11 speed chain on 1x8 mid drive.

[Retrorockit]

I decided to try this because 11 speed chains seem to be strong enough for a BBSHD, and last quite a bit longer (no idea why). Supposedly cross chain better too.
I'm going to put a little bit of "theory" out here because there are some "reasons" this might not work.
1- 8 speed chain is wider on the inside. This is true. 3/32"(2.38mm) inside. 9-11 speed is 11/128"(2.18mm) inside. Difference of .008". The teeth on 8s cassette are 1.8mm. Some cassettes with alloy cogs could be wider but they would all be made for 9-11s and not 8s specific. It's possible that you might find a 2.3mm wide chainring. if it has some wear on it it should work anyway. But 9 speed has been around for 20 years or so. Unless you go to a 3/32" single speed part (some Surly rings) you aren't likely to find these. But 2.1mm has been the standard for a long time.
2- 8 speed is wider on the outside. (7mm) As they add gears to the cassette the chains get narrower and narrower on the outside. The rear derailleur moves the chain centered on the guide pulleys, not pushing it from the outside like a front derailleur. The 11s chain will have no problem passing through the wider 8s derailleur and going to the right gear.
3- The 11 speed chain is narrower (5.5mm). That's quite a bit actually. But does it matter? Can it fall down between the cassette cogs? The 8 speed cassette has 4.8mm center to center on the cogs, which are 1,8mm thick. That leaves 3mm spacing between them. So it's not going to happen.

Now let's get back to reality. I bought the 11s chain and tried this Specifically a Wippermann 11sE Ebike chain. It's going on a BBSHD with a flat 50t Surly stainless steel chain ring (2.1mm). With a Shimano HG400-8, 11-40t cassette, and a Vintage Rapid Rise XTR deraillauer that may be 8s or 9s I'm not sure (M860) and a matching Shimano 8 speed Revoshifter so I can throw a bunch of shifts at once. This bike also has the Zip Tie Mod. So shifts can be made any time the bike is moving, pedaling or not, up or down, any number of gears at once. It has a toothed idler chain guide to keep the chain from flying off. if there is a problem with this chain conversion I will probably find it.

I installed the chain with the Connex link they supply with it. I had not been using them on this bike, but the smooth shifts with the Zip Tie Mod got me to try it again.
First ride I had chain skips in the top 3 gears. I rode to my favorite LBS because he works on whatever comes through the door and has probably seen it all. HE diagnosed it as the Connex link.
I don't have a tool to rivet the 11s chain. Mine just does 8-9 speed. The solution was to pull 2 outer plates, and pins from a piece of unused 8 speed chain and use them as a riveted master link for the 11 speed.
So the plates on the Connex have gotten thinner and I guess it distorts when cross chained under due to the egg shaped holes.
After getting rid of the Connex (or any other tool less link) this is working beautifully. It feels smoother and shift adjustment seemed easy because the narrow chain doesn't rub if it isn't perfect.
it seems to pop right into the next gear when shifting (LBS gut noticed this too). I haven't taken a long ride since fixing the connector issue. But the test ride around the neighborhood before it rained was excellent. full power in all gears, even the corsschain ones, and no skipping at all.

[Retrorockit]

I really didn't measure things when I did this. it was the only option I had at the time to get the bike going, and see if the Connex was the problem. I have some Shimano 9 speed coupling pins on the way. My tool can peen those also. It's not recommended to mix pins between chain brands. That's because they rely on a press fit to stay together. Mine will be peened on the ends (riveted) so that doesn't apply. The only thing the pins do is hold the plates together The roller spins on stamping on the inner plates. If the 8 speed outer plates, and 11s inner parts add up to 9s width I will switch to that pin setup. The tapered breakaway ends on the Shimano pins should be easier to work with.

There's a right way to do things, and there's a wrong way to do things. Then there's a right way to do it wrong.

[Retrorockit]

I got the Shimano 9 speed bullet pins which fit my Rohloff riveting tool. I tried just pinning the 11 s chain, and also replacing one of the pins where I had used the 8 speed pins and plates. The 9 speed pin with 8 speed plates had a little less side play than the other 2 setups. I X peened both ends of the Shimano pins
I'm not planning on going back and adding these where I spliced the chain already. It's not advised to break the chain twice in the same place.But going forward I will have some 9s bullet pins on hand. So if the Connex type link isn't working for you there is an option other than buying the $210 Rohloff 12s chain tool.
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[Retrorockit]

So I've had no problems since removing the Connex link and riveting the chain using 8 speed outer plates, and 9 speed Shimano pins cross peened with the Rohloff Revolver 2 tool. This is probably due to the full power launches in the cross chained lower gears. The 50t chain ring for top end, and hard launches in traffic are both important to me, so I'm going to keep doing it this way.

[Retrorockit]

I did my first drip wax of the new chain ( I had visitors and was off the bike a while due to that). The Mariposa wax is really nice. I put it on the newly broken in chain and WOW did it make a difference. With the zip tie mod the looser running chain is really noticeable. I don't recall seeing this kind of difference with the Squirt wax. I think I may use this more instead of less than the Squirt wax.

[Retrorockit]

I saw comments in 11s chain comparisons about the Wippermann snapping into gear audibly where others are quiet. I've found this to be true (IDK about others) it does click into each gear. This is useful at low wheel speeds because it takes some time for the wheel to rotate enough to make the shift. You click the shifter, and then you hear a click at the derailleur and you know you can safely apply power then. I don't recall the 8s chain doing this.

[Retrorockit]

Adam Kerin at Zero Friction Cycling (a Zero Fiction kind of guy) suggested that a SRAM EX1 chain would be a good choice for this mod. SRAM made a thicker Ebike chain for 8s on 10s spacing (I think). This is for their magic 8 speed Ebike group with a $400 forged "steal" cassette, special one gear at a time shifter and who knows what other nonsense. SRAM chains are the most durable at ZFC so this makes sense. Also this one is on sale for $12 at Jenson. So it's even cheaper than the low rent KMC and accepts wax lubes too! Comes with 144 links.

https://www.jensonusa.com/SRAM-EX1-E-Bike-Chain

In my own case if it's thicker than a 10s chain I should be able to join it with my Rohloff Revolver 2 and toss the quick link.
I've got one on the way for testing.