Newton vs DFPM

[jkase001]

I have been on the fence for a while about whether to invest in an iBike or DFPM (Powertap). I have used a PT in the past with success but currently my financial situation as well as the fact that I currently love my wheelset (Mavic Carbone SR) which I like to use for everyday riding has really made me take a hard look at iBike. I know there is plenty of blog posts out there on the two, mostly from people who are firmly in the PT crowd but I wanted to get some perspective from folks who obviously use the iBike on a regular basis. My profile is a former racer, currently an out of shape enthusiast, and hopefully a future racer again. I do most of my structured training on my own. I am most interested in getting consistent power readings for training purposes (tempo intervals, peak-fade, etc.) so I can monitor my training load, establish consistent training levels, and monitor improvement. I personally do not mind doing a lot of set up and calibration but my current situation (3 kids) minimizes my time to monkey around. So, I would like to invite folks to provide honest feedback on their iBike experience in the context of the information I just provided. Thanks and I look forward to hearing from everyone.

Thanks,
Jason

[racerfern]

Jason,

The iBike is very easy to setup. The easiest way is to select the FAST START process. In this procedure you set your height, weight, and normal riding position (hoods, drops, TT) . Then you do a two mile calride to establish your wind scaling. That's it. The iBike creates a profile and that's your setup unless you make significant changes in weight, or position.

Once you have your setup you'll perform a wind offset prior to your ride and away you go. Note that with the Newton this process is simplified further and much more consistent. You'll do a fitness test to establish your FTP and that's it. I highly recommend doing the FTP test since that will establish FTP based on your profile.

I do intervals from 2m at L6 to 20m at L4. I do them uphill and on flats. I climb up to 60m with a specific wattage setting goal and the iBike just keeps putting out the numbers. Every once in a while when I start getting IF numbers that seem high, I do another fitness test. Sure enough, my FTP is up 5-10w. It happens the other way also. Sometimes after a layoff, things go the other way. When I have trouble maintaining a certain level, a fitness test usually shows a drop after a vacation or a period of inactivity, usually due to work.

The Newton will make the setup even easier than described above and wind offset setting almost a thing of the past.

I am a beta tester for iBike, however I didn't need any convincing when I first started with the original version. To me it was obvious I didn't need to spend a lot of money and I had the plus of transferring from my carbon bike to my steel bike by simply switching profiles. I'm not a sprinter but I do work hard at preparing for centuries, double metrics, etc. So for me, the ability to see my intensity on the fly was all important.

I could go on, but you ask the questions and I'll give more specific answers.

[bjrmd]

Although I love the ibike and have owned every generation from the start it is no where near as accurate for testing/benchmarking as a powertap. I have both and use the ibike as the head unit. At best they are close but if the outside temp varies much(I know this may change with the newton) it can be way off. I like to do a 60 sec sprint to benchmark my fitness every few weeks, or a peak 5 sec sprint for max power. The kind of meaningful results that you can be sure of can only be gotten with a DFPM. But it is nice to know the head/tail wind, grade and you will need a head unit for the powertap anyway, so the ibike is great for that. I always wanted to do aero/equip testing with the cda feature but the accuracy was never good enough. Just my 2 cents.

[Jamesretro]

I have used a powertap (borrowed a friends) and just bought the ibike Newton. Newton is awesome, can't tell the difference in power readings from what I saw with the powertap on practically any section of rides I've done. Haven't raced with the Newton yet but have gone on group rides and I have to say....I'm extremely happy with the Newton!

[Russ]

Hey,

The only power meter (for bikes) that I have are iBikes. That said, I think bjrmd's comments may be a bit dated, see this thread with the effect of fixes shown graphically at the bottom, and a link into the power forum showing issues with strain gauge meters:

( in the general forum, title "Can Someone Weight in On this Thread")
http://www.ibikeforum.com/viewtopic.php ... &sk=t&sd=a

With that out of the way, I also notice a couple of bug fixes are still in the works. Point being that the iBike is continually getting better and is already probably good enough for your purposes, at worse with a little TLC

The Newton is clearly a giant step up from the Gen III and the Gen III is still quite usable (I keep a Gen III for backup, in case the Newton takes a dive).

Regards,
Russ

[rruff]

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 small performance gains, it's frustrating.

I'm still skeptical that the Newton has improved on that a bunch. I'd like to see a few comparisons in a variety of conditions.

[Velocomp]

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 small performance gains, it's frustrating.

I'm still skeptical that the Newton has improved on that a bunch. I'd like to see a few comparisons in a variety of conditions.

I cannot emphasize enough how much OS2 has improved performance--in sensitivity, consistency, accuracy, and responsiveness. I would love to say WHY iOS2 has made things so much better (believe me, we DO know why), but we'd have to disclose way too many secrets.

Unless you have a Newton you won't experience its amazing performance. And if you haven't used a Newton, it's really not appropriate to comment on its performance.

[Velocomp]

Although I love the ibike and have owned every generation from the start it is no where near as accurate for testing/benchmarking as a powertap. I have both and use the ibike as the head unit. At best they are close but if the outside temp varies much(I know this may change with the newton) it can be way off. I like to do a 60 sec sprint to benchmark my fitness every few weeks, or a peak 5 sec sprint for max power. The kind of meaningful results that you can be sure of can only be gotten with a DFPM. But it is nice to know the head/tail wind, grade and you will need a head unit for the powertap anyway, so the ibike is great for that. I always wanted to do aero/equip testing with the cda feature but the accuracy was never good enough. Just my 2 cents.

Here's a portion of a posting from the same user DFPM regarding accuracy, but this time using OS2 in his Newton:

Re: Possible bug in software
by bjrmd on Tue Sep 25, 2012 12:05 pm

...I just did a 15 mile loop and the avg power between the newton and powertap [is] with within 1 %.

You may note that this thread concerned a bug: though the bug has nothing to do with wattage accuracy, if you're curious you can read about it here:

http://www.ibikeforum.com/viewtopic.php?f=55&t=2407

[rruff]

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 variations
-Rough pavement
-Crosswinds and drafting
-Long climbs and descents... due to ~5% scatter in the barometric elevation change measurement

And then there are the inherent errors due to weight variation during a ride, and CdA variation with position, and barometric drift... that you wouldn't be able to do anything about. But I'm not worried about those.

The iBike has a challenging task, and I probably ride in one of the more challenging environments... all climbing and descending, windy, rough roads. A lot of the errors will average out over a long ride, especially with post processing, which is why I say it's ok for tracking training load. But often in real time I'd see power fluctuate +-200W when it should have been consistent.

[Velocomp]

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 variations
-Rough pavement
-Crosswinds and drafting
-Long climbs and descents... due to ~5% scatter in the barometric elevation change measurement

And then there are the inherent errors due to weight variation during a ride, and CdA variation with position, and barometric drift... that you wouldn't be able to do anything about. But I'm not worried about those.

The Newton uses a new wind sensor whose output and temperature stability are much improved over prior generations, so much so that we no longer recommend wind offset calibrations. We've said this elsewhere.

The rough pavement issue was addressed in 2008. We've said that elsewhere.

The new CrossFin vane addresses crosswind and drafting issues. We've said that elsewhere.

The baro sensor in the Newton is new and is more accurate. Earlier this summer we put out a firmware update that addressed an issue related to hill repeats. We've said that elsewhere.

After 8 years of examining ride files, we simply don't find material differences between DFPM data an iBike data attributable to weight and CdA variation. It's fun to theorize about, but meaningless to worry about. We've said that elsewhere.

And on top of all of this, OS2 does a much, much better job of processing the sensor data and giving accurate, consistent results. We've said that elsewhere, too.

Something that's true in practice cannot be false in theory. The Newton works extremely well--in all of the conditions you describe--and that's a fact.

[jazclrint]

I have an almost 3 year old iBike iSport. And at iBike, that is an eternity in evolutionary terms. I am an amateur racer at best, and when I have raced over the last decade, it's been off road. I use my iBike on my commuter bike, my MTB, and my road bike when I had one. I won a free month of coaching shortly after getting my iSport, and used it for that. It was a real pain for me to get it fine tuned because I was on a commuter bike with 40C tires, on rough Maine back roads where there wasn't a flat to be found. But I played with it, and tried to keep the tweeking as simple as possible, and eventually the readings seemed to level out and become consistent. Once I got there, and got an FTP I was happy with (the biggest issue I had) I used it to ride in zones my coach gave me and almost doubled my watts/kg (I really was in horrible shape) over that month. It got consistent enough that could guess my numbers without looking at the iBike.

The thing I like about iBike the most is the upgradeablility, and customer support. They are constantly updating all of the firmware and listening to us here on the forum for bugs, and accessories and features, which they actually make them happen! When it comes to programming it happens quick. Accessories take longer, but understandably so. Things have evolved so quickly here its a bit scary, really.

My 2 cents,
Rich

[heith]

Today's ride 11/23/12
I highlighted and area where a group was together before the major climb. You can see left of the graph the wattage from the DFPM(checked) and the Newton is pretty much spot on.
Below(bottom left) you can see the total avg. watts for the entire ride. It's within 4 watts(NP6) after 2 hours,34 miles, and 3,500ft. of climbing with 6 guys goofing around. The ride had everything thrown at it today..climbs, rollers, descents, attacks, etc. Plus, who's to say which one is right?

I rarely use the DFPM any more due to this accuracy. I was using the Virtual Trainer yesterday and was too lazy to swap wheels so you're lucky to get a visual.

[rruff]

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 with the Gen3 I also have issues on rough roads, cross winds, and altitude-change measurements (the amount of elevation change on a climb varies from one day to the next).

[heith]

Yes, I have a G3 and manually dialed the Newton+ in over a few rides. If you can borrow a DFPM and do that it helps considerably I have to admit. It takes a little knowledge to be able to look at sections of a ride to see what needs taking and giving to get the results you want. Issac has a DFPM analyzer but I got better results manually studying the data and tweaking. Like building a wheel it needs a human's touch. But after those tweakings I haven't touched it. I only check it occasionally because I'm coming from a Gen3 iAero which I had to tilt and check all the time. The Newton has proved much more reliable as I haven't touched it other than the wind scaling.

To be honest, the Newton with the newer OS is way easier to deal with than a gen3, it's just better everywhere. I never had the Gen3 Iaero give NP scores like the compared DFPM even though the avg. watts were some-what close. I like to use NP as a true guide when riding especially in groups. This really lets you see how it's dealing with all the minor and major accelerations, the newton is really accurate here. The Gen3, not so much in this area, even though avg. watts can be really close(50% of the time). But also remember the DFPM's takes avg. power per crank revolutions while I believe the Newton is picking up an immediate acceleration. So I would think this will cause a slight change or raise the NP while sprinting out of corners or accelerating from a coasting situations(crits and descents). I'm sure someone from Velocomp could let us know for sure, but DFPM's aren't perfect either and it's quite possible this could be an area where the Newton is more precise.

I looked through the file and I would say the winding 7.75 mile descent, avg. 5.2% that lasted 12'50" has the biggest discrepancy at 9 avg. watts.(NP13) for the newton, it read high. Just to let you know how we descended that pass, If I were to download it to Strava I would be about 6 seconds off from the KOM. Over 550 people have descended Glendora Mountain Rd. So we were pedaling hard and sprinting out of the corners. If we soft pedaled down and coasted, the numbers would be insignificant. But, yes, if there were an area where it could use work.....I'm just not sure if it will mean anything.
I don't do a lot of intervals going down mountains so it wont really affect training. But all the combined descents(major and minor) though-out the day is probably what adds the most to the overall wattage difference between the two(newton/DFPM) over the entire ride. I'm not going to try and fix this due to the fact, it's spot on with ascents, rollers, groups, and windy conditions. I'll give that one to the gods and just deduct a couple TSS points at the end of the day when doing group climbing rides, or probably not.

[racerfern]

Can you upload the file please?

[heith]

Yes.

[racerfern]

Thanks! I used to ride up GMR on a regular basis, along with HWY 39 up to HWY 2. Those are world-class climbs. I've even made it up to the ski lifts a couple of times. Of course I climb at about 210w and you're at 260w for the main part. Nice effort both up and down, although I might be a challenge for you going down.

BTW, have you done HWY 2 from La Canada to Onyx Summit? That's a full day for me!

[Velocomp]

Yes.

You may win the prize for the best calibrated iBike I've ever seen!

[heith]

BTW, have you done HWY 2 from La Canada to Onyx Summit? That's a full day for me!

Yes, it's a nice ride. Part of the ToC once or twice and a full day for anyone. I live in a pretty good area for climbing. I live valley between the Santa Monicas, San Gabrial Mtn. Range, San Bernardino Mtns., and Mt. Palomar.
Speaking of wattage.On the main climb(GMR Backside)I was riding with a 15yo kid we've been helping the last couple years. He has a FTP of 245 and only weighs 52.5kg. Needless to say, He now has the KOM to probably the most popular climb in SoCal. I use the term "riding with" loosely. Watching someone climb at 4.7w/per kg. is a vicarious pleasure.

[heith]

Here is another screen shot from today's ride to show the consistency that the Newton has. I left the Powertap G3 on again today so everyone can see it's not a 1 trick pony. It consistently reads accurately and the Newton in no way should be compared to the Gen3 models.

I highlighted the meat and potatoes section of the world famous Como Street ride rode today, 11/25/12. Again, the avg watts are within 4 watts and really take note on the NP. This shows that the Newton is reacting to most of the accelerations just like a DFPM would. This ride goes through a canyon pass with heavy cross winds in a fast group setting. So if anything would trip it up, it would be this ride.

You can see the numbers for the total 52 miles and it is showing 1 watt different.

[rruff]

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 that would often cause errors. The would be ~5% scatter that would effect the grade and power. It's tough to measure altitude changes accurately with a barometer.

[heith]

Same Loop 2 weeks apart

Lap 1:
Duration: 2:07:12
Work: 1471 kJ
TSS: 156.2 (intensity factor 0.86)
Norm Power: 249
VI: 1.29
Pw:HR: 9.62%
Pa:HR: -4.11%
Distance: 34.303 mi
Elevation Gain: 3500 ft
Elevation Loss: 3509 ft
Grade: -0.0 % (-10 ft)

Entire workout (193 watts):
Duration: 2:09:35
Work: 1496 kJ
TSS: 157.3 (intensity factor 0.855)
Norm Power: 248
VI: 1.29
Pw:HR: 10.76%
Pa:HR: 2.37%
Distance: 34.513 mi
Elevation Gain: 3622 ft
Elevation Loss: 3553 ft
Grade: 0.0 % (70 ft)

[rruff]

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.

[Velocomp]

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.

Assuming he rode equally hard in each ride, the difference in his power measurement from the two rides was 0.4%. His point is that his watts measurements were extremely consistent.

Your comment concerns a 3.5% difference in cumulative elevation measurement between the rides. We determine elevation from barometric pressure sensor data. Because weather changes all the time and affects barometric pressure, we cannot and do not make any representations about cumulative elevation measurement accuracy, either within a ride or between rides.

Furthermore, we do not use cumulative elevation data in our power calculations.

[rruff]

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 set my elevation precisely at home and it is 7000 ft. Due to atmospheric variations, the relationship between pressure and elevation is 3% below "standard" today. So when I climb to 10,000ft, the iBike reads slope and elevation difference as 3% less than actual, so the reading is 9910 ft at the top. Power on the climb is ~3% under reported as well. When I come down, the iBike thinks the slope is less steep than it really is, so power is inflated on the way down. When I get back to the beginning, the elevation reads 7000ft again, and the average power for the whole ride is about right. But the part I was concerned about was the climb, and power reading on that was 3% lower than actual.

This will occur on any climb or descent that is long enough for the barometric sensor to adjust the tilt. On the other hand, if you were riding on a flat road or one with short rollers, you'd never experience this.

[heith]

Yes, I probably should have not included the wattage data on my last posting as it is here nor there in retrospect to your question.
But to try and answer your question. The actual climb major climb showed a variation of 69Ft. from the "2 weeks apart" rides. To add, if I ride with others with Garmin 500's we all are within 50 ft. of each other on elevation gain. So I would say it tracks about as well as anything else.
John is right, My reason for posting on this particular thread was to show that if you want to take the time to calibrate your $500 instrument. You can make it work just as well as a $1,300 instrument, not including the minimum $250 instrument needed to record the former instrument's data.
Really, look and compare the graphs and numbers on the Como Street ride. I bet if I had a Sram(qarq) and a SRM it wouldn't have matched up any better.

Let me share one more thing people should take note of. I only make mine consistent with the Powertap because I have years of data with the Powertap. I have a personal power profile that I have tracked though-out and I'm used too seeing the progress consistent with Powertaps. If I had a Sram or SRM my FTP may very well be 10-15 watts different from now based on location of the measurement. I would then need to adjust my profile for the new found or lost wattage. Seeing I use two power meters, It benefits me to have them in sync with each other and the Newton is the only one that will allow doing so, as far as I know. If I didn't previously own a dfpm then I wouldn't have worried about it. The Newton has shown me it will consistently feed me data and that's the important part. As long as it gives you consistent day to day data, you have something that works. In other words, it tracks itself just fine.

[rruff]

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?

[heith]

Ok it was actually closer during the actual climbing portion.
Total Elev. gain on 11/10/12 was 1,532ft.
Total Elev. gain on 11/23/12 was 1,516ft.
This is the Gate to Gate portion on the back side of Glendora MTB Rd.(Back side) I actually hit the lap on this section so it highlighted for me in WKO.

On the 11/10 ride we didn't start til 10am and it was warmer and sunny. The 11/23 we started at 8am and was cold.

[rruff]

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, they must assume a particular gradient with altitude, but this varies depending on conditions... conditions in the air between you and outer space. For instance, if I just leave the iBike in one spot for a few days I can easily get a 300 ft scatter in the elevation reading at 7000 ft. It makes sense that a similar % error would occur in determining the *change* in elevation for similar reasons. I don't know if it is even possible to improve on their algorithm.

[KenS]

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?

As far as I'm aware, the iBike uses its accelerometer for power calculation - not the barometric altimeter. The accelerometer covers both acceleration due to power to the pedals and gravity.
The accelerometer is very accurate which is why the slope shown on the iBike display is much better than on my Garmin which uses only the barometric altimeter