Does Schlumpf chainring provide 2.5x benefit for rear hub motor, like numbers imply?

Mike leroy

Active Member
Is replacing the chainring with a Schlumpf gear box is worth considering? Either increase hill climbing, mid-range or speed gear ratios by 2.5 times. It would reduce chain twisting by requiring fewer cassette gears, e.g., 8 gear, rather than 11 gear cassette.

I searched EBR web site and found very little about the Schlumpf. I think it would be very useful to compensate for motor or gear weaknesses. Especially, bikes that are limited by the rear cassette width, e.g., fat bikes or Sonder's, due to a wide hub motor or narrow OLD.

The rationale is elaborated in this post.

 
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Shea N Encinitas

Active Member
Multiply or divide, think of it as a 2 speed front derailleur, just with internal planetary gears. The Stealth Fighter uses them as OEM. I've often wondered how the two ratios would work in daily use. Something to consider in a powerful DIY build for sure, would be nice to demo an existing build though. -S
 

Mike leroy

Active Member
Multiply or divide, think of it as a 2 speed front derailleur, just with internal planetary gears. The Stealth Fighter uses them as OEM. I've often wondered how the two ratios would work in daily use. Something to consider in a powerful DIY build for sure, would be nice to demo an existing build though. -S
So, if the gear ratio is so straight forward, why do people use 11 gear, rather than 8 gear cassette?

It seems 8 gears would reduce chain twisting. Use a more powerful hub motor to go faster with greater range. Seems like a clear winner. What is the catch?
 

Shea N Encinitas

Active Member
I imagine (actually read that) folks turn to the schlumpf drive when using larger motors (wide magnets & body) that limit the number of gears that can be installed for the axle width, or more accurately the bottom stays. The caveat being 2.5 is a pretty sizable jump up or down. Like having a 45 tooth & 18 tooth crankset. Cross-chaining concerns are over-rated IMO, is it shifts and stays on the bike who cares, you are going to replace it in 1,500 to 3000 miles anyway. -S
 

Mike leroy

Active Member
I imagine (actually read that) folks turn to the schlumpf drive when using larger motors (wide magnets & body) that limit the number of gears that can be installed for the axle width, or more accurately the bottom stays. The caveat being 2.5 is a pretty sizable jump up or down. Like having a 45 tooth & 18 tooth crankset. Cross-chaining concerns are over-rated IMO, is it shifts and stays on the bike who cares, you are going to replace it in 1,500 to 3000 miles anyway. -S
Schlumpf offers a third option, increasing the mid-range. Does it provide little benefit due to large gear overlap and duplication?

Seems to me that I could extend the battery range much further, perhaps double the range with better gearing? Simply use the motor less often and at lower PAS levels?

Amplification of low and high gear range without extrem speeds.

If you wish a wide range but not extremly low or high gears, speed-drive is your choice.
speed-drive "type 08" allows to mount chainrings with 27t. or bigger. This equals chainrings of 45t. or bigger in high gear mode.


Black bars in the diagram on the right show additional gears in combination of speed-drive with a wide spread 8-speed-hub.