I have my Scottish nicely set up for trials, but I want to make it easily converted to trail gearing. The plan is to swop only the rear sprocket to give me a top gear/rpm similar to a road bike, like maybe the 24DC. Question is, how much smaller should the rear sprocket be? I'm stumped on working out the overall ratio because I don't know the teeth number on the clutch. It's a 32A engine and box. I'm running a 20 tooth engine sprocket, 14 on the gearbox and 66 on the rear wheel. Perhaps I need the smallest rear sprocket I can find? Any pointers would be great.
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The clutch sprocket has 43 teeth. The overall gearing for the 24DC was 5.7 to 1 so to achieve this with the 14 tooth gearbox sprocket you need a 37 tooth rear sprocket. ie primary ratio 20 engine 43 clutch = 2,15, final drive 14 gearbox 37 rear wheel = 2.64 so 2.15 x 2.64 = 5.68 overall ratio. Not sure if a 37T sprocket will fit the hub, you may have to go a bit larger with slightly lower gearing.Last edited by John Wakefield; 06/04/2023, 10:51 PM. -
You need to take into account the fact that your rear wheel is bigger in diameterComment
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Yes that does need to be taken into consideration, its same dia on road & trial but tyre 400 x 18 on trials instead of road tyre 325x18 so about 3 teeth more on rear sprocket, ie 40 teeth. In practice the overall gear ratio needs to be slightly lower than road gearing if bike is being used for some off road work, ie green laneingOriginally posted by teamferret View PostComment
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That is exactly the info I was hoping for! Thank you very much fellers. Honorary PhD in arithmetic will be in the post! I do so appreciate this forum.Comment
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