Sprockets

[SneakyDingo]

Watch out! WAtch the road! Evel Kneivel did not have a speedometer on his bikes because it would give him a reason to look down,not at the road. Mod it,ride it. Maybe it is where I live,but I could outrun myself on the Red Rocket vs my KTM 390 ADV , or my DR 200.

I will keep that in mind when I plan to jump 14 schoolbuses on my Honda Trail.

 

[SLO]

I will keep that in mind when I plan to jump 14 schoolbuses on my Honda Trail.

If you jump just one with it, you will become a legend. I would wait until I knew I had nothing to lose before I attempted it though. You got time,keep us posted!

 

[SLO]

I'd trust the speedometer (with OEM tires and gearing) to give a more accurate read at low speed, GPS for a more accurate read when you're looking at top speed. You could certainly dial in the speedometer to be more accurate with a speedo healer or an aftermarket unit though.

Smartphones and dedicated navigation devices like a Garmin, TomTom, or even bicycle computers can account for curvature of the earth as well as elevation change for displaying speed. Surface mapping (2D) is different, but GPS signals provide data for 3D mapping and many newer consumer devices make use of it. Still not perfectly accurate. They GPS is not showing you nautical miles per hour unless you've got it set to, and it's not going to disguise nautical miles per hour as miles per hour since those are different units of speed.

GPS pitfalls are largely signal blockage, signal reflection around tall buildings, changes in speed or direction that occur in a short time or distance that the few meters range of accuracy isn't precise enough to account for when averaged out, and bad data from satellites often related to space weather events. Some of those issues can be partially compensated for on phones by using more sensor data (magnetometer, gyroscope, or accelerometer), A-GPS which uses cell towers to quickly and more accurately pick up on the device's location, or Wi-Fi positioning system which uses known WiFi network locations to get a rough idea of where the device is when there isn't an open sky for GPS or enough towers for A-GPS. IMO those features add privacy concerns, but not much different than carrying your phone along with WiFi and cellular enabled.

The CT125's speedometer reading is also an indirect measurement of ground speed. It's measuring rotation at the countershaft with no regard for chain and sprocket wear, variances in tire circumference from tread wear, load or pressure, or where contact is being made on the tire. I don't think Honda dialed it in to be very accurate when stock and new either, but instead targeted a percentage variance that doesn't under report the speed while accounting for what some average of those other variables might work out to be.

@vintagegarage put together a video comparing speedometer readings to GPS readings. If I caught highest speeds right, the speedometer hits a maximum of 57 mph while the GPS hits a maximum of 55 mph in the clip.

The difference in mph scales, so mph difference at low speed isn't very observable, mph difference at high speed is more observable while only useful given the context of that speed. A percentage scales, though basing a percentage on an imprecise unit of measure (mph in whole numbers, made as precise as we can by using the top speeds) results in a percentage that may not be very precise or accurate. Can still work that out for a rough number though.

Difference: 57 mph - 55 mph = 2 mph
Average of the two speeds: (55 mph + 57 mph) / 2 = 56 mph
Percentage difference: (2 mph / 56 mph) x 100% = 3.57%

Mine will go faster than even I deem safe. Curved roads,cows,deer, and I almost got taken out by a ground hog at 45 mph. I had just hit a straight stretch of road and backed off the throttle since I was going fast enough. That split second let the vermin pass in front of my front tire by about 6 inches.

 

[WParent]

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.

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I’m really interested in this gearing. I had an old 50 cub 1960 from a dealer in AZ that modified them for hunting. Not sure this will climb trees like my cub did but i imagine it improves the low speed torque considerably. Can the original 14 tooth from be used with this rear sprocket?

 

[Coldrider]

Have posted before on wanting lower gearing as first had installed the 13 tooth sprocket but found it to be only a small improvement. Next step was to install the 42 tooth reat sprocket but again found myself wanting yet lower gearing. So today installed the 45 tooth rear sprocket (JT269.45 from JT Sprockets) and finally found the gearing to be closer to what I needed. Was surprised that I did not have to switch to a longer chain when switching between the 42 and 45 tooth sprockets which is good as had installed a new O-Ring chain at the time I went with the 42 tooth sprocket. There is a ridge on the JT sprockets that slightly interferred with the attachment nut so ground the ridge down but am questioning if I really would have had to as the interferrence is minimal. So now I have the 13 tooth sprocket on the front and 45 on the rear. For my use I don't envision ever using anything other than 1st and 2nd gears and haven't so far so can't report on the effect on top speed.

 

[Shoot870p]

coldrider, what length chain are you running? 112 links?

 

[Coldrider]

coldrider, what length chain are you running? 112 li

I started out with 118 links but then used the chain brake to take out some links to fit. Next time I get out to the shop (23 miles away) I will look to see if I can find the links that I removed but am thinking it was four but not sure. I was able to use the same chain in switching between the 41 tooth and 45 tooth rear sprockets. Please excuse my ignorance in dealing with chains. With the original chain length of 108 links, then going from the 39 tooth rear sprocket to the 45 tooth am wondering if it would take 6 more links of chain length which would put it at 114 links ? As I remember, switching from the 14 tooth front sprocket to the 13 tooth resulted in a very minimal difference in the chain adjustment.

 

[Coldrider]

coldrider, what length chain are you running? 112 links?

I started with 118 links and after taking the amount showing in the picture I had ??? remaining. Am not good with chains so did I remove 5 links? 4 links?

 

[dmonkey]

That's 8 links removed. Each set of inner plates are a link, and each set of outer plates are a link. It will always be an even number to complete the chain since it's alternating inner and outer links.

 

[Shoot870p]

And my schooling continues!
thank y’all.

 

[SneakyDingo]

It will always be an even number to complete the chain since it's alternating inner and outer links.

One teeny tiny exception to this: there's such a thing as half links, where one end is an inner link and the other end is an outer link.

 

[Hunterhenderson]

Hello everyone, im looking at putting a 45 tooth sprocket on the back, can someone tell me what size(links) i will need on the new chain, assuming Ill need one

Bruce

 

[SneakyDingo]

Hello everyone, im looking at putting a 45 tooth sprocket on the back, can someone tell me what size(links) i will need on the new chain, assuming Ill need one

Bruce

Someone asked about how few links you can run. I did some math here.

How many links does it take…….

To Fit on a 22 trail with a 13 tooth front sprocket?

hondatrail125.com

Using a similar approach, a 14-45 combination would be 55.6" chain; 55.6" * 2 = 111.2 links or a 112 link chain. If you were to slide the wheel to the most forward position, it changes to a 54.1" long chain, or 110 links as an estimated minimum. So you'll very likely need to buy a new chain, and I'd start with cutting it to a 112 link chain since you can always cut a chain shorter, but not longer. These numbers were estimated on the red Honda Trail; if you have a newer model but it still uses the 108 link 428 chain by default then those numbers should still hold true.

 

[dmonkey]

Chains are often priced in ranges based on link count, where the price might go up every 10 links or so. If you have a chain tool or grinder and would like to keep a few spare links or have some wiggle room to stage the chain on the bike and measure twice before cutting once, then it might be worth buying the most links of chain that you can get before the next price bump. Instead of buying the exact length of chain that you expect to need ready to go, this approach gives you some flexibility and spare links.

 

[Hunterhenderson]

I just changed out my Canadian 2023 CT125 to 13/45, ordered a new chain and broke it to length, just got home from a ride, .....way better 0-50 kmph and about the same top speed, but acceleration is amazingly better, way faster bottom end

 

[CB Spoolmak]

Can anyone confirm the JTF273 13 sprocket fits the 2023 JA65 as well as the 21/22 JA55? There are subtle engine changes for '23, I am hoping the counter shaft isn't one of them.

 

[Hunterhenderson]

mine is a 2023 and it fits

 

[blav367]

Is there bigger than 45t rear?

 

[CB Spoolmak]

Is there bigger than 45t rear?

I have found JTR269 in 49, 50 & 56. I am running a 49 (114 links) & it fits fine under the chain guard. The 56 might need some trimming of the guard at the cutout for the shock to clear.

 

[Hunterhenderson]

i had a 13/45 on mine and it was too low, put the 14 back on and way better now, except for that dam abs light flashing