sprocket change M900

[lwszabo]

I was thinking of dropping a tooth in the front, or adding 2 in the back. I took my bike in for service, and the guy said I had a 41 in the back...it think stock it 39 right??? If I still dropped 1 in the front would it be a drastic change? are there any negatives to this?

[Duck-Stew]

There are some who feel the 14T fronts are a little too tight in radius for the 520 chain and that the gearing changes should occur on the rear sprocket only.  Personally?!?  The 14T front *may* shorten the life of the chain a bit...but hey, there's a cost for everything you do, so...

If you're running 15/41 right now then you may want to try 15/43 or 15/44 even...  It's all personal preference really.  I'm going to be changing my '95 M900 from 15/39 to 15/38 next week.

[greenmonster]

Carb stock is 15/39, ie 15/38.

[dlearl476]

are there any negatives to this?

What is your goal?  I went from a 41t rear to a 39t rear because I couldn't ride my '99 M900 in a parking garage without constantly feathering the clutch.  39t is just about right.  IIRC, with a 44, you'd be doing about 25 mph at idle, are you sure that's what you want?  It would lower your RPM at cruise, but IMO it may be difficult at slow speeds.

[Howie]

What is your goal?  I went from a 41t rear to a 39t rear because I couldn't ride my '99 M900 in a parking garage without constantly feathering the clutch.  39t is just about right.  IIRC, with a 44, you'd be doing about 25 mph at idle, are you sure that's what you want?  It would lower your RPM at cruise, but IMO it may be difficult at slow speeds.

 

[lowendmonster]

39 tooth is stock.

I went to 42.

Dump the clutch and hold on.

[BumpaD_Z28]

I run 15/41 on my '99 M900 ...

I originally tried 14/41 and although GREAT around town / canyons I felt that it was too low geared for the freeway runs ...

~DaVe

[Porsche Monkey]

What is your goal?  I went from a 41t rear to a 39t rear because I couldn't ride my '99 M900 in a parking garage without constantly feathering the clutch.  39t is just about right.  IIRC, with a 44, you'd be doing about 25 mph at idle, are you sure that's what you want?  It would lower your RPM at cruise, but IMO it may be difficult at slow speeds.

Think you got it backwards there buddy.

[Duck-Stew]

Think you got it backwards there buddy.

+1

Carb stock is 15/39, ie 15/38.

I know that in the US a 1999 M900 was 15/38 as stock because my M750 was mis-geared at the factory.  It should've been 15/40 but was 15/38...

[dlearl476]

Think you got it backwards there buddy.

Thats what I get for posting at work with people talking to me. 

[lwszabo]

What is your goal?  I went from a 41t rear to a 39t rear because I couldn't ride my '99 M900 in a parking garage without constantly feathering the clutch.  39t is just about right.  IIRC, with a 44, you'd be doing about 25 mph at idle, are you sure that's what you want?  It would lower your RPM at cruise, but IMO it may be difficult at slow speeds.

I think you are a little backwards, but I understand what you are trying to get at. My goal is to make the bike more rideable down low, but i just found out my bike was running very, very rich, to the point it almost quit running....so its in for new plugs, re-jetted, belts, etc......so Maybe the gearing will be perfect!!!

[ab]

I have question along same lines and get confirmation.  I just ordered chains/sprocket (14/46 and 520 - my current settings) but am thinking to send back the sprocket and get back to stock due to the rubbing chain issue(DMF thread explained the chain rubbing noise could be because of the front sprocket) .  Is stock setting for 620 15/46 ?  The bike has been dyno and setup with 14/46.  If I go back to stock, would I have to get the pc commander mappings and the other engine work dyno again and optimized?

[erkishhorde]

I have question along same lines and get confirmation.  I just ordered chains/sprocket (14/46 and 520 - my current settings) but am thinking to send back the sprocket and get back to stock due to the rubbing chain issue(DMF thread explained the chain rubbing noise could be because of the front sprocket) .  Is stock setting for 620 15/46 ?  The bike has been dyno and setup with 14/46.  If I go back to stock, would I have to get the pc commander mappings and the other engine work dyno again and optimized?

I really don't know much about dynos but...
While sprockets will affect the dyno readouts, the bike doesn't need to be dyno'ed again after sprockets are changed. Changing sprockets should shift the entire dyno chart up/down depending on what you do but getting the bike dyno'ed is used to change fuel/air mixture settings to smooth out curves and whatnot to get better engine performance.

If your 620 is '05+ I think your stock setting was 15/48 and if it was pre-05 it was likely close to 15/46. I got those numbers from the CA-cycleworks site.

[GAAN]

you are right

5 speed 620 stock ratio is 15/46

6 speed 620 stock ratio is 15/48

[Teutonics]

I was thinking of dropping a tooth in the front, or adding 2 in the back.

14/41 here and loving it. 

However, I do very little highway/slab riding, although have done some and didn't think the gearing was excessively low for moderate (80ish) highway speeds.  Changing back to 15/41 takes just a couple of minutes if I knew I was going to do some long distances.