Change bike's front chainring to increase top speed?

Karm

Member
I have a Giant MY19 XTC E+ Pro with MY19 Syncdrive Pro motor. The bike is derestricted and It's equipped with 27.5' Maxxis Aspen tires and DT Swiss EX 1501 wheel sets. But the top speed is only at 43 km/h.
I can hardly go faster like the motor's 120 rpm is at its max. And a 240W 80 N.m motor should be enough to push over 43 km/h.
So I am thinking if it is possible to change gears from the original 36T chainring to a 38T or a 40T and increase the top speed. I have a TB-1069 Ebike lockring tool to get off the chainring.
Chainring Clearance.png

Anyone has done this before?
 

JRA

Well-Known Member
"Anyone has done this before?"

Not sure but it is the only way you are going to get the higher gearing needed
 

Karm

Member
"Anyone has done this before?"

Not sure but it is the only way you are going to get the higher gearing needed
I need to know if anyone has done this. I haven't heard or seen anyone actually did it. It must have a reason.
 

BrianK

Active Member
I have a “hunting“ fat e bike with a Bafang BBS02 motor with a Sturmy Archer 3 speed IGH.

It was geared low and slow for riding off road and hauling trailers with game out of the woods. It was geared so low I couldn’t pedal fast enough to keep up with the motor at road speeds.

So I changed the front chainring from 34t to 46t. That helped some, but not enough for the road and rail trail riding I do, so I subsequently went up to a 52t chainring. Both of the chainrings came directly from Bafang USA.

The process was not difficult. I needed to get the tool to remove the pedal and pedal arm, then removed a couple Allen bolts from the chainring, swapped out the larger tooth chainring, refastened the Allen bolts and then the the pedal arm and pedal.

The “hardest” part was resizing the bike chain. I had to add several links to the chain each time, so I needed a chain break tool and another chain to add some length to the original chain. It would have been easier to just buy a longer chain but that’s what I had to work with.

Everything is working fine now. While I’m no bike mechanic I do have common sense and some mechanical skill. Overall it was not a difficult project.
 

FlatSix911

Well-Known Member
I have a Giant MY19 XTC E+ Pro with MY19 Syncdrive Pro motor. The bike is derestricted and It's equipped with 27.5' Maxxis Aspen tires and DT Swiss EX 1501 wheel sets.
But the top speed is only at 43 km/h. I can hardly go faster like the motor's 120 rpm is at its max. And a 240W 80 N.m motor should be enough to push over 43 km/h.
So I am thinking if it is possible to change gears from the original 36T chainring to a 38T or a 40T and increase the top speed. I have a TB-1069 Ebike lockring tool to get off the chainring.
View attachment 68906
Anyone has done this before?
Karm, welcome to EBR. ;)

I have changed a few chainrings to a higher gear ratio and it's an easy swap.
If your guide drawing is to scale, it appears that you have 12mm of clearance.
Going from 36T to 40T will increase the chainring Radius by 8mm, allowing 4mm of frame clearance.

You don't need to remove the cranks and can adjust your chain guide to accommodate the larger 40T front chainring.
Make sure that you purchase a 104 BCD, Bolt Circle Diameter front chainring that is the Narrow-Wide type... specs below from EBR.
I have two bikes with the Yamaha PW motors and they have been bulletproof reliable. Good luck and let us know how the swap goes!

OEM Stock: 104 Bolt Circle Diameter, SRAM X-Sync Eagle 36 Tooth Aluminum Alloy Narrow-Wide Chainring


1602951524815.png
 
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Thomas Jaszewski

Well-Known Member
I have a “hunting“ fat e bike with a Bafang BBS02 motor with a Sturmy Archer 3 speed IGH.

So I changed the front chainring from 34t to 46t. That helped some, but not enough for the road and rail trail riding I do, so I subsequently went up to a 52t chainring. Both of the chainrings came directly from Bafang USA.
52T with a BBS02B needs careful use of gearing. Lugging a BBS02, especially with a 52T chainring is an easy way to fry a BBS02.
BTW and FWIW Bafang USA is not "direct from Bafang" they are vendors just like Luna, Empoweredcycles, and others.
 

Karm

Member
Since you have switched to high gears, may I ask how much the increased top speed is after going from 36T to 40T?
My bike's gears are from Shimano XT m6000 series except the front chainring. I don't know where the chainring comes from, it's a no-brand OEM but seems very durable. Also, the chain is KMC e10s for ebike.
 

BrianK

Active Member
Since you have switched to high gears, may I ask how much the increased top speed is after going from 36T to 40T?
The magnetic pick up for my Bafang mid drive is on a rear spoke, so chainring changes do not change the top speed with the motor, which is governed by that rear wheel sensor. I have mine set at 25mph max, and chainring size had no effect on maximum electric assist speed on the bike.

However, it did make it possible for me to keep up with the pedal cadence at those road speeds. The motor spun the pedals faster than I could pedal with the smallest chainring otherwise. (I’ve had five strokes and have residual weakness in my left leg so my own pedal cadence pace is sub par, but definitely improving quickly riding the e bike.)
 

Karm

Member
Has anybody with Giant E+/Yamaha motor changed the chainring? I just got warning from Giant shop owner that changing the chainring will void the 2-year warranty for the Yamaha motor.
 

Gionnirocket

Well-Known Member
I bumped my 46th to 48th on my BBS02B /7SP 11t -28t MTB and though there was some increase in speed I did not like the extra effort it took me to pedal and I noticed a bit more drain on the battery so I switched back. As long as you monitor your current draw and your settings aren't too aggressive I think you'll be ok.
Having a bike that you don't enjoy riding just to maintain warranty seems pointless. Then again I'm scandalous and would probably just put the smaller ring back on to bring it in for service 🙃
 
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FlatSix911

Well-Known Member
Bump. Has anybody with Giant E+/Yamaha motor changed to a larger chainring? Can the motor handle it?
Yes, with no problems at all... my Yamaha PW-X is over two years old at this point and has been bulletproof. ;)
 
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