Sick Bike Parts dual range jackshaft gearing system

[Fabian]

Originally i used a tetra chainwheel system which allowed me to have 3 chainrings to power the final drive. In operation i rarely used the midrange gear (being the dished 30 tooth sprocket) so i've ditched the tetra chainwheel system and gone for a tri-wheel setup; removing the 30 tooth sprocket from the final drive and only using the 24 tooth sprocket as "low range" and the 38 tooth sprocket as "high range.
The dished 30 tooth sprocket still stays in the system but is now reversed to enable a lead-in ramp when the chain jumps to the 38 tooth sprocket. By doing this, there can be a larger gap between the 48 tooth jackshaft sprocket and the 38 tooth final drive sprocket, and a smaller gap between the 24 tooth sprocket and the 38 tooth sprocket, much better mimicking the sprocket gap found on a mountain bike triple chainwheel setup, which works in nicely with the indexing of a typical front derailleur.

A side note: the need for a right hand side chain tensioner can be plainly seen in the photo, as the front wheel sand blasts the chain drive system when on dirt roads. I have had chain stretch go from 25% to 80% in around 3 hours riding a trail that has a surface consisting of Lilydale Topping (a combination of sand, fine stones and cement powder) which is exactly what you see sand blasted onto the sprockets in the photo.
This particular surface mercilessly grinds away at the sprocket teeth and chain, and without a chain tensioner you are forever stopping to get out your spanners and adjust the tensioning rod.

 

[FurryOnTheInside]

Are the two final drive chainrings now spaced to match the indexing of a front derailleur shifter with ONE shift, and the deraileur's top position now locked out with the limiter screw (just what dual range bicycles usually do as they use a triple range shifter)? So the whole triple set is really just the same overall width as a normal triple chainset, and fits on what would be a "normal" bottom bracket axle width? That certainly seems like it would make things a lot easier to put together.
I'd seen your tetra chainring setup and thought it'd be good to go for a simpler dual range; though in my mind I was planning to use standard bicycle chainrings from a standard triple or dual chainset for the dual final drive and one from a track (single speed) or a road "racer" bike for the input. Standard bicycle chainrings have "shift ramps" or "shift pins" where you currently have the 30T, for the same effect (but a little less weight and easier cleaning too). Triple/dual chainsets usually have a maximum tooth-count difference between adjacent chainrings of 14 teeth, though shifting is generally a little bit smoother if it's kept to 12 teeth; though with only two gear ranges it's probably right to go for the absolute max as there's less redundant gears this way and the widest possible spread of gearing.

It looks like you've been riding on the moon! :O IMHO it really needs some sort of a chainguard to stop/reduce that sandblasting. That'd be time consuming to make (from fibreglass?) but IMHO the only thing that'll really help. 80% stretch in a few hours is STILL bad even if you're able to keep tension on with the RHS chain tensioner, as it's still ruining your chain ridiculously fast and also the teeth on the chainrings. I've been thinking about doing something along these lines to combat the salt spray issue I have where I ride along the coastal paths (and the salt-gritted roads in winter).

 

[Fabian]

Are the two final drive chainrings now spaced to match the indexing of a front derailleur shifter with ONE shift, and the deraileur's top position now locked out with the limiter screw

That is exactly how the system is set up.

I'd seen your tetra chainring setup and thought it'd be good to go for a simpler dual range

The dual range setup is simpler and just as effective and much easier to operate than the triple, because the shifter and sprocket spacing allows proper indexing.

I was planning to use standard bicycle chainrings from a standard triple or dual chainset

It's so much easier to order the sprockets from SickBikeParts because they have them in stock and they are designed to attach to the freewheel bearing - bolt everything together and it's job done!

It looks like you've been riding on the moon!

Very close to it

IMHO it really needs some sort of a chainguard to stop/reduce that sandblasting.

You are right on the money. I wished SickBikeParts would offer such a chainguard for their shift kit. As they don't i've been trying to think up a way of making a simple, yet effective chain guard to stop the chain and sprockets from being sand blasted with grit and debris.

80% stretch in a few hours is STILL bad even if you're able to keep tension on with the RHS chain tensioner, as it's still ruining your chain ridiculously fast and also the teeth on the chainrings.

That is exactly what it does, particularly when on a bicycle trail consisting of just about the most abrasive surface known to man: sand, stones and cement powder.
On normal dirt roads the wear is a lot less, but it still wears many times faster than when riding on dirt free surfaces.

I have thought of designing a syringe style oiling system; mounted on the handle bars, that sends lubricant to the various chains via thin plastic tubing, aimed directly at the chain links.

 

[FurryOnTheInside]

Idk how you do the multiple quote thingy!

The dual range setup is simpler and just as effective and much easier to operate than the triple, because the shifter and sprocket spacing allows proper indexing.
I was looking at the different bottom bracket units that SBP offer, and I'm sure there must be a way to have the standard spacing, triple range AND the input sprocket on the outside. It would need a wider BB spindle and therefore perhaps a wider jack shaft than the 5" standard one in the shift kit (I'm not sure how the new LHS chain tensioner and extra bearing works unless this comes with a wider jack shaft).


It's so much easier to order the sprockets from SickBikeParts because they have them in stock and they are designed to attach to the freewheel bearing - bolt everything together and it's job done!
I still think the SBP spider offers greater flexibility of set up: Bicycle chainrings are so widely available already, are often very cheap if bought used or can be found for free at the local dump! They have shift gates and shift pins if they come from a triple/dual chainset, and they come in every size from 24T up to 54T (or larger if you live close enough to a city with a velodrome which luckily I do). Sick Bike Parts offer three optional spiders (4 or 5 arm, different bolt hole diameters), these bolt directly to the freewheel and the standard bicycle chainrings can bolt directly to each other and the spider. There may be some weight saving using the spider, too.
I know you know all this already but it's not often mentioned; in fact I only found out about the spiders by having a really good look through the SBP website. It's also a bit easier if ordering parts from outside the USA to only need to import the spider (which never wears out) rather than all the chainrings in all the sizes you might ever need.

I can see myself wanting to change the chainrings often for different terrain, so may even think about splitting the chainrings for easier removal, so I can have a flat land/coastal gearing and a mountain gearing which can be swapped out without removing the right hand side crank arm and 2nd/intermediate chain, etc. Being limited to dual range rather than having a triple (and the maximum difference of 14 teeth between adjacent chainrings) is what made me think of this.

You are right on the money. I wished SickBikeParts would offer such a chainguard for their shift kit. As they don't i've been trying to think up a way of making a simple, yet effective chain guard to stop the chain and sprockets from being sand blasted with grit and debris.
I've heard of foam being used as a mould, fibreglass laid over the top, then the foam can be dissolved with solvent. I'm not sure what sort of foam they used, obviously one that doesn't dissolve in the resin. I have actually done something similar with a papier mache mould, using water as the solvent to remove the mould after the fibreglass resin is set. I think if SBP made it themselves, it would have to be stamped and pressed sheet metal in just one size and therefore wouldn't suit everyone's needs (different chainring sizes and downtube diameters/shapes).


That is exactly what it does, particularly when on a bicycle trail consisting of just about the most abrasive surface known to man: sand, stones and cement powder.
On normal dirt roads the wear is a lot less, but it still wears many times faster than when riding on dirt free surfaces.
Where I live we have wind-blown sand and salt water puddles with sand in the bottom. It is perhaps a little less abrasive than your Lilydale Topping but extremely corrosive, so I can expect to have a similar battle on my hands avoiding excessively short chainset life.
I have thought of designing a syringe style oiling system; mounted on the handle bars, that sends lubricant to the various chains via thin plastic tubing, aimed directly at the chain links.
Personally I would not try dripping oil onto the chain during use since excess oil needs to be wiped off before use (only the insides of the rollers needs to be oiled, not the links), otherwise dust particles will stick to all that excess oil and turn it into a heavy sludge which clogs every space it can find, ruining your gear shifting and adding to the drag in the system, not to mention that sludge acts as a very effective grinding compound. Multi chain systems already have a tendency toward excessive drag. (okay maybe drag isn't the correct technical term but you know what I mean!)

You might try some kind of syringe trick with water on your front brake disk perhaps? Would need a very large syringe of course and I doubt it'd be as effective as fitting a V-brake to use alternately with the disk brake.

 

[Fabian]

ou might try some kind of syringe trick with water on your front brake disk perhaps?

Now that is a great idea - water cooled brake caliper and disk.

What i really want is dual disk brake front hub + fork leg adapter to attach onto the right hand side fork leg, so i can run twin 9" disk rotors.

 

[FurryOnTheInside]

I saw it used in downhill mountainbiking around the end of the last century but not since. They also tried aluminium sandwiched between steel braking surfaces, again it didn't catch on. There must be a reason! Though it could simply be that downhill courses are rarely very long and have got very tame especially the world cup courses where riders opting to use enduro bikes are winning races these days. *rolls eyes at the whole downhill scene*

Ah, like the Magura Big Twin (meant for pedicabs and other cargo/work trikes) or the Gatorbrake which even comes with the hub and the caliper mount bracket?


A lot of (especially older) suspension forks have no internals below a couple of inches from the dropouts so there's plenty of room to simply drill, tap, and bolt on a piece of angle iron, as I've shown (I'm sure I posted this already) this is how my caliper is mounted on the left side of my old Marzocchi's on my dirt jump bike.



Anyway.. we're totally off-topic again.

 

[Fabian]

That twin disk arrangement looks awfully good.
What about the caliper attachment point on the right hand side fork leg that doesn't normally have an attachment point?

 

[FurryOnTheInside]

I know!!! I don't need one AT ALL but I do think I might end up with one, one day.

 

[FurryOnTheInside]

What about the caliper attachment point on the right hand side fork leg that doesn't normally have an attachment point?
Same as I've shown on the left hand leg. That old Marzocchi Bomber fork has no internals at the bottom of the fork leg, it's just hollow but thick alloy (I don't think it's magnesium, I think they switched to magnesium a couple of years later, after disk brake mounts became standard MTB fayre).

Some older Marzocchis DID have the RHS caliper mount.
Someone else's bike.. pic of the 'net:

 

[Fabian]

That's exactly what i want, and i want it real bad.