SOC15: 4iiii add-on crankarm power meter gets even smaller, includes factory install

Can someone tell me why it needs to be bonded on? I’ll take a stab at it ad say it needs absolute stability to be accurate, but I’d like to know more.

works with aluminium/steel only 🙁

Durianrider i don’t think so. A P2M is 599 crank included now wit renown precision and reliability. I really see no bragain in making a 50$ economy at the risk of messing with an almost diy solution like this.

Are these permanent once they are installed, or is there a way to uninstall it and transfer them to a new crankset?

Michael,
The manufacturing precision of any major alloy crankarm is such that variations from unit to unit are insignificant with respect to mechanical properties. The material (Al alloy) is almost universal across the industry, with respect to mechanical properties. I am sure 4iiii did calibration testing to prove out their accuracy.
The effect of crank arm length can be accommodated via software.
The only real issue is precision in placement.

This is simple strain gauge tech. 4iiii is finally giving it to people at a price more inline with the actual component prices (which are dirt cheap).

@ Michael,

Yes, as Alex said, there is a calibration step after the unit is bonded to the arm. The have a dummy spindle which is mounted to the crank arm in place of a pedal, and then a weight of known mass is hung off the spindle in a few different locations along its length. This allows them to determine the crank arm deflection characteristics under known loads, which can then be used to compute power. Apparently, it is still up in the air as to if this method will work on carbon cranks though, as they may not behave as consistently across the spectrum of foreseeable loads or extended time periods.

I hardly think this will force Quarq and P2M “shares” lower, especially when P2M already has a product that measures power from both legs for just a bit more than the price of the 4iii. Likewise, Quarq has dropped its prices. Not everyone is satisfied with power measured on only one leg.

SRM, however, is going to see its market share drop if it doesn’t respond to all the new, lower priced power meters on the market and all the price reductions from established brands. As for SRM’s alleged better accuracy, well, it’s not that much better at all than P2M, Quarq, and PowerTap, all of whom offer significantly lower prices. Even Rotor is offering lower prices, although the jury is still out on Rotor PMs’ accuracy.

Of course this is all good for the consumer.

@Psi Squared… Last I checked, this is no different than P2M, Quarq, Stages (for a start)…all of these (like the 4iiii’s) have the strain gauge on one side…any L vs R is a calculation/estimate, not necessarily true power. This would be where Vector, Pioneer, Look,( to mention a few) have some advantages (for additional $$) ….You want true L/R…wait a few more months, it sounds like 4iiii will address that for less money than anyone else.

@Mick: as Greg said, P2M, Quarq, and SRM are measuring strain in the spider which is created by each leg, so you’re getting power measurement from both sides.