chaadster

Hey folks,

Do any of you use, or have you used, an iBike Newton (https://ibikesports.com/NEWTON.html) power meter?

I do power based stationary bike training on a Cycleops 300 PT, so I naturally gravitated towards the Cycleops Powertap hub systems, but my trainer actually uses one of the older iBike units and recommended them to me. The Newton is their latest and greatest, and so while I'm inclined to trust a guy who runs a studio for cycling power training, I wouldn't mind hearing some feedback on the newer units specifically.

Apparently iBike has worked out a way to accurately derive power output based on air pressure (or, is air speed more correct?), so aside from sensors for crank and wheel speed, there's no need for special hubs, special cranks, or special pedals. Additionally, there are some features (particularly on the Newton+) that no other system that I'm aware of can deliver, specifically drag coefficients. Interestingly, if I read their website correctly, the Newton+ could actually link with a Powertap hub via ANT+ for some pretty sophisticated aerodynamic calculations.

The pricing for the Newton and Newton+ is $500 and $600, respectively, so they would seem to deliver great value, too.

So, I'm wondering if they're reliable, easy to use, finicky, or awesome...anything like that. The mounts look a little unrefined, but it may be that the unit needs to have some airspace around it for accurate readings. My trainer says the iBike power meters are quite accurate, and give results fairly identical to a direct measure system like Powertap.

Anyway, any feedback and comments are appreciated!

Looigi

IMO, it's a sound concept but: Basically, it determines power from airspeed, road speed, and barometric pressure (rate of climb). To do that, it needs to know the total weight, aerodynamic coefficient of drag, the rolling resistance, and drivetrain efficiency. There is a calibration you do by riding out and back, but it's unclear to me how it uses that information. One obvious shortcoming is it can't tell if your position changes from the drops, hoods or tops, or if there are other changes to your Cd, like changing wheels, wearing a jacket, etc.. Smaller, but still possibly a factor is accounting for changes in total weight. I would also question how it handles or accounts for crosswinds.

IMO, it could be a useful training tool if those limitations and caveats are understood and accounted for.

chaadster

Obviously the unit depends on a sophisticated algorithm to measure power, and I see from watching a video on Youtube that good readings depend on user input for things like riding position and rider weight, and bike weight. From there, it must estimate Cd, using input from the calibration ride. I suppose, then, that if you were going to change wheels, riding position, or clothes, you'd want to do another calibration ride to get the most accurate power measurements.

I'd also guess that the Newton+, which does all sorts of fancy aerodynamic calculations, is able to switch between algorithms for riding on hoods, or in the drops on the fly, without having to do another cal ride. It would probably be horrible having to push a button everytime you change hand positions, so maybe it does it some other way; I dunno.

Having to do at least some calibration before every ride (wind?) is something to consider when weighing systems against each other. I've never used a Powertap or other direct measurement system, but I presume that because it's actually measuring leg force (at crank, pedals, or hub), that you can just get on and go.

gregf83 

I think you'd be far better off with a powertap or crank based power meter. If you want lower cost there are wired used units for 400-800. Too many caveats required for accurate measurements from iBike.

Looigi

I don't imagine the algorithms are necessarily sophisticated as the principles are basic physics. There's no way for the device to know if you change positions on the bike without you telling it. For example: You're going along on the flat on the tops at a given speed then your speed increases. The device doesn't know if it increased because you started putting out more power or you went to the drops.

Yes, Powertap, SRM, Quark, all measure torque and RPM from which they calculate power, at the hub for power tap or at the crank for the others. This is direct and independent of other variables.

chaadster

I suppose "sophisticated" is equivalent to "incorporates many variables" in my mind.

As for your example of the device knowing whether a change in cruising speed is due to increased power or reduced aero drag, could it be sophisticated enough to distinguish between small spikes in airspeed/air pressure that are due to power, and perhaps a more gradual buildup of airspeed/air pressure that typically comes from reduced drag?

I don't know the answer to that; it's just speculation on my part. One thing that seems undisputed is that the Newton delivers very accurate results that are virtually identical to direct power measures. At least I haven't found any claims to the contrary yet, which is precisely why I'm asking here.