Schlumf drive - effect on gear inches?

[Time Waster]

OK I know virtually nothing about these other than they kind of multiplies gear range. For example mountain drive lowers gear range by 2.5x. Am I right in saying that if your chainring with the mountain drive a 50t then you drop to a 10t equivalent chainring? Assuming an 11t to 36t cassette you get 13.6 to 111 gear inches according to Sheldon Brown calculator on 32-559 / 32mm or 1.25" x 26" wheel. I'm looking at a recumbent with such a wheel on the drive wheel.

Is this correct?

The other two go up so you'd need a lower teeth count chainring to get a useable range I think. If you could get a 28t chainring with a speed drive you get 19 to 103 gear inches range.

How heavy are they and are they any better than a good triple setup? What about with recumbent bikes? Are they a good match especially for touring?

Explain like I'm 5!

 

[gom]

50t + 1:2.5 stepdown = 20t
That’s my understanding. 50 divided by 2.5. Or multiply by 2 and divide by 5.

I’ve been hankering to add one to my Brompton for years, but they are rather expensive.
So I’ve no real experience of them alas.

When googling it seems they are popular with recumbent owners. There are YouTube videos as well.
Might be worth a look, if you’ve not already done so.

 

[Chris S]

Firstly, Schlumpf Drives are located in the bottom bracket. There's a button on either side of the axle that allows you to toggle between high and low gears.

Schlumpf Drives raise or lower your final drive by a specific ratio. For example, the High Speed Drive will increase the final drive ratio by 1.5. If you are in a 40 inch gear and enable the High Speed Drive then you will increase this to 60 inches.

There's an article on Schlumpf Drives here. I'm not sure how accurate it is.

 

[Time Waster]

50t + 1:2.5 stepdown = 20t
That’s my understanding. 50 divided by 2.5. Or multiply by 2 and divide by 5.

I’ve been hankering to add one to my Brompton for years, but they are rather expensive.
So I’ve no real experience of them alas.

When googling it seems they are popular with recumbent owners. There are YouTube videos as well.
Might be worth a look, if you’ve not already done so.

Doh! Fat finger typing of 10t, obviously 20t step-down. My maths isn't that bad!

 

[Time Waster]

So I think the mountain drive turns my road bike from 50t/11t cassette to 20t/36t cassette. If my maths is right that's on revolution of pedals turns the back wheel 4.54 revolutions in top but engage schlumpf drive you get 0.55 revolutions of rear wheel. So development goes from what about 9m to about 1m.

If an upright tourer you're ideally looking for 18 to 20" lowest gear but a common chainring and schlumpf mountain drive gives just under 14" without losing top speed. I can understand which recumbent riders like them although I think it's mostly trikers that use them. IMHO uphill is harder on a two wheeled bent so 13.6 gear inches is a good solution. A triple setup could achieve that inches but at the expense of top end speed. Unless you go to the extremes of what is possible with long cage dérailleurs I suppose.

Is this kind of right or am I completely wrong.