OzVMX Forum

Clubroom => Tech Talk => Topic started by: jimson on March 22, 2008, 11:32:51 pm

Title: Sprocket size for a poor man
Post by: jimson 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

Title: Re: Sprocket size for a poor man
Post by: pokey 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  ;)

Title: Re: Sprocket size for a poor man
Post by: jimson 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

Title: Re: Sprocket size for a poor man
Post by: Doc 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.

Title: Re: Sprocket size for a poor man
Post by: vandy010 on March 23, 2008, 09:20:26 pm

jimson,
do you know what ratio the primary drive is?
crank to clutch?

Title: Re: Sprocket size for a poor man
Post by: jimson 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

Title: Re: Sprocket size for a poor man
Post by: vandy010 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.

Title: Re: Sprocket size for a poor man
Post by: jimson 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

Title: Re: Sprocket size for a poor man
Post by: vandy010 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?