Anyone else thinking of going to a larger front sprocket to get better mileage?  I currently have a 15t and am thinking of going back to stock or up to a 17t.  For those that have a 17t, how do you like it?

If you jump too high you will use more fuel as your making the engine work harder to turn  the wheel, Vs rev higher without working harder. i wouldnt go above stock 16 with stock 39 rear for milage. even then, im not getting much worse milage but by few miles when im nice on throttle, now when im doing abit of stomping, then i can watch the fuel just sing right on though the pipe.

Yea you in for a nasty shock ... no change in gas mileage and heck you lose top end and bottom end ... 15t works fine for all 3 - you dont lose any mileage, and gain bottom and might lose a hair on top ...
Cool.
Srinath.

Fact 1: A sprocket costs about $15.

Fact 2: From 16 teeth to 17 teeth = 6% fewer revolutions for the same distance covered.  For the purpose of this discussion, let's be generous and assume perfect efficiency from the 6% change.


Q: $15 is 6% of what?
A: $250

Q: $250 is how many gallons of gas?
A: $At $2.50 per gallon, that's 100 gallons.

Q: If I'm getting 50 mpg, how many miles do I have to ride to pay for the sprocket change?
A: 100 gallons at 50 mpg = 5,000 miles

And for all of those miles you'll have less "oomph", you'll have to rev higher to get moving from stops, etc.

I agree ... stick with 16 teeth.

Yeah the GS gets real bad gas milage anyway........

come on what other vehicle besides a scooter will go 250-300 miles on 5gal tank of gas???

Well, I could go from 15t to 16t for free.  There was a noticeable mileage difference in the 1 tooth drop, perhaps 5 miles per gallon.  I think it has less to do with the ratio and more to do with the fact that I tended to shift at lower rpms with the 16t.  With the 15t, I take it to 10 or 11k constantly when I accelerate up to 6th, where with the 16 I would shift at like 8 or 9k.  Also, I was cruising at lower rpms on the highway.

Quote from: conflicttheoristI think it has less to do with the ratio and more to do with the fact that I tended to shift at lower rpms with the 16t. [...] Also, I was cruising at lower rpms on the highway.

Good points.  The more "superslab" riding you do, the more it might make sense to at least try a 17-toother.  :dunno:

But like you said, the switch back to 16 is free.  When I said, "stick with 16 teeth" I assumed you were going to go back up by at least that 1 tooth.  Start there, I guess!  

Quote from: KerryThe more "superslab" riding you do, the more it might make sense to at least try a 17-toother.  :dunno:

I tried to make a picture of the theoretical RPM vs. MPH in each stock gear at http://www.gstwins.com/forum/viewtopic.php?p=150619#150619 .  From that, it looks like 6th gear is only 6500 RPM at about 85 mph.  I don't think I'd want less than 6500rpm at 85mph; the engine would lug.

So my first thought is that the stock gearing is already high enough for even 85mph cruising.  But I should check those "theoretical" numbers with a GPS.

yeah, but your gonna reach a point where you twist he throttle and nothing happens, specialy at the higher speeds.