Profile Ranges

[Avanti]

Hi all,

It may of already been covered and I know the guide is close to coming out, but can we have some guidelines on what 'normal profiles' look like ie:

aero: 0.0200 - 0.600
wind scaling: 0.800 - 1.500

etc etc, I have three wheelsets and vastly different numbers....which I can explain due to position changes and better rolling etc, I would just like to check things out to make sure I'm in acceptable ranges...Actually any info on these all the advanced settings would be appreciated to be honest aero, cda, fric baffle me. I love the power meter but gee it's really difficult to get your head around.

[Velocomp]

Here are some guidelines:

CdA

TT: 0.2 to 0.33
Hoods: 0.28 to 0.45
Drops: 0.26 to 0.42

Crr:

0.002 to 0.008

The smaller the number, the better your tires and the smoother the pavement. Towards the high end, you're on chip seal or even dirt

Wind Scaling Factor

Stem: 0.5 to 1.5

Handlebars: 1.3 to 4.5

Riding tilt:

0.0% to -1.2%

(riding tilt should never be positive)

Aero:

0.15 to 2.0

Aero depends on your CdA and your wind scaling factor; lower numbers would be for stem mount locations and TT ride positions

Fric

3.0 to 17

Fric depends on Crr, riding tilt, and total weight. Bigger numbers are caused by a combination of large negative riding tilt and large rider weight

[Avanti]

Thanks so much, exactly what I was after!

[Avanti]

And massive relief as well, all my profiles look good....This thing works as long as you follow the instructions to the letter, thanks guys love it!

One more question, if I wanted to see my fastest set-up....ie which wheelset / position generated the best numbers in regards to resistance. What are the key indicators there to look at?

[rruff]

Here are some guidelines:
Wind Scaling Factor

Stem: 0.5 to 1.5

Handlebars: 1.3 to 4.5

Could you explain why there is a huge variation? BTW, I have a Gen2 that is 1.05 on the bar, and have had two Gen3s that were 3.6 on the same mount.

[racerfern]

The way I see it is the wind sensor is a mechanical device. As such, variations in manufacturing of the sensor and even the iBike case can cause differences in wind scaling. I'm not sure it makes a difference if the scaling is .5 or 3.0. Sure, one is twice as sensitive as another but in the end as long as you get zero on a calm day for a cal ride that's all that matters.

[lorduintah]

Well - it would be nice to have a headwind be a headwind and vice-versa, too.

Tom

[racerfern]

A headwind is a headwind and a tailwind will always be a tailwind. However, depending on your wind scaling a headwind of 1mph could show as 1.2 and a tailwind of -1mph could show as -.8 or some other proportion. Of course it all varies on the scaling but zero is still zero. Properly setup you will never see a headwind as a tailwind or vice versa.

[rruff]

The way I see it is the wind sensor is a mechanical device. As such, variations in manufacturing of the sensor and even the iBike case can cause differences in wind scaling. I'm not sure it makes a difference if the scaling is .5 or 3.0. Sure, one is twice as sensitive as another but in the end as long as you get zero on a calm day for a cal ride that's all that matters.

Well... it's a factor of *6* in sensitivity... which is huge. If it can vary this much, I don't have a lot of confidence that multiplying by a constant is going to be accurate. When you do out-back rides to set the wind scaling, the range of speeds will not be representative of what you might see at other times. You might get it perfect at 20mph and it would still be off at 10 and 30mph. I also wonder it such a high scaling factor could indicate that something is wrong with the unit. It would be nice to know exactly what was causing the variability.

[rruff]

Properly setup you will never see a headwind as a tailwind or vice versa.

Not so. The iBike measures the absolute wind pressure and then determines the relative wind based on your bike's speed. If either the scaling or offset is off a little bit, you can easily get a tailwind reading when you actually have a headwind.

[racerfern]

Agreed, but the problem is if the scaling or offset is off. And that should only be numbers around zero. If you're in a 3mph headwind and seeing 0 or negative numbers there's something really wrong with the setup as a 3mph wind is pretty significant.

I think any issues with wind come down to proper wind scaling and proper wind offset. Wind scaling is relatively easy to nail down. Day to day wind offset with temp changes can be more of a challenge.

[lorduintah]

I can go along with the wind scaling and being able to get it dialed in. We have the issue, however, of the variability of the offset - which does not seem to be that constant or stable. Thus the issue of heads vs. tails

Tom

[rruff]

Agreed, but the problem is if the scaling or offset is off. And that should only be numbers around zero. If you're in a 3mph headwind and seeing 0 or negative numbers there's something really wrong with the setup as a 3mph wind is pretty significant.

I think any issues with wind come down to proper wind scaling and proper wind offset. Wind scaling is relatively easy to nail down. Day to day wind offset with temp changes can be more of a challenge.

3 mph? I see errors much bigger than that and it fluctuates... so there is no way to "fix" this by changing the wind scaling or offset. When the winds are blowing I can get a +- 200W power fluctuation when I'm going 35 mph or so... this is common. Do you really get consistent readings?

[racerfern]

The only way I go 35mph is downhill and I'm coasting 99% of that time. As a curiousity I've watched wind numbers and haven't seen that type of fluctuations. I've also watched the wattage numbers in CD mode and it generally hangs around 15-35w until I get to really high speeds then it really starts to climb. However I don't see where discrepancies at these high speeds are going to affect average rides.

FWIW, I'll do flyers up coast highway at up to 25-30mph in a group for 8-10 miles (tailwind) and I've never had wind issues. These same runs in a headwind are easily 10mph slower and I've not seen issues here either. It's not like I'm glued to the PM screen and I don't see any discrepancies in the downloaded data.