Cassette Noob Queston

[SpartyOn11]

I came across the Box Prime E-Bike cassette groups. They are 12-50 with a range of 12-14-16-18-22-28-34-42-50. They add one tooth to gears 1-3 over other cassettes. What is the point of this? What does adding a tooth do for the gearing? Is there a benefit?

 

[m@Robertson]

Commonly, an 11T rear cog is considered to be too small for a mid drive ebike because it bogs the motor. Mid drives like to spin fast so tiny rear cogs make the motor work harder than it should.

Generally speaking, the smaller the rear cog, the faster your top speed (and physically, the harder it is to pedal). As cog size increases, it becomes easier to pedal and your top speed is slower, but this is what makes it easier to pedal up a hill.

The Box rear clusters are IIRC manufactured by Sunrace, which are of very good quality in my experience. I use them on my 11s mid drive builds. The lower-than-usual (50T max) rear cluster is partly a response to the fact that an ebike is a '1X' drivetrain, meaning there is only one chainring in the front as opposed to the usual two or three. In a 1X system, all of your gear advantages have to come from the back end.

Also you'll notice there are only 9 gears. 9-speed clusters are commonly considered to be a good sweet spot for a mid drive because a) you don't need as many gears with a mid drive as mids stay happy in a wider range and shifts need not be so frequent and b) the chains/parts are in a good place for strength and low cost of replacement. I personally prefer 11-speed setups but I pay thru the freaking nose for the parts. My older 9-speed setups are downright cheap insofar as parts replacements are concerned.

I've always wanted to build with the Box components but when I have been in the market they have always been out of stock. The people that have them all seem to like them.

 

[AHicks]

Commonly, an 11T rear cog is considered to be too small for a mid drive ebike because it bogs the motor. Mid drives like to spin fast so tiny rear cogs make the motor work harder than it should.

Only for the sake of conversation - coming at the right answer for a different reason. We agree there's big power to be dealt with when power demands are high, especially when considering some of the big Bafang drives. The reason an 11t is to be avoided, to my way of thinking, is due to the load being placed on just a few teeth the chain is coming into contact with while on an 11t gear. That's placing a LOT more stress on the chain and the gear as compared to a gear with twice as many teeth with that same load spread out over twice as many teeth/chain links. 11t gears generally don't last as long as larger gears for that reason.

Another "opinion". As far as working harder than it should, your watt meter will answer the "how hard is it working" question much easier than what gear you are in/how many rpm the motor is turning. If the motor is working hard, it's pulling a LOT of amps/watts. If it's not working hard, it isn't pulling much in the way of watts/amps.

These are electric motors. As long as they aren't stalled or nearly stalled, you aren't hurting them. They do NOT need to be treated like a gas motor with only a narrow power band useful for making power, a fact made clear by Grin's power chart (IMHO). -Al

 

[m@Robertson]

^^^ Yes I skipped this other half of the issue for the sake of not making a long post longer. If you're going to snap a chain or crack a cog, it'll often be while lugging up from a standstill on a small cog for the reasons @AHicks mentions. 11T cogs are notorious for superfast wear on powerful mid drives.

I have a bike that, on its 42x12T gear, gets up to a top speed of 33 mph. It takes about 3/4 of a city block to inch its way up to that number. If I upshift to the next, 13T cog, it peaks at 32-33 mph but runs up to that speed in half the distance. If I go up to a 14T cog, my peak speed is about 30-31 mph and I get there more quickly still than the 13T... your bike is a lot more responsive and you sacrifice very little top speed by using a larger cog.

How To Ride a Mid Drive Ebike Without Breaking It

If you can ride a bicycle you already know how to ride a hub drive ebike. Not so a mid drive. Particularly a powerful one that can tear your chain apart. Fear not. The rules are simple.

talesontwowheels.com

 

[SpartyOn11]

So moral of the story is if you break a cog or want to change a cassette, 12T (smallest cog) is better than 11T for longevity on a mid-drive ebike. What you gain in durability outweighs what minimal speed loss you may have. Next question is if it really makes a difference for the biggest cog to be 50+ or in the 40 range? I would imagine if you are climbing monster hills, 50+T would be better.

 

[ruffruff]

There may be an upper limit to the number of your teeth. You can go too big for your derailleur cage to handle.

 

[SpartyOn11]

@ruffruff Thanks, I should have been more specific than just 50+. Box makes two options for ebike cassettes; 12-50T and 12-46T. I imagine the difference between the two are not much difference but not sure why you choose one or the other.

Box Three P9 X-Wide Single Shift E-Bike Groupset

Our Box Three tier delivers many of the same capabilities of its more famous siblings yet it's built upon a simpler platform. The cassette is E-bike Optimized at 12-50T, adding an extra tooth to each of the three highest gears. The derailleur exploits our Limited Slip clutch technology without...

boxcomponents.com

Box Three P9 Wide Single Shift E-Bike Groupset

Our Box Three tier delivers many of the same capabilities of its more famous siblings yet it's built upon a simpler platform. The cassette is E-bike Optimized at 12-46T, adding an extra tooth to each of the three highest gears. The derailleur exploits our Limited Slip clutch technology without...

boxcomponents.com

 

[AHicks]

2 things. First, regarding the 1st gear cog, the big one. Most production bikes use 34-36 teeth, and have PLENTY of poop for climbing hills. Getting up into the 46-50 area is getting pretty extreme for most of us.

Second, regarding the use of a 12-13t for your top gear. Sure, using the same front sprocket, they'll be slower than the 11t. If that's a challenge, that can be easily dealt with by changing the front sprocket to off set the loss of speed. Just go with one that's 1 tooth bigger. Point being, your final ratio is a combination of the front and the rear sprockets. You would tune using one or both as necessary.

 

[SpartyOn11]

@AHicks great answer as always. Much appreciated

 

[ruffruff]

Any worries about clown pedaling with 50t?

 

[TrailSeeker]

This might get me laughed at if I'm wrong on this... is the reason the cassette is harder to spin on the highest gear because each cog below the gear you have, also has to spin?

So gear 1 the big cog spins alone, gear 2 the big cog and the second big cog spin, etc until the highest gear they all are spinning?

 

[TrailSeeker]

If that's a challenge, that can be easily dealt with by changing the front sprocket to off set the loss of speed.

By changing, you mean replacing it with a 12 tooth chainring, right? Sorry, I have newb super powers lol

Edit: also where does narrow-wide chain types come into play? Are there chainring requirements for the number of teeth that are compatible? Sorry for all the questions.

 

[AHicks]

This might get me laughed at if I'm wrong on this... is the reason the cassette is harder to spin on the highest gear because each cog below the gear you have, also has to spin?

So gear 1 the big cog spins alone, gear 2 the big cog and the second big cog spin, etc until the highest gear they all are spinning?

Nope. The gears are all riveted together. You can't turn one without turning all of them.

Might be easier to think of them as pulleys. The smaller the pulley used on the back, the faster your load (the wheel in this case) turns. The big pulley offers more leverage, but doesn't drive the wheel as fast.

By changing, you mean replacing it with a 12 tooth chainring, right? Sorry, I have newb super powers lol

Yes, you have the power to confuse me with this question.

 

[TrailSeeker]

Nope. The gears are all riveted together. You can't turn one without turning all of them.

Might be easier to think of them as pulleys. The smaller the pulley used on the back, the faster your load (the wheel in this case) turns. The big pulley offers more leverage, but doesn't drive the wheel as fast.

Yes, you have the power to confuse me with this question.

Thank you @AHicks for answering that

I just meant how can you adjust a chainring? You would need to buy a different type and replace it right? I was wondering if you meant like angling it or adjusting your current one or replacing it with another type?

 

[AHicks]

If I'm following correctly, you would replace the chain ring with one you select that has the number of teeth you're considering. Generally, they aren't expensive or difficult to swap.

 

[TrailSeeker]

Thanks @AHicks! Yep, that's where I was going with it. Thank you for supporting a newb!

 

[m@Robertson]

So moral of the story is if you break a cog or want to change a cassette, 12T (smallest cog) is better than 11T for longevity on a mid-drive ebike. What you gain in durability outweighs what minimal speed loss you may have. Next question is if it really makes a difference for the biggest cog to be 50+ or in the 40 range? I would imagine if you are climbing monster hills, 50+T would be better.

Yes you have it exactly right above.

As to which is better, I would pretty much always recommend you go as wide as possible. But not quite for the reasons you may think. First, let me step back just a bit and give a speck of background.
I am going to be camping up @ Wishon Reservoir in the Lower Sierras in a couple of weeks, Lots of solid granite hillsides that you can ride a fat bike over without any sort of trail. I also want to run down from the top of Blackrock Road. This guy wrote about it but he went from the bottom up and I think he chickened out before he got to the top. I am riding from the top down where its deep granite gravel and dirt, with pines and even a few redwoods. I'll go down at most to the wooden bridges he has pics of here

The Sierran Death Highway, Blackrock Road

Back in 2016 I was pursuing dangerousroads.org looking for a interesting paved road akin to Kaiser Pass Road and Mineral King Road both whic...

www.gribblenation.org

Here is the bike. Since this pic was taken, for this trip I have switched the front chainring to a small 32T ring from the 48T you see. My biggest in the back is 46T, with the next one down 42T.

So I sure wish I had a 50T in the back. I wouldn't use it though. Here's the thing: Chain deflection is an issue on any mid drive. Skew the chain hard in one direction or another and the chain wear against the ring increases. Maybe by a lot depending on how bad it is. Also you can start skipping teeth if its off center by enough. Lastly, my bike has 90mm wide rims and 4.8" tires, which are wider than stock. That makes running on the inner 46T problematic. It rubs. But I knew that going in. Factory stock, this bike had a 42T big inner gear. I bought the 46T knowing I could only get to the next one down... 42T. So I am losing one out of 11 speeds (big whoop) and nothing insofar as my lowest gear is concerned. I have done this before and frankly I like having that big inner cog - as a chain protector. Thats right... a covert 'dork disc' to ensure that if I bounce hard one too many times or my derailleur goes out of whak the chain is not falling in between the cluster and the hub.

Moral of this long story is to think about where your *usable* gearing will be. I'd dig a 50T inner cog because it means the one next to it is something like a 46T, and thats the one I'll be using. Speaking of which, chain deflection is a problem both ways. The cluster you see above is 11-46T and yes thats right I try and never use the 11. It works and I can if I want to, but still I try and avoid it. So an 11-speed system gives me 9 usable gears. If it was a 9-spd, I'd be down to 7.

 

[AHicks]

OK, let's see if I can make this more difficult.
If the chain is rubbing on the tire in low gear, have you looked at changing the "dish" by adjusting the rear wheel spokes in an attempt to provide the necessary chain clearance? Is there room on the other side to move the tire over?

JUST learned how to build my own wheels, so the potential for something like this is fresh in my mind.....

 

[m@Robertson]

OK, let's see if I can make this more difficult.
If the chain is rubbing on the tire in low gear, have you looked at changing the "dish" by adjusting the rear wheel spokes in an attempt to provide the necessary chain clearance? Is there room on the other side to move the tire over?

JUST learned how to build my own wheels, so the potential for something like this is fresh in my mind.....

I don't want to dish the wheel. Yes it can be done, but on the deep dish (triangular profile) Nexties I am using the spokes originate dead center in the rim so its not quite as suitable to a lot of dishing. Also I am pretty sure I'd still have a problem. And when I upgrade to Snowshoe 2XLs (because I can) you'd need to re-address the dishing issue... As it stands I can go 2XLs and still lose just the one gear with the 90mm rims.

If I had wanted to try dishing it, I would have gone with 100mm Clown Shoes which are made to be strung offset on just one side if you want, or you go and use both sides' holes and dishing is a snap. but they have other negative issues. First of all the 100mm rims create an even worse problem that typically locks out the two topmost gears. Also tire mounting is much more difficult, but the big issue is dismounting in the field is *colossally* more difficult. that road I linked, at its upper end, is 'paved' with granite crushed over time by metal equipment treads so when its dropped fresh every year or so, its big and jagged. I will be traveling with my side bags and two spare tires... walking out of there would suck. A lot. I drove it a few months ago and I was afraid for my *suv* tires.

These Nextie rims are super strong (rated at 250kg which is the most by far of any fat rim), 90mm which kills only one gear and they are for-reals tubeless compatible. Surly Clown Shoes and the original My Other Brother Darryl rims are supposedly tubeless compatible but the stupid things are pinned not welded and you can guess how my trying to take the MYOBD rims tubeless went.

The wheels are mounted tubeless, in fact. Lots of FlatOut inside makes for an awesome tubeless sealant.

 

[AHicks]

More conventional rims, those used on production fatty bikes, are usually "just" 80mm or so, which is generally TWICE as wide as you might find in use on a production mountain bike. At least that's what I'm finding. Point being, 90 and 100mm rims are getting pretty extreme - and likely requiring an extreme setup just to get them functional.

I'm guessing the purpose of using something that wide is to spread out the tire tread for better grip?