Author Topic: Sprocket size for a poor man  (Read 2512 times)

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Offline jimson

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Sprocket size for a poor man
« on: March 22, 2008, 11:32:51 pm »
G'day viewers could someone with a bit of knowledge point me in the right direction please I need to replace the sprockets and chain on my 125 Indian it has a Minarelli engine in it with a 17rear wheel I am thinking of racing this bike in pre75 125 class more for fun then race anyway I would like to find a starting point with sprocket sizes  for VMX

428 chain 14/48

1st 10/34 3.400:1

2nd14/30 2.143:1

3rd18/27 1.500:1

4th20/25 1.250:1

5th22/23 1.045:1   is this enough to go off  :-\ jimson
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Offline pokey

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Re: Sprocket size for a poor man
« Reply #1 on: March 22, 2008, 11:48:33 pm »
Nuthin to do with chains nor sprockets mate but was some 125 indian stuff on oz evilbay this week like a chamber  ;)

Offline jimson

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Re: Sprocket size for a poor man
« Reply #2 on: March 22, 2008, 11:59:41 pm »
Yes Pokey I had a look at them seat frame and chamber at Liverpool bike wreckers I let them go no cash  :'( jimson
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Doc

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Re: Sprocket size for a poor man
« Reply #3 on: March 23, 2008, 07:36:36 am »
without knowing the motor characteristics or any special tricks or knowledge I'd say go about 10 teeth up on the rear. The 14/48 final drive is roughly the same as most Jap trailbikes of the time. The TS125 'kit' sprocket was anywhere from 60t to 67t as an indication.

Offline vandy010

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Re: Sprocket size for a poor man
« Reply #4 on: March 23, 2008, 09:20:26 pm »
jimson,
do you know what ratio the primary drive is?
crank to clutch?
"flat bickie"

Offline jimson

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Re: Sprocket size for a poor man
« Reply #5 on: March 23, 2008, 11:25:58 pm »
Vandy is this what your after  Helical gear 23/58  2.522:1 hope this helps.jimson
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Offline vandy010

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Re: Sprocket size for a poor man
« Reply #6 on: March 24, 2008, 02:25:49 pm »
that seems like a pretty tall primary drive, as a comparison my little mx is
74/19=3.894

here's what i do and i'll use my mx125a as an example,
  primary=74/19=3.894+
 top gear=22/23=0.956+
      final=49/12=4.083
                      =8.933
on my mx125, it still struggles a little with the taller gears and i'm thinking of going down to a 51t on the rear just to liven it up a little more.
to do all that math on your figures you'd be looking at around a 65/12 final drive with the 428chain. pretty close to what Doc was saying.
so yours would be,
primary=23/58=2.522+
      top=22/23=1.045+
     final=65/12=5.416
                     =8.983
i'm just thinking back to some pictures i've seen of Hodaka's and from what i recall, they mostly have large-ish rear sprockets.
just a guide and hope it helps.
"flat bickie"

Offline jimson

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Re: Sprocket size for a poor man
« Reply #7 on: March 24, 2008, 09:05:01 pm »
Thanks Vandy so 12/65 +17rear wheel now the hunt begins  :-\ the sprocket will look like a dinner plate on a 17 wheel  ;D jimson
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Offline vandy010

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Re: Sprocket size for a poor man
« Reply #8 on: March 24, 2008, 10:11:41 pm »
um? i overlooked the 17" wheel part.
allow for that wouldya...
any other brains out there with ideas?
"flat bickie"