch a slow-moving Toyota 'Landbruiser' that pulled out in front of me. You see both power and speed rise as I chase, peaking at around 865W and 45kmh or so; then as I get into the draft speed stays up (for a while, I didn't stay on as there's a nasty climb around the corner and I'm not that fit!) whilst power falls off sharply. The ibike seems to handle 'sucking wheels' pretty well. You can see that power falls away rapidly to zero until I hit the climb and have to get pedalling again. Speed falls away too and you can see me approach 300W on the lower part of the 10% climb (the bump on the right).

The next sreenshot shows a zoom-in on that power peak. You can see the effort to accelerate, the speed rising and then the power clearly falls off as I get into the draft, despite speed continuing to rise. In fact the car eventually accelerated, having suddenly realised that the rider they pulled out in front off at that T-junction was still there... and I let him go, as you see the speed dropping again. Wow.

Even better, the power breakdown (the colored box centre-screen) shows what was happening at the point where the cursor sits... all of that green in the pie chart is acceleration. The cursor itself is the black vertical line right on the power peak. So it all makes sense. When I move the cursor into the 'draft zone' the proportions all change... as you'd hope.

Bottom line? It works!

No comments: