From what I've read there are two main camps about sprocket changes 15 to a 16 tooth or one tooth more in front.
1st camp: Believes that 5th gear is rendered useless but all the other gears are a better range.
2nd camp: It is so much better overall and 5th gear is at lower rpms although top speed is unchanged. Something like that. Pretty much all gearing changes are "shifted" up in speed a little.
I know from riding my GZ around 1st to 2nd is a few feet or 10mph
2nd to 3rd is 20-30
4th to 5th is 30mph-40mph
5th 40mph+
I think I might just keep it simple for a while
I'm just writing down some stuff relating to cc's, mpg, and acceleration, stuff that comes to me right now. Feel free to ignore this post, but I'm trying to figure out certain things in this post.
Call it a brain quirk!
If you change your sprocket by a few tooth, top speed will be largely unaffected, and takeoff will feel a bit nicer, as you need to upshift less frequent, those first gears.
If you change it by more than 4 teeth, top speed might actually go down, and takeoff might become slightly harder (more clutch work), but the rewarding thing is that gearshifts feel a lot better!
If you change it by more than 25% (eg: 48T to 34T, or 43T to 31T), you can reach top speed in the second-to-last gear, while final gear will be a nice cruising gear, low RPM, and high gas mileage, in the usable range. Final gear will not become useless but quite often on a lot of bikes, instead of using 5th gear on a stock bike, to go from 30MPH to 80 or 100MPH, you can use it from 40MPH to 80MPH, and have plenty of better MPG results in that range!
If you want to surpass the 80MPH, you might need to downshift one gear, to get the RPMs up, to have sufficient torque/HP to accelerate.
The final gear would be called an overdrive gear.
It all depends on your bike too, but many bikes out there, are running 5-6k RPM on the highway @60mph, and for anything larger than a 150cc, that's highly unnecessary.
A 150cc needs the higher RPM's to have the torque/HP to keep up speed, but a 250cc scooter/chopper/bobber/cruiser can easily run 60MPH @ almost half the RPMs (3k RPM). No need for it to rev to 6k rpm.
It also depends on your driving style, and terrain; but most people going 60MPH, do that on the highway or interstate where it's usually long and boring continuous speed riding.
If you do have to surpass a slow truck on the highway, you can always upshift one or two gears, and have plenty of power to surpass it.
If you're into track racing, hill climbing, or are living in Hurricane land where the winds never are lower than 60MPH, you might actually prefer the bigger sprocket that can keep your top speed more constant, and give you better hill-climbing abilities.
But for the most part, on reasonably level ground,
A 500cc could run 60-70MPH at ~3k RPM, and a 750cc could run 80MPH @3k RPM.
Any of those engines need to build more torque to go faster at some speed, meaning they need higher RPMs, but I'm still into establishing what the best gearing is for cruising on a variety of engine sizes.
I find it a highly fascinating topic, how CC's and gearing could influence MPG, top speed, and acceleration!
There's a lot you can learn from these 3 variables (cc size, gearing, and acceleration), and how they can limit or extend your preferences on a bike (like eg: better or worsen your expectancy of MPG, or acceleration...)!
It's interesting to see that not everyone choosing for a 1,4 liter cruiser bike, has the bike that is really suited for them. In fact, if you want to get max gas mileage out of a 1,4 liter 4 cylinder engine, you'll need to put such large gearings on it, that at 2k RPM the bike is going 80MPH, and at that point it can not surpass 65-70MPG anymore.
So unless your plan is to ride a bike constantly at higher speeds than 80MPH, don't get a 1,4 liter bike; in fact, forget about any motorcycle above a 1 liter engine at all in this society where top speed is limited to 75, 80 MPH anyway!!
Most of those huge bikes (800cc+ even), are used to show off, and ride in a city @35mph, where not even 15% of the engine is used.
CC is directly related to how heavy of a gearing you can put on a bike. And MPG is directly related to how hard you want to feel acceleration kick in.
Almost any motorcycle below 600cc can reach 100MPG, without too much effort just as long as it has a tall final gear ratio.
If the engine size becomes too big, in order to get 100MPG, the engine must run at very low RPMs, and have a very tall gearing, to the point where that engine is running extremely inefficient!
Too small engines need to rev too high, and lose MPG as they rev higher, and wear out faster as well, and they often don't have the torque to quickly accelerate 20MPH higher when already going at a high speed .
I think so far, what I've learned from motorcycles and scooters, is that:
Optimal MPG's (100+MPGs) are achieved when a bike cruises as fast as possible with it's RPM's as low as possible. In practice that means a tall final gearing, at speeds around ~35MPH with RPMs between 1,5k and 2k.
35MPH is some kind of barrier, where wind resistance increases exponentially; logarithmically even!
There's very little wind resistance to overcome below 35MPH, but above it, resistance multiplies almost ten fold, when speed doubles; one of the main reasons why it takes so many extra cc's to get only a tiny bit faster.
In a real life situation,
Most people riding only in city or suburb traffic need a 75-100cc.
Most people riding very few highway rides, need a 150cc.
Most people riding frequent highway rides, need a 250cc.
You can add about 50cc extra if you have a passenger with you in above examples.
Most people riding long distance rides (daily highway rides, or frequently longer than 30 minutes highway riding) need a 300cc, and 500cc for frequent rides of more than 1 hour on the higway.
I would only get a 600 or 750 cc motorcycle, if I where to ride hundreds of miles a day, or did frequent long rides of at least 5 hours on highway speeds; and a 900 cc only makes sense if you want all of the above, AND you want to take a passenger, and luggage racks, a radio, and large windshield, etc... It makes no sense to get a 1600cc bike, when a 900cc bike can pull exactly the same, at better MPGs!
I think the above is a rough estimation, and meant for cruising, or mobility purposes. Not meant for sport or racing bikes.
From a certain point of view, it makes no sense to get anything beyond a 500cc cruiser bike for most people, as a 250 < x < 500cc engine can get you almost anywhere at an unbeatable gas mileage!
