Gearing the other way... for highway use

[rtking]

I've read the thread regarding changing the stock 14T counter sprocket to a 13T piece with keen interest. Sounds like a solid plan for those who do a good mix of trail riding and pavement.

But in SoCal, it seems that we're a concrete jungle, and there's lots of highway droning to get to any kind of trails. (At least, that's true of where I currently live.) And despite a 65 mph speed limit, riding at 70 - 75 is more often the norm than not.

The RX3 does fine at 70-75 mph, and I'm confident it can do it all day long. But sometimes I need to go a bit faster, and I've noticed that I'm spinning the engine past its power peak (which happens to be the 9,000 rpm redline.) I spoke with Gerry at CSC and he has been using a 42T rear sprocket and loving it, especially since he's got a long highway commute.

The 42T sprocket is about 5% taller than stock, so at my current peak speed, I can expect to drop 200-300 rpm. I thought about it over the weekend and put in the order today for the rear gear. At $35, it's inexpensive enough to try and, if it doesn't work, I can certainly re-install my 44T rear sprocket.

I'll report results after I install the sprocket. And in a few weeks, I hope to receive the windshield from forum member Winyoochanok and see if that makes a difference in top speed.

[SpudRider]

Good for you. :tup: I'm sure you will be pleased with the reduction from 44T to 42T. It is very nice to have a selection of sprockets available so we can tailor the final gear ratio to the type of riding we prefer. :tup:

[keithmaine]

Spud, this could turn into another dual sprocket thread like over on the TW200 forum :lol:

[SpudRider]

:hehe:

[Juanro]

I've installed a 15z front sprocket some 2000km ago and I'm loving it!

[SpudRider]

I've installed a 15z front sprocket some 2000km ago and I'm loving it!

Where did you purchase the 15T front sprocket?

[Juanro]

From a local manufacturer ("Catalano", http://www.catalano.com.ar/ in Argentina). I originally put the one for Suzuki DR350 but after Reading a post of yours about the difference in size (half a milimeter) checked the catalog and switched to the one for the Beta Chrono 2.5 (I don't know if that bike is available elsewhere with that or other name).

[rtking]

Thanks for the great info, Juanro! So with a 15T/44T combo, you have an effective 2.93:1 drive ratio (versus the 3.14:1 stock for the 14T/44T sprocket combination.) That's about 6.7% taller.

Can you tell us if gearing taller has allowed you to reach higher highway speeds? How is passing power in 6th gear?

I'll have to look into the Catalano catalog. I see the counter sprocket on page 128 of the online catalog. This has me thinking... :)

[SpudRider]

...I originally put the one for Suzuki DR350 but after Reading a post of yours about the difference in size (half a milimeter) checked the catalog and switched to the one for the Beta Chrono 2.5 (I don't know if that bike is available elsewhere with that or other name).
Thanks for posting the additional information, Juanro. :)

Did the Suzuki sprocket fit tightly on the counter shaft? Did you measure the Suzuki sprocket to see if the measurements are actually a little larger than the Zongshen sprocket?

[kumatae]

I'm surprised that there isn't one already. I could surely benefit with a 15T sprocket with my so cal commute as well. Will be monitoring this thread...

[SpudRider]

I'm surprised that there isn't one already. I could surely benefit with a 15T sprocket with my so cal commute as well. Will be monitoring this thread...

If you are willing to risk $8.99, you can purchase a Primary Drive, C/S sprocket for the Suzuki DR-Z400S, and test the fit. These sprockets are supposed to be 0.5mm larger in spline dimensions than the Zongshen sprockets. However, if you get a tight fit on the counter shaft, these JTF432 sprockets are readily available in the United States in sizes 12T-15T. ;)

https://www.rockymountainatvmc.com/p/3175/2105/Primary-Drive-Front-Sprocket?v=12255

http://www.jtsprockets.com/fileadmin/code/images/large/jtf432.jpg

[SpudRider]

However, if you don't get a tight fit on the counter shaft, the JTF432 sprocket will damage the C/S splines, and you will need to take the engine apart to replace the counter shaft. :ohno:

[Juanro]

Define "tight".
I didn't measure the sprocket, and it is cheap enough to replace one or the other without much pain.
Both fit snug to the hand in the spinning sense; and both have a Little axial play, as the holding nut can't reach to the face of it (the sprocket leaves about 1mm of exposed spline). A judicious use of spacers/washers fixed that.

Top spead hasn't increased, if any is a bit lower (in 6th). Overtaking reaction is still good, specially if you keep rpms above 6/7k. If not you can always downshit, a quick fix being a motorcycle. I'd say that 5th gear now is about the same as it was 6th before, leaving me with a 6th/overdrive for relaxed cruising (I'm lying myself, I don't cruise relaxed haha)
At high speeds, rpm droped about 600rpm for the same speed, or speed increased 5mph for the same rpms.
Overall very satisfied with the change. There was some fear that the bigger sprocket will not fit, and indeed is a snug fit (chain passes mere milimeter away from the clutch vertical axle and the gear change lever) but in the end if Works very well and doesn't rub any part.

[SpudRider]

Define "tight".
I didn't measure the sprocket, and it is cheap enough to replace one or the other without much pain.
Both fit snug to the hand in the spinning sense; and both have a Little axial play...

Thank you for your prompt reply. :)

I am interested in radial tightness, or 'spinning sense.' You stated both sprockets "fit snug to the hand in the spinning sense." Was the Suzuki sprocket as tight in this sense as the Catalano sprocket?

[SpudRider]

The JRF432 sprocket fits many Suzuki motorcycles, including the following bikes.

DR200
DR200SE
DR-Z400S
DR-Z400SM

Can anyone measure one of these sprockets with digital calipers? FastDoc has a DR-Z400S. I wonder if he has a spare C/S sprocket he can measure?

[Juanro]

Thank you for your prompt reply. :)

I am interested in radial tightness, or 'spinning sense.' You stated both sprockets "fit snug to the hand in the spinning sense." Was the Suzuki sprocket as tight in this sense as the Catalano sprocket?

Ah! I see, sorry for the misunderstanding. -Both- sprockets are Catalano; just one is the Suzuki model and the other, Beta. To my eye and for how they fit, they're the same or really close. Keep in mind that Catalano is... somehow a "Budget Company" and probably their tolerances are not the best.
But I have now over 1000km with the sprocket, and (due to a rear puncture) had the chance today, while cleaning the chain and mouting the rear Wheel, to inspect the sprocket/nut/spline and it looks as good as new. No play, no metal bit, no visible wear and all snug and aligned as it should be :tup:

[SpudRider]

Juanro,

Thank you for the clarification, and the update. :)

[SpudRider]

I'm surprised that there isn't one already. I could surely benefit with a 15T sprocket with my so cal commute as well. Will be monitoring this thread...

Are you using the stock, 14T/44T sprocket combination? If so, you can purchase a smaller sprocket for the rear wheel. CSC is selling a 42T rear sprocket.

http://www.cscmotorcycles.com/Rear-Sprocket-RX3-42-Tooth-p/csc-1100.htm

If you want an even higher sprocket ratio, you can purchase a 40T, JTR473.40 sprocket. This sprocket has the exact dimensions of the Zongshen rear sprockets, and will bolt directly onto your sprocket carrier. :)

http://www.amazon.com/JT-Sprockets-JTR473-40-Steel-Sprocket/dp/B005DL7JLO/ref=sr_1_1?s=automotive&ie=UTF8&qid=1430037764&sr=1-1&keywords=jtr473

http://www.jtsprockets.com/fileadmin/code/images/large/jtr473.jpg

[Juanro]

Just a heads up: with a 39Z rear sprocket, you are in the edge of having to remove links to the chain (and put a master link), or else you run out of space in the adjusters to remove the slack. That was tested by a fellow RXer here. I don't know with a 40. 42 should be fine.

[rtking]

Thanks Juanro and Spud.

I think the 15T may be the ticket if the 42T rear sprocket doesn't give me the rpm drop i'm looking for. But based on my calculations, I think the 42T is going to work best for me. While not as tall as a 15T/44T combo (which is 2% taller than the 14T/42T combo), I think it will preserve my top speed while not running past redline.

I've got the 42T rear sprocket en-route. Will advise as soon as I receive it and can install it.

[SpudRider]

You're welcome. :) Please do keep us updated.

[rtking]

Just so everyone knows, CSC doesn't mess around when it comes to shipping. I put in the order for the rear sprocket on Monday, and it was waiting on my doorstep on Tuesday evening. Granted, I live 40 miles away from CSC, but still... they had it in the mail that afternoon and on its way to me. Fantastic service!

I installed the sprocket on Tuesday evening, but had to correct an issue I introduced when reinstalling the rear brake caliper. I'll describe in detail further below. But wanted to do a quick write-up of the procedure that I took... there are likely easier ways, but this is how I swapped sprockets.

Tools Needed:
1. 12mm Socket (sprocket bolts, chain adjustment bolts, brake caliper bolt)
2. 14mm Socket (other brake caliper bolt)
3. 18mm Socket (left side bolt - rear axle)
4. 19mm Socket (right side bolt - rear axle)
5. 5mm Allen Head wrench - brake caliper pin for brake pads
6. 13mm open ended wrench [or 1/2" wrench will work] - chain adjustment bolts
7. Center stand, or floor jack to raise the rear of the bike off the ground
8. Rubber or urethane mallet

Tools recommended for job: (in addition to above)
1. Torque wrench
2. Breaker bar
3 Electric impact wrench
4. Friend to hold rear brake (not that I'm calling your friend a "tool") :hehe:


Removing rear wheel:
[Optional 1st step]: If you have a friend nearby that can hold the rear brake for you you can try to loosen the bolts that hold the sprocket. You'll want to be even on the bolts as any un-even torquing can/will deform the bolt face. An electric impact wrench makes this job easier.
1. Loosen the 19mm nut holding the axle. (This is easier with the bike on the ground.)
2. Loosen the chain adjustment nuts and locking nuts
3. Securely raise the bike either using the center stand or floor jack
4. Remove the 14mm bolt from the brake caliper (bolt furthest to the front of the bike)
5. Remove the 12mm bolt from the rear position of the brake caliper
6. Remove the caliper and pads and place out of way
7. Note the mounting position of the brake caliper bracket to swing arm This piece is loose, so you'll need to note the orientation of the piece for re-assembly.
8. Remove the 19mm nut on the right side of the bike. You may need to use he 18mm socket on the left side bolt-head to keep it from moving
9. Using the rubber or urethane mallet, gently tap the threaded axle on the right side of the bike so it slides to the left.
10. Once you have enough of the axle to grab onto, gently lift the rear tire to unweight the axle bolt. (A friend can help lift, or you can put a piece of wood under to help unload the weight off the axle.)
11. Pull the axle shaft out. When you do, you'll likely her the brake caliper bracket fall. Just put to the side.

Removing the Sprocket.
If you didn't remove the bolts holding the sprocket while the rear wheel was on the bike, you'll likely need some assistance via a helper or an electric impact wrench. These instructions are in the event you removed the wheel without loosening the sprocket bolts.
1. Remove the chain from the sprocket and lay aside
2. Carefully roll the rear tire out from the swing arm. Note that the bushings for the axle are held in by grease an rubber boots and can fall out. Take care not to lose or damage these bushings.
3. You can remove the sprocket and hub from the cush-drive by pulling up. It might be easier to leave the hub on the wheel if you can have a friend stand on the wheel to allow you to remove the bolts holding the sprocket. Or if you have an electric impact wrench, you can remove the bolts by yourself. If you do remove the hub, you can use a breaker bar between the fingers on the back of the hub as leverage points to hold the hub steady while removing the nuts.
4. Once you've removed the sprocket, installation is the reverse of all steps above.
5. Follow the chain tensioning guide to set the proper chain tension and ensuring the axle is aligned properly. Torque the 19mm nut on the axle to 50 lb-ft.

Special note on re-assembly - rear caliper:
1. Ensure that the rear caliper mounting plate is aligned with the square block on the bracket fits into the parallel guides on the swingarm
2. When reinstalling the caliper, start with the 14mm bolt and carefully thread as to not cross-thread
3. Make sure pads move freely once situated on the rotor, and before installing the 12mm bolt to hold the caliper down.
4. Test the caliper by pushing in/out to ensure the floating caliper actually moves. (this was my problem that prevented any effective braking.)


I haven't had a chance to ride the bike since installing the 42T rear sprocket, but will update this thread when I do.

[kumatae]

Checking in if you had have any updates to this. Thanks!

[rtking]

Work, life, family keeping me busy, so not much time to ride. I would like to get a longer freeway ride in to give my full impressions, but so far I can report:

1. I can stay in each gear slightly longer since the gearing is taller. Good for minimizing shifting through intersections / city streets
2. Quick freeway ride shows that my RPMs have dropped about 200 rpm vs. same speed with the 44T rear gear. This is what I was hoping to achieve

I haven't been able to check top speed with the new gear. Hoping to do that sometime this weekend if weather cooperates, or the following weekend. Will post back once I get that ride in!

[dave92029]

Changing the gear ratio also means that you are lower in the engines torque curve.

Orange County is pretty flat, but down in San Diego, we have lots of hills and I find that I need to down shift in order to have the engine power/ torque to pull the inclines. The mighty 250cc just doesn't have the power to maintain high speed up hills, and dropping the rpm would not help this issue.

A 300cc big bore kit would probably be more helpful in solving both issues: higher speed and power to pull up hills.

I have just resigned myself to stay off the freeways and ride the back roads where the mighty 250cc appears to be more fun.

Hope this gear change works for you.