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Old 01-25-2013, 07:33 AM   #16
Island Hopper
gunnerbuck's Avatar
Joined: Nov 2005
Location: N.V.I, B.C.
Oddometer: 4,345
Originally Posted by Hockeygod View Post
My 640 came with modified (lower) gearing. It has 15-44, so quite low. While excellent in the dirt, it doesn't like to go much over 60 mph / 100 kph! Not sure what rpm (can't remember) but it is revving high and some vibration is more noticeable than normal.

I primarily ride it from home on backroads, searching gravel and dirt, but wouldn't mind a little less buzzy on the pavement (running DOT knobbies and won't change until they are worn out - already have two of the same waiting to go on). I might have to ride 100 KM's one way to get to the dirt / gravel goodness...

One day I hope to ride the Divide (portions thereof) from Calgary AB to Moab, then backtrack to join up with the TAT heading west to Oregon, then home through WA / ID / BC. It would be nice to do it all at once, but life dictates this to be done in stages. Might try to transport bike part ways or heaven forbid, ride more pavement than desired to quickly get to the starting point / hurry home at the end.

With these parameters in mind, what say you inmates in the know?

Should I go to a 16 or 17 tooth front if I keep the 44 (being frugal... the 44 is a supersprox and in great shape. The front is starting to hook so will need to be replaced this spring. Need to check the chain.) Sounds like I will have to either modify or replace the chain guard if I go up to a 17; will I need to also get a longer chain / flip the blocks?

Thanks for your help / opinions in advance.

I run a 17/45 on one of my bikes... This is just a very slight lowering of gearing over stock... With a 17 tooth counter sprocket you either need to grind the hook out a bit on the case guard or order the part # guard for a 640 Duke... The larger sprocket combo offers a few small advantages:1- The chain touches the swingarm less so the rub block will last longer..2- The larger sprockets will mean less bend on the chain for smoother running and possibly longer chain life...

If you go with the 17 front you will be geared a minute {unnoticeable} amount higher than the stock 16/42... I would of gone for the 17/44 combo if a 44 tooth sprocket was easier to find... I ride my bike everywhere with my decided gearing and in the tight stuff slipping the clutch becomes my low gear... LC 4s have very strong, long life clutches...
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