[trikes] WHAT IS LOWEST GEAR INCH

[Richard Guy Briggs]

On Tue, Oct 05, 2010 at 10:46:42AM -0400, mgta4 at aol.com wrote:
> 
> What is my lowest gear inch with a Rohloff hub and a 17 tooth sprocket
> and a Schlumph Mountain drive with I think a 42 inch chain ring.
> Please don't send me somewhere to figure it out because I don't know
> how. Tried that already. 
> 
> Also with a speed drive. I don't have the chain ring size but is is
> small. Sorry I know that doesn't help. Fran

Rohloff		Low	High	Low	High
Schlumpf	Low	Low	High	High
========	===	====	===	====
Mountain	5.5	29.0	13.8	72.5
Speed		13.8	72.5	22.7	119.6
Speed2		13.8	72.5	34.5	181.22


The formula is:
GearInches = Chainring x Schlumpf / Sprocket x Rohloff x WheelDiameter

Where	Chainring =	42
	Schlumpf =	1 / 2.5		(mountain low)
	Schlumpf =	1 / 1		(mountain high)
	Schlumpf =	1 / 1		(speed low)
	Schlumpf =	1.65 / 1	(speed high)
	Schlumpf =	1 / 1		(speed2 low)
	Schlumpf =	2.5 / 1		(speed2 high)
	Sprocket =	17
	Roholff = 	.279		(low)
	Roholff = 	1.467		(low)
	WheelDiameter	20		(or 26 if you have one of those)

For the metric "meters of development", change WheelDiameter to
WheelCircumference which would then be 20 x .0254 x pi, which is 20 x
.0254 3.14 which is 1.5959.

>From my experience, the speed drive I with a 40 tooth chainring and a 17
tooth sprocket gave a decent range.  I have been tempted to get a speed
drive II, but can't quite justify it until my speed drive I just wears
out.  At that point, I may put in an even smaller chainring to extend
the low end.  We were able to tow 3/4 tonne with tandem cranks out of
phase at about 15 gear inches.

There are warnings about not going below a certain combined ratio due to
the possibility of breaking the Rohloff internal plastic overtorque
bushings, but considering your situation, I think that will be not a
concern.


As an update, I hadn't posted this to the list back in May...  We bought
a new stackable front-loading washer/dryer set and I got a bit impatient
with their delivery schedule, so I just went to get them myself.  :)
This load was 1/3 of the design load for the trailer (so 360 pounds) and
was easier than it looks, even in solo rather than tandem.
	http://tricolour.net/photos//2010/05/18/organ-trailer.html
I only had to use the 13 gear inch lowest gear once on that 9km haul and
that was on a fairly steep hill up a bridge (maybe 8%?).

For those who are newer to the list, here are the original articles
about the trike and the trailer:
	http://tricolour.net/gtvs6.html
	http://hpv.tricolour.net/organ-trailer.html



	slainte mhath, RGB

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