PowerPod and ShockStop Stem by Redshift

[the shovel]

Not a question, but thought I'd post about my experience with Shockstop, a new shock absorbing stem I installed on my bike a few weeks ago.

This is not a promotion for Shockstop. I added it here because the stem flexes slightly to reduce vibration and shock, and I was concerned that this flexing might adversely affect the readings from my handlebar mounted PowerPod.

They didn't. I compared the graph of one of my frequent rides with my old stem, and then a few days later with my new one. I tried to keep the level of effort about the same, and completed one ride in 1:37:58, and the other in 1:38:10. Close enough for government work. The traces for power were very similar, and the average power was, too. I didn't notice anything different in the readings of data with the PowerPod mounted on the Shockstop.

I installed this stem because I've been plagued by numbness in my 3rd and 4th fingers of both hands for the past year. I've tried different gloves, frequent switching of hand positions, and adjusting my overall bike position. The more miles I put on each week, the worse it got. Around mid-July last summer I was losing grip strength, and got new gel padded gloves and it moderated it to the point that my grip strength came back but I was still plagued with numb 3rd and 4th fingers.

In December I bought and installed a Shockstop Stem. Despite it being a little longer (110 instead of 100) and despite installing it inverted (6 degrees down instead of 10 degrees up) the numbness in my 3rd and 4th fingers is now barely discernible during or after rides.

[Velocomp]

This is interesting! If you could post a few files, from before and after installing your new stem, I would appreciate it.

[Disallowed Username]

Many thanks, the shovel, for checking things so thoroughly - I also put a ShockStop Stem on my gravel bike and was wondering how it will affect the Powerpod

[AussieDon]

I hope the OP is still on this forum as the original post is over 4 years old. I'd like to know what version of PP that these results were recorded on because it doesn't correlate with my experience using the Shockstop stem and a PP V2. I could never get the power reading to smooth out during a ride even with 3 sec power averaging. The power output was bouncing all over the place, so I emailed customer service and explained what was happened. I got a response from Tom (I think it was) who advised that it was probably the stem causing the problem. There was no solution to this other than to change the stem which I didn't want to do so I rigged up a fork mount and that helped a lot but I found it was susceptible to under-reporting in crosswinds, especially when the PP was in the lee of the wind protected by the fork. On calm days, the power output was consistent with the DFPM I have mounted on another bike.

My PP V2 battery life has declined quite a lot after countless discharge/recharge cycles so I'd like to take advantage of the trade in offer to get the PP V5 but I haven't found anything on the forum that would suggest the PP V5 would perform better with the Shockstop suspension stem. There are a number of posts to riders with front suspension MTBs that they have to lock out their front fork to get consistent readings from the PP so I'm inclined to think that the same would be required for the PP V5 with the Shockstop stem.

The orientation of the PP V5 is more horizontal than the V2 which is taller and thinner. The V5 is flatter and wider so I couldn't use the same approach as I did the V2 and mount it on the fork.

That's why I'm hoping the OP is still following the forum and can clarify which version of the PP was it that recorded these results. That might help me in making a decision as to whether to apply for the trade-in offer.

Thanks

[Velocomp]

Please post a .ibr ride file from your current setup

[AussieDon]

Here's a recent ride file with the PP V1 mounted on the fork.

[Velocomp]

Here's a recent ride file with the PP V1 mounted on the fork.

I looked at your ride file. The only bothersome thing I see are periodic speed sensor dropouts, which will cause power dropouts. What kind of speed sensor are you using, and where is it mounted?

I don't see any evidence that your shock stem is causing problems. MTB with front suspensions are quite different and potentially can cause problems.

[AussieDon]

It's a cheap wireless magnetless speed sensor (accelerometer type) made by CycPlus (China). I have it mounted on the rear hub because I've got a generator hub on the front and the sensor band is too short to go around the hub. I think I might have had interference from the hub as well so I moved it to the rear hub. I've never noticed the speed sensor dropouts on my bike computer but I tend to have the GPS turned on and maybe the speed on the head unit is coming from the GPS and not the speed sensor. It could also be due to a low battery in the speed sensor as I had to replace it not long ago.

That said, if you are reasonably confident that the stem is not interfering with the PowerPod measurements, I can try moving it back onto the handlebar, recalibrate and collect some ride data and send through the ibr files for your review. Before I do all of that, I'll turn off the GPS on the head unit and see if I can pick up the sensor dropouts.

[Velocomp]

It's a cheap wireless magnetless speed sensor (accelerometer type) made by CycPlus (China). I have it mounted on the rear hub because I've got a generator hub on the front and the sensor band is too short to go around the hub. I think I might have had interference from the hub as well so I moved it to the rear hub. I've never noticed the speed sensor dropouts on my bike computer but I tend to have the GPS turned on and maybe the speed on the head unit is coming from the GPS and not the speed sensor. It could also be due to a low battery in the speed sensor as I had to replace it not long ago.

That said, if you are reasonably confident that the stem is not interfering with the PowerPod measurements, I can try moving it back onto the handlebar, recalibrate and collect some ride data and send through the ibr files for your review. Before I do all of that, I'll turn off the GPS on the head unit and see if I can pick up the sensor dropouts.

You might want to consider using a magnet-based speed sensor. They have stronger ANT+ transmitters and they work on rear-wheels.

[AussieDon]

That ride file was from a ride where the Powerpod was mounted on the fork. I've remounted it on the handlebar and have done a cal ride followed by a road ride that I've done before with the PP mounted on the fork.

The ride files and profile are attached. If you change the scale of the charts to 'km' and compare the rides at approximately 19 and 38 km you can see that the power curves are different. The recent ride 2023/01/28) chart for power at those distances show more variation in the power readings than the earlier ride (2022/12/17). The segments are both climbs. At 19 km it's a steady climb topping out at about 7.6% and at 38 km there are 3 short, steep peaks with the middle one topping out at 10.6%. The distances are not exact in each ride file as there is a few hundred metres difference. I'm not sure why that is because I rode the same route both times.

My average power was about 10 watts less on the recent ride even though I covered the distance a bit faster with a higher average speed. The total climbing is 543 metres in the earlier ride vs 509 metres in the recent ride.

I think this is due to me getting out of the saddle frequently on the climbs as I'm not a strong climber. When that happens, the bar deflects due the Shockstop stem compressing under the additional weight and the PP regards this as a decrease in the slope and calculates a lower power output due to the slope being less steep than it actually is.

The OP didn't say how they prefer to climb but if they stay seated during the climbs then this variation may not have been apparent in their ride files.

I would appreciate your thoughts and insights on this scenario but it appears to me that the Shockstop stem is affecting the PP power calculations due to the way I ride on the climbs. That means the more accurate location for the PP would be on the fork and not on the bar which then means that I couldn't upgrade to the V5 because it would make contact with the fork due to its increased width.

I analysed the profile and Isaac recommended changes which would be noticeable but I was sceptical about the huge change in friction so I haven't applied any changes to the profile. The changes would have dropped the average power even further so that wouldn't improve the power calculations.

Aero 0.586 -> 0.665
Wind Scaling 1.922 -> 2.183
CdA 0.305 -> 0.305 m^2
Fric 1.016 -> 17.901
Riding Tilt 0.6 -> -1.7 %
Crr 0.0074 -> 0.0074
Cal Weight 75 -> 75 kg
----------------------------------
Avg Power 91.1 -> 90.5 W
Avg Wind -2.2 -> -0.7 km/h

[Velocomp]

Please provide photos showing where your PP is mounted for each configuration. Make sure you say which one is fork, the other bar

[AussieDon]

Here are the photos. I took shots from the front and side for both configurations to illustrate that there are no obstructions in the bar mounted position and to show the gap between the PP and fork in the fork mounted position. It's not a big gap so I think the PP V5 would not work in a fork mount configuration with my existing attachment.

I hope this helps.

[Velocomp]

Lots of comments:

1) I looked at the slope correction data for your rides. This data shows the effect of mount rigidity. There is some difference between fork and bar mount rigidity. The fork is more rigid, but at only one point in the bar ride (around 50km) is there a significant shift in calibration correction. This is on a downhill and might be a result of stem flex. This affected watts for only about 40 seconds; after that the unit self-corrected. Overall, I don't think stem flex is a material issue for you and you can mount your PP on your bar.

2) What IS worrisome is that you have spikes in your speed sensor data, both in the bar and fork files

Fork

Fork.png (329.68 KiB) Viewed 5091 times

Bar

Bar.png (331.17 KiB) Viewed 5091 times

Speed spikes will cause power dropouts and also might affect calibration. What kind of speed sensor are you using and where is it located? I would change its battery...

3) The biggest factor affecting your watts is wind. On the 12/17 ride (fork) you had a net tail wind for the ride of -0.6 km

Fork stats.png (409.9 KiB) Viewed 5091 times

On your 1/28 ride (bar) you had a net tail wind of -2.9 km/h

Bar stats.png (278.18 KiB) Viewed 5091 times

Riding In a tail wind takes less power, and the stronger the tail wind, the less power is required. . You rode faster because the tail wind was helping you. You had lower watts because the tail wind was pushing you forward more than required to achieve the slightly higher bike speed.

I don't think the lower watts are attributable to the shock stem, and I don't think the shock stem is a material factor in your ride stats.

[AussieDon]

Thanks for reviewing my ride files and your analysis and comments. I'll try to address some of your remarks.

Regarding the speed dropouts, I set the scale to '2 km' and scrolled through both ride files. Every time there is a speed dropout, it doesn't go to 0. The speed dips a bit and so do power and most importantly the cadence also drops at the same time. I think what's happening here is that I'm backing off the force through the pedals in order to shift up to the big ring. I've got an Ultegra drivetrain on my bike so shifting under load is not that smooth. So I back off a bit, shift up and increase the load on the pedals. It looks dramatic when viewing the entire ride but when examined in detail I think it makes sense that those drop-outs are big ring shift events and the speed sensor is fine.

I didn't pick up on the difference in the net wind in the ride files so the faster ride time on recent 'bar' ride could be due to the benefit of a bigger tailwind. I'll concede that but the tailwind difference wouldn't make that much of a difference on the climbs. Did you inspect the segments where I pointed out power variations in the 'bar' ride at kms 19 and 38? There are decent climbs at those distances and it seemed to me that the power curve on the 'bar' ride was more fragmented. That's where I would have been climbing out of the saddle and leaning more heavily on the bar. You didn't comment on that.

The post ride calibration analysis in Isaac for the ride on the 28th recommended a change to the profile but had a big change in friction.

Today's ride analysis also recommended a change but had a negative friction value? Is that legitimate or a sign that the profile is suspect and should be redone?

There was a long modest descent where the power spiked every time I went into the drops while pedalling. Could that have led to these calibration recommendations?

Aero 0.586 -> 0.542
Wind Scaling 1.922 -> 1.778
CdA 0.305 -> 0.305 m^2
Fric 1.016 -> -31.975
Riding Tilt 0.6 -> 5.1 %
Crr 0.0074 -> 0.0074
Cal Weight 75 -> 75 kg
----------------------------------
Avg Power 104.3 -> 95.8 W
Avg Wind 0.3 -> -0.6 km/h

[AussieDon]

Upon closer inspection of the ride files, it seems like the speed drop-outs are not all big ring shifts as the event happens at low speed. Instead, it could be a careful down-shift from the big ring in order to avoid dropping the chain. As far as I can tell, these events are always accompanied by a drop in cadence so they're either related to shifting or both the speed and cadence sensors are dropping out at the same time which seems unlikely. I have two individual sensors for speed and cadence so if it's not due to shifting I don't know what else could cause it.

[Velocomp]

Four comments:

1) The speed spikes are not a result of gear changes. Why? In each spike bike speed is reduced by 1 mph in one second, then goes back to "normal" in the next one second. These would be HUGE accelerations, not possible. What kind of speed sensor are you using? Where is it mounted? Have you installed a new battery?

2) There is no evidence of calibration correction at km 19. At km 38 there is a bit of calibration correction, but it lasts only 5 seconds. Furthermore, there is a speed spike at km 38, which may have affected the calibration correction. Note that when you're out of the saddle your power application will be much more pulse-like.

3) If Isaac is recommending a negative friction correction, this means that your PP position has changed substantially since its original calibration. You should probably do a new cal ride.

4) When you go into the drops you become more aerodynamic and pick up speed. Because PP doesn't know you've changed ride position, it interprets the higher speed as the result of more pedal power.

[AussieDon]

The speed sensor is a Cycplus accelerometer-type sensor mounted on the rear hub because I've got a generator hub on the front. I've changed the battery and redid the cal ride then went for a longer ride to check it out. There seems to be fewer speed drop-outs when I view the ride file at a '2 km' range.

I'm not too concerned at this point if there are a few speed drop-outs because all I'm trying to establish is whether the Shockstop stem is influencing the power readings as I would like to upgrade to the V5. I've kept the PP mounted on the bar.

I've attached the ride file and the new profile. It may still be a bit off because when I checked the calibration, the recommendations from Isaac would have dropped the average power by 10 watts and this would be a noticeable change. Should I accept these changes or do a few more rides to see if the profile will adjust? Not sure what to make of the proposed changes as none seem too radical but in total would appear to lower the average power which I'm loathe to do.

Aero 0.652 -> 0.616
Wind Scaling 2.141 -> 2.023
CdA 0.305 -> 0.305 m^2
Fric 1.016 -> 5.421
Riding Tilt 0.6 -> -0.0 %
Crr 0.0074 -> 0.0074
Cal Weight 75 -> 75 kg
----------------------------------
Avg Power 106.8 -> 95.0 W
Avg Wind 0.0 -> -0.7 km/h

[Velocomp]

Your cal ride is fine.

You are getting some odd cadence readings, along with the occasional speed spike. You might want to find an older-generation magnet speed/cadence sensor for your rear wheel.

I really don't see any strong evidence of problems caused by your shock stem. There are a few places where, at the start of a downhill, you are traveling at high speed and pedaling, where watts are a bit high. But, this may be caused by changes in your ride position.

"Check Calibration" should be used only for short, out and back rides. I would not change your profile settings.

[AussieDon]

I've ordered a 'Coospo' magnet-based speed/cadence sensor. I hope this will clear up the speed drop-outs. How do I go about re-doing the sensor pairing? The V5 instruction video for pairing says to press/hold for 4 seconds to get the device to search for the new sensors. Does that still apply for the PP V2 that I have? I know that a 5 second press/hold will put the device into calibration mode. That's just a split-second difference from the sensor-pairing button press so I'm not sure if I will need to re-do the calibration ride again after pairing the device with the new sensors. If I don't need to redo the calibration ride again but the device goes into calibration mode, is there a way to revert the device back to normal operating mode?

[Velocomp]

I've ordered a 'Coospo' magnet-based speed/cadence sensor. I hope this will clear up the speed drop-outs. How do I go about re-doing the sensor pairing? The V5 instruction video for pairing says to press/hold for 4 seconds to get the device to search for the new sensors. Does that still apply for the PP V2 that I have? I know that a 5 second press/hold will put the device into calibration mode. That's just a split-second difference from the sensor-pairing button press so I'm not sure if I will need to re-do the calibration ride again after pairing the device with the new sensors. If I don't need to redo the calibration ride again but the device goes into calibration mode, is there a way to revert the device back to normal operating mode?

1) Sensor pairing: make sure sensors are awake, then press=hold button for 4 seconds. Light will flash green during pairing, go solid green at end of pairing process. This also forces a new cal ride

[AussieDon]

I've installed the Coospo speed/cadence sensor, paired it with the PowerPod and did a cal ride followed by a road ride on a familiar route.

I've attached the ride file and the new profile.

It's not clear if the new sensors have eliminated the speed drop-outs entirely as there are a few places in the ride file that still look odd (e.g. @ km 12.3).

The one additional thing I've noticed from looking at the ride files recently is that the PP climbing measurement is lower than the elevation gain reported by my head unit (Bryton 420E). The climbing for the attached ride is 561 metres according to the PP but is reported as 663 metres by the Bryton. That's 100 metres difference over 61 km which seems like a lot. The head unit is using GPS measurements to calculate the elevation gain but the PP may be working it out by the change in slope over distance? Is there anyway to validate the PP's climbing stats? If the climbing gain was higher that would potentially increase the power calculated on the climbs, wouldn't it?

[Velocomp]

Your ride file looks fine. Speed spikes are gone!

At km 12.3 you stopped for about 20 seconds. I don't see any peculiar data there.

GPS elevation readings are unreliable. PP uses a baro sensor to directly measure changes in atmospheric pressure, which tie directly to elevation changes.

I don't believe the GPS elevation gain, and I do believe the PP elevation gain.