Do whatever feels right. On my bike, I use the "rule of 10"- that is, at every multiple of 10 MPH I travel, I shift into that gear. Thus, at 20 mph, I hit 2nd; 30 I hit 3rd, 40 is 4th, 50 and up is 5th.

 

Only one drawback to running the engine "too slow" (and that would be very slow)...your battery might suffer as the charging voltage could be low unless you have a dual stator machine, which a 900 does not have.
But like what Pat said, what ever you and the engine are comfortable with.

 

I rarely rely a tach to shift by. I shift up when it feels right, so I go more less by the seat of my pants. As long as the engine doesn't lug or ping when you upshift, you're not going too slow in whatever gear you happen to be in. OTOH, it's probably not a good idea to be going too fast in a lower gear causing the engine to overstress, but I don't know if the 900 engine can be unintentionally overstressed. It's a revver to begin with. Can't say what it would do to your gas mileage.

 

when you're riding down the road on flat terrain, doing the speed limit and pacing with traffic in front of you, is it more fuel efficient to let the RPMs be a little high in 4th gear, or should you shift to 5th to drop the RPMs, even though your speed might cause a little lugging on the engine?

To directly answer your question, no and no.

Even though 4th and 5th gears on the 900 are close(if it is stock), you do not want to run high rpms for a long time nor should you lug the engine for a long time.

As previous posters suggested, it is "seat of the pants" and a "feeling".

I don't think it is a problem running 4th @ 50 but it is not economical and in the same respect, running in 5th at 30-35 is not efficient and if you listen, the motor does not like it.

We all have to use common sense(if ya got any) and in a politically correct sounding statement, we should be ONE with our bikes....

 

I agree with everyone that it's about what feels right, but sometimes I feel like I'm riding in between gears. Too fast to stay in gear, but too slow to shift. I dunno. Maybe it's just me. I was thinking one may be better than the other, fuel economy wise.

 

Too fast to stay in gear, but too slow to shift

Ok! Here is a scenario...

I do not want to be in the wrong gear at the wrong time. You don't want to be in that "in between" area because you could be fumbling around with either needing to brake or speed up and in a split second of indecision, you become road kill(sorry to be so graphic).

Go ahead and get your rpms to that next gear and if you need to slow down, down shift and hang there with higher rpms for a little while because you may need to hit the throttle at any given time to move out of harms way. My 2 cents!

 

If the 900s are like my 800, if in doudt, use the lower of the two gears, they like to rev a bit. Had 39 tooth sprocket on the rear, changed back to the 42, which is stock on mine and picked up 2mpg consistantly.

 

Kawasaki says you can be in 5th at 31 mph. I will shift into 5th at 35 if I'm just cruising easily, and will let the speed drop to around 31 in 5th if it looks like the speed will be steady there. I will also lightly accelerate from that speed in 5th.
While 35 in 5th might be the slowest you want to go, you should always be in a gear where you can accelerate if traffic is a concern. In traffic situations, I would probably still be in 3rd at 35.

 

I ride mostly in the power band of the lower gear than have the engine lugging too slow. The 9's like to rev high.

 

I go like that around 20 2nd around 30 3rd around 35-40 4th and usually anything past 40 5th. Last time I check I was getting 49MPG. Like some one said I will let it go down on 5th all the way to 32 and then go down in shift. But I don't drive long time with low speed in 5th. I mean use common sense u can feel if your bike is holding u back up shift if u hear it is lagging down shift.

 

Knowing when to shift is not the issue here. I guess what I'm getting at is this: which burns gas faster, a high revving engine or a lugging engine?

 

The more times the cylinders fire, the more fuel it consumes.

You can test this by doing a tank at higher revs and then a tank at very low speed.

 

When my bike starts lugging I always down shift a gear. I would rather burn a little more gas then ruin my engine or tranny.