Regearing Ratio when upgrading e-bike

[slabbyd]

I own a perfectly nice Kona Dew-e. But no matter the grade, up, flat or down it struggles to exceed the 20mph cut off limit. On the long downhill into town I spin out in the low-20 mph. So I plan on installing a speed box. This is going to require regearing the bike. It’s used both in town as well as on some very steep gravel road grades so I need to expand high gears while maintaining low.

Current set up
27.5” tires
38T chainring
11-34 cassette 9 speed

I’me going to replace with microshift Advent components. Thinking

48T chainring
11-42 cassette

This should increase my max pedaling speed by ~25%. Seems adequate.

Could go with a 50t chainring and a 11-46 cassette though the ratios between gears start getting a bit extreme. And a worry about the quality of the shifting.

Really looking for advice based on experience. Thanks so much.

 

[AHicks]

That 20mph cut off limit is electronic, not something you're going to change with a gearing change, if that's of any help. It's built/locked into the motor controller, and not something the bike MFG will allow to be changed.

Regarding the gearing, you're talking about some pretty big changes. Suggest you try a couple of chain rings to get a feel for them before getting into the rear cassette changes. Easy and quick mod if you can get away with just a chain ring....