Gearing the other way... for highway use

[rtking]

I've read the thread regarding changing the stock 14T counter sprocket to a 13T piece with keen interest. Sounds like a solid plan for those who do a good mix of trail riding and pavement.

But in SoCal, it seems that we're a concrete jungle, and there's lots of highway droning to get to any kind of trails. (At least, that's true of where I currently live.) And despite a 65 mph speed limit, riding at 70 - 75 is more often the norm than not.

The RX3 does fine at 70-75 mph, and I'm confident it can do it all day long. But sometimes I need to go a bit faster, and I've noticed that I'm spinning the engine past its power peak (which happens to be the 9,000 rpm redline.) I spoke with Gerry at CSC and he has been using a 42T rear sprocket and loving it, especially since he's got a long highway commute.

The 42T sprocket is about 5% taller than stock, so at my current peak speed, I can expect to drop 200-300 rpm. I thought about it over the weekend and put in the order today for the rear gear. At $35, it's inexpensive enough to try and, if it doesn't work, I can certainly re-install my 44T rear sprocket.

I'll report results after I install the sprocket. And in a few weeks, I hope to receive the windshield from forum member Winyoochanok and see if that makes a difference in top speed.

[SpudRider]

Good for you. I'm sure you will be pleased with the reduction from 44T to 42T. It is very nice to have a selection of sprockets available so we can tailor the final gear ratio to the type of riding we prefer.

[keithmaine]

Spud, this could turn into another dual sprocket thread like over on the TW200 forum

[SpudRider]

[Juanro]

I've installed a 15z front sprocket some 2000km ago and I'm loving it!

[SpudRider]

Originally Posted by Juanro

I've installed a 15z front sprocket some 2000km ago and I'm loving it!

Where did you purchase the 15T front sprocket?

[Juanro]

From a local manufacturer ("Catalano", http://www.catalano.com.ar/ in Argentina). I originally put the one for Suzuki DR350 but after Reading a post of yours about the difference in size (half a milimeter) checked the catalog and switched to the one for the Beta Chrono 2.5 (I don't know if that bike is available elsewhere with that or other name).

[rtking]

Thanks for the great info, Juanro! So with a 15T/44T combo, you have an effective 2.93:1 drive ratio (versus the 3.14:1 stock for the 14T/44T sprocket combination.) That's about 6.7% taller.

Can you tell us if gearing taller has allowed you to reach higher highway speeds? How is passing power in 6th gear?

I'll have to look into the Catalano catalog. I see the counter sprocket on page 128 of the online catalog. This has me thinking...

[SpudRider]

Originally Posted by Juanro

...I originally put the one for Suzuki DR350 but after Reading a post of yours about the difference in size (half a milimeter) checked the catalog and switched to the one for the Beta Chrono 2.5 (I don't know if that bike is available elsewhere with that or other name).

Thanks for posting the additional information, Juanro.

Did the Suzuki sprocket fit tightly on the counter shaft? Did you measure the Suzuki sprocket to see if the measurements are actually a little larger than the Zongshen sprocket?

[kumatae]

I'm surprised that there isn't one already. I could surely benefit with a 15T sprocket with my so cal commute as well. Will be monitoring this thread...

[SpudRider]

Originally Posted by kumatae

I'm surprised that there isn't one already. I could surely benefit with a 15T sprocket with my so cal commute as well. Will be monitoring this thread...

If you are willing to risk $8.99, you can purchase a Primary Drive, C/S sprocket for the Suzuki DR-Z400S, and test the fit. These sprockets are supposed to be 0.5mm larger in spline dimensions than the Zongshen sprockets. However, if you get a tight fit on the counter shaft, these JTF432 sprockets are readily available in the United States in sizes 12T-15T.

https://www.rockymountainatvmc.com/p...rocket?v=12255

[SpudRider]

However, if you don't get a tight fit on the counter shaft, the JTF432 sprocket will damage the C/S splines, and you will need to take the engine apart to replace the counter shaft.

[Juanro]

Define "tight".
I didn't measure the sprocket, and it is cheap enough to replace one or the other without much pain.
Both fit snug to the hand in the spinning sense; and both have a Little axial play, as the holding nut can't reach to the face of it (the sprocket leaves about 1mm of exposed spline). A judicious use of spacers/washers fixed that.

Top spead hasn't increased, if any is a bit lower (in 6th). Overtaking reaction is still good, specially if you keep rpms above 6/7k. If not you can always downshit, a quick fix being a motorcycle. I'd say that 5th gear now is about the same as it was 6th before, leaving me with a 6th/overdrive for relaxed cruising (I'm lying myself, I don't cruise relaxed haha)
At high speeds, rpm droped about 600rpm for the same speed, or speed increased 5mph for the same rpms.
Overall very satisfied with the change. There was some fear that the bigger sprocket will not fit, and indeed is a snug fit (chain passes mere milimeter away from the clutch vertical axle and the gear change lever) but in the end if Works very well and doesn't rub any part.

[SpudRider]

Originally Posted by Juanro

Define "tight".
I didn't measure the sprocket, and it is cheap enough to replace one or the other without much pain.
Both fit snug to the hand in the spinning sense; and both have a Little axial play...

Thank you for your prompt reply.

I am interested in radial tightness, or 'spinning sense.' You stated both sprockets "fit snug to the hand in the spinning sense." Was the Suzuki sprocket as tight in this sense as the Catalano sprocket?

[SpudRider]

The JRF432 sprocket fits many Suzuki motorcycles, including the following bikes.

DR200
DR200SE
DR-Z400S
DR-Z400SM

Can anyone measure one of these sprockets with digital calipers? FastDoc has a DR-Z400S. I wonder if he has a spare C/S sprocket he can measure?