[Tern Verge P20] Replace sprocket 11 with 9?
 

Hello

The Verge P20 looks nice, but I'm concerned it won't be fast enough to my taste when riding on flat terrain: Tern says its top gear inches is 95", ie. about 7.60m (95 * 0.08).

35-406 = 1460mm
-> meters of development = 7.30m

Is it possible to change the lowest sprocket from 11 to 9 without changing the rest of the transmission?

Thank you.

I don't think you'll find a 9 tooth cog that will fit the hub.

I'll leave others to commit about the need for a higher gear and/or the OP's inability to spin :) Andy.

A bit of math might be apropos here.

The diameter of a sprocket at the wrapped chain's pin centers in inches is roughly 1/6th the number of teeth. Subtract 1/2" for the chain clearance below the pins, so a 9' sprocket would need to fit a hub with a diameter less than 1" where it's mounted.

Dude!! Where you planning on riding 35mph in the flats??

Tony Martin only just finished a feat of inhuman ability at 31mph on the flats in his recent time trial at his last race.

You might wanna hook up with one of the pro teams. They could use your help. ;)

55x11 = 131.4 gear inches(39.1mph@100rpm)

(edit) He has a folding bike with 20" wheels, but that gearing is good for 27mph@100rpm

Actually, the gearing is closer to 94 gear inches on a 20" wheel like the OP is asking about.

To answer the question, an 11 is the smallest cassette cog I have heard of. If you want a higher gear, you probably need to look for a larger chain ring, which could impact ground clearance.

EDIT: For a flat bar bike, I would think 94 gear inches is probably high enough unless you are bombing down hills... then I would coast.

All the "your gear is high enough" posters assume the OP is running at cadences similar to theirs. But cadence varies tremendously among riders, so the OPs request may be very valid - for him.

I agree that the only readily available mechanical option are larger chainrings. However Moulton used to offer hubs and freewheels with sprockets smaller than 11, though I don't know what the smallest was.

The downside is that it would require a new hub so change.

Higher gear options include building a new rear wheel around the Shimano Capreo parts group (smallest cog 9T) or building a new rear wheel around a SRAM DD3 or Sturmey-Archer CSRF3 rear hub with internal multiplication. These solutions are fairly common with smaller-than-typical wheeled bikes.

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