So I`ve been riding around for a few weeks using a 15 tooth front sprocket and stock rear. I replaced the rear tire and put the 14 back as I will be off into the trails shortly and now it feels as if the bike doesn't pull as hard as before.
I replaced the stock D605 with a Kenda 270...it is a 4.5-18 ( isn't this technically an ever so slightly smaller tire?) instead of the stock 4.6 -18. Is this the problem? Is this maybe what others have said regarding size and weight or is there some physics as to why the smaller front sprocket doesn't feel like it pulls as much? It should actually pull more...shouldn't it?
The stock tire was pretty much worn flat in the center making it smaller in circumference but it shouldn't make that much difference should it?

 

Are you using the instrument panel or a stand alone GPS device to determine this?

 

LOL. Ok...I hear you. No just seat of the pants.

 

Its probably pulling harder, but the gears are winding out quicker than you are used to, so it seems almost breathless?

 

Ya maybe. I was just out on it again. That's the problem with seat of pants...maybe I`m expecting it to pull harder than it is with the stock sprocket lol.

Fuel mileage was WAY better with the 15t. Interesting......better than when the bike was stock.

 

The way i check to see the difference when a new sprocket is installed is to check the speed at say 7000rpm. It was close to 100km/h when i had the 14/42 factory gearing, then when i changed to the 15t the speed @7000rpm was around 110km/h and when i changed the rear to go with the 15t, the speed went up to around 120km/h.

i plan to try out the 16t but even with the 15t the space is so tight i wonder how a 16t will fit though i know some of the guys here have installed the 16t before.

fuel mileage with sprocket change depends on where you are riding, if your doing plenty of highway with higher consistent speed, the fuel mileage for taller gearing will be better than lower gearing.

 

Just changed to a 13t, and at the same time the chain was replaced (it was 5 years old when I got it with only 550 miles). Got 58mpg on the first fill - actually an improvement over what I had been getting. The big plus for me with the 13t is that now 6th gear is actually usable. That's what I was hoping for - 1st gear was low enough before.