Gearing change on my Voltbike Kodiak.

[kojack]

I was thinking about changing the front chainring to give a little more top end speed, however after discussions here that would probably not work correctly, so what about dropping a tooth or two in the rear to compensate. I can hit 37km/h right now before my pedalling become ineffective and I run out of gear. If I could get a few more Km/h out of it to 40-42km/h It would be at our speed limit for our secondary roads which would make a huge difference in traffic for me personally. I think I have an 11t in the rear for the 7th gear. If I drop that to a 9 would it get me there or not? TIA!

 

[Stefan Mikes]

I think I have an 11t in the rear for the 7th gear. If I drop that to a 9 would it get me there or not? TIA!

Not doable. A standard cassette only allows 11 teeth in the smallest sprocket. Smaller sprockets require a special "driver" for the freehub body, and it is usually only available for expensive 12-speed cassettes. The rear hub must be either Shimano Microspline or SRAM xD compatible, which is certainly not the case with your e-bike. The point here is a 9 or 10t sprocket must hold onto something, it is not the case with less advanced drivetrains as yours.

No chance to install a larger chainring?

 

[kojack]

Impractical. A standard cassette only allows 11 teeth in the smallest sprocket. Smaller sprockets require a special "driver" for the freehub body, and it is usually only available for expensive 12-speed cassettes. The rear hub must be either Shimano Microspline or SRAM xD compatible, which is certainly not the case with your e-bike. The point here is a 9 or 10t sprocket must hold onto something, it is not the case with less advanced drivetrains as yours.

No chance to install a larger chainring?

I have been told it would screw up the drive system. I could pop on a couple of teeth more on the front if I could. That's easy.

 

[Stefan Mikes]

What is the current front chainring size in teeth? Please have a look at this place (where the chainstay changes the shape behind the chainring):

There is some clearance behind the chainring. The chainstay shape will limit installing too a big front sprocket. A bigger chainring wouldn't upset the drivetrain (you would only need a longer chain) but the design of your e-bike might prevent these changes.

On a different note: The assisted speed in Canada is only 32 km/h Why do you need to be a speed demon? 37 km/h is a really high speed already!

 

[stompandgo]

As Stefan says, changing the top cassette cog to a 10T or 9T would involve upgrading your entire drivetrain to 11 speed or 12 speed, potentially including the front chainring. The least expensive way would be to add a few teeth to the chainring and extend your chain. As you look for new parts, pay attention to frame clearance, as Stefan suggested above, but also offset between the chainring mounts and the chainline, as well as the mounting type (splines, bolts, etc.). For mid drives, frames are designed around motors, not the other way around. Look for chainrings for your motor model. For hub drives, match the chainring bolt circle, offset, and pitch.

 

[Jeremy McCreary]

For mid drives, frames are designed around motors, not the other way around. Look for chainrings for your motor model.

Maybe I lucked out on my mid-drive Vado SL 1, but to reduce the chainring from the stock 44t to a 40t better suited to my hills and legs, all I had to do was match the BCD and bolt pattern.

The Wolf Tooth narrow-wide chainring I chose went right on without a hitch. Now I have a 22-99 gear-inch drivetrain perfect local topography.

I know that going from stock to a larger chainring could run into clearance issues for the OP. Point is, the chainring may not need to be motor-specific.

 

[stompandgo]

I didn't mean to suggest that there are no motors that use standard bicycle chainrings.