Has anyone tried a 40 tooth rear sprocket?

[GadZukes250]

Thanks bonehead. Got the 39 tooth on order just as my 16 tooth front arrived. I'm gonna play with both configurations and see which I like best.

[bonehead]

Originally Posted by GadZukes250

Thanks bonehead. Got the 39 tooth on order just as my 16 tooth front arrived. I'm gonna play with both configurations and see which I like best.

Let me know how it turns out. I still have'nt been able to afford mine yet. I am reall interested in the 15/39 combo and what it does to top end cruising speed.

[jonathan180iq]

In a little-used part of the forum, there exists a very helpful post about all this stuff.

Possibly the easiest mod that you can do which will have a pretty drastic change to the way your bike performs is to change the final drive gearing.

The final drive of the GZ250 is a simple chain/sprocket combo. The final drive ratio is 2.73. This number is easily calculated by dividing the number teeth on the rear sprocket by the number of teeth on the front sprocket. In our case, since we have a factory sprocket combination of 15 and 41 (15 teeth in the front and 41 in the rear) the calculation would look like this.

41 / 15 = 2.73333333 (or 2.73)
The lower the gearing, the lower the revs. The higher the gearing, the higher the revs.
You'll almost never want to change any sprocket more than one or two teeth sizes in any direction over the factory number.

By comparison, switching over to a 16T front sprocket lowers the final drive ratio to 2.56 (41/16)

Switching between a 15 front and 40 rear would be the PERFECT combination of lowering highway revs while maintaing climbing ability, I would think. (40/15) = 2.666666667 ratio.

What does this mean in practical application?
The 16T front sprocket lowers cruising revs in all gears and allows the lower gears to be used for a longer period of time. However, you will probably notice a drop off in your top speed. While the factory gearing allows the GZ to reach somewhere around 80mph, the 16T front sprocket will lower that to around 70mph. The reason being that the internal gearing of 5th gear has a ratio of .818, which is basically an internal overdrive and seems to make the gear too "tall" for the mighty GZ to handle.


Where can I purchase a new sprocket?

The Suzuki factory part number for a 16T sprocket is 27511-37200
The JT Sprockets part number is JTF 434.16

Sprocket Specialists make both front and rear sprockets for the GZ250.
The front sprockets are available from size 10-16. Part number: 528-(number of teeth)
The rear sprockets are available from size 28-74. Part number: 461-(number of teeth)



How do I change my front sprocket?

http://www.gz250bike.com/viewtopic.php?t=317

[mrlmd1]

Jonathan you are indeed the Lord of the Forum, and welcome back again.
That post was friggin' incredible and right on the money with objective science behind it instead of subjective " I think this", or "in my limited experience, do that".
Way to go! :2tup: :bow:

[jonathan180iq]

Well, there are a couple of places when I said "I would think". But still, thanks.

I spent a lot of time compiling lots of info regarding that type of stuff. It often gets looked over.

[OBryan]

I'm running the stock sprocket on the Front..I had someone msg me asking where I got the new rear sprocket..I'm not sure if my reply made it or not..Laffs...couldn't figure out if it got sent or not..Anyway I'll post my answer here as soon as I find out..I had a guy with a shop order it for me..I remember he said it was from a man in Tenn who made sprockets

[jonathan180iq]

Getting a custom sprocket is certainly one way to go, but you can order one from www.sprocketspecialist.com.

I hope you didn't pay an arm and a leg for it. Mosy custom people that I know waaay over charge.

[patrick_777]

Bikebandit.com has them too.

[jonathan180iq]

I miss that awesome avatar you had of some guy blowing the crap out of another guy with laser cannons and missles and such.

[GadZukes250]

Originally Posted by bonehead

Let me know how it turns out. I still have'nt been able to afford mine yet. I am reall interested in the 15/39 combo and what it does to top end cruising speed.

I just installed the new 39t rear sprocket and I love the shift spacing now for in town. Though to get higher speed, 5th needs a push from 4th to go above 65 but I got it up to 70 against a 6mph wind and minor hills in the country this morning. I think the 40t might have been a better choice though. I don't like the performance of 5th now.