Author Topic: C15T Gearing...  (Read 271 times)

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C15T Gearing...
« on: 04 April, 2020, 17:38:06 »
My trials bike has been doctored to make it even lower geared than standard. so low you can ride rocky sections in 3rd gear and go at walking pace. As the trials I like to do involve road work 20 to 25 mph is a bit of a waste of time. Question is what number tooth sprocket was on the original gearbox drive and on the engine pulley ?  The idea is to gear it up more for green lanes and long distance tirals...   Thanks..   Griff
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Re: C15T Gearing...
« Reply #1 on: 09 April, 2020, 17:26:12 »
Hi Griffo

Just having a look at this for myself at the moment as I just bought a C15S, looks like there are a few options to up the final drive ratio.

1st option and the easiest/cheapest would be to see whatís on the final drive front sprocket, sprockets available are 13, 14, 15, 16, 17, 18 and 19 teeth, and the standard rear is 45t (final drive ratio: divide the driven by the driver) Highest with a 19t front (45 / 19 = 2.36:1) Lowest with a 13t front (45 / 13 = 3.46:1)

2nd option is the primary drive, canít see as many primary duplex drive sprocket size options but the documentation I have 18t for the engine and 52t on the clutch sprocket as std. However TMS Nottingham are showing a 23t engine sprocket, you may need a new primary drive chain to fit that though.
Highest with a 23t primary drive sprocket (52 / 23 = 2.26:1) Lowest with 18t primary drive sprocket (52 / 18 = 2.88:1)

The final option is the gearbox, looking through the documentation I have there are 3 ratio options for my build year (1962) Changing the gearbox would be extreme, I will be trying the first option, although I am also looking for a spare engine as a donor, depends what I can pick up for the right price.

Attached is the PDF from BSA showing all the ratio options.