Sprocket Questions, lowering RPM at 40mph.

[daftduc]

Yeah there seems to be a number of threads already on this but I wanted an OP specific to my questions.

'03 M1000

Current setup is 15 front/ 39 rear.  I'm not the original owner but I believe this is stock.  The rear sprocket is part Z39 with a ducati logo on it. 

Any recommendations on front and rear size?  Is there a standard mod that people go with? 

One thing I'd like to adjust is when I'm cruising at 40mph I'm right at the highest RPM I care to be in 2nd but too low when I'm in 3rd at that speed.  Which way would I want to go to make 40mph not as high in 2nd?

Higher top-end you either go larger in front and/or smaller in back, right?
Better acceleration you either go smaller in front and/or larger in back, right?

[Billyzoom]

For lower rpm at the same speed you'd go with a larger front or a smaller rear.  It doesn't necessarily give you more top end speed as your engine may not have the power to able to pull the gear as high as you'd like.

I run a rear sprocket that's two teeth smaller than stock, as I don't have trouble from stops and like the lower rpms at fwy speeds.  But my bike is a S4Rs, which has a ton of power and doesn't struggle with the low revs.  Having said that, I would have been happier only changing one tooth rather than two.  I may change to one tooth smaller than stock or go back to stock.

For higher rpm (or easier launches from a stop, which is the more common reason) you'd do smaller front or larger rear. 

I think the general thought process is three teeth in the rear are roughly equal to one tooth in the front.  In your case I'd say dropping one tooth in the rear would be a good option for you.  Any more than that and I think you might suffer elsewhere. 

Joel

[brad black]

15/43, use 3rd.

[daftduc]

15/43, use 3rd.

Hm, but I like being in 4th between 55-70. 4000rpms seems the most pleasing cruising speed to me (engine sound, among other considerations, is at the perfect hum/rumble for me) which I'm right at when going 60mph in 4th.  Would the 15/43 setup make me need to be in 5th then?

Does anyone know the ratio between changing front size versus rear in relations to RPM change.  Like one tooth change in front makes 100rpm difference while one tooth change in rear makes 50rpm difference?  I realize there's probably a number of factors that influence this but in general I'm just asking for.  

-Thanks for the responses

(not that it matters too much but after taking my bike out I noticed it's actually hitting 4250rpms in 4th at 60mph.)

[Speeddog]

1 tooth change on the front alters rpm by 6.7% (1/15).

So your '60mph in 4th gear 4000 rpm' would change to 4267 going from 15 to 14.
It would make your 60 mph in 5th a 3763.

Up 4 teeth on the rear alters rpm by 10.25% (4/39), so changes your '60mph in 4th gear 4000 rpm' to 4410.
It's *roughly* the same jump as between 4th-5th and 5th-6th.
It's about half the jump between 2nd and 3rd.
It would make your 60 mph in 5th a 3872.

Up 2 teeth on the rear alters rpm by 5.1% (2/39), so changes your '60mph in 4th gear 4000 rpm' to 4205.
It would make your 60 mph in 5th a 3692.

More info here (from Brad Black)
http://www.bikeboy.org/ducgearing.html

[Slide Panda]

http://www.gearingcommander.com/

[daftduc]

http://www.gearingcommander.com/

That's a cool site.  Thanks.

[Armor]

So you will never use 6th?

[daftduc]

So you will never use 6th?

I actually never have.  I didn't even know I had a 6th until a couple years into owning the bike.  I've been to 130mph and felt that was all she had thinking 5th was it.  Not sure if I'll ever take it up there again to even try 6th. 

[J5]

standard mod is -1 on the front

[MotoPsycho]

Stock for me was 15/41. I did 15/43 for the exact same reason and I'm pleased with the results. But I have a 5spd, not a 6. Hope that helps. I think 60mph puts me about 4800-5000 rpm or so. I still get decent mileage and have a little oomph left for the passing lane.

[Dry Martini]

On a 6 speed monster with factory gearing, 6th gear is superfluous.

I first went -1 in the front and was pleased with the results. I could actually use 3rd gear in town w/o lugging the engine. When it came time for a new chain/sprocket combo, I decided to +3 on the rear. That has been equaly pleasing. Now 6th gear can be used at highway speeds, cough80+mphcough and still keep the RPMs out of the cellar.

The monster line is gear too tall from the factory to start with. I would not want to make it any worse.