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Trials gearing 191 Sherpa 350


fastfred
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Couldn't tell you I'm afraid,  just starting out myself. Literally just got it running properly yeaterday after an engine rebuild. Done a few road trials in the chair of a 1950 Norton and thought I'd like have a go myself. 

taken yesterday after getting the idle sorted. Electronic ignition fitted and airscrew adjusted. Starts beautifully and sits and ticks over like a dream.

There's loads of more knowledgable people on this site.

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I and quite a few other ran 11/39. Puts first gear where second is on standard gearing. Quite a few riders found they never needed original first gear and the 11/39 made 3rd gear ace for hill climb sections and 4th ideal for moorland crossing, and a decent 5th for road work.

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11/46 is the correct gearing for your bike and should be fine, never seen a 10t front sprocket and I certainly wouldn't recommend gearing the bike up by putting a smaller rear sprocket on it, would make the bike a nightmare in any tight sections.

Cheers Greg

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Just try it and see how it is for you. I have three Sherpa`s and I run 11/42 on all of them but I do ride on the clutch so I just find the higher gearing makes first a lot more usable but you do have to use the clutch in the tight stuff. You chain will wear out faster with a ten tooth front though. Graham.

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18 hours ago, fastfred said:

I have 10 46 gearing is that ok ballpark for trials riding, I am a beginner. Thanks

FYI Mine has 10/48 fitted and it idles in first at far less than crawling pace which will make tight sections easy but I do hold up the traffic with road work !

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Just for reference, Sherpas have been delivered from the factory with basically the same first gear ratio since the M91/92 series

M91 1/2 chain   14/52 gearing  33.5:1  1st gear ratio

M92 1/2 chain   13/52 gearing  36.1:1  1st gear ratio [325 was geared down one tooth]

M124  up to and including M191  5/8 chain  11/46 gearing  37.7:1  1st gear ratio

Internal ratios changed from here on to provide higher top speed in 5th & 6th on 199B

M198/199  13/46 gearing   37.6:1  1st gear ratio [you can change the gearing on these models to 11/39]

                   11/39 gearing  37.7:1   1st gear [same ratio , smaller back sprocket]

M198A 199A 198B 199B    11/39 gearing  37.7:1  1st gear

Hope this clears up any confusion as the gearing really depends on which model you have,

Cheers Greg

 

Edited by sherpa325
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4 hours ago, sherpa325 said:

Just for reference, Sherpas have been delivered from the factory with basically the same first gear ratio since the M91/92 series

M91 1/2 chain   14/52 gearing  33.5:1  1st gear ratio

M92 1/2 chain   13/52 gearing  36.1:1  1st gear ratio [325 was geared down one tooth]

M124  up to and including M191  5/8 chain  11/46 gearing  37.7:1  1st gear ratio

Internal ratios changed from here on to provide higher top speed in 5th & 6th on 199B

M198/199  13/46 gearing   37.6:1  1st gear ratio [you can change the gearing on these models to 11/39]

                   11/39 gearing  37.7:1   1st gear [same ratio , smaller back sprocket]

M198A 199A 198B 199B    11/39 gearing  37.7:1  1st gear

Hope this clears up any confusion as the gearing really depends on which model you have,

Cheers Greg

 

Super info, thanks. Mine has 10/48 would that make a huge difference overall?

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20 hours ago, sherpa325 said:

Internal ratios changed from here on to provide higher top speed in 5th & 6th on 199B

As I understand it,  Sherpa 5-spd.internal ratios were changed to provide a wider spread of ratios, by lowering the intermediate ratios.

(Compared to the previous set-up)

As top gear remained unchanged and is direct (1:1), higher top speed in 5th.  would result only from changing the secondary ratio.

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These are the overall ratios with standard gearing as delivered from the factory  11/46 [M159]  11/39[199A & B]

            M159                   M199A              M199B

1st        37.7:1                37.7:1                37.7:1

2nd      29:1                    29.3:1                29.3:1

3rd       22.4:1                22.3:1                22.35:1

4th       13.7:1                13.7:1                16.4:1

5th        9.9:1                   8.4:1                 11.4:1

6th                                                              8.4:1

You can see 5th is taller on the 199A gearbox and all other ratios are near identical on the 5 speed boxes. Fourth and fifth are different on the six speed box  

The reason the bikes have a higher top speed is the changing of the final ratio from 11/46 to 11/39 which still keeps the first four gears the same overall ratio, but allows an overall taller top gear. The change also obviously uses a smaller rear sprocket as well, so less likely to be damaged.

 

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