Help with gearing issues on E-Bike conversion

Hello All,

I've got a 48V, 500W Tongsheng TSDZ2 on the way and am preparing for the conversion. One issue that's come to mind is the gearing. I am using this bike for primary transportation and love the gearing now, though it has a lot of overlap in the gears - generally a good thing, but it has 10 speeds in total and the overlap of the two chainrings is considerable. ... The issue has to do with the fact that the TSDZ2 comes with a 42T attached to the crankset and I'll lose my 52T that's attached to my old crankset and I have to do something about it.

The bike is a Raleigh with 27" tires. Original gearing is: T52 main chainring and a 40 added, with the following cassette EDIT: OK, it's NOT a cassette, it's a freewheel! THANKS GANG, for informing me! ... To wit:

1: 28
2: 24
3: 20
4: 17
5: 14

I understand from reading up that the smallest here, at 14 teeth, is actually pretty good in the sense that 11 is a bare minimum (I have read), and more teeth help with regard to converting to electric because there's less stress per tooth - not that my 500W system is all that powerful. However, there is some room to go smaller if desired.

We know from experience (you can read on the main TSDZ2 thread here on this site) that the TSDZ2, without over-volting, gives a typical upper-end cadence of 90 Pedal-RPM, give or take a little. Some complain that they like a faster pedal-RPM but the TSDZ2 drops out assisting above around 90, so they have to get a lower voltage unit and over-volt it because the highest voltage unit they sell, 48v, has a built-in cut-off preventing over-volting by much - a 52V (nominal) pack is known to not work when fully charged!

I personally am not concerned about going over 90 PRPM. However, I used this data to calculate my speeds at 90 PRPM and came up with this table (if you think this table may be flawed, DO PLEASE point it out to me! I've never calculated bicycle speeds before, so maybe I factored in the gearing incorrectly - but it looks reasonable to me). To wit:

Speed Table, in MPH, Target Pedal RPM: 90 (the dots are to keep table alignment)
gear:..1....2.....3....4.....5
52T: 13.4 15.7 18.8 22.1 26.9
40T: 10.3 12.0 14.5 17.0 20.7
42T: 10.8 12.7 15.2 17.9 21.7

I see two things of import in that data:

1) The 40T and 42T are so close that I can consider the 42T an effective replacement for it. And;
2) Clearly, my top speed with assist will be limited to 21.7 unless I do something about it.

It appears from the images on the official web site that the 42T that comes with the TSDZ2 can have a second chainring mounted to it. Perhaps my solution is just to get a 52T that can be added to the 42T. Or, if it's easily done and not too expensive, a slightly taller gear might be a good choice - we can do 28 MPH legally on the streets here, so a little taller might be a good thing.

Optionally, I could change out the cassette...

I've never done either! A few questions:

1) Am I headed on the right track with the chainring idea, going to a 52T or taller?

2) Are cassettes a mix-and-match affair? That is, I can get ONE gear and swap it around maybe?

... And please point out anything else a newbie like me might need to know!

TIA,
RTIII

... As my bike came with a 52T, clearly I won't have chain length issues with another 52 - or derailer issues, either!

But I just did some web searches about what's available plugged in various alternatives into my spreadsheet I rather like what a 58 tooth ring gear would do - WITH ASSIST! (Not sure I could pull it with just my legs!) ... In particular, it would not only give a better top end, but it would spread all the other gears a bit and give a LOT more choices (instead of virtually identical redundancy with a huge overlap). In particular, with a 58, I'd still have plenty of choices for where my legs likely CAN pull the speed up to where it was before, just in a lower cassette gear. SO... I'm seriously thinking about going to a 58T!

I'm sharp enough to know this could cause other issues, such as with chain length, that the curve of the front derailer might be an issue, etc. MAYBE a different cassette would be in order instead? A 52T in front and a different rear would solve any derailer / length issues...

Again, your thoughts appreciated.

If you have only five gears in the rear, it is not a cassette, but a freewheel. Today's multi-speed freewheels all mount on the same 1.37"-24 threads. If you have enough space for 7 speeds, use a 7-speed freewheel. If you don't have enough room for 7 speeds, you may be able to respace the axle, re-dish the wheel, and possibly spread the bike's frame to accommodate a wider cluster.

You can get a 13-28 7-speed freewheel from Shimano and an 11-28 7-speed freewheel from DNP (though the latter has made a reputation for poor durability).

You must be working with a really old bike, a really cheap bike, or perhaps both. What is it?

Chalo said:

If you have only five gears in the rear, it is not a cassette, but a freewheel. Today's multi-speed freewheels all mount on the same 1.37"-24 threads. If you have enough space for 7 speeds, use a 7-speed freewheel. If you don't have enough room for 7 speeds, you may be able to respace the axle, re-dish the wheel, and possibly spread the bike's frame to accommodate a wider cluster.

You can get a 13-28 7-speed freewheel from Shimano and an 11-28 7-speed freewheel from DNP (though the latter has made a reputation for poor durability).

You must be working with a really old bike, a really cheap bike, or perhaps both. What is it?

Click to expand...

Thanks Chalo,

...Really old: 1982. It's a Raleigh. ... All my "good" (more expensive) bikes have been stolen.

I kind of like this bike: durable as hell, not too heavy, pretty darned fast for what it is. It's got a custom-made luggage rack on the back which is darned cool.

The 13 / 28 doesn't help me too much but the 11-28 would be AWESOME when combined with a 52T in front...
So, a 52T in front - keeps the geometry basically what it was, and a 11-28 stack in back would gain more flexibility AND a much higher top speed. ... Looks like that's probably the best bet. I'll go look the bike over shortly and confirm there's room - but I think there is.

So, I understand that you just buy a whole set of gears all at once, no making a custom stack?

Now, how do I find out the bolt pattern / size for the TSDZ2?! I've been looking all over the internet for HOURS now with no luck... I've emailed the vendor - they must have Sunday off - the SLACKERS! :lol:

I'm getting a little lost in all your information, then someone wants more. All to care about is that you want to go 28mph. 1 mph for a 27" wheel is just over 12 rpm. One revolution being slightly over 7 feet, 12 revolutions topping 84 feet, etc. multiply by your 28 and you're thinking of what we'll round off to 340rpm for that wheel.

What will the rpm of the motor be? Will the sprocket be exactly the rpm of the motor or is there a reduction? If 28 teeth on the wheel are turning at 340rpm, if up front the rpm is 8 times that, then you have 8 times as many teeth up front, right? Oh, wait, that's a HUGE front sprocket, eh? If you have a 52 to turn a 28, the 52 would have to turn under 680rpm for the bike to go under 30mph. If you're using the 14 tooth in the back, you make the same calculation.

Chalo favors using quality equipment, which is great if you can afford it. Always nice to avoid the sort of 25mph faceplant that broken bikes can create. I'm always hearing people say they don't want to spend the money. So my first guess is you bought a WalMart bike at a garage sale, right? (Confirmed when my painfully slow connection today showed what else had been added.) Doesn't matter, you can make old junk work for this. If you're clumsy not even the expensive stuff will hold up.

Believe me, I know about stolen bikes. But they take the cheap junk, too. Someone I know they passed on his Dad's expensive roadbike and took his beat up old cheap mountain bike. For whatever their reasons.

RTIII said:

So, I understand that you just buy a whole set of gears all at once, no making a custom stack?

Click to expand...

Sure, you can take freewheels apart and swap stuff out, if you have enough of the right ones with the right parts. They don't all have the same size body or splines/spacing/etc., so they won't all fit each other.

In this post
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1227692
toward the end I discuss taking them apart to get specific sprockets off of them; there's other more recent posts by me (and others) around the forum about making custom setups but I don't have a direct link. (you might have to just do a search on "freewheel" or "sprocket" and look thru the resulting post list, which will be large and have a lot of non-relevant results).

Probably more on Sheldon Brown's site if you google around.

RTIII said:

So, I understand that you just buy a whole set of gears all at once, no making a custom stack?

Click to expand...

The days of sprocket boards and custom freewheel stacks are past us now. The best you can do in that regard is get a couple of freewheels with different gearing but the same body, and choose whichever sprockets you like best.

Your options get a whole lot more interesting if you switch to a cassette rear wheel. But if you do that, you'll definitely need to widen your frame spacing.

Dauntless said:

I'm getting a little lost in all your information, then someone wants more. All to care about is that you want to go 28mph. 1 mph for a 27" wheel is just over 12 rpm. One revolution being slightly over 7 feet, 12 revolutions topping 84 feet, etc. multiply by your 28 and you're thinking of what we'll round off to 340rpm for that wheel.

What will the rpm of the motor be? Will the sprocket be exactly the rpm of the motor or is there a reduction? If 28 teeth on the wheel are turning at 340rpm, if up front the rpm is 8 times that, then you have 8 times as many teeth up front, right? Oh, wait, that's a HUGE front sprocket, eh? If you have a 52 to turn a 28, the 52 would have to turn under 680rpm for the bike to go under 30mph. If you're using the 14 tooth in the back, you make the same calculation.

Chalo favors using quality equipment, which is great if you can afford it. Always nice to avoid the sort of 25mph faceplant that broken bikes can create. I'm always hearing people say they don't want to spend the money. So my first guess is you bought a WalMart bike at a garage sale, right? (Confirmed when my painfully slow connection today showed what else had been added.) Doesn't matter, you can make old junk work for this. If you're clumsy not even the expensive stuff will hold up.

Believe me, I know about stolen bikes. But they take the cheap junk, too. Someone I know they passed on his Dad's expensive roadbike and took his beat up old cheap mountain bike. For whatever their reasons.

Click to expand...

Hi Dauntless,

I wrote you a great reply and then, just before hitting post, my browser crashed!

I STRONGLY support quality over price every time, but I've had a bit of bad luck financially and am forced to a little more austerity than I want. :-( ...But I won't walk into a Walmart unless they're the only choice for an unreasonable distance of miles, and even then I won't buy much - minimum possible. They're a job-killer, encourage production of junk and are to be despised, ridiculed and avoided at all costs! Not sure why you'd associate ME with them! I'm an ethical guy!

I'm also a reasonable engineer... As for MPH, I have no idea what the TSDZ2 motor's RPM may be, but it doesn't matter because plenty of owners have reported here that there's a limit to the pedal-RPM at which it stops assisting - and that speed is about 90 Pedal-RPM. So, I just used this formula:

Max Assist MPH = (90 * (front tooth count / rear tooth count) * 27 * Pi * 60) / length of mile in inches

The first 90 is the pedal-RPM, the 27 is the tire diameter in inches, the 60 converts minutes to hours, and the final division converts to miles. I was thinking maybe I'd had an error in the way I handled gears, but the resulting values look good.

Thanks for pointing out the risk of high-speed crash - certainly don't want any of that! NO FACE-PLANTING HERE!

Thanks, amberwolf and Chalo,

I'll take the rear gear stack answer as, "sure, you can re-gear a freewheel if you want, but not if you're sane!"

I'm kind of annoyed with the Shimano 11-28 being taken off the market as the reports of the DNP-Epoch product are not great. Still, the gearing they offer is unique at this point in time. There are several versions available now, 11-28, 11-30, and 11-32. None have great reviews if you take the time to read enough. They're just not well made.

So, I am looking at these options, NOT in sorted order:

1) Screw the quality, install the new 11-32 DNP freewheel and be done with it - STILL NEED A NEW FRONT GEAR, but it can be 52T as original to the bike. The bike will handle exactly as before but with new power from the TSDZ2, and a terrific top speed. Or;

2) Due to quality issues with the 11/anything freewheels from DNP (and nobody else offering them right now) split the gear change between front and rear by going with a Shimano 13-28 because of the quality, and then push the front gear up a bit because I have to get a new front gear anyway. This should cost about the same as option 1, but even with a 58T up front it still won't equal the 52T with 11T rear. Or;

3) Do the low-cost option by leaving the rear alone and make all the change in the front with a 58T - BUT, it might well NOT be the low-cost option if it causes derailer issues or if I have to buy a new chain. It won't help the pedal-only situation as compared with the original - more torque needed in upper speeds. Or;

4) Run a 52T front ring and try and fit a modern cassette on the rear somehow with an 11 top gear. This would be the best bet, but also the greatest cost. I've made a preliminary search and it doesn't look readily possible (read: easy) to replace this old 27" wheel with one that will take a cassette - unless building a wheel ones own darned self with a modern axle in the 27" (X 1.25") size is easier than I had thought...

Hmmm...

And I still don't know what the mounting size is for the chainring on the TSDZ2!

Regarding durability of various stuff; probably none of these will be an issue for you with low power/torque, but a heads up just in case:

--the smaller the front rings are, the smaller the rear rings you have to run on for the same speed, and the higher the torque level presented to the rear would be.

--Smaller rings/sprockets also means higher wear rates.

--the smaller (faster) rear sprockets are on the outer part of the freewheel (or cassette), which puts them farther from the support bearings. Not a huge deal but it means more bending loads on the axle and the hub and freewheel. The higher the torque load the worse the bending problem is. You can add sealed bearing units that fit over the axle and just inside the outer end of the freewheel, so that the loads aren't bending.

amberwolf said:

--the smaller (faster) rear sprockets are on the outer part of the freewheel (or cassette), which puts them farther from the support bearings. Not a huge deal but it means more bending loads on the axle and the hub and freewheel.

Click to expand...

This is a problem for hub motors, that have their freewheel threads attached to thin, low quality cast aluminum side covers. But it's not a problem for regular bicycle hubs. They were designed to be pedaled.

There have been posts about broken freewheels (probably bearing problems?, don't think anyone ever opened theirs up to find out) when running higher-torque middrives thru the outer sprockets (I think when using those at startup from stop and/or hill climbing rather than downshifting, but I can't remember anymore). I tried to find the posts but can't ATM. Have to figure out a better search term set.

Bent axles, too, but I don't think that's going to be an issue for this particular member (unlike on my old CrazyBike2's powerchair drivetrain, which destroyed a wheel with the pulling torque when I had a derailment/chain tangle problem at the front end of the transfer chain).


But yeah, there's plenty of reports of hubmotors getting their covers cracked or broken under just regular pedal power, much less a middrive with higher torque.

amberwolf said:

--the smaller the front rings are, the smaller the rear rings you have to run on for the same speed, and the higher the torque level presented to the rear would be.

--Smaller rings/sprockets also means higher wear rates.

--the smaller (faster) rear sprockets are on the outer part of the freewheel (or cassette), which puts them farther from the support bearings. Not a huge deal but it means more bending loads on the axle and the hub and freewheel. The higher the torque load the worse the bending problem is. You can add sealed bearing units that fit over the axle and just inside the outer end of the freewheel, so that the loads aren't bending.

Click to expand...

Good points of course. ...As a land-speed-record holder for some years, of course, I'm well aware of how the gearing works, but it's good to repeat for those new to gearing issues. You'll note I already put my formula on a previous post.

As mentioned earlier, to help me work out what I want, I created this spreadsheet and have - prompted by your comments here amberwolf - decided I'll make it available to whoever. I've put the spreadsheet on a web server I have access to - you can find it here:

http://ScienceTools.com/misc/BicycleWheelGearChart.xls

It's in Microsoft Excel format.

I wrote it for my own needs, of course. It's in imperial units! (Miles and inches!) That's simply because our speed limits here in California are in MPH. However, out of habit, most of the features in the formulas are data elements you can edit easily, such as the target Pedal RPM, and that makes it handy to alter both for me and now for you! It would be easy for anyone interested to convert it to metric, add gears, and so forth. I added multiple "sheets" for different gear choices so I could easily compare. I also took the time to spell out many front gear choices as I don't yet know what I want and, again, making it easy to compare was the whole point!

Freewheels are not the best thing for crank-drives because the top gear hangs a long way out from the bearings. Much better would be to chuck the whole back wheel and get a used cassette (free-hub) one from E-bay. You can often get them with the cassette for about $30 -$50, or try your local bicycle recycling centre. You can also get shifters and derailleurs for not very much from Ebay if your present one is not compatible. The cost of all these things is relatively insignificant compared with the cost of the electric kit.

d8veh said:

Freewheels are not the best thing for crank-drives because the top gear hangs a long way out from the bearings. Much better would be to chuck the whole back wheel and get a used cassette (free-hub) one from E-bay. You can often get them with the cassette for about $30 -$50, or try your local bicycle recycling centre. You can also get shifters and derailleurs for not very much from Ebay if your present one is not compatible. The cost of all these things is relatively insignificant compared with the cost of the electric kit.

Click to expand...

OK... I agree about derailleurs and ebay, overall cost differential and so on. But that's NOT the question; It's a 27" X 1.25" wheel setup; are there wheels in this size with cassettes available or not? I've been looking, and so far NO LUCK AT ALL. Am I looking for a purple unicorn or what? (I've asked this question here in this thread, on other forums, etc, and nobody has yet replied with any clarity / certainty.) Your reply strongly suggests that I am NOT looking for a purple unicorn, but a lovely brown-eyed brunette - not on every corner, but out there to be found...

BTW, my vendor says in an email this morning I'm delayed quite some days more because they're out of stock on the 500W motor... :-(

You just need a hub. You can swap your rim to it, so you can buy any size whhel and cut the rim off or just buy the hub. Make sure you get the right number of spoke holes in the hub for the rim.

RTIII said:

It's a 27" X 1.25" wheel setup; are there wheels in this size with cassettes available or not? I've been looking, and so far NO LUCK AT ALL. Am I looking for a purple unicorn or what?

Click to expand...

27 inch wheels went out of production for new bikes at around the same time cassettes became the industry standard. So there never were any OEM bikes that came with 27" cassette rear wheels. 27" is still supported, kinda, but it's supported with cheap old fashioned parts for old bikes.

If you can slide your brake pads down 4mm, you can fit a 700c wheel in the same bike with no other modifications. (You might need to spread​ the rear spacing for a wider hub, and reset the derailleur limits.).

I do 700c conversions of 27" bikes all the time. I also fit 27" bikes with new 27" wheels pretty frequently. What I don't do is build up new 27" wheels on cassette hubs, because a custom build like that is sightly more expensive than even a new stock 700c wheel plus a new longer reach brake. And then you don't get the benefit of the hugely improved tire selection in 700c.

If your bike has a steel rear rim, just forget it and convert at least the rear wheel to 700c. Steel rims are weaker than aluminum, and heavier, and they don't brake nearly as well-- especially when wet. If it has an aluminum rim in good condition, you can choose to try it as is, or lace it over to a cassette hub (which is a lot of exacting work), or replace it with 700c anyway because that's easiest. But you probably will not find a 27 inch replacement wheel with a cassette hub anywhere.

Chalo said:

RTIII said:

It's a 27" X 1.25" wheel setup; are there wheels in this size with cassettes available or not? I've been looking, and so far NO LUCK AT ALL. Am I looking for a purple unicorn or what?

Click to expand...

27 inch wheels went out of production for new bikes at around the same time cassettes became the industry standard. So there never were any OEM bikes that came with 27" cassette rear wheels. 27" is still supported, kinda, but it's supported with cheap old fashioned parts for old bikes.

If you can slide your brake pads down 4mm, you can fit a 700c wheel in the same bike with no other modifications. (You might need to spread​ the rear spacing for a wider hub, and reset the derailleur limits.).

I do 700c conversions of 27" bikes all the time. I also fit 27" bikes with new 27" wheels pretty frequently. What I don't do is build up new 27" wheels on cassette hubs, because a custom build like that is sightly more expensive than even a new stock 700c wheel plus a new longer reach brake. And then you don't get the benefit of the hugely improved tire selection in 700c.

If your bike has a steel rear rim, just forget it and convert at least the rear wheel to 700c. Steel rims are weaker than aluminum, and heavier, and they don't brake nearly as well-- especially when wet. If it has an aluminum rim in good condition, you can choose to try it as is, or lace it over to a cassette hub (which is a lot of exacting work), or replace it with 700c anyway because that's easiest. But you probably will not find a 27 inch replacement wheel with a cassette hub anywhere.

Click to expand...

THANK YOU, CHALO! This is exactly the kind of thing I needed to know!

In the last week, I have done a lot about this particular challenge...

...I've been updating the main TSDZ2 thread here about it, but last night I got a private message asking about gearing and realized the answers to the questions raised by my original post here should be here, so someone else, later, can find the material all in one place! ... And without having to sift through 800+ comments to find it!

To wit:

Rear, Wheel / Gearing

I got a new Shimano 36H rear axle that takes a 7 gear cassette - narrowest width at 130mm. I got a new Sta-Tru wheel in 27" X 1.25 with 36 spokes, and de-laced it. I then went to relace it and it didn't go well; I had expected the new spokes from the new wheel would work, but they appeared to be too long. In some long discussions with amberwolf, I learned some of the more nuianced details of lacing a rim. (Thanks amberwolf!) Circumstance has prevented me from completing the work, but I'll put the results here. It should go OK now, just have to have the right spokes. I have some on order that should do the trick, but as I'm still a newbie, there's more uncertainty at the moment whether the spokes I ordered are really the right ones. ...The discussion with amberwolf on this topic is on this thread (near the present end):

https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1299147#p1299147

I also secured a Shimano 11 - 28 (7 gear) cassette (new, of course). The tallest two are identical to the stock freewheel, and the next three are one tooth taller than the stock freewheel, and the two new gears are very tall at 13 and 11 teeth.

Chainrings

In the front, I first tried just adding a steel chainring between the TSDZ2's stock 42T and the spider where it mounts. This only moved the chainring inboard by 2.9mm, but, unfortunately, that was too much. I then, bravely, tried cutting down the steel thickness where it mounts down to 2mm, since the stock Tongsheng 42T is only 2mm thick, but this failed, too. And, not finding a good solution already made, I designed my own adapter.

My first adapter I designed (and the only one I've actually fabricated so far) with the idea that perhaps it could be done to mount THREE chainrings, and if so, how would you do it?

To answer that, I first looked at any technique to move the stock 42T inboard to help straighten the chainline. But, first, I realized that as a practical matter, the answer is no because the point of interference of the gear to the motor is NOT out at the teeth, but where the gear's dish inward is done, and even if you tried to make a whole new gear, there's just no diameter left after stepping over the motor's obstructions before the teeth. That is, you could possibly make a gear with MORE than 42 teeth that would work and could move over a little. But then you have the second problem that even then you could at most move it over about 1mm, NOT curing the chainline problem, or risk running the chain against the motor housing, especially on the lowest gearing in the rear when the chain is angled inboard considerably.

Therefore, I concluded that one has to leave the stock 42T alone. And therefore I made an adapter that mounts to the original spider and is 3mm thick at the mounts, flat on the spider (inboard) side, and "countersunk" on the outboard side.
To this, another set of 5 X 110 BCD bores are made, 36 degrees offset from the first set. These, I back cut by 3mm because I calculated that, assuming steel gears of 3mm thickness, mounting a chainring exactly in line with the offset mounting of the stock 42T would give a 7mm gap for shifting, and still leave another 7mm gap for another chainring mounted directly against the adapter, using a 5mm or so spacer between them. Doing this would require either a 14mm mounting bolt set, or 16mm if you want to run a protective cover mounted via the chainrings, as a great many bikes have, including the TSDZ2.

Here are images of my new adapter:

Being made, the outside face:



Completed, the inside face:



Mounted to the spider:





Of course, since the stock 42T is mounted in the stock position on the spider, there's no question it will fit and work. The only remaining question then is whether one gets the spacing right for a further one or two gears, such that the chain can't come off, and shifts smoothly between chainrings. Since this is certainly possible, the hard part is now over!

At the moment I'm still waiting on ready-made 16mm length chainring mounting bolts to arrive so I can complete the assembly, though I only plan on running two despite the fact I made my adapter to potentially do three!

And, from that, I got a private message from someone who I won't "out" (since they wanted to be private), who wrote me:

What a great adapter you have made for 110 bcd !!! I want to put 34t 44t on it! Please, please give me a sketch or a drawing, that I could do it! Thank you very much!

Click to expand...

For this application, since there is no existing 34T that is deeply offset (of which I am aware), no adapter is necessary! You can use the stock spider with a "dual chainring" mounting. This may end up with a chainline that's just too far outboard, even with the longest available chainring bolts (16mm, I think) and longest spacers you can get away with. So, instead, you could make a simpler adapter using the same basic idea and mount it to the INSIDE face of the spider then have a second set of mounting holes and mount even further inboard from there. Your challenge will be getting your new chainring as deeply toward the motor as possible without rubbing. You probably can't match the factory's work in this regard, but you can probably come close. You'll have to work out the spacing inward yourself. However, the basic ring is simple enough - sorry, can't do an engineering diagram, but you should be able to follow this:

The ID should be just big enough to fit on the spider, and the outside diameter doesn't really matter unless you're putting a chainring on the OUTBOARD side of the adapter, which none of my designs would do. The standard chainring hardware is nominally 9.8 to 9.9mm OD, so that's your bore. I like a tight fit and used a W sized drill bit, then clearanced by hand with a file. The countersinking bore doesn't matter either, but I think I used 1/2" because it was convenient. The only thing that DOES matter is that you don't let the STEEL mounting locations be thinner than 2mm (and the main part 3mm and more, but I'd consider even 2mm too thin - I used 3mm because I don't like fatigue cracks / failures. (Keep in mind the chainline is steeply offset, so the torque is pulling outward all the way around!) If you do it in aluminum, don't go thinner than 4mm for the main body of the part and maybe don't even countersink, but if you do, keep it, again, to a minimum of 3mm.

DO NOTE: I didn't put it down already because I figure everyone who would attempt something like this has basic geometry / math skills. But it occurs to me to point out a circle is 360 degrees, and if you have two 5-bolt circles, you've got 10 holes and if you want them evenly spaced (NOT a requirement!), then 360 / 10, or 36 degrees between holes...

Thank you very much!

Yeah, that is a beautiful piece of work. It will be great to see how the 2 chainring set-up works.

Is it just me, but that stock chain ring looks different than a typical bicycle chain ring. The teeth seem a lot taller than typical bike components.

This is part of the new SRAM ebike mid-drive specific drive train they recently released.
This bad boy is a 11-42 tooth 8 spd steel cassette. They have a derailleur and a chain to handle it.
Only it's $390, so I'm out.
The idea is to give you a large gear range without all the small steps a regular bike rider needs.


Maybe someday.....https://www.sram.com/sram/mountain/family/ex1#sm.000lzjug7gdgf9l10mn1vma70wya0

Norton said:

Yeah, that is a beautiful piece of work. It will be great to see how the 2 chainring set-up works.

Is it just me, but that stock chain ring looks different than a typical bicycle chain ring. The teeth seem a lot taller than typical bike components.

This is part of the new SRAM ebike mid-drive specific drive train they recently released.
This bad boy is a 11-42 tooth 8 spd steel cassette. They have a derailleur and a chain to handle it.
Only it's $390, so I'm out.
The idea is to give you a large gear range without all the small steps a regular bike rider needs.


Maybe someday.....https://www.sram.com/sram/mountain/family/ex1#sm.000lzjug7gdgf9l10mn1vma70wya0

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Maybe they're forgetting that sometimes your battery is flat and you have to do all the work with pedal power! IMNSHO, they're being silly in omitting workable gears for the poor soul whose stuck in a pedals-only condition!

RTIII said:

..Maybe they're forgetting that sometimes your battery is flat and you have to do all the work with pedal power! IMNSHO, they're being silly in omitting workable gears for the poor soul whose stuck in a pedals-only condition!

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Mathematically this is still a big top to bottom range of gears. (I hate the work HUGE these days...)
It's just not as many fine ratio steps as a modern 3 x 10 drive train.

SunRace makes an 8-speed cassette in 11-40 that I've seen listed online for as little as $14. Even at twice that price it would be a swell bargain. It's called CSM 680. My shop carries the 9-speed version for $40 retail, but none of our distributors carry the 8-speed one.