Modifying Drive Train on Topstone Neo Carbon 3 to reduce cadence at top speed

Alaskan

Well-Known Member
The one thing about the OEM drive train on this speed version of this bike that I felt compelled to change was to slow
down the cadence in the mid 20mph range in the smallest, 11 tooth cog.

Shy of scrapping the GRX setup and putting a Sram Eagle 12 like the Neo 1 or a 2x1 like on the Neo 2. The easiest path
was to put a larger chain ring on the bike.

So I found a 46 tooth to replace the stock 44 tooth that came with the bike. I then replaced the 11-42 cassette with a
Sunrace 11-46 which works surprisingly well with the stock derailleur despite the fact that Shimano specs it out to a
max of 42 teeth. Another factor that helped was replacing the stock 42mm tire with a WTB Byway 650b x 47.

The bottom line is that in the final 11 tooth cog I am spinning at 70 rpm while traveling at 25 mph whereas OEM I was
spinning at 80 and can sustain this speed for miles on flat ground with the assist set at tour.

Mission accomplished. I took an outstanding bike and made it even better, IMO.

I completed the installation of the 11-46 tooth cassette and new longer chain. I installed the Sunrace CSMX8 in the black
color It is a bit less money in straight silver but looks way cooler and does not look dirty so quickly. I have been using this
cassette for over two years on another bike that has a Shimano XT group set and found that it is at least as durable and
offers crisper, more accurate shifting.
FSA G3/4 Bosch EBike Bicycle Cycle Alloy 104 BCD 1X11 Chainring Black
ebay.us

FSA G3/4 Bosch E-Bike Bicycle Cycle Alloy 104 BCD 1X11 Chainring Black | eBay

BCD 104mm. With chainring bolt / nut. Motor Type:- Bosch.
ebay.us
Holy Mackerel!!! The 46 tooth chainring arrived from England yesterday. It was waiting on our porch when we got home
from our covid shots. Tis was ordered on Sunday and it arrived in Bellingham Washington on Thursday. I swapped it out
with the stock 44 tooth before dinner. Test ride probably won't happen for a few more days. The chainring delivered to
the door was $69.83. Kudos to the .ebay seller, Velozone Cycles...
20210311_163351.jpg


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SunRace | CSMX8

www.sunrace.com
www.sunrace.com
I used Shimano 11speed chain (CNHG70111) 116L w/QuickLink Chain NIB https://ebay.us/I0vczb

It did take lowering the derailleur a bit to accommodate the 46 tooth cog, using the stroke adjustment bolt found on page
17 of the dealer installation pdf manual - copy attached below. I have not road tested it but it shift up and down well on
the stand. I hope to get out and test it in real life tomorrow.

Here are two photos, one in the smallest cog and one in the largest. This took the gear range from 382% to 420%.

20210315_144854.jpg
20210315_144934.jpg

I used this bike gear speed calculator https://www.bikecalc.com/speed_at_cadence

I came up with the following results you can enter your own data and change speeds from mph to kmph.
This is the result with OEM drive train as per spec

Neo 3 OEM drive train gear speeds 44 FTR  11-42 cassette.jpg


This is the result with my mods.
Everything is entered accurately except tire width which were in preset increments.
Mine are 47mm but 50mm was the closest value I could select.


modified drive train on Neo 3   44 tooth ftr   11-46 cassette.jpg
 

Deacon Blues

Well-Known Member
My new 46T chain ring arrived yesterday. 🥳 😁🥳
I'll have to do some research to find out if I'll need a longer chain and if the motor will need to be reprogrammed.
You went from a 44 to a 46, but I'll be going from a 42 to a 46, so I may need a couple of links added on. If I do I'll probably just go with a new chain, since my old chain has 3500km on it.
 

Alaskan

Well-Known Member
My new 46T chain ring arrived yesterday. 🥳 😁🥳
I'll have to do some research to find out if I'll need a longer chain and if the motor will need to be reprogrammed.
You went from a 44 to a 46, but I'll be going from a 42 to a 46, so I may need a couple of links added on. If I do I'll probably just go with a new chain, since my old chain has 3500km on it.
New chainring + new chain...you might consider a new cassette at this stage as well so everything matches up per spec. If the smaller cogs on your cassette are getting at all worn and dished out, a likely thing with , they will accelerate the wear on the new chain which eventually will transfer to that new aluminum chainring.

Personally I would chance getting an error message and just go for it. You can always have them reprogram for the bigger chainring if it becomes necessary and there is a good chance that it won't be needed. I did a 15 to 18 tooth with the gen 2 CX motor on my derestricted Delite, added the same 11-46 XT cassette that I put on the Neo 3 to recover lost climbing oomph and have ridden almost 6,000 miles since without issues.