Has anyone increased their front sprocket size? Any concerns or issues?

ck1224

Member
As I have 20" wheels, I have a Rattan e-bike with a Prowheel 52T #40 chain front sprocket on the bike, but I want to increase the size to 80T #40 chain if possible to increase efficiency at higher speeds. I think it is Type A sprocket with a 1 inch bore size. I am inquiring around for the parts to do this, and how much a bike shop would charge to do it. Most bike shops are not aware of how to do this as they deal with analog bikes, but I did find an electric bike shop here in Austin.

At 28 mph, my cadence in 7th gear is a whopping 110 (revs/min).

I wanted a foldable bike for my first ebike, so 20" wheels, but I think the next ebike will be much larger in size and power.

Well, when I am going 25 to 28 mph in 7th gear, I'm pedaling like crazy to try and increase the speed a little bit more and when I peddle like crazy it
isn't that hard to turn the crankshaft, but the pace of my pedaling wears me out fast. I figured that I need to really boost the sprocket size to
get were I want it to be. Even after about 21mph, I want the sprocket to be bigger.

Has anyone increased their front sprocket size on their e-bike?
 

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rich c

Well-Known Member
An 80 tooth is a monster increase. I don’t think Tour de France bikes use over a 53T and they sprint at nearly 50mph
 
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ck1224

Member
An 80 tooth is a monster increase. I don’t think Tour de France bikes use over a 53T and they sprint at nearly 50mph

I think a big issue is that I have 20" wheels (23" diameter wheel height), not 26" to 29" wheels like the racers have.

Well, when I am going 25 to 28 mph in 7th gear, I'm pedaling like crazy to try and increase the speed a little bit more and when I peddle like crazy it
isn't that hard to turn the crankshaft, but the pace of my pedaling wears me out fast. I figured that I need to really boost the sprocket size to
get were I want it to be. Even after about 21mph, I want the sprocket to be bigger.
 

rich c

Well-Known Member
I think a big issue is that I have 20" wheels (23" diameter wheel height), not 26" to 29" wheels like the racers have.

Well, when I am going 25 to 28 mph in 7th gear, I'm pedaling like crazy to try and increase the speed a little bit more and when I peddle like crazy it
isn't that hard to turn the crankshaft, but the pace of my pedaling wears me out fast. I figured that I need to really boost the sprocket size to
get were I want it to be. Even after about 21mph, I want the sprocket to be bigger.
Could it be that you bought the wrong eBike for high speed? Based on wheel size, crank length, and a 7 speed freewheel, it might have been obvious it would not be a high speed bike. No idea why a LBS would not be able to change the chainring and cranks. It's just the right bolt circle for the chainring, width for a 7 speed chain, and correct length of chain. Simple bicycle stuff, but an 80t has to be tough to find.
 

EVH5150

Member
you might want to increase the length of your crankarms. You gonna need the extra leverage/torque to turn that monster 80T chainring (front sprocket;))
 
I think a big issue is that I have 20" wheels (23" diameter wheel height), not 26" to 29" wheels like the racers have.

Well, when I am going 25 to 28 mph in 7th gear, I'm pedaling like crazy to try and increase the speed a little bit more and when I peddle like crazy it
isn't that hard to turn the crankshaft, but the pace of my pedaling wears me out fast. I figured that I need to really boost the sprocket size to
get were I want it to be. Even after about 21mph, I want the sprocket to be bigger.
Not sure which model you have but I'm guessing that all the 20" wheel models have the same 14-28 rear cassette, which would be a much easier modification to reduce your cadence at 28mph. A rough calculation from me suggests that you should hit 28mph at just below a cadence of 90 with 52T on the front and 12 on the rear, whereas you are looking at almost 100 cadence for 52x14. A lot cheaper than having an 80T chainring cast (which would actually need less than a lazy 70 cadence to hit 28mph with 14T on the rear).
 

ck1224

Member
Not sure which model you have but I'm guessing that all the 20" wheel models have the same 14-28 rear cassette, which would be a much easier modification to reduce your cadence at 28mph. A rough calculation from me suggests that you should hit 28mph at just below a cadence of 90 with 52T on the front and 12 on the rear, whereas you are looking at almost 100 cadence for 52x14. A lot cheaper than having an 80T chainring cast (which would actually need less than a lazy 70 cadence to hit 28mph with 14T on the rear).

yes, I believe it is 14 on the rear. The tire is 23" in diameter at 18psi. I think an 80T #40 sprocket is about $70 bucks, and would I need to buy existing
#40 links on the existing chain or just buy a longer chain? I think I still like the idea of an 80T front sprocket, but as you mentioned I could get a smaller
rear cassette (11 or 12). 80/11 or 80/12 ratio.
 

ck1224

Member
you might want to increase the length of your crankarms. You gonna need the extra leverage/torque to turn that monster 80T chainring (front sprocket;))

That is food for thought also. The crank arm is 6 1/2" long (which would be the same length as the radius of an 80T #40 sprocket.
So, rear cassette, front sprocket and crank arm length adjustments sound like possibilities?
 

FlatSix911

Well-Known Member
yes, I believe it is 14 on the rear. The tire is 23" in diameter at 18psi. I think an 80T #40 sprocket is about $70 bucks, and would I need to buy existing
#40 links on the existing chain or just buy a longer chain? I think I still like the idea of an 80T front sprocket, but as you mentioned I could get a smaller
rear cassette (11 or 12). 80/11 or 80/12 ratio.

I would recommend trying a new 11-28 or 11-32 rear cassette before changing the front ring or cranks.

You will also appreciate the increased gear range with the larger cassette and will not need a new chain. ;)
 

ck1224

Member
Could it be that you bought the wrong eBike for high speed? Based on wheel size, crank length, and a 7 speed freewheel, it might have been obvious it would not be a high speed bike. No idea why a LBS would not be able to change the chainring and cranks. It's just the right bolt circle for the chainring, width for a 7 speed chain, and correct length of chain. Simple bicycle stuff, but an 80t has to be tough to find.

Well, due to space issues in my sedan car and garage, I wanted a folding e-bike with a 750W motor and Rattan was the cheapest model I could find at 1,200. Of course, it is a learning curve as this is my first ebike and learning about what I want in a future ebike or modified current bike as I am wanting to peddle with more efficiency at higher speeds, etc.

A 26" fat tire is about 29" diameter instead of a 23" diameter would be helpful with more powerful motor/battery. My next ebike in the future. Alibaba and Aliexpress have some decent higher speed e-bikes at affordable prices $2,000 to 2,500.
 

Timpo

Well-Known Member
Could it be that you bought the wrong eBike for high speed? Based on wheel size, crank length, and a 7 speed freewheel, it might have been obvious it would not be a high speed bike. No idea why a LBS would not be able to change the chainring and cranks. It's just the right bolt circle for the chainring, width for a 7 speed chain, and correct length of chain. Simple bicycle stuff, but an 80t has to be tough to find.

No it's not.. took me 5 seconds to find on AliExpress 😁
 

Timpo

Well-Known Member
ck1224,

we call it "chain ring", not sprocket like motorcycles.

also we call swingarms "chain stays", just a little motorcycle to bicycle terminology difference. :)
 

Timpo

Well-Known Member
As I have 20" wheels, I have a Rattan e-bike with a Prowheel 52T #40 chain front sprocket on the bike, but I want to increase the size to 80T #40 chain if possible to increase efficiency at higher speeds. I think it is Type A sprocket with a 1 inch bore size. I am inquiring around for the parts to do this, and how much a bike shop would charge to do it. Most bike shops are not aware of how to do this as they deal with analog bikes, but I did find an electric bike shop here in Austin.

I wanted a foldable bike for my first ebike, so 20" wheels, but I think the next ebike will be much larger in size and power.

Well, when I am going 25 to 28 mph in 7th gear, I'm pedaling like crazy to try and increase the speed a little bit more and when I peddle like crazy it
isn't that hard to turn the crankshaft, but the pace of my pedaling wears me out fast. I figured that I need to really boost the sprocket size to
get were I want it to be. Even after about 21mph, I want the sprocket to be bigger.

Has anyone increased their front sprocket size on their e-bike?
One issue I can think of is ground clearance, if you get a significantly larger chain ring, you will hit speed bumps and all that stuff.
 

Timpo

Well-Known Member
and you might hit chainstays (swingarm) or anywhere on the frame if chain ring is too large.
 

Sierratim

Well-Known Member
The OP might want to take a look at Sheldon Brown's GEAR CALCULATOR. You can input your wheel size, crank arm length, chainring tooth count, preferred cadence, etc to see how changes in the chainring and free wheel gearing impact your speed.

For example with 20x1.25 tires, a cadence of 90rpm, a 52t chainring, and a 14t small cog on the free wheel your speed would be 18.3mph. Going with an 11t cog gets you to 23.3mph.
 

Manu

Active Member
your foot touches the ground and the plate, is very easy, and to move that 80 plate you have to stand up on the bike.
 
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ck1224

Member
One issue I can think of is ground clearance, if you get a significantly larger chain ring, you will hit speed bumps and all that stuff.

yeah, right now I have 10" clearance, with the new chain ring it would be about 7 1/2 to 8" inches. I think that is ok?
 

ck1224

Member
your foot touches the ground and the plate, is very easy, and to move that 80 plate you have to stand up on the bike.

I'm using the motor to move me mostly anyway, and I can always gear down to 80/28 at slower speeds as well and then back up to 80/14 at higher speeds
you might want to increase the length of your crankarms. You gonna need the extra leverage/torque to turn that monster 80T chainring (front sprocket;))

I'm not sure how much more they could be increased without my toes hitting the ground. I think the pedal turned downward has 5" of clearance right now on the bike with 6.5" crankarm length.