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. :)

Spud, Was the sprocket carrier all you needed to order from CSC? Did it come with the bearing and seal, etc???

I ordered my sprocket carrier from Taobao, and it came exactly as shown in the photographs. In addition to the bearing, dust seal, and bushing, it also included a stock, 44T rear sprocket. ;)

The dust seal, sprocket carrier, bolts and nuts are listed as separate parts on the CSC website. I suggest you give them a call to make sure you get all the needed parts. ;)

Thanks again, Spud! I'm sure you're right - that the 13T/46 might be the ticket. I am thinking of trying out just the 13T front sprocket as my calculations show that the top speed of 82 or 83 mph (GPS speed) should be achieved at the hp peak of 9000 rpm.

I've still not hit top speed on my RX-3, but without the panniers, I hit a GPS reading of 79.5 mph today, and had a little acceleration left. Unfortunately I got a little wobble in the steering head at that speed, so I backed-off. I'll try again on another stretch of road as the highway I was on was concrete, so I'm not sure if it was the surface or the bike. The bike is very stable up to 75 mph however, and I think with stock gearing, the advertised 84 mph top speed as measured by GPS is achievable.

I got to 80 indicated (probably 75 actual) yesterday with the 13T sprocket, but it was downhill and I'm pretty sure I had a tailwind. I didn't feel any wobble, but didn't stay there very long. My RX3 seems much happier at or below 75 indicated.

That's why I prefer to travel an actual 65 mph during the infrequent occasions I decide to ride the interstate highways. ;)

Hi
I wanted to make a taller gearing. Is there any known 15T front sprocket that would fit this bike? I'd like to go that way instead of lowering the rear

Thanks

I don't know of any other counter shaft (C/S) sprocket which has the same dimensions. Therefore, you risk damaging the counter shaft on your motorcycle if you use another C/S sprocket.

Does your bike have the rear cushion hub, or the older rear hub?

Hi, thanks!

So I guess the only way is playing with the rear sprocket then. Only problem would be the chain length, it would be too short.. either I add some links or wait until it stretches :)

Not sure about your question, I'll upload a picture later so you can take a look

Edited: mistake about long/short

Please do post photos of your rear hub. If you have the same, cushioned rear hub as the bikes sold in the United States, you can install a 40T rear sprocket, and remove two links from your drive chain.

Yes, some people here even went to 39T rear sprocket.

I just wanted to go the easier way an add one on the front, but I probably end up doing the rear mod. I just want to lower the RPMs a bit on highways, and I don't weight a lot so the bike should not even notice the change :)

If you have the same rear hub as the U.S. bikes, you don't need to modify the rear hub to install a smaller rear sprocket. If you have the older rear hub, you can also find many KTM rear sprockets, which might be smaller.

I understand
Thank you!

I'll post a pic later so you can take a look at it

If you want higher gearing, you will need either a larger front sprocket or a smaller rear sprocket. With a smaller rear sprocket, you might have to remove a chain link, but there may be enough room in the adjustment to move the rear wheel back far enough.

Higher gearing will theoretically give you a faster top speed. I say theoretically because your engine only has 25 HP max, and there are other factors that reduce engine power, like elevation above sea level, valve adjustment and engine oil weight. Air resistance from luggage, hills and total weight of you and the bike will also affect acceleration and top speed.

One downside of higher gearing is that it will tighten the available power band. The factory HP charts on this page show the power and torque curves of the RX3. You can see peak HP at 9000 RPM, although in my experience above 5000 ft in Denver, it peaks around 8500.

Having used both the 13T and 14T sprockets, I've found that:

• The stock 14T/44T combination gives usable power between 5500 and 8500 RPM.
• Changing to 13T/44T widened the usable power to between 3500 to 9000 RPM.

But going the other way with a 15T/44T (if you can find one) would likely tighten the usable power band between 7500 and 8500 RPM. The idea is that in order to turn the tall gears you're talking about, you'll need to keep the RPM closer to peak HP at all times to keep things moving (and prevent stalling).

Shorter ratios are able to do more work with the lower power on both sides of the power curve. A lower RPM also keeps you closer to the engine's peak torque, improving performance on hills, with higher loads or in headwinds.

So you would conclude that it is a bad idea?

Well, it wouldn't work for me and my riding conditions. But it might be perfect for someone lighter than me at sea level who rides in mostly flat areas.

I didn't mean to discourage the idea. Sprockets are cheap and you won't hurt anything by trying it out. I just like to explore the mechanics behind things and I got on a roll :)

Personally, I think the Zongshen RX3 is geared too tall from the factory with the stock, 14T/44T sprocket combination. ;)

I am currently running a 13T/46T sprocket combination on my RX3, and I like it a lot. :) I really don't think there are many benefits to be gained by gearing the bike taller than the stock sprocket ratio, which is already very tall. :shrug:

However, a 40T sprocket is not expensive, and it certainly doesn't hurt to experiment with different sprocket ratios. :) The only way to discover the optimal sprocket ratio for each of us, as individuals, is to experiment. ;)

Picture
The thing with changing the rear sprocket, is that once I've cut the chain there's no goin back :(

This pic maybe helps a little more :D

CSC is going to offer a 42T rear. That's only 2 teeth smaller than stock. I wonder if there's enough room in the axle adjustment to take up the slack.

Thanks for posting the photos, amigo. You have the rear cushion hub, which is the same rear hub we have in the United States. The JTR473.40 is a 40T sprocket which will fit your hub without any modifications required. :)

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

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

You can easily find this sprocket for sale by searching the internet; just type "jtr473.40." This sprocket is for sale on Amazon for $21.36, with free shipping.

http://www.amazon.com/JT-Sprockets-J.../dp/B005DL7JLO

You can purchase this sprocket, and it probably will fit your drive chain. However, the worst case scenario is you will need to remove two links. ;) As Detours stated, CSC has promised they will be stocking a 42T C/S sprocket, which will undoubtedly fit the stock drive chain.

If you wish to modify your sprocket carrier, which is the topic of this thread, you can follow the instructions in the first few posts. ;) The JTR1826 sprocket fits the modified sprocket carrier, and it is available in 41T, 42T, and 44T versions. :)

Alright, gracias for all the awesome info :)

Cheers

Can't find the sprocket carrier from Taobao
 

Spudrider,

Thanks for all the great info and ideas you've provided:clap:. I have gone through this thread several times looking for the link to the Taobao for the sprocket carrier you mention and can't see it:hmm:, you usually post the links to the items you refer to:tup:. So I have gone through the Taobao main site page for the Zongshen NC250, have used it many times now,

https://world.taobao.com/search/sear...cb&abtest=null

and have gone through all 11 pages several times trying to find the carrier:hmm:

[QUOTE=SpudRider;191666]I ordered my sprocket carrier from Taobao, and it came exactly as shown in the photographs. In addition to the bearing, dust seal, and bushing, it also included a stock, 44T rear sprocket. ;)

Can you share the link to that Taobao carrier you purchased?

With the lack of available stock parts here in Iloilo I need to build my own little warehouse and I want to be able to run that 46 sprocket, going to order that today if I can't find one in the city this morning.

Thanks,

Can't find the sprocket carrier from Taobao:

I'm looking in the wrong area aren't I!!! I'm using the NC250 search, that's the engine, silly me, maybe need to try under RX3 search?

Well that hasn't worked yet either...

You need to use either of the following search terms. ;)

Zongshen RX3
ZS250GY-3

I can't find the sprocket carrier currently listed at Taobao. Some of these items come and go. Perhaps it will show up again, later. ;)

You can order the JTR811.46 rear sprocket, and wait for it to arrive. After it arrives, you can trim 2mm from each of the radial arms on your current sprocket carrier. ;) However, you might have trouble getting the 46T sprocket to fit on the stock, 110-link drive chain. Therefore, it might be best for you to wait until the sprocket carrier appears again on Taobao. ;) Of course, you could also order a spare sprocket carrier from CSC.

Spud, question for you. Would boring out the sprocket hole accomplish the same thing w/o having to buy and modify the carrier? Or is the sprocket to hard to bore out? Or am I missing something else? rj