Author Topic: 18, 19 or 20 tooth gearbox sprocket?  (Read 1434 times)

Offline Rookie_V#60

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18, 19 or 20 tooth gearbox sprocket?
« on: 12.02. 2014 09:55 »
Hi all,

for further optimize my longstroke I have the question which gear is for what purpose the best (no sidecar operation). Any experience?

Thanks, Rudolf
1923 James Model 12 500ccm v-twin
1926 Douglas EW 350ccm flat-twin
1936 Motosacoche 500ccm single
1948 BSA A7 Longstroke 500ccm parallel-twin
1955 Ariel Square Four MKII
1960 C1, 1967 C2, 1979 C3-gone!

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Re: 18, 19 or 20 tooth gearbox sprocket?
« Reply #1 on: 12.02. 2014 18:55 »
G'day Rudolf.
According to my books 18 is standard. With a standard 46 rear the ratio is 2.55 : 1.
19/46 is 2.42 an increase of 5% and 20/46 is 2.1 an increase of 17%.
So speed per revs will increase by those %'s but hill starts will be harder.
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline Triton Thrasher

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Re: 18, 19 or 20 tooth gearbox sprocket?
« Reply #2 on: 12.02. 2014 19:40 »
Go for standard solo gearing at first.

Then when you later overgear it in search of mythical "relaxed cruising" and fuel economy, you'll at least remember how good it was to ride with the lower gearing.

Offline vinver

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Re: 18, 19 or 20 tooth gearbox sprocket?
« Reply #3 on: 14.02. 2014 02:06 »
I tried that on my A50- used a 21 tooth sprocket. Poor thing didn't have the guts at 60mph in top gear, had to gear down on long hills. I would think same effect on the A7, it will do more harm to lug the engine than to ride it as it was originally geared.
1948 A7- the perpetual 25 year restoration.  1954 A10 , 1957 Ariel Huntmaster

Online KiwiGF

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Re: 18, 19 or 20 tooth gearbox sprocket?
« Reply #4 on: 14.02. 2014 10:43 »
ive recently changed the standard gearing on my a10 (with a 356 cam so slightly more hp than std, hopefully) by fitting a 22 tooth engine sprocket instead of the standard 21 tooth, the reason is that I wanted a more relaxed engine at 100km ph, its actually not made much difference to the cruising and it still seems to me to be revving a bit high, and it has meant more changes up into 3rd up hill it previously would do in top, so I would say gearing up is of marginal benefit for new zealand roads, so bsa got it more or less right. I definitely would not gear up more eg to 23 tooth.

Just my 2 cents worth!
New Zealand

1956 A10 Golden Flash  (1st finished project)
1949 B31 rigid “400cc”  (2nd finished project)
1968 B44 Victor Special (3rd finished project)
2001 GL1800 Goldwing, well, the wife likes it
2009 KTM 990 Adventure, cos it’s 100% nuts