Gearing up the front crank for higher speeds pedaling

[kojack]

WIll it mess with the electronics for the ebike part of my bike if I install a larger chainring on it?

 

[m@Robertson]

Depends on the motor ecosystem. If you did the conversion yourself, no absolutely not. However, for all mid drives, they like to spin fast. Electrical energy that does not convert to motion (motor rpms) instead converts to heat. One of the classic mistakes to make on a mid drive motor is to bog it down with a big chainring. So, as is the case with many things... moderation is the key.

Unless you have a hub drive, in which case it doesn't matter one bit.

 

[kojack]

I do have a hub drive. It's a voltbike Kodiak. It's under geared a little bit. I can pedal with pedal assist and get around 35-37kph. If I could top 40 - 42kph while pedaling it would be perfect for my town.

 

[harryS]

Increase the front crank gear and/or decrease the smallest derailleur gear, If you have a Shimano freewheel, their smallest gear is usually 14T. You can swap in a DNP freewheel with 11T as the smallest gear.

 

[Jeremy McCreary]

WIll it mess with the electronics for the ebike part of my bike if I install a larger chainring on it?

You also have to worry about chainstay clearance when upsizing a chainring, and drivetrain efficiency and wear rate when downsizing your smallest rear cog.

You're looking at a 14% increase in ground speed from 35 to 40 kph. That means a chainring with 14% more teeth and therefore 14% larger diameter. Or a 13% smaller rear cog.

As @m@Robertson noted, with a hub-drive, you have to keep up wheel speed — and therefore ground speed — to keep up motor efficiency. The more efficiency you lose, the less mechanical power out per watt of electrical power in.

So the more you let a hub-drive bog down on a hill, the less assist you'll actually get, the more the motor will heat itself instead, and the harder you'll have to pedal to keep from losing even more ground speed.

A larger chainring might help you mitigate that by hitting the bottom of the hill at the highest possible speed. But by reducing all your gear ratios at once, it might also compromise your ability to finish the climb with available leg power.

If your routes involve steep enough hills, that might push the trade-offs toward a cog-based solution.

I recommend getting your bike shop involved.

 

[kojack]

I am my bike shop. ha ha. I am just new to E-bikes. I have bicycle mechanic certifications for "regular" bikes. Just never did the E-Bike stuff as it was not a thing when I did my training.

 

[Jeremy McCreary]

I am my bike shop. ha ha. I am just new to E-bikes. I have bicycle mechanic certifications for "regular" bikes. Just never did the E-Bike stuff as it was not a thing when I did my training.

Ah, then you're loaded for bear on the mechanical side. Looking forward to hearing your final solution.

I think a lot of ebike owners miss out by blindly accepting stock gearing. To deal with my hilly terrain without killing my old knees, my 500W, 65 Nm hub-drive eventually ended up with one more gear, a smaller chainring and smallest cog, and a bigger largest cog.

On my lightweight low-power mid-drive — which cares about cadence, not wheel speed — I reduced the chainring to keep my preferred cadence in the motor's sweet spot (80-90 RPM) on steep hills.

Lost some top end in both cases. Wrong direction for you, of course, but these were good trade-offs for my legs, knees, and topography.