RX3 rear sprocket teeth available? Compatible to?

[NzBrakelathes]

I was looking at the options of teeth count for the RX3 - what is the current easy available apart from stock? is stock what people want/need or would other smaller and bigger be an item people would like?

Seems custom rear sprockets are available in China if you are willing to wait and spend the money (5 times more expensive then the stock sprocket)

I am more talking about the unit with cushy drive - I have seen the non cushy drive offered but doubt many folk have that version.

I spotted the following tooth counts:
39
41
44
47
49
52
60
70
Some are isted as "stunt" maybe not for common use on an RX3 lol but they offer custom specs too.

[calvarez]

Changing the front is very easy, and doesn't require a chain replacement. Changing the rear has 1/3 as much effect, and only makes sense if you really want to fine tune an exact gear ratio. A one-tooth change won't do much, and two+ teeth requires a change in the chain. Also you can already get various sizes from CSC for $28 each.

From my perspective, I don't see why the rear would be messed with. I did go down a tooth on the countershaft, and that made the bike better all around at my altitude of around 1700 feet. There's a surprising amount of high end power loss compared to when I was riding it at sea level in Los Angeles (where I bought it).

[rjmorel]

I found that the RX3 is geared perfect for what it was meant to do. If your going to do more slower trail type riding, gearing it down like some have done helps. But then I would get a TT250 for those duties.
I go between the 13T and 14T countershaft. I geared it up once when doing the Iron
Butt and wished I hadn't cause in the hilly states I was riding in 6th became useless except on long down hills.
Now with the 300 kit installed I'm back to stock gearing and doubt I'll ever need to change. I don't do much trail type riding with it and would just work the clutch if I did need to compensate for gearing. rj

[NzBrakelathes]

General road riding without much off road I think stock gearing is close to rught when you got the 300 kit, 14 tooth front
Maybe could reduce rear a couple teeth to reduce rpm for cruising etc
I asked cause I’ve not seen much before but wondered if there was a need in some situations for some people

[calvarez]

I rode around town for a few hours today, and was making mental note to update this thread. The 13 front is a HUGE improvement over the stock 14. All the places where I'd be pushing to hold 70 are now no problem. I'm only shifting when I get down to about 60. In my town, 70-75 is the normal highway speed, and 45-55 on major streets. The stock gearing was a huge challenge on the highway.

[NzBrakelathes]

Originally Posted by calvarez

I rode around town for a few hours today, and was making mental note to update this thread. The 13 front is a HUGE improvement over the stock 14. All the places where I'd be pushing to hold 70 are now no problem. I'm only shifting when I get down to about 60. In my town, 70-75 is the normal highway speed, and 45-55 on major streets. The stock gearing was a huge challenge on the highway.

You are about right without the 300 kit, once you get your brother to fit that 300 kit you will get all that and maybe a little better with the 14 tooth sprocket.

[willy dog]

around here the mighty zong sees mostly dirt roads i found the front 14t a little high in 3rd gear and to low in second the 13t fits my needs perfect when it starts to get tired will look into 300 kit but right now i love it

[sqwert]

13t is at least 8% reduction in sprocket and chain lives compared to 14t. Best to run the biggest countershaft sprocket you can, then choose a wheel sprocket to provide the final drive ratio you desire. Select a high quality ringed chain to maximize lives of all three components. Lube enough to prevent surface rust and you can reasonably expect 25,000 miles (40,000km) out of a chain and sprocket set. Typically, largest countershaft sprocket that will fit and appropriate chain and wheel sprocket to match will need lube twice while traveling the same distance that will flat wear out smaller sprockets and a cheap chain, sets I've worn out in 5000 miles (8000km).

Chains and sprockets wear to fit each other. A worn one of the three parts, doesn't matter which, and very quickly all 3 will be worn. To maximize chain and sprocket life replace all three parts at the same time.

Anywho, RX3 trans ratios are too close together for an adventure bike that needs to run terrain and highway. Much of the improved powerband width of the 300 kit is simply wasted. Of course, if you want to tweek the stock displacement for more power peak and a narrower powerband the ratios are just about perfect. I have 4 TW200 Yamahas, modified for different purposes, and they have 3 different sets of transmission ratios, so I know how critical trans ratios can be to the overall performance attributes ratios can provide.

Wish I could get tooth counts on all the RX3 trans gears so I can get started on the math to calculate an appropriate set of ratios for a stock engine with the 300 kit for adventure use. Once such an engine is built anyone who rides it will have orgasms from the much improved feel.

[calvarez]

Spent a little more time just running around the local area, and yeah, the 13t front is really the best choice for this bike. It simply improves everything from mild dirt roads to 70-some MPG highway time. The biggest improvement is in 40-50 MPH street time, which is common where I live.

[sqwert]

Originally Posted by calvarez

Spent a little more time just running around the local area, and yeah, the 13t front is really the best choice for this bike. It simply improves everything from mild dirt roads to 70-some MPG highway time. The biggest improvement is in 40-50 MPH street time, which is common where I live.

Yes, your choice of gear ratio is a major improvement.

Stock sprockets are 44/14, 3.143:1 ratio. Too tall out of the hole, especially when loaded or in a power demanding situation, such as uphill or in a material such as mud or sand. Also, uncomfortably fast pace in 1st gear engine can't pull at idle, especially in terrain. Engine dies, rear wheel locks, bike stops and falls over, but not much one can do to prevent the fall when standing on the pegs using counterbalance steering.

44/13 is 3.385:1 ratio, which is much better overall. If you need a change and want to run out the OEM chain and wheel sprocket, a 13t countershaft is an inexpensive solution in the short term. The 44/13 set is a fantastic improvement in hole shot and slow speed control. The fewer miles on the chain and wheel sprocket, the longer the set will last after being changed, so final drive ratio needs to be one of the first mods considered.

47/14 is 3.357 ratio, almost as much an improvement as 44/13. 48/14 is 3.429:1. Yes, you'll need a longer chain. However, if you are waiting until your OEM chain and wheel sprocket wear out to change your final drive, not much more money involved than 44/13, and will last much longer, so a good choice.

If you are going to run a taller rear tire, such as 130/80 or 130/90, especially if switching to a significantly more aggressive, taller tread, you are going to need lower gear than that.

Starting at 44/14 (stock), effect of sprocket changes on engine speed at a given RPM:

44/13 = 7.1%
47/14 = 6.4%
48/14 = 8.3%
49/14 = 10.2%
50/14 = 12%

You'll need to calculate your engine rpm at specific speeds to predict the effects of changing final drive geometries--sprocket tooth counts and tire outside diameters are mathematically related to engine speeds at various rpms. Simply changing from a 130/70 tire to a 130/80 tire reduces engine RPM by over 4%. As narrow as the stock RX3 power band is, that's significant. A 130/90 tire reduces engine RPM by 7.8%, and a 130/100 tire provides an 11.3% reduction compared to a 130/70. Since the RX4 is already over geared, that isn't what you want unless building a road racer.

That is assuming the tires are of the same type and build. Tires of the same size but different purposes can vary 1 1/2 inches, (38mm) in diameter, easily a 6.2% reduction in engine speed at a given RPM. Changing tire size or type can have a far more radical change on final drive ratio than minor sprocket changes.

For instance, going to a 130/100-17 knobby can reduce engine RPM 17.5%, which would require a 54/14 sprocket set simply to retain the stock final drive ratio when tire size is considered. To end up with the same engine RPM at a given speed with 44/13 sprockets, you will need 58/14 sprockets if you switch to taller aggressive knobbies.

So, you can see that tire diameter, or better, rolling radius times 2, is also a critical dimension to include in calculations.

Thoroughly confused? Don't worry, so is just about everyone else. They just think they will appear stupid if they ask a question, so they choose to remain ignorant instead.

Rolling radius (RR) is the radius of a tire, measured from the ground vertically to the axle center, when the rider, fluids, and accouterments are loaded on the bike, and the tire is properly inflated. It is a 2 person job since simply loading weight on the seat does not result in a representation of the real rider's weight distribution. Even with the same tire, most everyone's rolling radius will vary a bit.

Tire rolling diameter (RD) for closest calculations is rolling radius times 2. First you have to actually measure the rolling radius, then multiply by 2 for the rolling diameter. RR x 2 = RD.

Then, your rolling circumference (RC) is determined by RD x 22/7. 3.14159265359 . Not enough decimals? Try this. Yes, that is the constant referred to as Pi. Sorry, don't have a button for that on my calculator. I use the fraction 22/7 or the decimal 3.1416. Close enough.

Once you have RC, convert to your measure of distance that goes over time on your speedo to calculate how fast your rear tire has to turn to provide the appropriate engine rpm for you. If you have and like 44/13 and the stock tire, you'll need 54/13 or 58/14 to maintain about the same engine speed with a gnarly knobby with a 90 or 100 cross section.

Oh, crap, I just gave away the answer! What a Super Highly Intelligent Teacher I am.

[sqwert]

Anywho, anyone know of a 15t countershaft sprocket for the RX3? Usually the countershaft sprocket is quickest to wear because it has fewer teeth, and the more teeth the less sharpness to the angles of movement between the chains side plates so less wear on plates and rings. My experience is about 10% increase in sprocket and chain life for each tooth added to the countershaft, because the wheel sprocket then needs to be bigger, so less wear there, too.

It seems different rear wheel sprockets have been used. Are they interchangeable as far as mounting bolts and offsets go? Currently running the 46t from CSC, but considering a bigger tire.

Hey, didn't I see such a list posted a few days ago?

[sqwert]

Is the JT part number for the countershaft sprockets to fit the NC250 JTF276.xx?

[NzBrakelathes]

I have heard of a 15T front sprocket but unsure if true fit or if the hole is there for the locking nut.
Sorry I do not know

[sqwert]

Last person I wanted to bother with my question, but I appreciate your input. I do not like adventure treads in the dirt so looking for more aggressive tires, but none seem available in 130/70-17 with DOT approval. If I have to go to a taller tire, I'll need more aggressive final drive ratio, and since I'd have to buy a new set of three parts, thought maybe a 15 would be the way to go to promote longer life.

[rjmorel]

I don't know about a 15T counter shaft Sprocket if it will even fit in there and have clearance for the chain to go around without grinding on something expensive. Haven't seen one for sale and haven't heard of anyone installing one ????? rj