Replacing Rear Sprocket

[Easy Rider]

Originally Posted by Quimrider

That 65-70mph brick wall gets annoying on the freeway.

If you do a lot of freeway riding above 65, you might have the wrong bike. <Gasp>

[Quimrider]

:??: What! you mean this bike isn't meant to drive 155 continuous miles mostly at wide open throttle? :lol: I actually did that last weekend. Something I wouldn't recommend on a regular basis.

My daily commute involves a 10 mi stint on the freeway. There are no good surface streets to take. Sometimes I take them anyway so I can have a longer ride It gets a little white knuckled at times when I can barely keep up with the morons in cages at rush hour. A little xtra headroom would help.

[jonathan180iq]

Originally Posted by Quimrider

sounds kind of interesting. let us know how the 16/42 works. I've had the back wheel off before to replace a tire. It's really not that big of a deal to take the back wheel off unless you don't have a lift or haven't made wood stands for your bike. You might even be able to get away without unhooking all the rear brake stuff, but it's just a couple xtra nuts to take off anyway. not a big deal. It is convenient how the sprocket literally falls off the wheel once the axle is taken out. I might consider going to the 15/40 if they make a 40t sprocket that fits the GZ250. That 65-70mph brick wall gets annoying on the freeway.

Sprocket Specialist part # 461-40 for the 40T rear sprocket.

[Quimrider]

Originally Posted by jonathan180iq

Sprocket Specialist part # 461-40 for the 40T rear sprocket.

Thanks for the info. Not worth $53 though. Maybe I'll try it when I wear out the rear sprocket in several thousand miles. Speaking of that, anyone know the ballpark on how long sprockets, chains are good for?

[tazzman]

I'm new to the bike world, but I was thinking, Wouldn't a 16T front and a say 38T rear work better? What would the gear rateing be on that? :??:

[Easy Rider]

Originally Posted by tazzman

I'm new to the bike world, but I was thinking, Wouldn't a 16T front and a say 38T rear work better? What would the gear rateing be on that? :??:

WAY, way too low, numerically.....2.375
You'd have to help push with your feet to get it moving and 5th gear would be useless.

[Quimrider]

38/16=2.375 That would be very tall. The engine probably wouldn't be powerful enough for 5th gear to be usable. The taller you make it the fewer RPM the engine turns to go the same speed in the same gear. It also requires more power from the engine. If you've got an 18 or 21 speed bike think of this as using the biggest front sprocket and the smallest rear sprocket. you will notice it's very hard to pedal especially from a stop.

The reason to go to a 16t front sprocket is that it spreads out the gears by making the final drive ratio slightly taller. By "spreads out the gears" I mean you don't have to shift up thru the gears quite as fast spending more time in each gear. It is many people's opinion (myself included) that the stock gearing is too close. The negative side effect of going to a taller sprocket ratio is that it lowers your top speed. About 5-10mph for the 16t sprocket.

With the factory sprocket ratio of 41/15 which is 2.73 in 5th gear you will usually run out of engine power just before or near redline (8000 RPM) which is 80mph.
The 16t sprocket would yield 2.56. So going with a taller sprocket ratio (ie. less than 2.56) you would run into top speed problems due to lack of engine power and going with a shorter sprocket ratio (ie. greater than 2.73) would put the gears even closer together and your top speed would be limited by over revving the engine.

To calculate the sprocket ratio, you simply divide the rear sprocket by the front sprocket to get the ratio.
41/15= 2.73
41/16= 2.56
42/16= 2.63
43/16= 2.69

Hope this explains things a little more clearly.

[jonathan180iq]

Yep. They're right.

[tazzman]

OK, maby bikes are differant? :oops: I normaly work on cars, and in automotive rear diff. the closer the ratio the faster the top end. Buy the way what is the base HP on this GZ250? :sad: What cuold i do to get more power out of it? Would a 300cc or400cc head (cylinder) fit the 250 crankcase? (ie. a bore and stroke job, shave the head to increase compretion,stuff like that) I like the allready talked about K&N airfilter and muffler swap ideas, but there got to be more that we can do to it, since everyone whants to go faster on a 250? I don't plan on doing much if any of this to my GZ250 (it's fast enough for in town rideing that I do) but since others seam to want to go faster and not just get a bigger bike, I thaught , why not beef it up with more power and taller gears?

[Sarris]

You'll spend more time and effort to build a GZ motor than the bike is worth. There ain't much available to fit the GZ. There are a few mods on this site to bump power, but they aren't going to do a lot. The 16 tooth front sprocket IMHO is the best as the others just make more noise and decrease mpg.

Enjoy the bike for what it is and if you want more, buy a buy a bigger bike. Keep your GZ if you can afford to, as it make a fine addition to any bike stable.

The GZ is an inexpensive, fun to drive, and high gas mileage commuter. It is what it is.

Oh yeah, the motor puts out about 18 hp.

Welcome brother.

:2tup: