AeroPod, PowerPod and Newton

I believe the Powertap G3's and Newtons are more accurate in crit style racing than a SRM(Bold statement) I had my SRM for 3 weeks before selling it to a friend. I can match my newton to a G3 within 2% during a crit. Couldn't do it with a SRM. Can you post real-time plots of the comparison (Newton ...

It might be good to spend a little time investigating the matter before you shoot your mouth off.

It doesn't *use* the barometric reading to determine slope, and I never said it did. It uses the barometric reading to *adjust* the tilt, using data from the last 5 minutes.

iBike uses the barometric altimeter to adjust the tilt. It uses the previous 5 min of data to do this... it checks what the elevation change should be based on the distance and tilt info, and compares this to the altimeter... then adjusts the tilt to match the altimeter. So on any long climb or desc...

That is pretty close... but you would need a few more to tell. I have a lot of runs on a 2200ft climb and got ~5% max scatter in elevation increase with the Gen3. The barometric pressure depends on the weight of the air that is above you. When pressure measurements are made to determine altitude, th...

The other computers do not rely on slope to compute power... the iBike does. It *isn't* consistent day to day. If the elevation change on a climb is off, the power will be off about the same %.

What was the total elevation gain on that climb where the variation was 69 ft?

The iBike determines slope and tilt from barometric sensor data. And the error I'm experiencing isn't due to the pressure change with time. It's inherent in calculating elevation *changes* based on pressure. Atmospheric variations effect the pressure vs elevation relationship. For instance... say I ...

Don't know if you were answering me, but it is better to track just a long climb. I'm not sure how iBike filters up and down. But if you compare the total climbing on the two files, the difference is 3.5% which isn't trivial.

Thanks heith... looks like the Newton is definitely working better than the Gen3. Downhills will always be tough for an iBike. If you have any long climbs that you've ridden many times, can you check to see if the elevation gain on that climb is consistent? That was one thing I noticed with the Gen3...

Hi heith... so do you have a Powertap? Did you use it for calibration? The iBike files do tend to average out, especially if your ride was similar to your calibration. Can you tell us what parts of the ride had the biggest discrepancies between the two? I'd suspect descents to be problematic, but wi...

Out of sheer curiousity I have checked the wind offset number and it has varied from as high as 5.6 to a low of -4.2 but I have not hit the center button once in order to zero it. Can you say some more about that? That is a very large swing... doesn't that effect your power readings a lot? If not, ...

That's why I was looking for a Practical Way of setting profile up. Instead of fixing Crr and computing CdA, you might instead get a good handle on CdA with good tires on the road, then fix CdA (bump it up a little for fat knobby tires) and compute Crr, with your MTB tires. Then add some more to Cr...

GWPOS wrote:crr should be more like 0.0100-0.0130 range for a mtb. I used it on my mtb for 3 years. Bigger/wider/heavier tires, lower tire pressures etc give you a higher crr than 0.008.

Don't forget the bumps and the softness of the dirt being big influences.

donnybike wrote:Will cda with 0.0080 be the same with the former, more and less?

CdA will be quite a bit lower.

It's great to hear that the Newton is improved over the Gen3... but I wonder about the specifics. I don't think you'd be giving any secrets away by detailing what has been improved and how much. Some things that led to pretty large errors on the Gen3 were: -Wind offset variations -Wind scaling varia...

I have no Newton experience (just a Gen3) but I also have a PT SL... and the places where the iBike is in error are much more and a greater amount than the PT. If you are just wanting to get numbers to track your training load the iBike is fine for that... but if you want data for pacing or to track...

If your numbers are correct, it must be caused by a consistent baro sensor error.

That probably isn't bad, but could be problem if your odometer isn't perfectly dialed. Do you have any significant hills that you climb to the top of?

Don't know what tires you are using but .0055 is good guess for good tires. Your CdA should come out ~.35 if you do the procedure properly.

GWPOS wrote:These were not climbs to the top but timed 20 min climbs, so the end point could vary some.

In that case look at climbs where you *can* identify the bottom and top.

I haven't seen anyone complaining about *minor* discrepancies.

Look at starting and ending elevations for the climb, both in the Gen3 and the Newton. Tell us what you find. It's possible that your baro sensor is faulty, and is leading to an incorrect tilt.

When you start a new file, of course you need a good tilt if you want accurate data for the first 5 minutes.

The gradual downward drift of the Gen3 elevation is most likely caused by barometric pressure changing. The Newton would do this too, if it was happening.

I generally look at the average slope on the "up" portions, since this is a number that directly effects power.

Since you aren't concerned about power, what are you using the slope, wind, temperature, etc data for?

The auto correction for tilt was to take care of a large number of people who had difficulty setting their tilt correctly. But the only times I noticed a significant problem on the Gen2 was when I was on rough pavement. I actually prefer to *not* have auto tilt most of the time, but there is no way ...

I haven't tested this, but I think it continuously upgrades the tilt based on the last 5 minutes of data... not at 5 minute intervals.

A change of 3 over a 25F range is extremely good. Really? 3 N/m^2 off is a pretty big error, and 25F is a very common range on a ride. BTW my Gen3 experiences very little offset change going from 70-110F. It's good in the summer. In the winter I see changes >3 and it appears to be unstable... ie I ...

Not Travis, but I guess 5 minutes of data is used (vs 1min) so that small errors in barometric altitude do not lead to wide gyrations in the slope determination. I wouldn't worry about your position changing the slope very much. Back in the day (Gen2) I noticed ~+.1% going up steep climbs and ~-.1% ...

I'm guessing that you mean the Garmin and Joule give fluctuating grade readings if it is windy. The iBike would give less accurate grade data also, if it only relied on the baro pressure sensor. It uses the accelerometer for grade and the baro sensor only as a 5min correction to grade.

I don't think wind is going to effect it... at least not enough to matter. But there are things that do. See my recent topic about elevation change errors.

http://www.ibikeforum.com/viewtopic.php?f=6&t=2456