I just bought a CT125 2023. As you know it has a 14" front sprocket and a 39" rear sprocket. I am going to use this cycle for hunting 80% of the time and have realized that the stock configuration is not going to work. I want to be able to able to go thru the woods at a walking speed or close to it and have enough power to climb hills etc. I may encounter while doing it. So slow and powerful. I am 76 years old and want to get to those places I used to hunt but are 4 or 5 miles into the woods. One of the reasons I bought the CT125 was it is automatic transmission and was a newer version of the CT90 I owned many years ago which had low/high gearing, the low gearing was great in the woods and the high was great down the dirt roads but sadly they did away with that. I will be on old logging roads, paths, and lots of times just thru the woods. I was thinking a 13" front and 45" rear but don't know if that is enough of a gear down to do what I want. I think top end on this is 55 or so mph, I would be happy with that being 40 to get the correct low gearing. Any suggestions as to rear sprocket size. THANK YOU.
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Chain and sprockets
- Thread starter skippy
- Start date
BaldRider
Well-known member
2023 has a 38 rear. Lots of discussion on the forum about sprocket changes. Probably the easiest thing to do is swap out the front for a 13T and see how that works for you. You can always go up in the rear but, at some point, you're going to have to get a longer chain.
In New Zealand the CT125 is offered with a "farm kit" that likely has some overlap with your intended use. It's been discussed a bit on this forum: https://hondatrail125.com/index.php?threads/ct125-farm.2574/
The kit has a 13T front and 51T rear sprocket, 114 link chain. You could piece those parts together yourself without being in New Zealand.
JT Sprockets JTF273.13 front sprocket, JT Sprockets JTR269.51 rear sprocket, and a #428 chain of your choice cut to length. Be aware that because vehicle speed is measured at the countershaft, changes to gearing can fault the ABS and they can make the speedometer/odometer/trip meter (more) innacurate unless you install a speedometer healer to compensate for the change in gearing.
The kit has a 13T front and 51T rear sprocket, 114 link chain. You could piece those parts together yourself without being in New Zealand.
JT Sprockets JTF273.13 front sprocket, JT Sprockets JTR269.51 rear sprocket, and a #428 chain of your choice cut to length. Be aware that because vehicle speed is measured at the countershaft, changes to gearing can fault the ABS and they can make the speedometer/odometer/trip meter (more) innacurate unless you install a speedometer healer to compensate for the change in gearing.
Farmer Mike
Active member
BaldRider is correct... drop the front to 13, the existing chain will be fine... and just see. I doubt it will be enough for your application, but you can probably go up a couple teeth on the rear before you have to get a new chain. These sprockets are pretty cheap really... so having an assortment isn't a bad thing. Wear parts are always a good thing to have around. Dig around on here in the sprockets thread, and you will find that you can't use the stock nuts on the JD rear sprockets. (well you can, but it's not advised).. you need something that is 13MM hex on the outside... readily available, I think the 14's that are on there are the anomaly. They have those at both Tractor Supply, and Lowes (that I'm aware of)... but if you want something maybe "better"... McMaster Carr. or if you have a FastenAll or equivalent in your area they can fix you up. There are other ways around that, but the simple fix is to just get new nuts.
Here's a link to the ones I'm using with a JT rear sprocket, in case you go that route: https://www.mcmaster.com/catalog/130/3645/93625A300
eastema
Active member
Skippy, if you will need low gearing 80% of the time, that large additional rear sprocket set up like on the early ct90s might be for you. Just keep a length of extra chain and master link to go around larger sprocket.
dmonkey, Thanks for the info on different nuts. Not being very good at this nut thing can you point out the product number that is in blue on the msmaster.com page that you mentioned in your shortcut above, that would be a great help, then I can order that exact item, THANK YOU.
Product number: 93625A300
This is a more direct link to the ones I have paired with a JT rear sprocket: https://www.mcmaster.com/93625A300/
18-8 Stainless Steel Nylon-Insert Locknut
M8 x 1.25 mm Thread, 13 mm Wide, 8 mm High
This photo was reusing the OEM lock nuts and illustrates how they sit against the ridges of a groove on the replacement rear JT sprocket:
OEM Staytite-style lock nut on the left, smaller head width nylon insert lock nut replacement on the right
The nylock installed flush (filthy after a downpour this morning)
This is a more direct link to the ones I have paired with a JT rear sprocket: https://www.mcmaster.com/93625A300/
18-8 Stainless Steel Nylon-Insert Locknut
M8 x 1.25 mm Thread, 13 mm Wide, 8 mm High
This photo was reusing the OEM lock nuts and illustrates how they sit against the ridges of a groove on the replacement rear JT sprocket:
OEM Staytite-style lock nut on the left, smaller head width nylon insert lock nut replacement on the right
The nylock installed flush (filthy after a downpour this morning)
Well I really thank you for all the info, it is much appreciated and will save me lots of time finding these. Thanks again. I bought a 13T for the front and a 51T for the rear as well as a 114 link chain. Will let you know how it goes.
Farmer Mike
Active member
Planning to climb trees? 
Here in Florida I think the high spot in my county is less than 200 feet above sea level... with just the 13 tooth front sprocket I have no problem trudging along at 3 mph on my property, just on dirt trails... I guess in Vermont you might have true elevation to deal with. That should certainly do it. Stock ratio between a 14:38 is 2.71... you are moving all the way up to 3.92 (assuming you do both). If you haven't see this chart before you can go search it out, if this isn't clear enough. Print it out, and hang it on your shop wall. I refer to this thing all the time. There are calculators that will give you detailed info on every gear, final ratio's, and even theoretical speeds in each gear, plus top speed, based on actual tire size... pretty cool. It's at: https://www.gearingcommander.com/
This chart, and the link above came from more seasoned people here, but it's certainly moved my understanding of my bike forward a good bit, and made my life more interesting.
It's not that I haven't understood this principle for a while, I have played around with ratio's between pulleys before for home projects, but this chart just makes your life much easier.
Here in Florida I think the high spot in my county is less than 200 feet above sea level... with just the 13 tooth front sprocket I have no problem trudging along at 3 mph on my property, just on dirt trails... I guess in Vermont you might have true elevation to deal with. That should certainly do it. Stock ratio between a 14:38 is 2.71... you are moving all the way up to 3.92 (assuming you do both). If you haven't see this chart before you can go search it out, if this isn't clear enough. Print it out, and hang it on your shop wall. I refer to this thing all the time. There are calculators that will give you detailed info on every gear, final ratio's, and even theoretical speeds in each gear, plus top speed, based on actual tire size... pretty cool. It's at: https://www.gearingcommander.com/This chart, and the link above came from more seasoned people here, but it's certainly moved my understanding of my bike forward a good bit, and made my life more interesting.
It's not that I haven't understood this principle for a while, I have played around with ratio's between pulleys before for home projects, but this chart just makes your life much easier.
bryanchurch06
Well-known member
- Joined
- Nov 4, 2022
- Messages
- 757
I currently run 13t front and stock 38t on back, I'm thinking about going back to 14t front and increasing to 42t on the back which if I'm reading the charts correctly should give me the same gearing and eliminate any future chain issues with to small a diameter in front. Do I need to order a longer chain than 108 link? My stock chain has 120 miles on it. I don't want to run a oring or xring chain at this time as I break the chain when I pull the back tire off, it's just easier for me to remove the chain guard and chain for clearance issues. Thank you for your help.
Last edited:
Farmer Mike
Active member
On the Gearing Commander website, there is a chain length calculator. playing around with the stock sprockets it looks like the generic distance from center of front/rear sprockets is likely 20.5 inches...
using that... looks like a 14:42 would yield the following... it will certainly get you in the ballpark. You could also likely double check that with sprocket center via customer support if that's where you plan to buy your stuff...
using that... looks like a 14:42 would yield the following... it will certainly get you in the ballpark. You could also likely double check that with sprocket center via customer support if that's where you plan to buy your stuff...
Got the nuts and everything worked as you said. 13t on the front, 51t on the back, 114 link chain, thanks so much.
RosscoP
New member
I've followed your post Skippy, because I have new 2024 coming and would like to do similar for similar reasons (I am only 74 though
) I might stay 14 on front. Did your chain guard still fit? Does ABS light come on?I have been doing a bunch of work/mods to my "new to me" 2022 CT125 to make it fit my applications. These mods included experimenting with front and rear sprockets to see if I could make this into a proper trail bike with some low end grunt and can better handle the steep terrain in my area. My neighborhood is "hilly" (steep) and lies at the base of a large mountain range. My house is at 5200 feet above sea level and I ride the mountain trails behind my house that go up to 9,000+ feet . I'm 6' 4" 225 LBs and I always carry extra gas, water and some gear/tools with me on the bike so, I know I'm asking a lot of this little bike to begin with.
I started by putting a 42 tooth rear sprocket with the stock 14 tooth front, which apparently is the same ratio as putting a 13 tooth on the front with a 39 stock rear. I certainly didn't get the effect I was looking for, but it was a little better pulling the steep hills both on road and off. I had a new 13 tooth front I order with the 42 rear and I knew it had to go on as well. The bike does much better now in all conditions for me. With the new Kenda K262 tires on it did great climbing some wet sandy and gravel hills without a complaint. The same hills I had to help it a lot with my feet when stock.
On the flat or slight hills the bike will always accelarate now and is way less boggy in every gear/rpm range. I can hit 47 mph on the speedo, which I know isn't accurate now, but is plenty fast for my area. I don't feel like the bike is over reving at all. My ABS light did come on, but not until after several miles of riding. I put a cheap $19 RK 110 link chain on it for now. I wanted to see what size chain I would end up needing after I settled on the sprocket set up. The 110 link leaves only about one inch left on the painted portion of the swing arm as far as adjustment. The stock 108 will fit, but you lose some wheel base and it puts your rear tire a little close for my liking toward the front of the fender. A 109 link would probably be about perfect for the 13/42 sprocket.
I started by putting a 42 tooth rear sprocket with the stock 14 tooth front, which apparently is the same ratio as putting a 13 tooth on the front with a 39 stock rear. I certainly didn't get the effect I was looking for, but it was a little better pulling the steep hills both on road and off. I had a new 13 tooth front I order with the 42 rear and I knew it had to go on as well. The bike does much better now in all conditions for me. With the new Kenda K262 tires on it did great climbing some wet sandy and gravel hills without a complaint. The same hills I had to help it a lot with my feet when stock.
On the flat or slight hills the bike will always accelarate now and is way less boggy in every gear/rpm range. I can hit 47 mph on the speedo, which I know isn't accurate now, but is plenty fast for my area. I don't feel like the bike is over reving at all. My ABS light did come on, but not until after several miles of riding. I put a cheap $19 RK 110 link chain on it for now. I wanted to see what size chain I would end up needing after I settled on the sprocket set up. The 110 link leaves only about one inch left on the painted portion of the swing arm as far as adjustment. The stock 108 will fit, but you lose some wheel base and it puts your rear tire a little close for my liking toward the front of the fender. A 109 link would probably be about perfect for the 13/42 sprocket.