3x7-8-9 speed MTB to 1X mid drive drivetrain conversions.

[Retrorockit]

I just thought this deserves a thread. The old 26" MTBs with 3x drives are good bikes for conversion. 29ers came out in that era also.
There are a lot of new parts becoming available for this. Wide range cassettes, and matching derailers with clutches and capacity up to 50t. Shimano and SRAM have moved on to 1x 11-12 speed stuff, so this is mostly 2nd tier brands. Sunrace, Microshift and Box to name a few. Some are Shimano compatible, others are not. Shifter and even chains can be specific to each brand. Then there are the hacks to make the old stuff work. In my own case 8 speed Rapid Rise low normal derailer with a Gripshift and 11-40 cassette. Maybe some secret part numbers? Experiment that did or didn't work out? What the hell is a direct mount derailer?
My parts list.
Surly 50T Stainless Steel chainring on BBSHD 130mm spider. The Surly ring is 1 speed and 8 speed width. Known to be tight on 9 speed chain until broken in.
Roller chain guide off of the seat tube. Li'l Chap bracket drilled out for longer 8mm bolt to reach. Blackspire roller.
The roller guide got seriously upgrated during the "zip tie mod". Now it a 15t Terra Cycle recumbent idler. Both mods game changers for this old bike.
Wippermann 8SE chain $$. No Quick link. Riveted with a Rohloff Revolver chain tool. $$$
Sunrace 11-40T 8 speed cassette.
Updated to custom 11-12-13-15-18-22-28-36 cassette Full power in all 8 gears now.
Shimano XTR GS (mid cage) Rapid Rise derailer. RD M960. 9speed part, but no 9 speed Rapid Rise shifters exist.
Welded up extended derailer hanger. Cut 2 Wheelsmith 6016 hangers 2/3 long and had it welded with 6016 rod. LBS guys look at it funny, but it can be bent back into alignment. You can buy an extender online if you prefer. Broke the welded hanger, stock hanger with 11-36t cassette
Shimano RS-SL40 *8 speed Rapid Rise Revoshifter (Twist shift). You probably won't find one in the US.
I suppose I should mention the front freewheel zip tie mod, and 15trecumbent idler for chain management I've added since starting this thread.

Sunrace- Tends to be Shimano compatible.
https://sunrace.com/category/product...?speed=9-speed

https://sunrace.com/category/products?speed=8-speed

Microshift- Shifters and derailesr can have their own ratios for cable pull.

https://www.microshift.com/

Box Prime 9 (there is an 8 speed e bike option) Does their own thing. Probably best as a groupset. BMX DH background.

https://boxcomponents.com/collections/prime-9/prime9

There is a SRAM EX1 8 speed E bike groupset. Too high end for me, maybe for these old bikes too.

[atlarge]

Regarding old 3 x 7… After my BBSHD conversion I adjusted the derailleur and could never get coverage for all 7 gears. Thinking it was me I took it to an LBS and they couldn’t get it any better. The reason I was told was some derailleurs don’t work as 1x ???
So, in actual use though it’s cycling through them all with few hiccups. A couple chain drops now and then but nothing major. (Yes I have a sensor but, no guide installed) Almost like it just needs a load on the chain to move properly. Was I given some BS?

[73Eldo]

Did you have to use any spacers to get the gear case to clear the chain stay? What chain ring are you using? With no or just a couple MM of spacer and a stock chain ring or one with at least the same offset I would not expect a problem on a classic 3x bike.

[Retrorockit]

That setup may have expected you to be in the big ring for the top gears, and the bottom ring for the low ones. Lot's of hubmotor bikes are running 1x7 freewheels so there are some parts that work for that layout. I would try an 8 speed derailer. They use the same chain and 8/9 speed hangs the last cog over the end of the cassette.The older 7speed stuff had a 13t top gear because it was fully inboard from the lockring.

[K442]

Funny you should mention. I just converted my old 3x9 'iron horse' workout bike over to 1x11. First ride today. So far, so good.

On paper the 11-52 rear cassette and 46 tooth front gave just a bit more range on both the low and high ends compared to the old middle and upper ring and full range of the 9 speed. I never used the lowest ring up front as it seemed to be geared for climbing straight up walls and typically 15-18% grade is about the highest I encounter.

atlarge - As an old friend of mine would say, "Something seems fishy". Unless you had some wild chain line due to the 1x...like the front sprocket setting in line, or even outboard of the small cog in back! Seems like most any derailleur would cover the advertised range, plus some amount...and you'd use the upper/lower limit screws to dial it in so it 'only' covers that range and doesn't throw the chain off the top or bottom sprockets. Hard to say without actually seeing it, but there is a lot to consider.... upper/lower adjustments, "B" screw adjustment, indexing with the shifter, cable length/adjustment, any binding in the shifter, cable, derailleur joints, alignment of the derailleur with the plane of the wheel/cassette, wear of any of the above, weak or worn springs, and probably half a dozen more things to check.

[73Eldo]

A classic 3x I think is what the BBS's were designed for. A classic 3x was 28-38-48. The HD with the stock 46t 19mm offset ring puts the chain line in about the location of the big ring was stock and should clear everything fine since sock there was clearance for a 48. Big to big isn't a ideal combo on the stock bike but should have worked so it still should work with the BBS.

On the 3x's I have done which were all HD's and used a stock ring I left the front derailleur on as a chain guide. There should be enough range in the stop screws to lock it down so you don't need a cable or shifter. I have not put a ton of miles on them myself but have not got any complaints about chain drops.

[atlarge]

My original outside chain ring was 48t and the HD came with 46t. Kept the original chain and no need for spacers. It’s about perfect in line for 3rd or 4th and the little bit of extra chain length is undetectable. Besides adjusting I just cleaned and lubed the derailleur and the chain thoroughly. Runs pretty quiet too so no complaints on it or the Bafang. Just didn’t see why the derailleur would care if the chainnrings were 1x or 3x. When I look up different Shimanos online they always state the numbers of cogs on the cassette but never the number of chainrings? I think he was pulling my leg because he couldn’t improve on my tweaks.

[73Eldo]

That sounds like it should work just fine and agree that the chain length should be fine. I would have to go look but some of mine may only be straight on like 5th or 6th (10 speed). What happens if you go to those lowest gears? I just wonder if you got some more complex alignment issue like a bent hanger or cage going on and your shop / mechanic is a dud? The cage you can sometimes eyeball but the hangar unless its extreme often requires tools that are not practical for a occasional DIYer.

The number of gears has to be listed because that effects the spacing between cogs and how much it moves vs cable movement. Some do talk about 1x or 3x but its to do with how much slack in the chain they can take up. Others also give a max size which is a combination of slack and just physical reach. In the 90's a 14-21 and 42-52 would have been a hardcore road range almost like a single speed is today and a wide range MTB would have been maybe a 13-32 with that 29-38-48. Today you can get a 12 speed that is 10-52 so not only do you have more chain slack to take up you also have to be able to physically be able to track that several inches up and down to feed the chain straight onto the cogs.

[Retrorockit]

The old 3x derailers all had what is today rather small cassette limits. 34T was considered Mega Range. 1x 40t and up is now normal. So a hanger mod, or derailer swap and maybe even chain and shifter is needed. Larger than normal or smaller than normal chainrings can both have chainline issues due to flat adapters.When you get into derailer cage length the smaller ones can limit the front chainring options.

[Retrorockit]

There is a spec. for Max. casette teeth, which in the old days would have been 32-34t. This can be changed with a hanger mod. But there is also a spec for total capacity. This has to do with the length of the idler cage.An 11-52 cassette would need 41t. Many older 3x derailers had 22t front (44-32-22) and 11=34 rear for 43t total and could handle this. Newer parts designed for 1x would not list front chainrings separately. Older stuff does. So to use an older derailer on a 1x you would use the total capacity, and a long derailer hanger to use the larger cassettes. Mid cage can be used up to a point.
Older 1x bikes such as commuters, and DH bikes could run a mid cage derailer for better chain retention and ground clearance. Road bikes with very close gear ratios could run even shorter cages.

[Retrorockit]

My bike dropped the chain fairly often with the stock Bafang ring. I also wanted more than the stock 48t x11 gearing the bike came with. it should go faster with a BBSHD right?
First I tried the front derailer as a guide, and it worked OK. But when I went to 50t on a spider adapter which made the chainline worse than 46t, but not much further out than the stock 48t was.
I tried the Wide Narrow 50t flat rings but I had to have a counterbore machined in them to space them in, and if you get it one tooth off it jams up against the guide. Still needed the guide with N/W 50t.Also the black ring looks ugly when the aluminum gets exposed by wear. So I went with a Surly stainless steel 50t. I tried a couple home made chain guides but finally broke down and bought a roller guide. That's where I'm at on the front. I did just recently have a disaster when I took off WFO from a stop with the chain in between cogs in the rear. The chain skipped sideways down to the small cogs, and got enough angle and slack to sidestep the roller. Folded over the ring, and wrapped the chain around the motor. bent the SS bolt I used for a roller shaft New ring, new cassette, new chain, and have the bent derailer hanger straightened. Fortunately the XTR Rapid Rise derailer was OK. Took the BBSHD apart for a lube and new 1 way clutch and gear, had the hubs serviced, and sealed bearing headset installed. Those things and the Tannus Armour in the rear tire has the old HT riding better than ever.
Part of the reason I had chain drops was I was dropping in off of curbs at 25mph. I kind of stopped doing that.
As far as the offset Wide Narrow rings that are normal for 1x, the inset doesn't work for my high geared 26" bike. If you have bigger wheels or don't need 35mph gearing they probably work just fine.
In the rear I already had Rapid Rise and still want it But only if I can have a gripshift also. So far this keeps me out of 9 speed.
I had some XTR cassettes from my XC bike and used those at first. But replacement cost for rare 8 speed racing parts made that impractical. I didn't particularly need more range than 11-32t but the gears were too close together for stop light takeoffs. I always had to skip a cog here and there to not waste time on extra shifts. I stacked up my own cassettes but then found Sunrace made just what I needed 11-13-18-22-28-34-40. That 22t in the middle instead of 21-24 was what I needed. I could have just blocked off the 8th speed 40t But I decided to keep it and mod the derailer hanger to keep the Rapid Rise derailer. Some where along the way I switched from the long cage Nexave derailer to a mid cage XTR Rapid Rise. My derailer and hanger are right at their limits with a 40t cog. I think I need to add a bottom chain guide. If I overshoot a crosswalk control and need to roll the bike back the chain starts to come off at the bottom. When I lubed the BBSHD I found there are a lot of empty 4mm bolt holes on the back where I can hang something. My last 2 chain drops were both at crosswalks.
I'm gathering parts to try for a 9 speed Rapid Rise setup with a hacked SRAM Rocket front gripshifter. I ordered a 9 speed cassette with 11-12-13-15-18 progression. If I can get the shifter to work with it on my XC bike I will stack the 18-22-28-34-40 Sunrace series on it with 9 speed spacers. The shifter works in the right direction (low normal) and has the right number of stops. The test will be whether the cable pull comes out right. The gain will be an extra cruising gear to adjust my cadence and spread the wear between more small cogs.

[Retrorockit]

I'm going to rant about Rapid Rise some more because it was common on older 1x bikes. But only from Shimano and only 9speed and older. You might encounter this, or decide to add it to your build.
Rapid Rise is also known as Low Normal. The cable releases to reach a lower gear. Front derailers are all Low Normal. So 3x bikes already have this function in the front derailer. 1x bikes don't.
To shift to a lower gear in High normal the cranks must be turning. In Low normal they don't. You can release cable for several downshifts at once, and the shift will happen the next time you pedal.
With a 3x setup you can dump a range of gears in the front. To do this in the rear you need Rapid Rise. Many MTB ridere feel they can force a downshift while pedlaing better with high normal. Since they still had a Low normal front derailer Rapid Rise fell out of favor and was discontinued. Now that 1x is common it may be worth a 2nd look.
The biggest problem with trying Rapid rise is the shifter situation. They work backwards. A lot of people think it's just the numbers that are backwards, but there is more to it than that.
1- Trigger shifters. The problem here is that they are set up to give single upshifts and multiple down shifts. With RR they lose the multiple downshift function when reversed. So many who tried it found no advantage. I prefer gripshifts anyway so IDK if there are RR trigger shifters out there. None have popped up in my searches.
2- Gripshifts are great for multiple downshifts and don't ration them in either direction. SRAM made Shimano compatible gripshifts in 7-8-9 speeds. Many people have used them for this and they do work. These would be the Attack, and Rocket series shifters. All the X series are for SRAMs own cable ratio. The only problem is that the detent is loaded harder in one diredtion than the other to allow for the spring force in the derailer. With RR you get very easy downshifts (with the spring) but very hard upshifts against it. In the wet upshifts can be impossible.
3- Shimanos own Revoshifters. These are RR twist shifters. Mostly in Asia and Europe where 1x commuter bikes are more common. ASFAIK RR 9 speed doesn't exist. But E bikes do just fine with 8 speeds. If you want to try this I would suggest sticking to 8 speed. I don't think wide range cassttes are available in 7 speed. Be sure and get the Rapid Rise version of these.
On flat ground where downshifts are related more to hard braking than increased load Rapid Rise is good to have. if downshifts are related to hard climbing offroad opinions vary. Many old school 1x DH bikes ran it. The supply of mid cage RR derailers is actually pretty good. Long cage is not hard to find either. They were available in many Shimano groupsets. XTR ,XT,LX, Saint, C505, Nexave, Tourney. Suopply of derailers is enough for the limited demand. They're not RARE parts.The shifter suppyl is very limited. SRAM is most common but not ideal.

[Retrorockit]

I tried another mod that I found very useful. and might make my Rapid Rise stuff unnecessary. Gripshifts are still valid though.I lashed my hub to the cassette with 3x zip ties to lock out the freewheel. This makes the freewheel in the BBSHD the clutch between the wheels and the motor.
This is a normal Motor-Clutch-Transmission layout. You drive it that way too. Stop pedaling to cut power and release the clutch, make your shift, and resume pedaling. This produces smooth quiet and rapid shifts. No shift sensor needed.
Here's the thread on this. It wanders around some but this is very easy to do and worth trying.
 https://electricbike.com/forum/forum...ge2#post155283

[Retrorockit]

I've ordered a Sunrace M900 derailer. It's Shimano compatible for chain cassette and shifters. It's a clutch type derrailleur with an 11-50t range. 9 speed design, usually works for 8 speed too. I'll find out soon enough. It's not Rapid Rise so I can use my SRAM Rocket and Attack grip shifters, Sunrace wide 8 speed cassettes, and a standard derailer hanger. <$40 makes it about the same as vintage $himano MTB stuff.

With the zip tie mod I'm not using the Rapid Rise feature very much anymore. I also need to ride a little differently with the zip tie.

https://electricbike.com/forum/forum/main-forum/diy-discussion/156222-mid-drive-cassettte-zip-tie-mod

IMO the zip tie mod requires gripshifts to use what it has to offer. Multiple up and downshifs w/o pedaling.

Microshift makes an Acolyte wide 8 speed clutch derailer also. But needs a proprietary shifter, and no Gripshift option (which is strange because they make them for all Shimano stuff except Rapid Rise)
It got better reviews than the Sunrace M900 in a Youtube MTB comparison.

Box Components also makes one, but it's a whole groupset. Chain, shifter, cassette are all unique to them. Again no gripshift option. It's affordable stuff though. They're big on single gear shift for E bikes. Looosers.

[BadBac]

I remember the Shimano rapid rise driveline. It never made sense to me as the advantage of shifting multiple gears to a LOWER gear was much more advantageous than the opposite. When approaching a hill at speed, the ability to slam down to a much lower gear quickly so I could be in an appropriate gear for climbing worked so much better for me. I understand your mileage may vary though.

[Retrorockit]

I'm pursuing a different mod now that uses the front freewheel in a mid drive and locks out the rear one. needs a top chain guide to keep it together. Shift up or down any time the bike is moving w/o pedaling. You might like that one better.

https://electricbike.com/forum/forum/main-forum/diy-discussion/125827-brake-cable-mods

[Retrorockit]

If anyone wants to play with 1x8 Rapid Rise with a proper Shimano twist shifter There is only one place in the world I can find them any more.

https://www.ebay.com/itm/183788744370?hash=item2acaa9aeb2:g:uu8AAOxylpNTR9se&amdata=enc%3AAQAHAAAAoOOYrLnI1y%2B9dP7TviOkEGpnsHtQNeeXfDQkSxiIe66s8LN%2BtYkCkKpg3PuJbau5qCikepTs27v%2BWX9tnCiN1gukjpuzAQp6orKXywBJbQA0XHemxx2TDhAWfz%2BlG%2BFfLLJUhqyX5CcX80KAji2zT80y0D1%2FsEGoMXeJ0A2gGKWLM7yvnfAv88EwrNdXkDeMY93fgUN4fPwiyXAGgWVJsL8%3D%7Ctkp%3ABk9SR-zn6eKxYQ

Shipping from UK is about 3x the price of the part. I ordered 3 for the same shipping to have some spares, and get the unit price within reason. This and the zip tie mod gives just about the same shifting experience as an IGH.
7 speed is fairly common, 8 speed very rare, and I don't think 9 speed exists.

[Retrorockit]

I just preselect the shift with Rapid Rise, then lift the bike up by the rack with my right hand to do this when I have to. No brake, just let the ground stop the tire. You don't want to be screwing around on the center stand in SoFla traffic. I save the center stand stunts for in the driveway. With good chain management and the zip tie mod I'm already in the right gear most of the time anyway.With Rapid Rise ( and no zip tie mod) i could dump 5 gears ahead of time at 30mph, pedal it into gear just before I stop, and be ready to go.I only needed to do this if I didn't dump the right amount of gears. Usually at night when I can't see the shift indicator.

[Retrorockit]

I post a lot of mods in this forum that are not common knowledge. They're street rat stuff. Some people try it and then say it doesn't do anything for them. Like setting up your bike so it can shift w/o pedaling, and then refuse to stop pedaling. Or offroad guys who think power shifting one gear downshift at a time up a hill some how has something to do with dumping 5 gears in traffic with the rear wheel locked up. So here is my advise on this stufff. If you NEED this you will already know it. Don't buy up all the rare Rapid Rise parts and then whine that it does nothing for MTB riding. Bike racing "experts" too. They do one standing start each day (down a ramp!). I do one every 1/2 mile on my 22 mile lunch ride.

[AZguy]

Wouldn't be surprised the 36t works fine, so close to the 34t

I went well over the max my derailleur (XT M8000) is rated for (46t) putting 51t in and it was accommodated but now room for more! With the jockey gear further from the cassette the upshifts are slower in the higher gears...

[Retrorockit]

I got a ride in and the 50x12 is really nice. I could just stick a 12t on the Sunrace 11-40 and work with that. But I would still need a new hanger welded up. I'll see how often I make the shift to 50x11t.But with a stock hanger and stock derailer 11x36 is working just fine on my 2004 bike.But definitely not a stock cassette. I didn't take anything out of the chain for the smaller cassettte. With the dreaded zip tie mod in there a little extra slack may be useful.

[Retrorockit]

When a lot of these old 3x8 bikes were built 11-32t was the wide cassette option. 34t and 36t were considered Mega Range.
I've been suggesting that old 3x8 MTBs are ripe for conversion. I thought I should give some specific examples of how to do that.
With extended derailer hangers, and Sunarce M900 derailers and cassettes wide range gearing is possible. But not always what's actually needed.

[Retrorockit]

Gearing for old 26" bikes with a BBSHD kit. These bikes are pretty much obsolete for trail riding. So I'm talking street here. Tire size is a part of gearing, and these bikes were pretty much 26x2.25 tire size limited. At 30 psi perfect for street use on a HT. Suspension seatpost, and Tannus liner in the rear are worth having.
Sheldon Browns Gear Calculator has what you need. Solve for speed@90rpm is useful. Top speed may be at 100 or more.

https://www.sheldonbrown.com/gear-calc.html

These 3x8 MTBs will all come with either a 44t or 42t chainring. Don't listen to the Big Wheels, Fatbike kids who think that is enough,
44x11t is 4:1 and you will be spending a lot of time there wearing out that small weak cog. 48x12 is the same ratio. It's actually a pretty good gear, but not good enough.
FWIW back in the day I could wind out 4:1 on a 26" bike with leg power.
Lets look at 48t first. It comes in Wide/Narrow, and inset spacing. But with a short 26" MTB it may not sit in that much. This is the easy way. A simple top chain roller will help.
48/11t= 4.36:1,48/12=4:1,48/13=3.7 That's a nice set of gears if you don't need to go much over 30mph (which burns a LOT of battery). With an 11-13-15 cassette you'll still be in 11t a lot.
Now for 50t. flat ring with adapter Wide/Narrow can be found but doesn't help much with a bad chain line. Almost no inset possible. This is the hard way.
50/11t=4.55:1,50/12t=4.16:1,, 50/13t=3.85:1 The 11t is a rarely used but useful run for your life overdrive 32-35mph gear. 50/12 is nicer than 4:1, and 50/13 is good too. Even with 11-13-15 the 50/13 is better. But the 50/11 not as useful. A recumbent 15t idler for a chain guide can keep this together in the lower gears.
I'll make another post on cassettes for this. But you can do all 3 chain rings at once, and any cassette you like at Sheldon Brown and see what looks good to you.
Of course if it's not flat where you ride everything changes.

[Retrorockit]

The simple answer for a cassette is the Sunrace 11-40t 8 speed cassette. In 7speed you will probably be limited to 11-34t, and 9 speed you can have some options. I'm doing 8 speed because I run a Low normal (Rapid Rise) derailer, and matching grip shifter which doesn't exist in 9 speed. Also 8 is enough. The Sunrace has some nice features like wider spacing in the mid gears, a nice low gear, and it's cheap enough to be swapped out with each worn chain. This can extend the life of your expensive chain ring. 11-13-15- top gears are not ideal but work OK. It will require either a modern 8 speed derailer, or an extended derailer hanger to use it. There is no advantage to an Ebike having close gear ratios except at the very top end. By this I mean speeds above 28mph. Many places you may not want to go there any way. But the full power of a BBSHD can go there. Even without those speeds the acceleration of the BBSHD is very useful.
Now for the physics (it's not theory). Torque produces acceleration. Power produces speed. The math is Torque xRPM/5252=Power. So if RPM=0 so does power. An Ebike can produce torque at
0 RPM, so can you. Multiply the torque with gears and the bike can accelerate from 0 speed. But as speed increases so does the need for power, and so does the need for RPM. But the motor produces peak power a at certain RPM. The faster you go the more power is needed and the closer you need to stay to that RPM to get the power. The complication is that the motor produces power at a higher speed than you do. In practice this means 2 things. The percentage in change between gears should be smalller the faster you go to stay closer to the peak power of the motor. Especially at the highest speeds. The other thing is that some of these gears will be there so you can pedal along with the motor at various speeds. You need closer gearing than the motor does. But too close and you waste time making unneeded shifts when accelerating. At Sheldon Brown just about every cassette made is in the drop down box. The percentages are given also.
Punch in the above cassette with 46,48, and 50t chain rings. Speed @90rpm. Now manually remove the 40t cog and add a 12t in the 2nd position. Or just swap the 11t for 12t
You can open a 2nd SB window so you don't lose the first chart. Then you can drop the last 34t cog down to 36t. See what's happened with the percentages. There is one gear below 10mph in all cases. For a street bike that's my definition of enough gear range. With a BBSHD throttle in that gear going up hill will flip the bike over backwards.
I break my gearing into 3 sections. Top gears are 11-14t. The faster you go the closer they should be. The steps are either 1 tooth, or 2 tooth. Nothing in between.
The low range. How slow do you need to go? 28t and under . My bike will lift the front wheel in all gears from 28t down. So i'm not leaving much on the table here. 28t will run a little further before I need to shift. 34/ 36t is quicker if I'm going to sprint and stop. 40t is a crawler.
The mid gears need to be comfortable cadence at all speeds. You will be spending a lot of time here. But wide enough that there are no extra shifts during acceleration. The Sunrace 28-22-18 -15tt Progression is better than others for this. If you chart the more common 28-24-21-18-15 progression you will see small weird % changes. Plus it wastes a gear that could be useful some where else. I'll get into cassette mods next.

[Retrorockit]

I suppose I should put something in a about riding while pedaling vs riding on the throttle with these cogs.
Pedaling is pretty straight forward. Accelerating, the gear slpits will have you cycling between about 80 to 100 rpm each gear from takeoff on up. If you went for 1t splits t the top end you will be able to stick pretty close to 90rpm there. With 50x11t even less if you want.
For throttle only the motor can go to 140 rpm. At lower speeds under about 22-24mph you can upshift 2 gears and let the torque take over. Over a bout 24 mph you can actually just leave it each gear to full rpm. You need the rpm to make the power for higher speed. At 140rpm you won't need the top couple of gears. But you will need them to add power by pedaling. At lower assist levels for cruising you will use them a lot.
Switching from throttling at 140rpm to pedaling will require a 2 gear upshift to drop the RPM back down into human range. This is one reason why I run grip shifters, and disagree with BOX Components about 1 gear at a time for E bikes. This is even with the wide gear splits the Sunrace cassette provides. Other cassettes may take 3 gears to do this

[Retrorockit]

Stacking a custom cassette for these is not too hard. 7,8,9 speed cassettes are all the same thickness overall. The 9 speed chain is a little thinner, but the rear cogs are all the same thickness. The difference is the thickness of the spacers between them, or on them if they have them built in like the top gears. So for the top cogs you need to get them from cassettes that match your shifter, but you can pull large cogs from any of them that don't have riveted spiders. Some XTR hubs have alloy freehub splines and need alloy spiders in the cassette. There is no reason to burn up these rare and expensive parts on an Ebike. You can interchange cogs and cassettes between Shimano and SRAM. The 11t top gear needs a smaller lock ring than the 12t. The chain won't sit down all the way if you get that wrong. I've used 12t top gears in the 2nd position, the 11t sat down inside the serrated section, but this might not always be the case.
Cable pull on SRAM, and Shimano shfter/derailer sets is different. X series SRAM stuff is SRAM, but Attack, and Rocket shifters from SRAM are Shimano versions. Microshift makes some gripshifters also. I always take trigger shifters off and install gripshifters. I posted some stuff on Rapid Rise earlier, so I won't go into that again here.
Short stacking is possible for a bad chainline by just moving extra cogs to the back of the cassette to maintain the thickness. But there are chain management solutions that allow the all gears to work. But this can get a new build going while waiting for parts. A longer Lo limit screw is needed to limit derailer travel. But you coulld put together an 11-28 6 speed cassette that would work just fine if you had to. Block off the 2 lowest gears on the Sunrace 11-40t cassette and you're there.
Before I had good chain management I used the 2 lowest gears w/o power, and rode street in the top 6 gears. it definitely works.

[Retrorockit]

FWIW Luna is thinking about getting out of the DIY market and going for prebuilt bikes. So if this interests you now might be the time to do it.

[Retrorockit]

This is working well for me. I'm using all 3 of the close 11,12,13t high range cogs. The 36t low is getting more use than the 40t ever did. Somehow one of the cassettes I used for parts had big plastic spiders between the lower cogs. I used them, and with full power in my cross chained low gears the extra support might actually be doing something for me. The simple version of this would be to just drop the 40t from the Sunrace 11-40t and add the 12t at the top . This would give a 34t low gear. This has a much better mid range progression than other 11-34t cassettes. But I wouldn't have the plastic spiders.The spiders did cover up some holes I'd been using for the zip tie mod. but I just had to go around the whole arm of the inner cog instead of through it.

[Retrorockit]

I put a photo up of my recumbent chain idler/guide in the Zip Tie Mod thread.

https://electricbike.com/forum/forum/main-forum/diy-discussion/156222-mid-drive-cassettte-zip-tie-mod

This is letting me run a flat 50t ring in all 8 gears.

[Retrorockit]

I left out something important about these older MTBs. The good brakes back then were Avid BB7 cable disc brakes. Any bike that had these would probably have a good wheelset and good fork too.
They're stiil good brakes. With bigger rotors 200mmf/180r, or the older 203mm/185mm sizes, and metallic pads they're up to fast Ebike service. These would indicate a bike where they were not cutting corners on quality. Don't assume just any hydraulic brake will be better. Many are not. Good rims would have brass eyelets around the spoke nipples. Another corner that often got cut.