Switching Ibike Mounts

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bob524
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Switching Ibike Mounts

Post by bob524 »

I am switching from a handlebar mount to a stem mount. Do I need to do new calibration rides ?
Velocomp
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Re: Switching Ibike Mounts

Post by Velocomp »

Yes, very much so.

Although you might think there is little difference between locations, in fact the stem mount will give you a MUCH different calibration for wind than the handlebar mount.

For example, on my bike I have both a stem mount and a handlebar mount (OK, I test more than one iBike at a time...)

The wind scaling factor for my stem mount is about 1.2

For my handlebar mount (where the iBike is only about 1 inch away from the stem) it is 2.97

This is nearly a 3:1 difference, which will make a HUGE difference in wind measurement performance.

So, take the 5 minutes needed to do a new EST AERO for your stem location, and 15 minutes for a new Cal Ride.

You will get great results.
John Hamann
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lorduintah
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Re: Switching Ibike Mounts

Post by lorduintah »

John -

Does this mean the angle of attack of the wind port is a primary factor in the wind scaling? - - I have my mount on the handlebar and the mount is almost level to the ground/bike tires. It seems to me the stem mount would have some 7 degree or so angle to raise and change the exposure of the wind port.

Maybe this means that an angled mount on the handlebar could lower the wind scaling to something closer to 1.0....


Tom
Velocomp
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Re: Switching Ibike Mounts

Post by Velocomp »

No, it is much more about WHERE the mount is located with respect to the incoming wind, as opposed to at WHAT the iBike angle is with respect to level.

The image I use all the time is the sleek car ads where they show the aerodynamic steamlines going over the top of the car.

If you're in direct line of attack of those streamlines--such as you might be when on the stem, where the handlebars push air into the wind port--then your WSF will be higher.

But if you've placed your iBike in one of the low pressure zones--as is in the case when the mount is on the handlebars--then you need more sensitivity to get the wind reading correct.

The critical thing to know is this: if you do a Cal Ride, the iBike will figure out what the correct wind scaling factor is. The Cal Ride will compensate for things effortlessly. You don't need to worry about where your iBike is located, or at what angle it is mounted.

Indeed, it really doesn't make any difference where your iBike is located--either with respect to angle or position--once the cal ride is done.

But this is why the cal ride is so important: at the factory there is no way we can predict where the iBike is mounted, or at what angle. The Cal Ride figures all of that out.

I know this is complicated and surely there must be a better way :-)
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racerfern
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Re: Switching Ibike Mounts

Post by racerfern »

It's pretty easy right now.

1) Do a calride after installing the iBike wherever you like.
2) Input your personal data into the est Aero screen.
3) Do a fitness test to establish a baseline.
4) Set a training plan, stick to it and test every so often.

After four years and three generations of iBikes it comes down to those four steps. Sure you can tweak aero and fric numbers until you're blue in the face but the bottom line after all is "You're either improving or you're not?"

iBike even gives you built in training plans with purpose built intervals. Are you suggesting it's going to get easier?!
Fernando
bob524
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Re: Switching Ibike Mounts

Post by bob524 »

Jon

Can you take a look at my Calibration nos since I switched to the stem mount... Thanks
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Velocomp
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Re: Switching Ibike Mounts

Post by Velocomp »

All is well. That's quite a roller coaster of a Cal Ride route you have!

There was very little wind the day you did your ride (a good thing) and you did 9 coast downs, too, immediately after the Cal Ride. Just what the instructions ask... :D

Wind Scaling and Ride Tilt are completely normal for the (light) person that you are.

By the way, your measured CdA was 0.326. Your Estimated CdA would be 0.341. So, the Fast Start procedure would have given you great results, too.

This is a very well done full calibration of an iBike, done properly, in good wind conditions, with good results.
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John Hamann
rruff
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Re: Switching Ibike Mounts

Post by rruff »

Velocomp wrote:If you're in direct line of attack of those streamlines--such as you might be when on the stem, where the handlebars push air into the wind port--then your WSF will be higher.

But if you've placed your iBike in one of the low pressure zones--as is in the case when the mount is on the handlebars--then you need more sensitivity to get the wind reading correct.
Are factors of 2 or 3 difference in these what you'd consider ~average? Is the iBike's pressure sensor calibrated to give a WS of ~1 with the stem mount? It seems that the handlebar mount is seeing closer to the freestream pressure, while the stem mount is seeing an amplified amount.
Zoltan
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Re: Switching Ibike Mounts

Post by Zoltan »

I guess that WSF of stem was chosen to be 1 vs that of handlebar, because not the freestream is important, but the windspeed which affects mainly on the moving object. And it is the body of the rider which has far the biggest area perpendicular to the moving direction, and it is just partly affected by the freestream, since partly affected by some increased pressure due to the eddies/vortices (sry my English is not good for these terms) caused by first wheel, front tube and handlebar.

My guess is that the ratio of the second effect is much much bigger.
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