Hello all,
I've had a GZ250 for almost a year now. I love it. It does everything I need it to do. I would however like to take it down the highway at 65-70 MPH without feeling like I'm killing my sweet machine. I have read many posts in which the front sprocket was changed from the stock 15 tooth to a 16 tooth. This would take the gear ratio from 2.733 to 2.5625. I have read a lot of complaints that after the switch the top end speed goes south. If I were to change the rear sprocket from the stock 41 tooth to a 40 tooth it would give me a gear ratio of 2.666. That would fall pretty much in the middle of the differential between a 15 and 16 tooth front sprocket. I'm thinking that the one tooth off the rear sprocket will be enough to keep the bike in it's power band therefore allowing maybe a little extra power at highway speeds while simultaneously reducing the rpm's its kicking out and all the while improving the MPG's. (I know I'm a dreamer) If anyone has tried this mod please share your results.

Welcome!

You didn't tell us where you are......and the riding geography has a good bit to do with it .......and this doesn't answer your question.....BUT:

65-70 is still doable on the flat without a significant headwind with a 16T sprocket, but it takes a while to achieve 70 and you can't maintain that over anything but the slightest hill. It does, however, allow you to maintain 60-65 under adverse conditions (headwind or uphill) in 4th for short stretches. This is my experience with a 180 lb. rider and a large windshield.

I suspect the answer to your question is: NO. Changing the front is so quick and easy I doubt anybody has gone the other route. Is there a reason that you don't want to try that first ??

A rear sprocket change wouldn't kill anyone. I'd say if you can get one and put it in .... more power to you. No pun intended.

So knowing that i'm completely ignorant to the subject what would happen if you had a 16 tooth front and 40 tooth rear.

You would want to be going downhill a lot and rarely use 5th gear except under ideal conditions. A 40 tooth rear sprocket might be just the thing. Pulling off the rear wheel is easy. Try it and let us know how it works.

+1!

Yeah, and Bob tells us that changing your own tires is easy too !!!

One man's food is another's poison.

Thanks for the responses. Looks like I may get to be the first to try this one. I found the 40 tooth rear sprocket at http://www.sprocketspecialists.com/ for $53. The item # is 461-40. Their website lists it as being for a 1999 - 2004. I called them today and they said that it will work on current GZ's. My father has been a mechanic for better than 45 years which in my case means that I realize what it means to be a mechanic and that I am not one. It always ends up with excessive cussing and broken stuff. I am fortunate enough to have friends that are good at turning wrenches on bikes. I'm in Northern Indiana so it will be a little while before the weather will allow any significant riding. When I have this mod done I'll let you guys know the results. Does anyone know how to calculate the rpm's it'll be kicking out with the 40 tooth rear sprocket at 70 mph? I don't want to run on here but, I have felt the joy of the seat on long rides like many others on this post. The aftermarket seat choices are slim and expensive. Has anyone taken their seat to a furniture upholstery place to have stiffer foam put in it and re-upholstered?

Boy have I got a deal for you!!

If you can wait until (late) spring, I'll give let you ride a 16T to gauge the difference.....before (or after) you go to all the trouble of changing the rear. I'm in Central Illinois and, unless you are in FAR NE Indiana, we could make a good day trip out of it.
....AND.....
I have a spare seat for sale, cheap. I tried the re-upholster route and did exactly the WRONG thing to it; basically am selling it for the pan but the new cover is really nice......although totally the wrong shape for me.

What leads you to believe you need stiffer padding?
I REALLY don't think that is the problem.

P.S. Being in Indiana, I don't suppose you have many hills, so if you don't plan on doing much Interstate riding, then I can't see the point is spending twice the money and at least twice the time changing out the rear for just one tooth. I rode mine to Atlanta and back last year......and did just fine, through the mountains, but NONE on an Interstate.

Hey gahmp, about the seat "enjoyment" issue, check out my seat mod, it works for me.

http://www.gz250bike.com/forum/viewtopic.php?f=9&t=1599

How about a follow up. Did you put the rear sprocket on? If so how did it work? I'm thinking about doing the rear sprocket for the same reason. Did the front and the carb mods but in 5th it just falls on its face.

Don't know how throughly or carefully you read all the previous posts about the 16T front but I had been trying to emphasize the situations where is is NOT apporpriate to up the gear ratio......by any means, including a rear change.

Riding in situations where "falling on it's face in 5th" is a serious consideration is one of them.
My recommendation is to put it back stock......but if you have the time and the money to try and "fine tune" it, then go for it !!!

That's exactly what I am trying to do. The power band just seems to lag off in 5th. It is slow to get to 60-62mph and that it about top end with throttle to spare. The 40t rear might just bring the r's up to where there is a little more power in 5th. But still, I have to justify 50+ dollars and time to do the swap.

Yes, most of us KNOW that already. Suzuki did a good job engineering the final drive ratio right on the EDGE of the Horsepower limit.

If performance in 5th gear is of primary concern to you......and it sounds like it IS.....then you should PUT THE STOCK 15T SPROCKET BACK ON THE FRONT. Easier and cheaper and guaranteed to work.....unless you have mucked something up in the carbs.

The GZ doesn't have enough engine to spare. Re-gearing on both ends for more speed/lower RPMs will probably put you past the limit for any 5th gear usage unless you are going downhill. I personally think Suzuki got the stock gearing as good as possible without sacrificing bottom end or top end performance with the available power. This wonderful little bike was never meant to run down the highway and keep pace with traffic at higher speeds. City streets, 2 lane black top secondary highways is where it shines and is happiest.

While you and I are in basic agreement here, I think we disagree on the detail.

If you need a bike that will "keep up" on the freeway, then you got the wrong one with a GZ......in ANY configuration. With it's stock gearing, it will BARELY keep you from getting squashed.

With that in mind, I think it is a MUCH better city and back roads machine with a little higher gearing. You can "cruise" in the city in 3rd or 4th....and run it up to 60 if need be to launch you into 5th, which is pretty much useless IF you think you need to go fast.

If you can accept that you aren't going to go fast and stay at that speed (above 65) for very long AND it takes a while to get there..........then the 16T front makes perfect sense. Most who try it love the result.

BUT IT IS NOT FOR EVERYBODY; nobody ever said it was. I've got a hunch that those who can't STAND to loose 5 mph or so on the top end aren't going to be happy with the little beast very long anyway regardless of what you do to it.

And then there are those who LOVE their GZ but seem to be incapable of resisting temptation....

There still are times I wish I had it back.

In theory, the lower rear sprocket (40T) with a 16T front sprocket should work well as predicted.
My Yamaha 650 (I know, bad comparison) comes with a stock 17T/ 34T sprockets. Many owners are going to a 18T/30T ratio. The R's go down along with the vibrations. Will it work with a GZ? ...

The cost of the sprocket at $52.99 is really high. Plus it is aluminum, not steel. How long will that last? I'd rather have steel.

Is the GZ chain a 520 or a 530?

TIME OUT !!!

Something is wrong with this picture.

I had to go back to the beginning of this thread and get the rear tooth count........
SO......
Increasing the teeth on the front makes the gearing "taller"........
Decreasing the tooth count on the rear does the SAME THING, makes the gearing higher.

Upping the front one tooth PLUS dropping the rear one would make matters even worse (top end loss).

I think the intent was (or should be) using a 40 rear with a 15 front.

You know what, that just may work. Funny how THINKING is such a hard process at 50+ years.

That is just because of all the accumulated knowledge and an overworked filing system. You can reboot the system with a pleasant ride in the country and a few twisties for good measure.

Gz chain is 520

Yes you are right that is a horrible comparision, if you have something with plenty of grunt to spare, then doing that could dramatically raise the ridability of your bike at higher speeds, (and raise your top speed for that matter) but considering the GZ barely has enough grunt to go "high speeds" in the first place, if you lower the rpm's at higher speeds (on the weak GZ) then you take away the only power the GZ has at high speeds in the the first place. It just simply doesn't have any torque to spare to sacrifice any for higher speeds, there are riding lawn mowers out there with more HP/Torque than the GZ has.

I did not say horrible, I said bad. Bad is dropping your bike and skinning your knee. Horrible is dropping your bike and then realizing your leg fell off. Afterwards, everyone nicknames you Eileen.

By the way Music man ... what is high speed to you?

I think the chain is a 520 don't you?

I did not mean that in any kind of derogatory terms whatsoever, I am sorry if it came across that way. And by the way, yes the GZ does have a 520 chain on it.


And high speed to me (on a motorcycle) is whatever the speed limit on a given road is,+10-15mph, that is high speed to me, if you need to go any faster than that, then you are definitely trying to modify the wrong motorcycle, and also need to find a Track where you can get some laps in on, because you don't need to be going that fast on a public road, Period, much less on a motorcycle.


Again I did not mean anything derogatory, I guess using the word horrible was a little extreme.

Speed wise ... I agree, on the x-way Raven gets to 80 and is a little light in the rear at that speed. 70 is fast enough for me when I need to use the x-way. Which is not a lot.
So, when are you buying that sprocket? We need a tester (Guinea pig).