Regearing Ratio when upgrading e-bike


New Member
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.
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....