Rotor INspider Power Meter DM 110x4

The Rotor INspider is a power meter that forms part of a modular setup that can allow fitment to almost any style of bike including road, gravel or mountain bike. It is very well made with precise tolerances and multiple options. It offers dual-sided power measurement, and a rechargeable battery with long lifetime. While the cost of the power meter itself is competitive, creating a full system is expensive.

The spider must be fitted to a compatible axle, with various diameters and widths available, and compatible cranks – Rotor's Vegast, Aldhu or new Aldhu Carbon road/gravel options are all compatible, as are its Kapic, Kapic Carbon and R-Raptor mountain bike options. I tested the INspider on a road bike with Vegast cranks, a 30mm axle and UBB (universal bottom bracket).

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The spider has a 110x4 fitment and Rotor has a range of chainrings that will fit. Rotor is a company known for oval/elliptical chainrings so it is unsurprising that the INspider is one of the few power meters that is officially tested and compatible with oval chainrings. This is not a requirement, though – round chainrings are also fine to use.

Fitment

The modular system from Rotor is very easy to connect together, with very precise connection of the spider onto the axle, with the cranks then slotting onto the axle.

The overall system I have is reasonably common, with 50/34-tooth compact chainrings. It can also be used with a 1x setup, assuming the appropriate chainring is used.

There are more crank length options available than most manufacturers offer. The Aldhu cranks, for instance, are available in 150, 155, 160, 165, 167.5, 170, 172.5 and 175mm lengths. One big benefit of a modular system like this is that, should you change frames or bikes and need a different axle size, you can simply change the axle rather than needing a whole new crankset.

Rotor also provided the INspider Aero crown, which keeps the whole unit looking clean with all bolts hidden, but it's an extra £44.99. It isn't a necessity, though; without it, the only real difference is the bolt heads will be visible.

Initial setting up of the power meter was relatively simple. I used the Rotor app to register the device and then perform the initial calibration. The calibration process does involve a few more steps than other power meters, although it doesn't take much longer. Rotor says the device does not need to be calibrated every ride – every week is the suggestion.

To calibrate, first the power meter needs to be 'woken up' and this process can take a little more effort than others; a short ride was usually best, as I found some force was needed – simply spinning the pedals backwards was not sufficient. Once the unit is connected it needs to be calibrated twice. Upon the first calibration, ensuring the bike is upright and still with pedals vertical, a figure of '1000' should be shown, then the pedals need to be rotated backwards at least twice and calibrated again, with a different figure then shown. This can be done on any of the major headset units likely to be used to display the data.

Data accuracy

Claiming accuracy when testing in real life, outside of a lab is not possible, but I did compare the INspider against various others including a Tacx Neo2 power meter, Vector 3S pedals, Favero Assioma Duo pedals and 4iiii single-sided power meter. While there were small differences, the general reading was consistent throughout, with the Rotor INspider reading slightly higher in the majority of cases.

For outdoor rides I was able to compare directly against the Assimoa Duo pedals, which are similar in being dual-sided. Data was captured at the same intervals and compared. For one specific ride, almost three hours in duration, the average power difference between the two was 10 watts (195.6 watts for the Assioma vs 205.1 watts for the INspider), which works out as an average of 5.1%.

Comparing the data directly against the Assioma pedals, the INspider responds to power changes at a similar rate, and even smaller changes in power are equally well picked up, but it seems to remain higher at all times showing a consistent trend. This was evident on multiple rides and while calibrating all power meters on a regular basis.

There is no way of stating which is correct, but the data was consistent and repeatable, and when compared against other manufacturers the difference was always similar and within the same range each time. The largest difference seen when correctly calibrated was usually 5%, which equated to an average of approximately 10 watts between two different power meters. This is measuring the average power on rides of several hours or more.

The biggest and most important factor with any power meter is receiving data that is repeatable and here the Rotor INspider seems very good. The power seen on the head unit was at similar perceived levels of exertion and also, over multiple rides the data was comparable against other power meters, being a similar percentage above on each occasion.

The only issue here could be if you use power meters from different brands on different bikes, and specifically train to power and power zones. The same would be true of any power meter brand to an extent; you would need to know the difference and adjust the data/zones depending on which bike you are riding.

Left/right power

One area that I was not able to resolve was an imbalance in the recorded left/right power figures from the device. Despite lots of riding, testing and calibration attempts, I found that the figures provided were considerably different to 'normal' or a value I would consider to be correct. The figure varied, but was showing between 60/40 and 52/48 on most occasions, in favour of the left leg. When compared directly against a Favero Assimoa Duo on the same ride, the biggest difference seen for that was 48/52, in favour of the opposite leg, which is what I would normally expect to see.

Does it matter? For most riders I would say it is not important – overall average power and having a consistent unit is far more important. There are times or training sessions where a separate left/right display might be preferred, but I expect even this will be very minimal.

I did contact Rotor to see if someone was able to give a little insight into the difference, but at the time of writing I'm still waiting for a response.

Battery and charging

There are pros and cons to a rechargeable battery. The INspider's rechargeable battery has a claimed life of 200 hours, which is quite impressive. Recharging is via a USB connection lead with a magnetic attachment that connects to the front of the spider. I found the cable quite short, just 1m in length, and if you wish to charge from either a desk or a socket that isn't near the ground you might need an extension cable.

I had no issues at all with battery life. Although I did not attempt to run it flat, it was pushed close to 100 hours before recharging, with no problems and no loss of data. The only problem I can envisage is that, given the battery length is so good, you might simply forget to charge it. But if your head unit has a battery warning display, that should prevent that. If you did an average of 10 hours a week, that would mean it only needed recharging once every 20 weeks.

Torque 360

You can use the Rotor app to provide and store many details for riding, such as time, distance, elevation and all power details, although I suspect most riders would be more likely to choose to display this on a separate head unit.

One area that is different is the section called Torque 360, which dives into more detail and can show you a live track of where your power is provided around the full pedal stroke. It will also show your L/R power split, cadence and one big positive for riders who also use Rotor elliptical chainrings: the optimum chainring position (OCP). All Rotor oval chainrings have the option of five different positions, giving 5 degrees of adjustment, but the INspider-compatible chainsets have further 2.5-degree options for fine-tuning your OCP.

The Torque 360 function will analyse the data provided and give you a best OCP position for the oval chainrings, should you use them. Prior to this function, choosing the position was often a best-guess scenario, with most people, including myself when I used oval chainrings, selecting a middle ground.

If you do not use oval chainrings, the Torque 360 function of the app won't be as useful, simply showing how circular your pedal stroke is, should you wish to know.

Durability

Throughout testing I have used the INspider on some long rides, including a 500km non-stop challenge, and through some very wet and also incredibly cold weather. I had no issues at all, with no dropped signal, and no problems with the battery or connection to the head unit.

The INspider has a waterproof rating of IPX7, which means that it can withstand being submerged in water to a depth of a metre for 30 minutes which, as you can imagine, will be more than sufficient for riding. If Rotor wishes to add 'as tested in the wettest parts of Wales' to the product description, it can do, as it has stood up to some very poor weather over the test period.

Comparisons

If you already have compatible cranks and axle, adding the Rotor INspider at a cost of £585 (rrp) looks good value compared with two popular options that can also measure power from both sides, the Favero Assioma Duo pedals at £699, and Garmin's Vector 3 at £789.99. (Both are also available in single-sided versions for much less.)

If you're having to buy a new axle (£45), cranks (Vegast £112, Aldhu £225 or Aldhu Carbon £349) and chainrings, which vary in price depending on the size and setup, things start to look a little more costly. The full chainset as tested would total £932, including the aero cover and bolts.

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Some chainset-based power meters are also limited to needing specific cranks and/or chainrings, including SRAM's AXS power meter which is €446 for the power meter alone.

Weight

The INspider itself weighs 152g, but factor in that a standard 110x4 spider is 53g and the weight added is less than 99g.

In comparison, the Favero Assioma Duo pedal-based power meters weigh 306g for a pair, which is good for a standard pedal and reasonable even compared to a higher end pedals such as the Look Keo Blade Carbons at 236g for a pair.

Overview

While some questions remain over the L/R split of power, for overall measurement the INspider delivers a repeatable, hassle-free option for capturing your power metrics. The numbers given were consistent through a range of conditions, and it is also built to withstand the very worst weather conditions with a fully sealed unit and battery life between charges.

If you're looking for a power meter and prefer oval chainrings, then Rotor is one of the only manufacturers that officially allows them to be used without affecting data, but even if you prefer round rings the INspider offers consistent and reliable data in a package that is water tight and not too susceptible to wear. With the entire system being modular there are endless options of what type of bike and bottom bracket it can be fitted to, with the only proviso being that it will only work with a Rotor axle and cranks.

Verdict

Impressively weatherproof design with consistent data figures