SunRace CSMX3 42T 10-Speed Cassette : My, What Big Teeth You Have Granny… *munch*

One of the biggest problems with running a mid-drive motor is that you end up having to throw away your front derailleur and gearset. This means you have to settle for whatever gear range you end up getting from your cassette. Most cassettes go from an 11T to 32T (for a 21 tooth ‘range’) which is sorely inadequate for any electric fat bike. If you have a 10-speed cassette then there are a host of 36T Cassettes on the market which will allow you to have a 25 tooth ‘range’. The market has been flooded with ginormous overprices X1 cassettes for 11 speeds with 42T but the Sunrace CSMX3 is the first 10-speed cassette I’ve found with a 42T granny giving you a whopping 31 tooth ‘range’. That is about a 47% increase over running a 32T granny cassette. Not bad granny, not bad at all.


Little Red Riding Hoodlum better run when she sees the size of this Granny’s teeth.

I bought my CSMX3 from Universal Cycles for $67 here with $4.99 pick-a-product shipping. Although that is a lot of dough to blow on a cassette, the only other option is the all-steel cog CS-MS3 for $58 located here which was 445g vs the 392g for the CSMX3. The CSMX3 has a 7075 aluminum granny (every other cog is steel) which I may regret buying in the not too distant future when it bends in half. I actually recommend the cheaper CS-MS3 which looks nearly identical but with black aluminum brackets and a steel 42T granny.



Wolftooth 42T cog, the original monster granny that brought derailers to their knees

For a long time, many people just opted for a 42T Wolftooth granny cog and would throw it on their 10-speed cassettes. This created a bunch of problems because not all 10-speed cassettes can just take a different granny gear, especially one that is such a massive jump in size from the next gear down. Then there is the cost, the Wolftooth 42T granny is not cheap at around $75 street price. This solution fits quite firmly in the sub-optimal category.


The anodized aluminum spacers were incredibly solid and should give you years of use abuse

Installation of this cassette was more of a pain than I anticipated. I knew I was going to have problems adjusting the derailleur and I was skeptical that the massive 42T granny was even going to fit. When I mounted the cassette the first problem I noticed was that my all steel cogs on my Phat Phuk build were actually eating into the cassette splines pretty bad. It was so bad that I had to tap the new cassette on with a rubber mallet because I couldn’t get it to go on. This should not be a problem with this cassette because the granny gears share a wide chunk of metal with a large contact area. I’m glad I caught this problem before it got much worse.

side by side.jpg

This shows the stock 36T cassette compared to the massive 42T monster. Filthy. Makes me want to incessantly wash my hands just looking at it.

If your bike ships with a 32T granny there is a very good chance that your derailleur will just not be able to accommodate a 42T granny unless you get a longer angle adjustment screw. When I fit the new cassette and tried to adjust for the 42T granny I screwed the angle adjustment screw down as far as it would go and it still was not really quite enough. The derailleur then sits MUCH farther away from the cassette for the higher gears, but if it is properly tensioned & aligned then it should not be a problem. I had to adjust my low limit screw so the chain would not commit Hari Kari and throw itself into the spokes (I’ve had enough, life is just too hard ….)

low gear.jpg

The first derailleur wheel becomes distant from your highest gear when adjusted properly

Once you have mounted the cassette it is important to go through all the gears one by one to make sure the chain is not getting hung up and is shifting correctly. If you are having problems with the wheel is spinning freely you can be assured that you are going to have massive problems when you are pumping 1500W through the drive train and try to shift.


Expect no clearance from 42T Godzilla Granny

On the trail, your derailer must be tuned perfectly or you are guaranteed to have chain problems. It seems like when you are using a normal X7 derailleur meant for a standard 11T-36T spread that putting a cassette like this on really tests its patience. Pay attention to what direction the chain is trying to skip to under load and then tighten or loosen the barrel nut adjuster at the trigger shifter accordingly. Do not ride your bike without the derailleur adjusted properly or something will break.

rings compared

Pick your poison, either one will bring you long life, prosperity, and lots of sex.

I found the 42T gear a perfect match on the super steep inclines with the 42T Lekkie Bling Ring. I’m quite certain that this cassette would also be a fine match with the Luna Eclipse 42T Chainring as well or the monstrous steel 46T crappy chainring that Bafang gives away free in their cracker jack boxes. I found the torque to be far superior to the stock 46T ring especially if you rode the BBSHD at higher RPM speeds that were way too fast to keep up with pedaling. The only downside was the insane wheelie popping torque, which I found myself having to shift into a higher gear in order to avoid. This cassette and a 42T chainring can take your singletrack riding to a whole other level.

Thanks to Dale for turning me onto this cassette, we both agree that the worst kind of cassette was the old Kenny Rogers 8-track that my old man used to torment me with when riding in his car.

You gotta know when to hold ’em, know when to fold ’em, know when to walk away and know when to run……. *AHHHHHHH* Make it stop.



Banned under the Geneva Conventions of 1949 as torture.

Kenny Rogers was one of the many reasons I moved out at 16 and lived in abandoned buildings and ate out of dumpsters for several years. (true story)

Ride On.

Update: Forget about the aluminum version of this cassette, only buy the steel version CS-MS3 do NOT buy the CSMX3 which will catastrophically fail under any real power. You have been warned.



I barely tapped the throttle of my BBSHD with a 65Amp Lyen controller and this granny ripped apart. Boo Who.


25 thoughts on “SunRace CSMX3 42T 10-Speed Cassette : My, What Big Teeth You Have Granny… *munch*

    • That one only goes to 40T and not 42T and it’s also $130 (ouch).

      Yes the 8 & 7 speed chains are much tougher and single speed BMX chain is the toughest of all. I have had broken 10speed chains but I bring a quick link and a chainbreaker and it only takes 5 minutes to fix.

      I would not go with an 11 speed system because they are stupid expensive and the chain is even MORE expensive.

      I think the best setup is an 8 speed with a megarange 36T steel granny. Cheap and tough, for a 42T on a BBSHD with a Snoeshoe 2XL (which has an insane tire diameter) a 36T granny is just not enough.


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    • The high end chain is the Wippermann E bike chain. 8SE for 8 speed Ebikes. The Connex link is stronger than KMC part. If you use a Park CC-2 chain stretch gauge that actually measures the amount of stretch you can stay ahead of chainring and casettte damge caused by a stretched chain. I would try a KMC and see how it does for you. The list price of the 8SE is eye watering, but it breaks in at .2mm stretch and holds that for quite a while. If I can find them on sale I buy them.


  5. really. you’re going to blame the cassette for not being able to survive on an electrically assisted, already heavy ass fatbike? the cassette, along with all others, are made for regular mountain bikes, unless it says it’s specifically made for e bikes.


  6. Great review, thanks. Wish I’d found it earlier, already bought my parts nowbut think they’ll be ok.

    I am currently building an ebike from the frame up and bought a gear system off the internet in China, it included a sunrace csms8 11 speed 11-42t cassette, shimano m8000 long cage derailleur and 11 speed shifter plus a kmc 11 speed chain, all for 130usd. I don’t think that is expensive. Should I be particularly wary of any of these components malfunctioning? I plan to power the bike with bbs02b 750w motor.

    The reason for my choosing the 11 speed is that I’ll be mostly riding flat (want good top speed) and want to stick with the bafang 48t chainring (or maybe 52 if it fits!) but there is a mountain that I ride once or twice a month that will need that 42t to keep the motor spinning fast whilst going up it.


    • I have never had a bike with an 11 speed chain. I have more problems with the 10 speed chains than the 9 speed and more problems with the 9 speeds than the 8 speed chains and more problems with the 8 than the single speed.

      Lube your chain after every ride and keep your derailler tuned right and don’t shift under load. You’ll be alright.


      • Thanks Karl, I’ll stay on top of the chain lubing, disengage the motor before shifting and pray to the chain gods that it doesn’t break! Will probably heed your advice and carry a quicklink to be safe.


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  8. Karl this write up has answered a long waited thought Ive had about what is the right gearing. I too have the BBHD (hot-rodded) & both the bbhd and eclipse chainring from Luna Cycle. A 10sp 12/30t cog.
    So my understanding is to go with a bigger granny gear right. Thx so much.


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