Zongshen RX3: Sprocket Carrier Modification

[sqwert]

Hmmmm? Stock sprocket has 86mm diameter bolt circle. Proposed JTR replacements are 84mm diameter bolt circle. Question the wisdom of preloading the rubber shock absorbing in the hub with misaligned shanks? Expect bushing holes to obligate over time.

Hmmm? Can't seem to find aluminum 17 x 3 36-hole rim on the internet. Any known source. Not confident 3.50 will fit, not interested in bigger tire to fit bigger rim.

[SpudRider]

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.

[SpudRider]

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.

[Riceburner]

Spudrider,

Thanks for all the great info and ideas you've provided. 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, you usually post the links to the items you refer to. 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

[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,

[rtking]

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.

[detours]

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.

[SpudRider]

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

[peperino]

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

[SpudRider]

Originally Posted by peperino

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?

[peperino]

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

[SpudRider]

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.

[peperino]

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

[SpudRider]

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.

[peperino]

I understand
Thank you!

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

[detours]

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.