A Comparison of Spider Power Meters

By: kiritozhang　　Translator: alanyu

I have used several spider power meters (PMs) after my test of Power2Max NGeco, so why not have a comparison of them?

Tested PMs list:

Power2Max NGeco (Shimano BCD 110 model with Rotor Aldhu cranks)

Quarq Dzero No.1 (Sram 8-bolt BCD 110 model with Red cranks)

Quarq Dzero No.2 (Sram 8-bolt BCD 110 model with Quarq cranks)

Quarq Dzero No.3 (Sram 8-bolt BCD 130 model with Quarq cranks)

Sigeyi AXO No.1 (Shimano BCD 110 model with Incolor Skypivot cranks)

Sigeyi AXO No.2 (Shimano BCD 110 model with Incolor Skypivot cranks)

Xcadey Xpower-S (Sram 3-bolt BCD 110 model with Xcadey cranks)

Pica-S No.0 (Sram 8-bolt BCD110 model with Quarq cranks)

Why not test SRM spider PM? There are two reasons: 1, SRM spider PM has been proved to be extremely stable and accurate, and it is used as a reference by many different brands. 2, the truth is: I don’t own one.

Player 1: Power2Max

P2M NGeco is the entry-level product, which is a lite version of NG. It inherits the stability and accuracy, but some prime function such as L/R balance is limited and you need to pay for it.

It uses a CR2450 battery and is claimed to work for 400 hours, which is the biggest difference between NGeco and NG.

Since here I use the heavy Rotor Aldhu cranksets (Rotor products have never been light weight) and Shimano R8000 50-34T chainrings, the total weight reaches 803g. R8000 chainrings is around 150g and you can shave off 20-30g by using R9100 chainrings. (Translator’s note: my R8000 50-34T rings weigh 148g while R9100 50-34T rings weigh 125g.)

Player 2: Quarq

Yes, it’s our old friend, Quarq. I have used Quarq PMs for several years, from the last generation Elsa to the current Dzero. The reasons why I chose Quarq are: 1, SRM was really expensive several years ago and the custom service in China is not good. It needs to be delivered back to Germany to change the battery, which means a lot of time. 2, I was and am keen on carbon cranksets, but there was no agent of Power2Max, FSA didn’t release Powerbox PMs and Easton didn’t release EC90SL cranksets either, so I have no choice other than Quarq at that time.

One significant change from the old Elsa to the current Dzero is the bolt pattern. Dzero has the 8-bolt pattern, more stable, which is good for PM. The old 3-bolt pattern is an open patent, which means any brand can use it after application.

Quarq insists on CR2032 battery and claims a 200 hours battery life, which of course depends on your battery quality and the environment, because the battery is self-discharging all the time when it is not used.

The 170mm, 386 spindle Red Crankset combo with 50-34T red chainrings weighs 707g, which is 100g heavier than the non-PM version. The new Red AXS crankset is optimized a lot on the structure, resulting in a much better weight.

Player 3: Sigeyi AXO

Here comes our new friend: the superlight carbon cranksets Skypivot from Incolor and Sigeyi AXO Spider PM combo. Incolor cooperates with two different Chinese PM brands and thus two basic choices: Sigeyi and Xcadey. You can also choose the SRM spindle version, which can be mounted with SRM spider PM as its name indicates.

The spider bolt pattern is a new 4-bolt pattern. The spider is mounted onto the spindle independently, ensuring the flatness and the tolerance. The battery is the chargeable Li-ion battery and it uses the magnetic charging.

In this report we only review the AXO PM, while Skypivot still needs more time to ride and test.

The 170mm, 386 spindle crankset combo with R8000 50-34T chainrings only weighs 556g, which is amazing.

Play 4: Xcadey Xpower-S

Another Chinese brand released their spider PM crankset combo, which is made of alu and sells at CNY 2080 (USD 295) w/o chainring. One of its selling points is the adjustable crank length. They also have spider PM with other interfaces such as Rotor and Sram.

It also uses magnetic charging and comes with a charger. The LED indicator will turn red if the battery is low.

The crankset uses Sram 3-bolt pattern, which means you can switch the cranksets from other brands, such as the discontinued Sram Force 22 carbon crankset.

The crank-length-adjusting function is reached by a pair of metal parts. You can change the direction of the metal parts or switch to another set to change the crank length.

I use the 170mm crankset, which has two pairs of metal parts. One pair is 172.5mm while another pair is either 170 or 175mm. A pair of metal parts weighs 18g.

The crankset + FSA 50-34T combo weighs 854g, which is a big problem if you want a super light bike.

Official claimed data

	P2M NGeco	Quarq Dzero	Sigeyi AXO	Xcadey Xpower-S
Battery	CR2450 easy to change	CR2032 easy to change	Li-ion Magnetic charging	Li-ion Magnetic charging
Battery Life	400h	200h	300h	150h
Water Proof	IP67	IPX7	IPX6	IPX6
Accuracy	±2%	±1.5%	±1.5%	±1.5%
Weight	158g	128g	115g	101g
Models	Rotor, Specialized, Campagnolo, TA, Easton, FSA, Praxis Works, Sram 3-bolt, Cannondale, Race Face, Shimano MTB	Sram 8-bolt, Specialized, Sram 3-bolt (discontinued)	Sram 3-bolt, Sram 8-bolt, Rotor, Easton, Cane Creek, Incolor, Specialized, Shimano MTB, Race Face	Sram 3-bolt, Sram 8-bolt, Rotor, Praxis Works, Cane Creek, Incolor, Shimano MTB,

P2M has a best the battery life, while Quarq has the least models. Though the claimed IP level of P2M NGeco is the highest, the rubber seal ages a bit quickly, reducing its water proof. The claimed accuracy is either ±1.5% or ±2%, only a small difference, but what is the truth?

PM test

My test doesn’t include the indoor trainer comparison, because usually you cannot find the design/structural defect indoor of a PM unless it is really bad designed. The indoor trainer environment is just, too stable.

The reference (baseline) in the test is a pair of SRM EXAKT PM pedals, which is complicated to mount but has an extremely high stability and accuracy after the correct install, so it is suitable to be used as a reference. Here we take P2M NGeco for example. There will be a couple of seconds difference due to the manual control of the GPS computers.

The blue line is SRM EXAKT while the yellow line is P2M NGeco in the figures below.

Control variates method is used in the test, and we choose 200W as our baseline, which is around FTP of most riders who has a PM. (Translator’s note: I doubt that 200W is a bit higher than reality in China) In this test I first rode on big chainring and medium cog, and then small chainring and small cog, both around 90 cadence and 200W average output, to compare the different PMs. This test aims at the structural defect which causes the error due to different chainrings.

The power curve of two PMs matches quite well with each other.

Big chainring AP: SRM 209W, P2M 200W

Small chainring AP: SRM 204W, P2M 198W

SRM EXAKT reported a higher AP than P2M NGeco under both conditions, which is quite ideal, since SRM has official claimed that their spider PM is around 5% difference compared with PM pedals.)

Low cadence test aims at the accuracy under high torque. Some riders are used to low cadence (grinders), which is not recommended, as your muscles get tired quicker and thus easier to hurt yourself.

The power curve still matches with each other well and SRM reported a bit higher than P2M.

AP: SRM 205W, P2M 202W.

Low power test aims at the accuracy under the low torque, which reflects the situation like the slow weekend riding. The curves match well and the average power is almost the same around 90W. (89.96W vs. 90.29W)

One-minute high output test, which is usual in a crit and the power can change rapidly. There is small difference between two curves but in average is similar. (Translator’s note: if we align the zero at the end, there is a delay of the P2M report, compared with SRM, which is a property of the spider PM vs. pedal PM)

AP: SRM 377W, P2M 380W.

The difference is very small, but the peak power of SRM is 653W while that of P2M is 612W.

There is some deviation in the curves during the sprint test. (Translator’s note: again, the delay of the spider PM)

AP: SRM 429W, P2M 420W

Peak: SRM 826W, P2M 795W

Cobble test aims at the filtering algorithm. Though the data on the GPS computer changes per second while ANT+ transfers the data once each second and BT transfers four times each second, the gauge in the PM can read and report hundreds of times in each second and these data is flitted before transferred to the GPS computer. While you ride on the cobble, the gauge reading is jumping now and then, the data received by GPS computer depend a lot on the algorithm. (Translator’s note: it also depends on the sensitivity of the cadence sensor, if your cadence is not that stable on cobble) The curves again are similar to each other, except one missing peak of P2M.

AP: SRM 108W, P2M 104W

Summary

Quarq, as a big brand under Sram now, can be considered as stable in quality, though there is some deviation between different individuals. The difference to SRM EXAKT of each individual is small, which can also be influenced by different chainrings used here. Moreover, Quarq officially lowered their retail price in 2020, which is one big competitiveness, though the new model can only match SRAM DUB cranksets.

Power2Max NGeco has a high value to its price, and it is very stable under different conditions, not-too-much more expensive than Chinese PMs, which is also a good choice for those who don’t trust Chinese PMs. It has a lot more models than Quarq.

Sigeyi is the elder PM brand in China and it has amazing results in the test. Two individual spider PMs are both highly consistent with SRM EXAKT in different conditions, even better than some PMs from international big brands. However, some riders have reported that there is some fluctuation or unexpected peak power, of which reason is unknown. (Translator’s note: I have met this in the earlier firmware but it seems to be resolved after 3.2) When the big brands decide to lower their price, only high quality can make Sigeyi take hold in the market.

Xcadey, as another Chinese brand, its PMs’ performance is not as good. The first tested PM failed due to the problem between the spindle and the crank while the second one is broken in the electronic hardware during the test. Only the third one can pass through all the test. In most situation it performs well actually, while there is a big deviation during the sprint. (Translator’s note: Xcadey claimed that they had solved the sprint problem by FM update)

Pica, a perfect negative example. It deviates from SRM and other brands significantly. Although they have gone bankrupt, there are still some products on the second hand market, which should be aware of.

Off Topic

1, There is a design defect in Xcadey crankset and they are recalling their products as of press time (June, 9, 2020)

The locking structure of the crankset is confusing and stupid: there is an inclined surface and a split ring at the end of the spindle, and the crank cap works like the expander bolt to lock the crank by expanding the spindle from inside.

However, the diameter of the cap is smaller than the inner diameter of the crank, so there is no enough lateral pressure on the crank. Thus, it needs to be pressed manually and if you don’t have put enough force on it, there will be a gap and thus it will be creaking all the time. Moreover, this structure is prone to be loosen while you ride on it, and finally may dismount itself.

2, Incolor have recalled their earlier products, whose threaded metal parts for pedals may be broken. I will post the review of their crankset after a while. (Translator’s note: my Skypivot is broken due to the spacer and thread part failure. Though it’s free to have a replacement after the end of June.)