Drivetrain
Chain and sprocket wear
A chain is the one part on the bike with a hard, measurable replace limit, and it is also the part most often replaced on a guess. The limit is 3 percent elongation. Everything else, including every kilometre figure you will read, is a prompt to go and measure it.
The 3 percent limit
A motorcycle roller chain, 420 or 428 or 520, is replaced at around 3 percent stretch over its original pitch length. Do not carry a bicycle number across: a bicycle chain is finished at 0.5 to 0.75 percent, because it has to shift between closely spaced sprockets. A motorcycle chain runs on one fixed pair of sprockets and tolerates far more before it starts destroying them.
Loam Moto treats a measured elongation as the only signal allowed to mark a chain red. It uses the 3 percent limit as full life, so a reading turns amber for a closer look at about 2.25 percent, which is three quarters of the way there, and red at 3 percent.
How to measure it
Put the bike on a stand, get the chain under light tension on its top run, and measure across a span of links, pin centre to pin centre. Compare that against the same span when new. The chain standard gives you the new figure without needing a new chain to hand: 420 and 428 chains have a 12.7 mm pitch and 520 has 15.875 mm.
- Over 20 pitches, a new 420 or 428 chain measures 254 mm. The 3 percent limit lands at about 261.6 mm.
- Over 20 pitches, a new 520 chain measures 317.5 mm. The 3 percent limit lands at about 327.0 mm.
- Measure at several points around the loop. A chain rarely wears evenly, and the worst span is the one that counts.
Your own service manual may specify a different span and its own service limit. If it does, that wins. So does the physical test: a chain with a tight spot, a kinked link, or a link you can lift clear of the rear sprocket teeth is done, whatever the tape says.
Why the kilometre figure lies
Every source publishes a different chain life, and they are not close to each other:
| Source | Figure | What it actually is |
|---|---|---|
| Sur-Ron and Ultra Bee manuals | 20,000 km / 24 mo | A scheduled service-table maximum, with staged checks from 5,000 km. Not observed chain life. |
| Independent e-moto sources | 1,000 to 5,000 km | What owners report replacing at in real off-road use. One well-known guide says 1,000 to 1,500 km. |
| Another independent source | annual, or 6 mo | Calendar, not distance, with 6 months for hard off-road use. |
| KTM and Husqvarna 4-stroke enduro | inspect 15 h | Not a life figure at all. Inspect the chain, sprockets and chain guide at every 15 hour service, and clean and lube every ride. |
That spread is not sloppiness, it is the honest answer: chain life depends on mud, sand, water, chain care and how hard the bike is ridden, and those move it by more than a factor of ten. Loam Moto therefore uses distance only as a late reminder. Past roughly 8,000 km it starts prompting a mid-life inspection, and past 20,000 km, the manufacturer scheduled maximum, it raises an amber prompt to measure. Neither goes red, because distance alone has never earned the right to tell you a chain is finished.
Free play, the number that varies by bike
Chain slack is per model, and the published figures genuinely disagree, so this is one to read out of your own manual rather than off a table. For reference, from the manuals themselves:
| Bike | Free play | Confidence |
|---|---|---|
| Sur-Ron Ultra Bee | 10 to 25 mm | From the owner's manual and confirmed. |
| Talaria Sting R and MX4 | 15 to 25 mm | Manual only. No second source found. |
| Sur-Ron Light Bee, 2019 to 2021 | 10 to 15 mm | From the manual of that generation. |
| Sur-Ron Light Bee, 2022 to 2023 | 10 to 20 mm | From the manual of that generation. |
| Sur-Ron Light Bee, 2024 and later | 15 to 30 mm, unverified | The figure appears in the manual but our verification pass found the same 15 to 30 mm quoted elsewhere as brake-lever clearance. Check your own manual before setting it. |
Measure the slack at the tightest point of the loop with the bike unladen, and remember the swingarm pivot geometry: a chain set correctly on the stand can go bar tight under full suspension compression if it was adjusted at the wrong point. Too tight destroys the output bearing and the chain together, and it does it quietly.
Lube, which is most of chain life
Nothing else you do moves chain life as much. Loam Moto runs a re-lube distance clock alongside the wear clock, defaulting by lube type:
| Lube | Re-lube | Notes |
|---|---|---|
| Dry lube | 100 km | The default when the type is not set. Sheds dirt well, needs re-applying constantly. |
| Wax | 250 km | Stays cleaner in dust, wants a properly clean chain to start with. |
| Wet lube | 300 km | Lasts longest and collects the most grit. Not a licence to skip cleaning. |
Mark a ride as wet or muddy in the app and the re-lube clock shortens to 60 percent of that distance until you lube it again, and the drivetrain clean nudge pulls two weeks earlier. Water and grit strip lube fast. For comparison, the Talaria MX4 manual asks for a clean and lube roughly every 1,000 km or every month and at each service, and the Sur-Ron schedule lubes at 100, 500 and 2,000 km early in the bike's life. Off-road, every ride is closer to the truth.
When the sprockets go with it
A stretched chain no longer matches the pitch the sprocket teeth were cut for, so it climbs slightly and reshapes them into hooks. Once that has happened, a new chain on old sprockets wears out fast, and new sprockets under an old chain do the same. If either sprocket has hooked, pointed or unevenly worn teeth, replace the chain and both sprockets as a set. The front wears faster: far fewer teeth share the same load, so each one takes more of it.
Nobody publishes a sprocket life figure that survives contact with off-road riding, so this stays condition-driven. The soft prompts Loam uses are an inspection nudge around 12,000 km on a petrol bike and around 6,600 km on an e-moto, which is the same interval scaled for the extra weight and torque. Like the chain distance prompt, it is amber at most and never a replace order. The manufacturer service tables that do list sprockets, on the Sur-Ron Light Bee and Ultra Bee, stage them the same way: a check from 2,000 km, a check-or-replace at 5,000 and 10,000 km, and replacement with the chain at 20,000 km or 24 months.
Conditions decide this one more than any other part. Sand is the worst thing that happens to a chain, mud is next, and a pressure washer aimed at the drive side undoes a good lube job in seconds. A chain that lasts a season of dry trail can be finished in a handful of wet rides. Measure rather than assume, and check free play and condition before every ride the way the manuals ask.
What the app does with all this
Enter a measured elongation and it drives the real status, amber from about 2.25 percent and red at 3 percent, so the number on screen is yours, not a guess. Without a measurement the chain stays quietly healthy until it passes the typical distance window, then asks you to go and measure it, and it never escalates further on distance alone. Re-lube runs on its own distance clock from the last time you marked it lubed, and replacing the chain resets the wear clock while leaving the sprockets on theirs.
FAQ
When should a motorcycle chain be replaced?
At about 3 percent measured elongation, or immediately if it has a tight spot, a kinked link or a link that lifts clear of the rear sprocket teeth. Around 2.25 percent is the point to start watching it closely.
How many kilometres does a dirt bike chain last?
There is no honest single number. Service tables say up to 20,000 km, independent off-road sources say 1,000 to 5,000 km or simply replace annually, and both can be right depending on conditions and chain care. Use distance as a reminder to measure, never as a replacement date.
Do I have to replace the sprockets with the chain?
If the teeth are hooked or pointed, yes, and as a set with the chain. A worn chain reshapes sprocket teeth, and mixing new with old wears the new part out quickly. The front sprocket goes first because it has the fewest teeth.
Measure once, and let the app remember
Loam Moto keeps your measured chain elongation, your re-lube distance and your sprocket inspection prompt on separate clocks, fed by the distance you actually rode. It never claims a chain is finished on kilometres alone. Any motorcycle or e-moto, petrol or electric, with your garage and your GPS tracks staying on your phone.
