Where is your iBike mounted?

[lorduintah]

For those who have mounted the iBike on handlebars.

Mine (iBike-Pro Gen III) is mounted just inside of the grip - so 1/2 the way from the stem and the hoods. I see a fair amount of vibration or variation in power on graphing the ride - the surface I ride is almost entirely concrete. Is the vibration from the sway of the bike from side to side (and to some extent a few cracks in the concrete) or is it enhanced because of where I have the mount placed?

Would be curious to know roughly where on the bar most people place the iBike.

Thanks. Tom

[rruff]

I think posting a screen grab of the variation you notice and why you think it a problem would be helpful... but offhand I don't think your location is ideal. The iBike works best if it has a clear view of the airstream. Your hands might be interfering with that in cross-wind situations. Mine is mounted right next to the stem.

[turbomentor]

On my road bike, it's mounted to the left of the stem on the handlebars.

On my tri rig, it's mounted on the stem. Seems to work just fine there so far.

[lorduintah]

Here is a recent tide - typical of what I see - Incidentally - my hands do nit interfere in a cross wind with the input port for wind speed.

Tom

[Velocomp]

Please attach the ride file that you used to generate this graph.

[coachboyd]

Right away it looks like your wind scaling is off. When the iBike is mounted on the handlebars you can sometimes get pretty high wind scaling numbers (Even above 3.0). Your cda also looks to be a little low. It might be a good idea to redo your coastdowns and calibration ride.

[lorduintah]

Here is a previous and new calibration profile from today. (Screen shots of the profile values).

Tom

[coachboyd]

Those profile numbers look a lot better. If you did you coastdowns on really smooth asphalt, but your riding typically sees you on rougher roads, then you might want to raise the crr by a little bit. The roads where I ride are usually not freshly paved and I have my crr set at .0060.

But the numbers you got should be giving you better results.

[djconnel]

Was there any difference in procedure between the two calibration runs?

I wonder if more consistency could be gained by raising the coast-down speed range to a top value of 30 mph from 20 mph. This would increase the peak ratio of wind resistance to rolling resistance by approximately 225%, allowing for greater differentiation. I realize that Joe-hybrid may not be able to get up to 30 mph regularly, but a user-programmable range would be really nice. It's not so hard to write an extraction procedure which uses a variable velocity range.

This has been suggested here before, I realize, although I can't find it now.

Here's a plot I made showing the relative partitioning of resistance to rolling and wind from these parameters (I really need to get back to work ):



You can see the log-log slope comes much closer to the wind resistance limit between 25 and 30 mph than it does, for example, between 15 and 20 mph.

P.S. One comment: I think one of the reasons for the relatively low Crr is Mg is relatively large. Crr tends to be lower for higher mass, as not all components of rolling resistance are actually mass-proportional.

[lorduintah]

Interesting plot.

No - nothing significant as far as differences - I rode the same road for the coast-downs - roughly the small amount of wind on each day. Only difference here was one day coast South the latest was to coast North on the same strip of road. The temps were fairly similar. The out/back was the same route I took each time for the cal-ride. Same wheels/tires and pressure.

The section of rode is not traveled - so I had no cars running bye either occasion that might have altered my air path and it is not inclined one way or the other - so no bias from that.

Both times I did the coast-downs, I intentionally rode and coasted into the light breeze. (2-4 mph at most)

Tom

[djconnel]

I remembered where I saw the quote... it's from this early nyvelocity.com review:

I spoke with the iBike's inventor Glen Cunningham at Interbike, and he said that part of the problem is that the coastdown calibration is done from 20 mph to 8 mph. It would be more accurate at a higher speed, but they wanted to set it at a speed EVERYONE could hit on the flat. A faster coastdown option might be a future firmware upgrade.

[lorduintah]

I did another calibration - this time all of it was on the bike path I ride at White Rock Lake in Dallas. The Crr is still around 0.004x nothing near 0.006.

Profile file is uploaded.

Friction remains low at ~10. Wind scaling got a tad lower and tilt correction is now -0.5.

I suspect the discussion on MAX allowed speed for coast-downs is germane.


Tom

[coachboyd]

Bike paths will typically have lower than normal crr values. Because no vehicles travel on them, the road condition stays very nice and smooth. If the roads you typically ride on are like the bike path, then keep your crr number the same. If the roads are a little rougher, then you might want to slightly raise it.

I am down riding in southern Florida right now and found out the roads around here have about a .004 for rolling resistance. I guess when there is never any freeze and roads don't get chip sealed, they are quite smoother. Plus in Greenville, SC area we aren't exactly known for putting money into road conditions.

Of course, we are talking for you about the difference of just a couple watts. . .maybe 6 at the most.

[ChrisS]

It would be great to be able to do the coast downs starting from a higher speed. Keep the 20mph for thoses who can't or don't want to use a higher speed but have a high speed option as well.

A user selectable speed would be best but a second selection, say of 25mph would be good and do'able for most riders. I feel that 20mph is on the low side for measuring CDA.

Also 8mph is a bit high for Crr. I know I can manage to coast down to lower speeds. I have done low speed coast downs to measure Crr using John Tetz's Tcoast spreadsheet and with that I start the coast downs at about 8mph. Any faster and you do not get good data.

Chris

[nreimche]

My Ibike is mounted under the handlebars, on the right of the bar extender (type) mounting apperatis. Has anybody had problems, w/wind speed calculation, power data, etc, with this kind of setup. Further details include: The extender is attached to the stem underneath; the extension bar is going from left to right, so the Ibike (gen 1) is pionting forward when mounted; again the Ibike is on the right side of the heatset/stem; and is as flush/parrellel/level as the handlebars. For some reason, and maybe I have a bad windport, coachboyd (in another post) said my wind port seemed blocked, but the front of the Ibike was only 2-4 inches from the stem and the cables are behind or not 6 inches (left) or less of the front of the Ibike.

In addition to the above questions: How much would it cost to get the Ibike's windport inspected by VELOCOMP to see if it is faulty, since my warranty has expired? Boo Hoo!

Unimportantly, I miss the Ibike, because I think my WIRED mount is not working! I get no speed, the Ibike will stay turned off even when the magnet is a thumbnail away from the center of the sensor. The Ibike only turns on when I push a button (on it?)