Zongshen RX3: Sprocket Carrier Modification
 

The Zongshen RX3 sold by CSC in North America has a rear cushion hub. The sprocket carrier which inserts into the cushion hub is designed to hold rear sprockets with the following dimensions.

http://www.jtsprockets.com/fileadmin...rge/jtr473.jpg

Zongshen only manufactures the stock, 44T rear sprocket. As shown above, Sprocket Specialists manufactures the JTR473 sprocket, which is available in 37T, and 40T configurations. :)

http://www.jtsprockets.com/catalogue/sprocket/JTR473

I was told CSC will soon offer for sale aftermarket sprockets with 42T, 43T, 45T, and 46T configurations to provide more options in addition to the stock, 44T sprocket. :)

While awaiting the aftermarket rear sprockets to arrive at CSC, I decided to modify a spare sprocket carrier so I could experiment with different sizes of rear sprockets. Trimming 2 mm from each of the radial arms on the sprocket carrier, I was able to modify the sprocket carrier to accept the following sprockets, with the following configurations. :)

JTR811

http://www.jtsprockets.com/catalogue/sprocket/JTR811-48

http://www.jtsprockets.com/fileadmin...rge/jtr811.jpg

This sprocket fits the Suzuki DR200SE motorcycle, and is available for sale in the United States in 39T, 45T and 46T configurations.

JTR1826

http://www.jtsprockets.com/catalogue/sprocket/jtr1826

http://www.jtsprockets.com/fileadmin...ge/jtr1826.jpg

This sprocket fits a variety of Suzuki and Kawasaki ATVs, and is available for sale in the United States in 39T, 40T, 41T, 42T and 44T configurations. :)

The photograph below shows how I removed 2 mm from each of the six radial arms on the sprocket carrier.

http://i442.photobucket.com/albums/q...psm57bzrqf.jpg

I purchased a JRT811.46 sprocket from eBay, so I could experiment with a 13T/46T sprocket ratio for my RX3. I have now ridden about 250 miles with this lower sprocket ratio, and I like it even better than the 13T/44T sprocket ratio I installed earlier. :) Here are several photographs of the JTR811, 46T sprocket installed on my modified sprocket carrier.

http://i442.photobucket.com/albums/q...ps9ocha8rn.jpg

http://i442.photobucket.com/albums/q...pswaipjmbo.jpg

Finally, here is a photograph of the JRT811.46 sprocket installed on the rear wheel on my Zongshen RX3.

http://i442.photobucket.com/albums/q...ps3xixqm1i.jpg

I was barely able to fit the 46T rear sprocket with my stock, 110-link drive chain. Therefore, I'm sure you would need to get a longer, 112-link drive chain, to fit a tight new chain onto a 13T C/S sprocket with a 46T rear sprocket. ;)

I didn't lose any top speed by switching to the larger, 46T rear sprocket. However, I gained torque in all gears, and I really like this sprocket ratio. Here are the engine RPMs I recorded at the following speeds. These are actual speeds from my GPS calibrated, SpeedoDRD dashboard. ;)

50 MPH: 6,200 RPMs
55 MPH: 6,800 RPMs
60 MPH: 7,400 RPMs
65 MPH: 8,100 RPMs
70 MPH: 8,800 RPMs
75 MPH: 9,500 PRMs

I usually ride at lower speeds, so I like the increased torque with this lower gearing. Also, I am able to maintain speed with higher gears while climbing long, steep grades with this lower gearing.

I also plan to experiment with a JTR811.45T rear sprocket. Depending on my riding conditions, I can now switch between 13T/44T, 13T/45T, and 13T/46T sprocket ratios. I don't plan to go any lower than my current, 13T/46T sprocket ratio. ;)

Switching between my stock sprocket carrier, and the modified sprocket carrier, I now have the following options for rear sprockets available in the United States.

37T, 39T, 40T, 41T, 42T, 43T, 44T, 45T, 46T

If desired, I can also purchase a 48T rear sprocket from the Ukraine, Russia, and other European countries. ;)

You can purchase 13T and 14T, counter shaft (C/S) sprockets from CSC, and Taobao. With this variety of C/S and rear sprockets available, you can tailor many different sprocket ratios. :tup:

I would like to see a more comprehensive RPM vs Speed sprocket chart. I did the same thing with my KLR, had a non-stock 16T front sprocket paired with a different rear sprocket. I can't recall if it was a 46T or not, but I made my decision based on an already published sprocket ratio guide due to my riding style and what I was trying to accomplish.

Man SpudRider, great idea, I hadn't thought of getting a new carrier...

Need to see if I can buy any of those sprockets here locally.

Great idea, just great.

Riceburner

Perhaps another RX3 rider could chime in here. It would be great to have a GPS-proven speed vs. RPM table in all gears at the stock ratio for comparison.

Excellent write-up, Spud.

Very cool. I will likely go to a 13/45 ratio when it becomes available from CSC. 75 mph at 9500 is past redline and I would be more comfortable doing 75 at 9000.

The analog tachometer shows the redline starting at 9,000 rpms, but I think the actual redline is higher. ;) The engine in my Zongshen ZS200GY-2 has a redline of 10,000 rpms, and it isn't designed to spin as fast as the NC250 engine. ;)

In any event, I am content to cruise at 65 mph on the interstate highways. I much prefer to travel secondary and tertiary paved roads. When planning a trip, I try to incorporate gravel and dirt roads, as much as possible. :)

The 13T/45T sprocket combination is certainly an excellent choice. Besides being a compromise between the 13T/44T and 13T/46T sprocket ratios, I think you could install a new, 110-link drive chain over the 13T/45T sprockets. You need to get a 112-link drive chain if you plan to install a new chain over the 13T/46T sprockets. ;)

Thanks Spud… good to know. It's unusual (at least, to me) to have redline right at the horsepower peak. When riding, I'm noticing that I'm naturally shifting as soon as I feel a decrease in power… which is around 9,500 - 10,000 rpm, and that's where the bike feels best upon acceleration.

Since I do a fair amount of super-slabbing, I'm trying to figure out the right combination of sprocket and rear gear to get me to top speed of the RX-3 right at the horsepower peak of 9,000 rpm. But good to know there are choices available to experiment with, and the cost of the sprocket or rear gears are reasonable.

You're welcome. :) I agree; the bike does seems to generate maximum power around 9,000 rpm, and that is surely lower than the engine's redline. ;)

I think the 13T/46T sprocket combination might be the ratio you seek. The more I ride with this sprocket combination, the better I like it. :)