Where to buy lower tooth rear sprockets?

[isaac]

I know this has been gone over, but I've searched and can't find where to actually buy the damn things. I usually go through ebay or bikebandit for this kind of stuff. I'm looking for a 38 tooth rear.

Of course I'm sure a few of you guys are thinking about how a 38 tooth won't work and all. Too tall, not enough power on the open road. Keep in mind I'm in Florida. We're pretty flat here. I've had a 16 tooth front for a few hundred miles and it's a nice change but it's not low enough revs for me on the 50mph roads. That's just how I like it. I don't care about the marginal changes in acceleration because this thing's not beating much anyway and I probably mitigated it with all the mods I've done.

So ideas? Thanks!

[Water Warrior 2]

Check with Bike Bandit. Their site says they are having a sale on JT Sprockets that will fit a GZ.

[jonathan180iq]

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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)

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)
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[jonathan180iq]

If you go with a 38 in the rear and still use the 16 up front, I don't know that you'll be able to roll from a start in 1st.

Final drive gearing alone is going to drop from 2.56 (with 16T) down to 2.37... That's a crazy amount of difference.
The switch from factory 15T to a 16T up front lowers the final drive from 2.73 to 2.56. You're going to double that drop if you go with a 16/38 combo. So you would be looking at going from the stock 2.73 down to 2.37.... I wouldn't do that.

15/38 would give you a 2.53, which isn't all that different from simply leaving in the 16T. If you want to do this, I wouldn't go lower than a 40T in the rear, which is only a 1 tooth drop and will give you an overall drive ratio of 2.5 even.

[Water Warrior 2]

A little further thought has lead me to think you wouldn't like the change. Flat ground or not you might be in 4th gear more than 5th. The GZ just doesn't have the power to pull a 16/38 gearing. You are asking the bike to do something it was never meant to do.
Likely you will need a new longer chain too so the investment will be a costly experiment if it doesn't work.

[isaac]

The 16 made me have to adjust the wheel forward. The 38 will make me adjust it backward again. I'm thinking it comes out in a wash. But if we're dealing with worst case scenarios, I'll deal with the 10 minutes it takes me to add a link to the chain.

As for rideability and the 7.3% reduction in mechanical advantage (rectified with the downward press of the shifter), considering I've already experienced the purportedly devastating ~7% drop in mechanical advantage with the 16 tooth front sprocket for a few hundred miles now with no ill effects, I think I'm prepared for that. I'm not too worried about the possibility of having to swap back. It's not like I'm experimenting with compression ratios. Ten miles worth of new rear sprocket is a 20 minute easily resellable mistake I'm willing to make.

I appreciate the sprocket specialists and bike bandit sale suggestions. I'll look into it. If I go ahead and do this, I'll be sure to report back about whether the bike can still cruise well at 60-70. This engine sounds like it's murdering itself above that speed anyway. Considering how very rarely I'm on the freeway, even if it loses a few mph I'm not sweating it. On my 30-minute ride to my brother's house (the longest I go with any regularity) the fastest road is a 50mph stretch of two lane for about two miles.

[Water Warrior 2]

Keep us updated. Actual results may be quite surprising.

[bwader]

I wouldn't do it, but I'm curious of an update or if someone tried a 15/40 15/38.