KS16-S first impressions

[esaj]

4 hours ago, Christoph Zens said:

Update after some real world experience:

• Range: I did two rides. First one was on tarmac, almost no elevation changes, 50km (KS app) / 45km (GPS http://www.gpsies.com/map.do?fileId=ovalwomlzvpujtfp). After this ride, there was 50% battery left and the app showed a remaining mileage of 30km, so that would add up to 80km total under these most optimal conditions. Rider weight is around 80kg. Second ride was off road for the most part, dirt, stone, roots, muddy pot holes, some insanely steep inclines, 400m elevation change, 20km total. This ride was done in 2 hours and the wheel showed 75% battery and 40km available range at the end. So that would amount to 60km range under difficult conditions. I think these results closely match the data claimed by KingSong.

I've now had some longer 30-50km rides with the battery charged all the way to full (<=50mA charge current flowing at end), so I can get the watthours vs. ridden distance, the typical consumption seems to hover around 12Wh/km for me (11.5...12.7Wh / km), fairly similar as with the Firewheel usually. Haven't had so "optimal" conditions as when I got the FW consumption down close to about 10Wh per km. I gave up early on using the KS app for measuring distances, and instead use the city zoning map with distance tools, usually the KS app -seems to show higher number than the distance has been in reality, but I've also seen the total mileage go up 26km in the app, when the real distance was 33.5km    Never ridden it all the way to empty, so I don't know how empty you can actually go (ie. can it be ridden all the way to so low that it actually charges 828Wh or so into the battery), but based on the 828Wh -number (59.2V * 14Ah = 828.8Wh), I should be able to get up to about 70km. 

 

Quote

• Off road performance: The off road ride got the wheel to 50°C and the fan turned on for the first time. You can't hear it while riding, it's really quiet. Only humming a little when the wheel is stopped. First thing I learned when going from Tarmac to off road: You can't use Player Mode. Off road needs Riding Mode, otherwise it's impossible to get this wheel going up a 20% incline of washed-out stones and roots. Luckily, riding mode can be changed through the app while riding (unlike the NB1, where you have to turn the wheel off and back on to activate the new setting). So it's really not a problem to switch riding modes as required by the terrain during the ride. Next thing I noticed: This wheel is really stable in off road conditions. I compare it to another 16 inch wheel (NB1 E+), not a 14 inch. Given the same tire dimensions (my NB1 has the same tire width as well), I was amazed by the big difference. This wheel goes over uneven dirt and small roots much easier than the NB1.
• Climbing: The only thing I didn't like was the fact that I still don't know how to actually leverage the full potential of this wheel when it's getting really steep. Even on tarmac and still on riding mode, going up a steep road, I can't push the wheel to more than 1kW power output. There should be plenty of power left, but I don't know how to push further without falling off the wheel. The pedals just seem too short, or I am not heavy enough, or don't know how to properly lean forward on this wheel. Maybe I need to play with the level calibration, as @HermanTheGerman suggested. On the same road, I can easily push the NB1 to its 1.5kW limit, at which point is reaches somewhere around 7kph speed. I expected the KS16 to hit at least 2.5kW and go up this hill much faster, but no success so far. I guess I need more training regarding climbing techniques...

Haven't ridden the S in off-road that much yet, but today took the B to about 38km trip with a friend, off which 10+km was off-road. The B's (also) in Riding Mode, and I hit the same issue as you, with steep off-road uphills with lots of rocks, roots and crevices, it sometimes seems really hard to get it to power up hills, as I need to stand more tip-toed on the pedals to get it to climb, and that doesn't really work too well when the wheels also jumping up and down all the time when hitting the rocks etc. Maybe the Learning mode might be better there, but how well it works with off-road riding in general is another matter, the ground clearance might get too small with the pedals tilting. The B's a little bit more "soft" in the Riding Mode than S, but there isn't really a big difference. S was hard to get to accelerate up steep hills even in tarmac with the Player Mode, but the Riding mode helped there a lot. Another trick you can try is to squeeze the shells between your legs and bend your knees to push the pedals downwards, but it's not really comfortable IMHO.

[Christoph Zens]

27 minutes ago, esaj said:

Another trick you can try is to squeeze the shells between your legs and bend your knees to push the pedals downwards, but it's not really comfortable IMHO.

Great, thanks for the tip, I will try something along these lines. Did some more tests today on my 'standard' hill and improved my climbing a little. According to the App, I almost hit the 1.5kW mark. On the NB1, I would shift my foot position forward for climbing, having a good part of the foot hanging over the pedal in front, to an extent where lifting off the heel is no longer possible. Even so, this was the best way to get it going. However, on the KS16 I now switched to standing more in 'normal' position, with less overhang and the ability to shift a lot of the weight forward until the heel is lifted off the pedal. Not very comfortable and not suited for off road or longer duration, but it can give that extra impulse.

But now the strange thing: Pushing the KS16 near 1.5kW power makes it roll up my standard hill at least twice as fast as the NB1 (maybe even 3 times). Either these power values are not at all accurate, KS and NB are measuring different things alltogether, or the 1.2kW rated KS motor is much more efficient at this operating point than the 500W rated NB1 motor. Also good to know: While the NB1 could take this only for a short period of time (running at peak power), I could push the KS16 like this until my feet can't take it anymore or the battery is empty. Maybe that's kind of a safety feature as well. They built the wheel such that it's almost impossible to push it beyond its rated constant power output (1.2kW) for extended periods of time. Avoids overload conditions.

I wonder if someone actually managed to get the KS16-S to the point where it says "overload" (if speech warnings are enabled)...

[HermanTheGerman]

Interesting results.

Yes, one of the reasons why I calibrated the wheel upward was, that it was difficult to force it to a decent speed going uphill (though it might be already fast compared to older wheels like the NB1, but I don't know that). On asphalt I can now climb a long steep street in our village with around 25 km/h (~20%).

On the other hand you are completely right about the offroad behaviour:  When going steeply uphill offroad, it is still now (with the calibrated wheel) difficult to push the wheel to a decent speed forward, though I always had the feeling it could do it, and that I'm just not able to push it hard enough, because I could not put enough force in front of it (though this is KS16B, and I always tried only in player mode). As you mentioned, it would be necessary to lean forward too much to be able to keep balance or being able to handle the wheel while rolling over bumpy terrain.

But I see, it may be worth to do another try in "riding mode" (sigh), though I don't like it.

However, I think this is something they could possibly change in the firmware, because I believe they do not test it much for offroad riding.

 

[Christoph Zens]

8 hours ago, HermanTheGerman said:

But I see, it may be worth to do another try in "riding mode" (sigh), though I don't like it.

However, I think this is something they could possibly change in the firmware, because I believe they do not test it much for offroad riding.

I tried riding mode in the garage doing all kinds of maneuvers and didn't like it, but off-road it really isn't that bad, because the wheel is constantly moving under your feet anyways. Since it can be switched while riding, I can go from riding to player when leaving an off-road section and switch back to riding mode when entering the woods. I really need to try the calibration next. I wonder if one has to watch the roll angle as well as pitch, or if only pitch is calibrated and roll is fixed. I mean, do I need to have the unit perfectly vertical during calibration? I couldn't determine this from the sparse English manual... 

[US69]

8 minutes ago, Christoph Zens said:

I really need to try the calibration next. I wonder if one has to watch the roll angle as well as pitch, or if only pitch is calibrated and roll is fixed. I mean, do I need to have the unit perfectly vertical during calibration? I couldn't determine this from the sparse English manual... 

I would advise to be as vertical with your wheel as possible....there have been reports, that if not done very good vertical, that you can experience a dip in curves when driving.

Hard to describe, when trying a curve your wheel tends to dip down into the direction you wanted to move.

 

But as said: This can only happen if you have it not vertical while calibrating. It is easy to calibrate it to the horizontal Level you want, for example, having the front a Little bit up.

But always try to have it staying as vertical as possible!

 

And btw: This vertical allignement is also needed on other brands, where you can experience a dip in curving otherwise also....so it is not just a KS "fault" :-)

[Lukasz]

Initial review of the KS16S below....  Please subscribe...    

 

 

[HermanTheGerman]

On 12.6.2017 at 8:31 AM, HermanTheGerman said:

On asphalt I can now climb a long steep street in our village with around 25 km/h (~20%).

........

But I see, it may be worth to do another try in "riding mode" (sigh), though I don't like it.

Today I tried a long distance in riding mode.  Maybe I could get used to it, though I was riding in playermode since more than 9 months.

On steep hills ridingmode is really a lot better: I could go up the above mentioned street now with full speed (beeping, and between 29 and 32 km/h), thanks for the tip !     This was not possible before.

 

On 12.6.2017 at 5:13 PM, Christoph Zens said:

..... I really need to try the calibration next. I wonder if one has to watch the roll angle as well as pitch, or if only pitch is calibrated and roll is fixed. I mean, do I need to have the unit perfectly vertical during calibration? I couldn't determine this from the sparse English manual... 

I described it here a little bit, maybe it helps:

 

[Lukasz]

Kingsong KS16S high speed - 35 km/h ...

 

 

[Christoph Zens]

12 hours ago, HermanTheGerman said:

I described it here a little bit, maybe it helps:

 

Thanks, I calibrated according to this tip (lean the wheel against something until it almost tips over). Great way to find the balance point, because you can't use the phone on the pedals for that (they are tilted inwards). Interestingly, the app I used on my phone did not show 0° before calibration, more like 2.5°. So, assuming that absolute values are maybe not really correct, I just calibrated another 2° offset, going to 4.5° as per my measurements. It makes a big difference! Before, I sometimes felt like my toes were pointing downwards while riding, now it is the opposite. I think my first measurement before calibration was not accurate and I now do have quite an upward angle. I should maybe reduce it a little... But I think everyone should take the time and calibrate his/her wheel for optimum personal comfort!

I always assumed these wheels come perfectly adjusted from the factory and the user could only make things worse, so better not touch it (I never touched this on my NB1, it was just perfect the way it was).

In any case, it doesn't only help going up hill, it also helps braking when going downhill. It's now much easier to really push down on the heels from a slightly upward position, as opposed to trying to push down on the heels when the toes are pointing downwards...

There is a really steep road section I drive sometimes, coming out of the woods and back on the street, where I start at crawling speed before the descend, as the wheel is picking up speed going down because I just can't hold it. I could not stop at this (short) road section. It's frightening. I'll try again after calibration and see if it improved. I hope so.

[US69]

On ‎11‎.‎06‎.‎2017 at 9:57 PM, Christoph Zens said:

But now the strange thing: Pushing the KS16 near 1.5kW power makes it roll up my standard hill at least twice as fast as the NB1 (maybe even 3 times). Either these power values are not at all accurate

I dont know which app you are using...but i would not give to much on the "Watt" and "Amp" values....

First and most important:

From experience with all my KS wheels(14/16/18)...it is/was easy to push them to the Limit of about 2500-3000Watt. No Problem on a Little hefty acceleration or on a very steep hill.

Second: It is a totally new board, who knows which values it is giving to the BT modul

Third: KS also changed there Batterie config from "daisy chained" to a "real parallel" where both packs are directly connected to the board. Perhaps this Plays a role also.

Thats probably old things for you, but: Recommended apps for value catching/statistics on a KS:

- for Iphone/IOS: gyrometrics..or my new favorite: DarknessBot...

- for android: wheellog (unfortunatly it seams that the author Kevin Cooper stops that Project :-( )

[Christoph Zens]

6 hours ago, KingSong69 said:

I dont know which app you are using...but i would not give to much on the "Watt" and "Amp" values....

First and most important:

From experience with all my KS wheels(14/16/18)...it is/was easy to push them to the Limit of about 2500-3000Watt. No Problem on a Little hefty acceleration or on a very steep hill.

Second: It is a totally new board, who knows which values it is giving to the BT modul

Third: KS also changed there Batterie config from "daisy chained" to a "real parallel" where both packs are directly connected to the board. Perhaps this Plays a role also.

Thats probably old things for you, but: Recommended apps for value catching/statistics on a KS:

- for Iphone/IOS: gyrometrics..or my new favorite: DarknessBot...

- for android: wheellog (unfortunatly it seams that the author Kevin Cooper stops that Project :-( )

Thanks, that's interesting! I'll try it again, with the re-calibrated wheel and me having a little more experience in pushing the wheel up steep hills. I guess it really may be a matter of the old app not being compatible with the new -S firmware. Also, the braking current is totally wrong with this firmware. Only shows 70A (positive)... So they might have changed something in the -S firmware that makes it incompatible to the current app (Amp readings at least), and they don't fix it since they are working on a new app anyways.

[Lukasz]

On 6/14/2017 at 5:09 PM, Christoph Zens said:

with the re-calibrated wheel and me having a little more experience in pushing the wheel up steep hills.

Hello Christoph,

Which firmware is Your KS16S?  I have V1.02 version and I see no issues with climbing hills, also the current in the KS 1.4 application (green one) is listed OK, (but in WheelLog not - it always show 4000W...)  

 

[Christoph Zens]

4 hours ago, Lukasz said:

Hello Christoph,

Which firmware is Your KS16S?  I have V1.02 version and I see no issues with climbing hills, also the current in the KS 1.4 application (green one) is listed OK, (but in WheelLog not - it always show 4000W...)  

20170615_144237.mp4

Hi @Lukasz, my wheel has firmware 1.00. Forward current is OK, but braking current, which should be a negative number, always shows 70A (power shows some 4500W). I use app version 1.4 too, and both the KS app and WheelLog show the same problem. I reported it to KS and they basically acknowledged the problem but did not say anything about where and when it would be resolved. @esaj found out that the KS app expects an unsigned (positive) 2-byte value for the current, which would not work if the wheel actually reported negative values for braking current (like the NineBot does). Maybe in firmware 1.02, they changed it back to the way it was in KS16-B/C/D so that the existing app can handle it. Now braking current seems to be positive again, like normal driving current. That's bad, because its somewhat wrong, but better than the 70A reading...

I tried again with the calibrated wheel and it does OK with climbing in general (17kph on a hill where my 500W NB1 would go 7kph at best). However, the app reading never shows more than some 1300W, maybe a little more when I push it really hard. I guess the reading is just wrong. My NB1 shows close to 1500W going up this hill at 7kph speed, so something can't be right with these numbers. The KS16 can't be 10kph faster using less power than the NB1. Also, @KingSong69 reported that he can get 2000-3000W readings from his KS16 (not S).

If you happen to watch the power reading while going up a hill, I would be interrested in the readings you get.

Also, I don't see an option to upgrade to 1.02 yet. When I go to firmware upgrade in the app, it only shows the curret version 1.00 and nothing else. I suspect that this green app isn't even able to do a firmware upgrade on the new wheels, they need to get the new app ready for that. I guess.

[US69]

3 hours ago, Christoph Zens said:

Hi @Lukasz, my wheel has firmware 1.00. Forward current is OK, but braking current, which should be a negative number, always shows 70A (power shows some 4500W). I use app version 1.4 too, and both the KS app and WheelLog show the same problem. I reported it to KS and they basically acknowledged the problem but did not say anything about where and when it would be resolved. @esaj found out that the KS app expects an unsigned (positive) 2-byte value for the current, which would not work if the wheel actually reported negative values for braking current (like the NineBot does). Maybe in firmware 1.02, they changed it back to the way it was in KS16-B/C/D so that the existing app can handle it. Now braking current seems to be positive again, like normal driving current. That's bad, because its somewhat wrong, but better than the 70A reading...

I tried again with the calibrated wheel and it does OK with climbing in general (17kph on a hill where my 500W NB1 would go 7kph at best). However, the app reading never shows more than some 1300W, maybe a little more when I push it really hard. I guess the reading is just wrong. My NB1 shows close to 1500W going up this hill at 7kph speed, so something can't be right with these numbers. The KS16 can't be 10kph faster using less power than the NB1. Also, @KingSong69 reported that he can get 2000-3000W readings from his KS16 (not S).

If you happen to watch the power reading while going up a hill, I would be interrested in the readings you get.

Also, I don't see an option to upgrade to 1.02 yet. When I go to firmware upgrade in the app, it only shows the curret version 1.00 and nothing else. I suspect that this green app isn't even able to do a firmware upgrade on the new wheels, they need to get the new app ready for that. I guess.

As far as i know there is now "new" firmware over 1.00 for Ks16s at the moment?

So i would just not count on the numbers you see...thats just not possible!

cant you try Darknessbot or Gyrometrics on an Iphone?

[Christoph Zens]

9 minutes ago, KingSong69 said:

As far as i know there is now "new" firmware over 1.00 for Ks16s at the moment?

So i would just not count on the numbers you see...thats just not possible!

cant you try Darknessbot or Gyrometrics on an Iphone?

No, I don't have an iPhone. But it's really not a problem, I was just wondering why that is. I think climbing performance is normal on my wheel. However, @Lukasz definitely has firmware 1.02 on his new wheel. You can see it in his video and his braking current is no longer 70A, as is the case with 1.00, so there are some changes in 1.02.

[US69]

6 minutes ago, Christoph Zens said:

No, I don't have an iPhone. But it's really not a problem, I was just wondering why that is. I think climbing performance is normal on my wheel. However, @Lukasz definitely has firmware 1.02 on his new wheel. You can see it in his video and his braking current is no longer 70A, as is the case with 1.00, so there are some changes in 1.02.

Ok, sorry then, i did not see that version in their bin files :-) it s not that iam not believing anyone ;-)

[esaj]

The app fetches a json-file describing the version numbers, downloadable binary locations, changelogs etc. for different KS wheels from  http://apkdomain.duapp.com/kingsong/versions.json

At least Chrome won't show the line changes correctly, but pasting it in some proper text editor (Notepad2, Notepad++ or such) shows it better. The KS16S is not even listed so far, KS-14D is at 1.02, all others are at 1.25 (look at the versionCode, not versionName).

[Christoph Zens]

Just now, KingSong69 said:

Ok, sorry then, i did not see that version in their bin files :-) it s not that iam not believing anyone ;-)

I guess they already use it for production, but did not publish it yet (and maybe never will)... Actually, that happens with our company too  Sometimes we will ship devices with newer firmware than available on the website. But usually we get that resolved within a week or two.

[esaj]

I set the calibration to lean back about 3 degrees today and took about 45km spin around, mostly on paved bikelanes and with a few kilometers in off-road, but there weren't any steep off-road hills on the way. I think it's now easier to brake & accelerate in steeper hills, but I need to take it to some much steeper ones to really know for sure. Other than that, the slight backwards tilt doesn't make riding harder, and it's not really even that noticeable.

[Lukasz]

 

4 hours ago, Christoph Zens said:

If you happen to watch the power reading while going up a hill, I would be interrested in the readings you ge

I have quite steep hill just outside the place I live, so I will make the test  of the current when going uphill and downhill. In fact precise current readouts would be nice, but for me much more annoying is the issue with  the application not connecting back when You switch the wheel of and on again.

In KS16 firmware 1.23 even if You switched the wheel off, or went with phone far enough to loose the connection - it was connecting back automatically (KS application and WheelLog also connecting well). From the firmware 1.25  (and in V1.0 and V1.02 for KS16S)  Kingsong says that in the new firmware they improved safety - unfortunately I can not get out from Kingsong clear information what was changed  - but the outcome of the "additional safety" is manly the problem that each time You switch the wheel off, it will loose the connection to the phone, and the only way to reconnect is manually press scan in the application (so each time You have to take your phone off the pocket, press scan, switch back to wheellog, check if it also connected, then you are ready to go again....   If You want to use wheellog, it will not connect unless You connect with the KS application first and then switch to wheellog....  annoying...   This problem appeared exactly just after the upgrade of the wheel firmware from 1.23 to 1.25...

Kingsong admits that they have some issues with application development...  

I am looking forward for the clear information what was changed in the communication initialization (in firmware V1.23 wheel was probably "announcing" its presence, so the application was connecting automatically, in the further versions - application on the phone must be modified to scan automatically when connection is lost.  Hopefully with this information from KingSong we can ask Kevin Cooper to make modification in WheelLog  (BTW - Wheellog in my opinion is really the best application for the KS/Gotway wheels - great ergonomic and all necessary functions present!)  

I have some technical/enginering knowledge, 3d printing, tests, etc, but unfortunately ZERO experience with coding /  BT communication programming details... Is there a way to "listen" or scan the BT radio communication and see what is sent from the android phone when "SCAN" is pressed on the screen? Maybe there are some programmers around  Esaj? who can find out quicker than KingSong will tell us - so this scanning functionality can be added to WhelLog ( By Kevin, or other person as Kevin was very kind and provided source code to WhelLog...     Any programmers with BT communication knowledge around? 

[Lukasz]

2 hours ago, KingSong69 said:

cant you try Darknessbot or Gyrometrics on an Iphone?

I do not have Iphone unfortunately... 

I confirm that the firmware in my KS16S is  1.02  - production date for my wheel is 2017 June 08  (however this version is not available online / as upgrade) 

[US69]

@Lukasz

for wheellog: as i heard Kevin Cooper does not work on wheellog anymore... he closed the project.

that even lead to the situation, that the 84v Version of wheellog was withdrawn from the GW Facebook Group, as it was a modification from another Korean member.

so i guess ...no changes in wheellog anymore?!

[esaj]

I took the S off-road last night, and I'm pretty sure that even the slight backwards tilt calibration (around 3 degrees) seems to have helped with accelerating uphill and braking downhill (but, I'm not 100% ruling out just being more bolder now or it being just a psychological thing), it feels I don't have to "tip-toe" on the pedals (at least as much, higher backwards tilt might help even more, up to a point where it becomes inconvenient in general riding) to get it to accelerate faster. I did run into a couple of new "problems" (that are just a matter of practicing and being a bit more wary): accelerating up a hill with lots of loose gravel on top, the wheel started skidding   I was pretty sure I'm going to fall, as it was slipping from side to side, but managed to get it back in control. Just a matter of poor traction + lots of torque, the gravel feels sometimes like riding on ball bearings  Same thing in braking downhill, I can feel it sliding a short trip as the tire loses traction/gravel rolls under the wheel. 

 

Not even a steep hill, and this part of the routes was otherwise in very good condition, but the city has dumped gravel on top, probably to fill out holes caused by winter frost.  

 

 

[Christoph Zens]

7 minutes ago, esaj said:

I took the S off-road last night, and I'm pretty sure that even the slight backwards tilt calibration (around 3 degrees) seems to have helped with accelerating uphill and braking downhill (but, I'm not 100% ruling out just being more bolder now or it being just a psychological thing), it feels I don't have to "tip-toe" on the pedals (at least as much, higher backwards tilt might help even more, up to a point where it becomes inconvenient in general riding) to get it to accelerate faster. I did run into a couple of new "problems" (that are just a matter of practicing and being a bit more wary): accelerating up a hill with lots of loose gravel on top, the wheel started skidding   I was pretty sure I'm going to fall, as it was slipping from side to side, but managed to get it back in control. Just a matter of poor traction + lots of torque, the gravel feels sometimes like riding on ball bearings  Same thing in braking downhill, I can feel it sliding a short trip as the tire loses traction/gravel rolls under the wheel. 

 

Not even a very steep hill, and this part of the routes was otherwise in very good condition, but the city has dumped gravel on top, probably to fill out holes caused by winter frost.  

Same here. Calibration helped, the super-steep downhill section is not that frightening anymore. I also have some off-road sections with loose stones, too large to even call it gravel. It's really annoying and very hard to ride on. Also, one has to watch out for stones which are too large to fit underneath the pedals when going close by, or between two of them. During the first off-road test I had to drop the wheel due to such a situation (at crawling speed, normally would have catched it but missed this one time ).

But now some update on the pedals: After 200km, the grip tape is starting to peel off. I guess I can just renew it myself. Still a little annoying that this happens after such a short time using it. The pedals on my NB1 are not that slippery too, and hold up nicely for 2 years and 2000km now. On the KS16, it looks like I have to work on the pedals every 2 months, so that's 6 times a year servicing the pedals... 

Maybe it's from riding off-road? Or maybe because recently I did some highly repetitive training sessions. For example one hour just doing figure T in a small area (so lots of direction changes and sharp turns). I go forward, sharp quarter turn left, stop, reverse, sharp quarter turn right, continuing in the same direction but now riding backwards. Stop and do the same again in the other direction... I guess I repositioned my feet a lot during this training. Could have accelerated the problem. I wonder where to get such a grip tape 

 

[esaj]

8 minutes ago, Christoph Zens said:

But now some update on the pedals: After 200km, the grip tape is starting to peel off. I guess I can just renew it myself. Still a little annoying that this happens after such a short time using it. The pedals on my NB1 are not that slippery too, and hold up nicely for 2 years and 2000km now. On the KS16, it looks like I have to work on the pedals every 2 months, so that's 6 times a year servicing the pedals... 

Maybe it's from riding off-road? Or maybe because recently I did some highly repetitive training sessions. For example one hour just doing figure T in a small area (so lots of direction changes and sharp turns). I go forward, sharp quarter turn left, stop, reverse, sharp quarter turn right, continuing in the same direction but now riding backwards. Stop and do the same again in the other direction... I guess I repositioned my feet a lot during this training. Could have accelerated the problem. I wonder where to get such a grip tape 

I've got around 475km clocked on the S, but the grip tape is nowhere near that worn out. Might depend on the shoes, weight or you grind the tape if you turn your feet while leaning on the heel? Skate shops probably sell all kinds of grip-tape, but sanding paper might work as well, if glued properly