Sick Bike Parts dual range jackshaft gearing system

[Sidewinder Jerry]

Fabian here is a shifting style I teach pedal only riders for a 21 speed bicycle. Uphill 1(1,2,3); level ground 2(3,4,5); downhill 3(5,6,7). This style of shifting eliminates gear redundancy, cross chaining and chain droop. The only time you shift the front chainrings is when you're in 3 or 5 in the rear. This gives you 9 easy to understand none redundant gears instead of 21 confusing redundant ones. If you must stop going up a hill be sure to be in 1(1) before stopping. For all other stops be in 2(3) before stopping.

Here is my favorite setup 24 speed. Front chainrings 28, 36, 44. Rear 8 speed DNP Epoch freewheel 34-11. Uphill 1(1,2,3); level ground 2(3,4,5,6); downhill 3(6,7,8). So the only time you shift the front chainrings is when you're in 3 or 6 in the rear. This gives you 10 easy to understand none redundant gears instead of 24 confusing redundant ones. A tachometer is a must for knowing when to shift.

 

[Fabian]

I've got an even simpler system: The bike operates on the high range 38 tooth chainring (powering all the gears on the rear cassette) and when the hill gets too steep for high range 1st gear the chain is selected to drop onto the 24 tooth low range gear; being ridden through low range 1st and 2nd gear and 3rd gear before changing back up to high range 2nd gear.

By carefully organising the ergonomics of the rear derailleur grip shifter and front derailleur thumb shifter on the left hand side of the handle bars, you can operate both the front derailleur and rear derailleur with one hand; at the same time.

 

[FurryOnTheInside]

I've been using the Sheldon Brown Bicycle Gear Calculator to look at different gear set ups, so made this one just out of interest. Does this look somewhere near correct for the gearing you are currently using, Fabian? I've included a 52T high range just for fun!




I need to make a chart to check out the (possible future) Sick Bike Parts 21T LHS jackshaft sprocket and either 9:44, 10:48 or 9:48 RHS shift kit sprockets (and a standard 11-34T 8spd Megarange for myself) at 40, 60, 80 and 100 RPM (@ pedals) as I don't want gear changes to be above 100RPM (some riders might prefer to change at 90RPM but I tend to spin quite fast) so I'll do that later today.

 

[FurryOnTheInside]

By the way, have you seen these SRAM 3-speed IGH hubs that accept 8/9/10 speed cassettes? No idea how long they'd last, of course, and they don't mention what the 3 speeds actually are. - EDIT: I just found it: 0.73, 1.0, 1.36
http://harriscyclery.net/product/sram-dual-drive-disc-brake-hub-36h-135mm-sku-hu2571-qc49.htm

 

[Fabian]

I really like the concept of the SRAM Dual Drive, and i was contemplating using one, but i wasn't sure how durable the internal planetary gearset would be when having to transfer high levels of torque.

The big problem (if you are a long way from the car, or immediate assistance) is the fact that you can't fix a smashed up set of internal planetary gears so you can at least limp the bike home.

If i could be guaranteed that the internal planetaries were bullet proof, like an external gear drive system, the SRAM dual drive would be on my bike tomorrow.

 

[Fabian]

Your gear ratio calculations for the 24 and 38 tooth front chainwheel sprockets and the 36 tooth through to 11 tooth cassette sprockets are exactly what my bike can theoretically produce on the road and at the rpms it needs to achieve it.

In my location a motorized bicycle is limited to 12.42 miles per hour, so my bike is always traveling no faster than 12.42 miles per hour. I hope this provides comfort to the Department of Motor Vehicle spooks lurking on this forum, and i reiterate, my bike travels no faster than "EXACTLY" 12.42 miles per hour, even if i hoist it to 2,000 feet in a Cessna 172 and throw it out the side door.

 

[FurryOnTheInside]

AWESOME that means I DIDN'T screw up the calculation and my figures are actually useable!

Of course it is never travelling faster than 12.42 mph! However you can dismantle the RHS connecting chain (and unlimit your front derailleur if you like) to make your bike a pedal-only bicycle that carries and engine as cargo but cannot be powered by that engine, any time you like.

I had a quick go at making a chart for a 10:21 - 9:44 shift kit. It looks promising. I wonder at what point it becomes too difficult to pedal start the engine.. 10:21 - 9:48 might be taking it too far.

 

[Fabian]

You need to make a change to the literature: rpms over 5,000 just kill the connecting rod bearings.

 

[Fabian]

If you adapt a compression release from a chainsaw, you don't have to worry about gearing ratio impacting on pedal starting effort.

Scroll down to see the compression release device,

http://www.motoredbikes.com/showthread.php?39239-Twin-Spark-Plug-Cylinder-Head

 

[FurryOnTheInside]

You need to make a change to the literature: rpms over 5,000 just kill the connecting rod bearings.

Okay, will do. It was quite an old thread of yours that I swiped the info from.