Sprockets

[r80rt]

A couple of weeks ago I put a 13 tooth front sprocket on my little red donkey. I like the lower gearing, it's the same 3.00 sprocket ratio the old CT90's and CT110's had.
But I would rather go up a few teeth on the rear sprocket because small front ones wear fast. When I had the rear wheel off to change the tires I carefully measured the rear sprocket and sat down with a JT sprockets catalog and read till my eyes bled. It payed off and I found a 45 tooth rear and a 15 tooth front sprocket that fit. It's the same size sprockets the old bikes came with . No issues with clearance and I used a new D.I.D heavy duty chain, 112 links.
The bike is much more capable off road with the lower gearing, and doesn't effect the top speed except for a bit higher RPM. There is some speedometer error but I don't care, I will never be breaking any speed limit on this bike. Just my personal opinion, but these sprockets should have been standard.

 

[G19Tony]

I ordered a 13T front, and a DID X ring chain.

 

[r80rt]

You'll like the gearing with the 13T front. Honestly the standard gearing isn't bad, but for me and what I do, there are better choices.

 

[G19Tony]

You'll like the gearing with the 13T front. Honestly the standard gearing isn't bad, but for me and what I do, there are better choices.

Were you the one on ADV having issues with the ABS? Could be the sprocket?

 

[r80rt]

Not me, I haven't noticed any issues with the abs.

 

[Southwest ORV]

That looks nice! So the overall net affect was lower gearing, and less sprocket wear, correct?

 

[r80rt]

Yes, it's the same sprocket sizes that came stock on the CT90's. The CT125 comes with a sprocket ratio of 2.79 and these sprockets have a ratio of 3.00. For me it's the perfect set up. If I were going to stay on pavement I'd keep the stock gearing and tires. Here is a chart to help with sprocket gearing. These bikes have a bout 1.2 horsepower more than the old ones, it's not a lot, but on a motor this size it's pretty big. With the lower gearing the extra power is noticeable.

 

[Southwest ORV]

Awesome. Thanks! My usage will be residential streets mixed with forest roads and trail riding. I almost always gear my ATVs and bikes down, for example I just dropped the countershaft sprocket from a 14 to a 13 on my Raptor 660R for better bottom end and low-speed trail riding, plus more usable reverse. I bet I'd gear down the 125 as well. The chart is awesome!

 

[Migolito]

Seriously WOW! I just did my test ride with the 13T front and the differenece was outstanding. I'm 210 pounds and the OEM was pretty decent on road. However, with the 13T the pull away at stop lights was very noticibly faster. Top cruise was easier to reach as well. I'll be adding 30 pounds per side in my soft luggage and try that out tomorrow.

 

[r80rt]

Proper gearing is great ain't it?

 

[AZ7000']

I've gone up a handful of trails on the 125, have updated sprockets on the big baja bikes so I'm into it when I see the need. For the 125 i made it up everything i needed pretty deep into the woods, clearance was the weak point IMO. Maybe 180 dressed and a six pack w ice in the basket!!

With 2 up and the "L" range on the 1974 I can climb walls!

 

[r80rt]

I really had no trouble climbing with the 125, but It wanted to go faster than I did when creeping along slow. The lower gears cured that, and helped it all around too. Yeah my old 90's and 110's with low range were amazing.

 

[Southwest ORV]

I've gone up a handful of trails on the 125, have updated sprockets on the big baja bikes so I'm into it when I see the need. For the 125 i made it up everything i needed pretty deep into the woods, clearance was the weak point IMO. Maybe 180 dressed and a six pack w ice in the basket!!

With 2 up and the "L" range on the 1974 I can climb walls!

So cool that you have both the old and new. Nearly 50 years in between.

 

[fernf5]

r80t-
I like the idea of achieving lower gearing by going to larger sprockets. From the beginning when I found out these bikes didn't have the Hi/Lo gears I knew I would be playing with sprockets. I think the 15/45 is perfect for around town and on pavement. A little extra power up hills and from take off etc.
When I'm camping where I'll only be on dirt roads (no need for high speeds) and trails for extended periods I'll want even lower gearing. So if I have the 45 tooth rear on already it would be easy to go to a 13T front sprocket a really have a trail crawler. Not practical around town. Also, 13/45 might require a different chain length. Don't know. I'll hang on to the original chain (will buy a new one for the 15/45 combo) and adjust if necessary. So when I go camping I would take the adjusted chain and sprocket or change it before I leave. 10 minute job on each end, coming and going.
13/45 will be 3.46 gearing according to your chart. Still nothing like the Hi/Lo gears we have on the early bikes but with the 125 motor, fuel injection and this low gearing I think I would be pretty satisfied with the trail crawling ability. I don't really want to get into the motor for more power as in larger displacement or change exhaust. I like it stock and I don't want to do more than change gearing on a brand new bike.
Since you have hands on experience with all the parts involved and I'm just thinking out loud at this point, do you think this would work out? Hypothetically. No pressure, no big deal, just curious.
I'll probably do it when I can get my hands on the sprockets and new chain. I'm not in a big hurry, just some time in the future.
Actually, since we may never get the Hi/Lo I'm hoping somebody comes out with a sprocket change setup like on the old CT200.

 

[AZ7000']

With your varied needs I would suggest running it stock first. I'm at altitude and can run it almost straight up 90 degrees from the trail for a 180 turn when I couldn't make the trail due to clearance and needing to go over rocks...

These are pretty nice as is, but the mods are inherent to us who would buy this bike. Ironically I haven't done anything to the 1974 except the reg/rect upgrade and a milk crate!

 

[r80rt]

I don't see why it wouldn't work just fine. I chose the 15/45 because my old trail 90's came that way stock, I knew it was pretty good gearing.
I have heard of sprocket changes causing he ABS to show a fault, but I haven't experienced that. You might try 14/45 and have a happy medium?

 

[r80rt]

With your varied needs I would suggest running it stock first. I'm at altitude and can run it almost straight up 90 degrees from the trail for a 180 turn when I couldn't make the trail due to clearance and needing to go over rocks...

These are pretty nice as is, but the mods are inherent to us who would buy this bike. Ironically I haven't done anything to the 1974 except the reg/rect upgrade and a milk crate!

You are right, the gearing on these bikes is pretty good as is, my only complaint was it wasn't slow enough in first gear. I wanted to go slower on some of these steep roads covered in gravel and loose golf ball sized rocks.

 

[fernf5]

OK thanks for the input guys. I'll probably give it a go later on. Gonna ride her as is for a while!

 

[r80rt]

Good plan, after a couple of hundred miles you'll know if you want to change anything. Give it time to speak to you.

 

[Spydie]

Were you the one on ADV having issues with the ABS? Could be the sprocket?

That was me. Every 10 miles on the highway (without any stopping) the ABS light starts flashing and the ABS quits working (fault light). Opmid, where my new speedometer comes from, said that is expected and you need a speed compensator to overcome that. They'll have one out in May. Off road, no problem because of the occasional rear wheel spin.