Tetra Chainwheel system for SickBikeparts (Sick Bike Parts, SBP) shift kit

Ok this method of packing 4 chainwheels into the space of two allows the use of a triple chainwheel system with fully functional front derailleur, making use of all the available chainwheel sprockets from SickBikeparts - the 24 tooth; 30 tooth and 36 tooth sprockets and the optional 48 tooth sprocket to take drive power from the jackshaft.
This gives an insane amount of pulling power when coupled to a 9 speed 29'er casset with it's 36 tooth large sprocket and good road speed when substituting the 12 tooth sprocket with an 11 tooth sprocket.

My custom ratios are made by grinding away the locking pins on a Shimano 29'er cassette and an 11-34 tooth 9 speed cassette, then reassembling the following individual cassette sprockets in the following order:

11 - 12 - 13 - 14 - 16 - 19 - 23 - 28 - 36

These sprocket sizes were worded out after numerous road trials of different sprocket sizes. It gives meaningful jumps in the low range sprockets and a close ratio set of gears for higher speeds.

It needs to be mentioned that the front derailleur needs to be a specific style, in that it needs to have a flat outer face (as per the photo) so it can almost come into contact with the 48 tooth outer most sprocket on the chain wheel system - the sprocket that receives drive power from the small jackshaft sprocket.

What also needs to be mentioned is the style of front derailleur suitable to make this system work. It not only needs to have a flat outer face but also to be a down-pull mechanism with a built in cable landing-stop (as per first photo) and ideally to be a mountain bike derailleur as per the second last photo. If using the more common road style derailleur with the open slots, the 9 speed chain will tend to bind under the derailleur mechanism on power upshifts and also for the outer plates of the chain to catch in the open slots. Currently i'm using a road style derailleur with melted plastic filling in the open slots. The only time i've had problems is when trying to shift under engine revs. If using the clutch and gently pedalling the chain from sprocket to sprocket, there has never been a problem with the chain catching and tearing up the derailleur.
At the end of the day, the best method is to use the mountain bike style derailleur with a down-pull mechanism, as the flutes extend down lower and prevent the chain binding under the derailleur.

A noteworthy mention and shown in the last two photos are a 1mm plastic seperator that prevents the jackshaft chain and the final drive chain to rear cassette from coming into contact with each other when the chain is running on the 36 tooth chainwheel sprocket and the smaller cassette sprockets. If there is no seperator, the two chains will come into contact with each other, tearing off the outer chain plates.

For this system to work with perfect reliability, you "MUST" use 9 speed chain on both the jackshaft drive sprockets and the final drive to rear cassette, as there is only 2mm of clearance between the chains when the 36 tooth sprocket is driving the 11 tooth sprocket on the cassette and relative to the jackshaft chain.
The spacing and facing of the chainwheel sprockets is also critical and i can give you this information if you so desire to replicate my setup.

So far i've traveled 600 miles with perfect reliability on the tetra chainwheel setup and it is a joy to have a 24 tooth super low range first gear - just the ticket to pull houses and SUV's and anything else you may wish to tow.

email addy: yldflight@hotmail.com

Cheers Fabian

The 1mm plastic separator for jackshaft and final drive, 9 speed chains.

This separator is critical due to the narrow spacing between 36 tooth freewheel sprocket and jackshaft sprocket.
Fitting four chainwheels in what is effectively the space designed for three chainwheels allows only a 2mm gap when transferring drive power to the smallest 11 tooth sprocket on rear cassette.
If no separator is fitted and when in the three smallest cassette gears, the chains will catch on each other, tearing off outer chain plates.

This method is a simple solution to the packaging issues of such compact spacing and has worked perfectly.