New Zongshen RX3 (ZS250GY-3) Dual Sport

[Weldangrind]

Originally Posted by SpudRider

The stock, 15-inch rear tire is a street tire, and all tires of size 130/90-15 are about 610-615 mm in diameter.

Now let's examine some 17-inch tires. The CST C6017 is also a street tire. The C6017 tire in size 130/70-17 is 640 mm in diameter.

I'm doing something wrong. When I do the math, I get 615mm for the 15" and 614mm for the 17".

How did you arrive at your numbers?

[Weldangrind]

Originally Posted by jimjr21

For those of us that like to do nice break in programs, that is out the window. The put the hammer down on these bikes with zero time.

I am really really really liking my Christmas present upgrades!

That's what I was thinking. Nevertheless, the big four Japanese manufacturers do the same thing.

[rtking]

Originally Posted by Weldangrind

I'm doing something wrong. When I do the math, I get 615mm for the 15" and 614mm for the 17".

How did you arrive at your numbers?

I'm guessing it was a typo? The 15" wheel and tire is indeed 615mm, but the 17" wheel and tire combo is 613.8mm. I'm curious if the 2.6% difference Joe mentions is because of tire tread variance in the 17" version that makes the real world difference of 2.6%? (In automotive tires, I've noticed that just because a tire is marked as being one size doesn't mean that a competing tire has the same circumference despite being labeled as the same size.)

Whatever the case, it looks like we now have (as standard) a breadth of options for the rear tire. Well done, CSC!

[rtking]

Originally Posted by jimjr21

For those of us that like to do nice break in programs, that is out the window. The put the hammer down on these bikes with zero time.

I am really really really liking my Christmas present upgrades!

Good news is that the factory has ensured the rings are sealed against the cylinder walls. The hone will never be as sharp as when the bike is first starte, so having the engine under load on a dyno and through its full rev range means that those rings are likely well seated!

[SpudRider]

Originally Posted by Weldangrind

I'm doing something wrong. When I do the math, I get 615mm for the 15" and 614mm for the 17".

How did you arrive at your numbers?

I quoted the manufacturer's specifications for each tire. If you follow the links I provided, you can verify all the information I posted.

Originally Posted by rtking

I'm guessing it was a typo? The 15" wheel and tire is indeed 615mm, but the 17" wheel and tire combo is 613.8mm. I'm curious if the 2.6% difference Joe mentions is because of tire tread variance in the 17" version that makes the real world difference of 2.6%? (In automotive tires, I've noticed that just because a tire is marked as being one size doesn't mean that a competing tire has the same circumference despite being labeled as the same size.)

Whatever the case, it looks like we now have (as standard) a breadth of options for the rear tire. Well done, CSC!

No, I didn't make any typographical errors. I realize it's a long post, but the information I posted is entirely accurate. Mathematics and tire sizing is not an accurate way to determine the actual size of a motorcycle tire. One needs to check the manufacturer's specifications to know the actual dimensions.

I have some experience in this area, because I changed the 15-inch rear tire of my Zongshen ZS200GY-2 to an 18-inch rear tire. I also changed the 18-inch front tire of my Zongshen ZS200GY-2 to a 21-inch tire. In addition, my Honda XR650L is very tall, with a stock saddle height of 37 inches. One can easily raise, or lower the saddle height of that bike by 1/2-inch merely through the proper selection of tires.

Also, as I stated in my previous post, knobby tires are larger in diameter than street tires, even if they are listed the same size. Mounting knobby tires is the only reason to switch to a 17-inch rear wheel. If one is happy with street tires, the 15-inch rear wheel will work just fine. Knobby tires which are readily available for sale in North America are definitely larger in diameter than the stock, 15-inch street tires mounted on the Zongshen RX3. One must check the manufacturer's specifications to determine the accurate dimensions of any motorcycle tire.

[SpudRider]

I also speak from experience with regards to the bike's stock gearing. Unlike most other Chinese motorcycles, my Zongshen ZS200GY-2 was geared high from the factory. I needed to change the sprockets to gear down the bike for off road riding, even with the stock 15-inch rear tire.

Forum member Recracer owned a Megilli bike with the same NC250 engine, and he has reported the transmission is geared too high. Also, several of the motorcycle magazine testers have reported the RX3 is geared high. Therefore, I am pretty sure the RX3 is geared a little too high for technical, off road riding, even with the stock, 15-inch rear tire. If one installs a 17-inch knobby tire bought in America, I'm pretty confident the rider will want to gear down the sprockets. This isn't a problem, as long as a variety of larger rear sprockets are available. If the counter shaft (C/S) sprocket is sized with 13 teeth, one will be pretty much required to install a larger rear sprocket, since it's not wise to go smaller than 13T on the front sprocket.

One way or another, we can fix the problem. If necessary, we can order custom sprockets, or find another sprocket we can modify. However, it is much easier to have a variety of larger sprockets available from the factory.

I really like the cushion hub, but it employs a rare sprocket size. The 17-inch rear wheel on the Minsk uses a hub which appears to employ commonly available, inexpensive Honda or KTM sprockets, which are manufactured in a wide variety of sizes.

[tikitarik]

Originally Posted by SpudRider

*snip*
I really like the cushion hub, but it employs a rare sprocket size. The 17-inch rear wheel on the Minsk uses a hub which appears to employ commonly available, inexpensive Honda or KTM sprockets, which are manufactured in a wide variety of sizes.

So the 17" cush hub has a different sprocket style than the minsk? Do we know which brand/type it is?

[SpudRider]

Originally Posted by tikitarik

So the 17" cush hub has a different sprocket style than the minsk? Do we know which brand/type it is?

Yes, the 17-inch hub of the Minski TRX 300i employs a different hub. You might enjoy reading the following thread, which discusses this topic.

http://www.chinariders.net/showthread.php?t=14104

[SpudRider]

I'm betting the cushioned hub will work out well. In all likelihood, the sprocket ratios can be adjusted properly either by switching to a smaller, counter shaft (C/S) sprocket, and/or switching to a larger rear sprocket. A cush hub is certainly a very nice feature which greatly extends the life of the entire drive chain.

I think CSC made a good decision. I prefer to get the bike with the excellent cush hub, and work with the available sprockets. If the available sprocket options for the cushioned hub don't work out, one can always lace either a 17-inch, or an 18-inch rim to the original rear hub. This procedure will get you the same rear wheel as the Minsk. Also, if the rear sprockets for the cush hub aren't large enough, Zongshen might be persuaded to manufacture some larger sprockets.

[SpudRider]

Thank goodness, the 17-inch rear wheel is a fait accompli. Now we can start talking about a lacing a 21-inch front wheel.

Raising the front fender should not be a problem. It appears all you need to do is add four short pieces of 1/8" X 3/4" aluminum bar to the four supports at the bottom of the fender.

http://www.lowes.com/pd_24403-37672-...bar&facetInfo=







It seems the lower fork guards attach to the fender, so they will move upward with the fender.



The current speedometer is 15 percent optimistic. After examining the specifications of a few tires, I discovered the circumference of a 21-inch tire is approximately 13 percent larger than the circumference of an 18-inch tire. Therefore, switching to a 21-inch front tire would improve the accuracy of the speedometer, making it almost perfectly accurate.

[SpudRider]

If Zongshen can't/won't fix the inaccuracy of the speedometer, I don't care. If you stick with the 18-inch front wheel, mentally subtract 10 percent from the reading. If you switch to a 21-inch front wheel, the speedometer will be very accurate. I don't care about the fuel gauge. I use the trip odometer for that purpose.

Dare we ask for a 21-inch front wheel from the factory?

[tikitarik]

Originally Posted by SpudRider

If Zongshen can't/won't fix the inaccuracy of the speedometer, I don't care. If you stick with the 18-inch front wheel, mentally subtract 10 percent from the reading. If you switch to a 21-inch front wheel, the speedometer will be very accurate. I don't care about the fuel gauge. I use the trip odometer for that purpose.

Dare we ask for a 21-inch front wheel from the factory?

That would be particularly nice. My only concern would be how it affects seat height and clearance to the O2 sensor wire. I vaguely remember there being an issue with it's clearance or routing. I could of course be completely wrong.

Honestly though, even with a raised seat height this will still be a fairly low bike. The only other thing I can think of is would the wheel change affect the suspension or steering geometry?

[SpudRider]

Originally Posted by tikitarik

That would be particularly nice. My only concern would be how it affects seat height and clearance to the O2 sensor wire. I vaguely remember there being an issue with it's clearance or routing. I could of course be completely wrong.

Honestly though, even with a raised seat height this will still be a fairly low bike. The only other thing I can think of is would the wheel change affect the suspension or steering geometry?

No, we won't have any clearance problems with the wire from the O2 sensor. We have discussed adding a short extension to the front of the skid plate, and protecting the O2 sensor wire by routing it behind the extension.



Since your butt is approximately located over the rear wheel, increasing the size of the rear wheel has the greatest effect on raising saddle height. After you install a 17-inch rear wheel, increasing the size of the front wheel won't add as much to saddle height. Of course, if someone is short of stature, he/she can keep the 18-inch front wheel. However, as you stated, the bike will still have a nice, low saddle height.

After increasing the diameter of the stock rear rim by 2-inches, increasing the diameter of the stock front rim by 3 inches can only improve the steering geometry. If necessary, you could also raise the forks in the triple tree about 1/2-inch. I enlarged the rear wheel of my Zongshen ZS200GY-2 from 15-inches to 18-inches, and kept the 18-inch front wheel for thousands of miles. The steering geometry was not adversely affected. After I also enlarged the front wheel from 18-inches to 21-inches, things only improved.

Increasing the size of both wheels will increase ground clearance, and the 21-inch front wheel will certainly improve steering agility.

[SpudRider]

Needless to say, the selection of suitable front tires will increase greatly after switching to a 21-inch front wheel.

[SpudRider]

The Zongshen ZS150GY-10 motorcycle has a 21-inch front wheel. I think there is an excellent possibility this wheel employs the same hub and brake rotor as the Zongshen RX3. If so, Zongshen could swap the two wheels before closing the shipping crate, and we could modify the front fender when we assemble the motorcycle. If the hub or rotor is slightly different, the two wheels might still employ the same spokes. In that case, Zongshen could lace a 21-inch rim to the RX3's front hub.

Dare we ask for a 21-inch front wheel from the factory?