Rear Chain Sprocket (45T) | Honda CT90 / Trail 90
High mileage, a loose chain, and missed lubrication all chew up rear sprocket teeth — and once the teeth go sharp and uneven, the sprocket starts eating chains. This is a 45-tooth replacement rear chain sprocket in high quality steel for the Honda CT90 / Trail 90, made for the factory 428-pitch drive chain.
Why You Need This
Worn rear sprocket teeth become sharp, pointed, and unevenly worn. The rear is the driven sprocket and is made of softer steel than the front, and unlike a Honda front sprocket it cannot be flipped over for a second life — one direction only. The good news is that rear sprockets last a long time when the chain is kept lubed and adjusted, because chain care is what preserves sprocket life.
When you do replace it, put a new chain on with it — a fresh sprocket under a stretched, worn chain wears out early, and the same goes the other way around.
Specifications
| Replaces OEM Part Numbers | 41201-053-505, 41201-053-020 |
| Fits Models | CT90 K0–K8 (1966–1977, see K0 note), CT90 (1978–1979) |
| Chain Pitch | 428 |
| Tooth Count | 45T (factory stock) |
| Sold As | Sold Individually |
Note: Early CT90 K0 models used unique overlay sprockets instead of the dual-range setup on later K0s. This sprocket fits Trail 90 K0 models from Frame SN 138201 and up.
Note: Always fit a new drive chain with a new rear sprocket, and lube it before riding.
Installation
Difficulty: Beginner
Torque the sprocket holding nuts to 13–18 ft-lb with a drop of blue Loctite on the threads, then fold the special locking washers back up against the nut flats so nothing backs out over time.
Once the wheel is back in, set the chain free play to about 20 mm (0.8 in.) measured midway between the sprockets with the bike on the center stand, and keep the chain lubed and adjusted from there.
Our Sprockets 101 video covers how sprockets wear, why front, rear, and chain get replaced as a set, and how to figure chain length after a change.
Frequently Asked Questions
Is 45 tooth the stock size for the CT90?
Yes. The factory CT90 setup is a 15-tooth front sprocket, this 45-tooth rear, and a 104-link 428 chain.
Will this fit my early CT90 K0?
From Frame SN 138201 and up, yes. The earliest K0 models used unique overlay sprockets instead, and this sprocket does not fit those.
Do I need a new chain too?
Yes — always fit a new chain with a new rear sprocket. Our CT90 428 drive chain is cut to your specified link count before shipping.
How do I know my rear sprocket is worn?
Look at the teeth: sharp, pointed teeth with uneven wear mean it is done. The rear cannot be reversed to stretch its life the way a front sometimes can — once it is worn, replace it.
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Last updated: June 2026
