Gearing

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knackeredMk1
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Gearing

Post by knackeredMk1 » 20 Nov 2011, 18:16

All CRM250 gearbox 'gears' are interchangable. So you can swap one Mk with another. Mk2/3/AR basically have the same gearing but the Mk1 is a tighter box.

Copied from Honda Mk2 briefing document (dotted line is Mk1. Mk2 is 'New CRM') -
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Japanese SuperMoto riders often swapped later gear ratios/cogs (5th & 6th) for Mk1 cogs to get closer ratios. If you are going to swap gears then beware that Mk2/3 & AR are easy to swap complete with the shafts but the clutch shaft on a Mk1 runs on a 1mm larger diamter bearing than the others. So to swap ratios you need to swap cogs and keep the same shaft, grind out the Mk2/3/AR bearing or bush/weld the smaller shaft to make it bigger.

Mk2/3/ARs have a 6th gear ratio that is ~ 7% higher than a Mk1.

Sprocket ratios have a big effect on acceleration/top speed/cruising speed. As do wheel and tyre sizes.

Sprocket ratios vary a lot between riders but those who do Greenlaning or Long Distance Trials only tend to use 14:45.

Those who race tend to use lower ratios ~ 13:45

SuperMotos ~ 15:42

You can get the exact ratio by dividing the rear sprocket teeth by the front sprocket teeth so different sprockets can give you virtually the same gearing. E.G. 14/45 = 3.2143. You can get essentially the same gearing by using 13/42 or 15/48, so one tooth on the front ~= three teeth off the back.


Jeram has put the AR on to the 'Gearing Commander' -

http://www.gearingcommander.com/

If you have a rear sprocket larger than ~45 teeth you need to use a dropper plate between the swing arm and the chain guide -

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Otherwise you will wear the chain and the guide. A small amount of adjustment can be achieved by working the holes in the chain guide for the mounting bolts.


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