Service tips
Why your eMTB is eating chains, and how to stop it
A mid-drive will happily pull you around in the hardest gears. The chain and cassette are what feel it.
Riders keep coming in with a chain that skips under power, usually on the smallest cogs, after only a few hundred miles. Almost every time it's a full-power mid-drive, and almost every time those miles were in high assist and the hardest gears.
It isn't a defect. Some of the gentlest riders we know have done it. The motor makes a hard gear feel normal, so the chain takes a load you would have shifted out of on a regular bike.
From our service stand
A new cassette and chain at 250 miles
A few weeks ago a customer brought in a Turbo Levo Expert. Skipping under power, about 250 miles on it. He wasn't rough on the bike. He rode nearly every mile in the highest assist modes, in the 10, 11 and 13.
The chain was past its wear limit, and the small cogs had worn with it. A new chain alone would still skip on those teeth, so it was a chain and a cassette. On a 12-speed eMTB drivetrain, that's a lot of money for 250 miles.
It's not just trail bikes
We wrote a service bulletin for this
We started seeing the same thing on the Aventon Ramblas. A lot of our customers use it as a fast commuter, and bike after bike came in skipping on the small cogs, well before we'd expect. Often enough that we wrote a service bulletin for the mechanics and for customers.
The pattern was the same. Flat pavement, over 20 mph, smallest cog the whole time. Cruising fast in that gear is fine. The damage was everything in between: every stop sign and light launched in the smallest cog, slowing down without a shift, Turbo to get rolling again. On a commute with a lot of stops, that's a high-torque start on a few teeth, over and over.
Shift down as you slow for a stop, start in an easier gear, and shift up as you build speed. Ramblas owners can ask for the bulletin at either store, or call us with questions.
What's going on
Why mid-drives wear out drivetrains faster
On a hub-drive, the motor pushes the rear wheel. On a mid-drive, the motor turns the cranks, so the motor's power and yours both go through the chain and cassette.
Chain "stretch" isn't the metal stretching. The pins and rollers wear, so each link gets a tiny bit longer. Once it's long enough, it no longer sits on the cog teeth. It rides up, skips under load, and wears the teeth to match. That's why we want to catch it early. A chain is much cheaper than a cassette.
Gear guide
Which gear for which speed
Modern eMTBs have very wide gearing, often a 10–51t cassette. The smallest cogs are for going fast. Here's roughly how fast you need to be moving before each cog makes sense at 65–85 rpm.
| Rear cog | Speed at 65–85 rpm | When to use it |
|---|---|---|
| 10t | 19–25 mph | Fast riding only |
| 11t | 17–22 mph | Fast riding only |
| 13t | 15–19 mph | Fast, flat cruising |
| 15t – 18t | 11–16 mph | Cruising, rolling terrain |
| 21t – 28t | 7–12 mph | Trail riding, mild climbs |
| 33t – 51t | 4–7 mph | Starting out, steep climbs, technical trail |
Based on a 34t chainring and 29" wheels, which is common on eMTBs. Your bike's numbers will be a little different depending on chainring, wheel and tire size.
If you're in the 10t or 11t under about 20 mph, cadence has dropped and you're grinding. The motor will still pull you. The chain is the part paying for it. Shift easier.
Ride smarter
Four habits that save your drivetrain
If your legs are turning slowly and the motor is doing all the work, you're in too hard a gear. A steadier cadence is easier on the chain, and most mid-drives are happier there on the battery too.
Keep an eye on it
Signs your chain needs attention
Chains wear out on every bike. Replace yours before it takes the cassette with it. Watch for:
- Skipping or slipping when you pedal hard, especially in the smallest cogs
- Shifting that gets noisy or hesitant, even after an adjustment
- A chain that looks dry or gritty, or that you can pull away from the front of the chainring
Keep it clean and lubed, and have it measured with a chain checker. On a full-power eMTB that can mean every few hundred miles. Most 11- and 12-speed chains should come off around 0.5% wear. Catch it there and you'll often get two or three chains out of one cassette.
Questions
eBike chain and cassette wear
Why is my eBike chain skipping on the small cogs?
The pins and rollers have worn, so the chain no longer sits on the smallest teeth and it skips under power. On a mid-drive this can show up in a few hundred miles if most of the riding was high assist and the hardest gears.
Is a worn chain or cassette covered under warranty?
Generally no. Chains, cassettes and chainrings are wear items. Every manufacturer we work with treats that as maintenance, not a defect. That's why the gear you live in matters so much on a high-torque mid-drive.
How long should an eMTB chain last?
It depends on how the bike is ridden. With smarter shifting and less time in the highest assist, we've seen chains go well past a thousand miles. Mostly high assist and the smallest cogs, we've seen the chain and cassette done at about 250.
What cadence should I ride at on a mid-drive eBike?
About 65–85 rpm. If your legs are turning slower than that, shift easier. It's easier on the chain and cassette, and most mid-drive motors are more efficient there too.
Do I need to replace the cassette when I replace the chain?
Not if you catch the chain early. Once a chain is badly worn it shapes the cog teeth to match, and a new chain will skip on them. Then it's both.
Chain skipping? Bring it in.
Our Erie and Longmont service teams can measure your chain and check the cassette, and tell you whether it's one or both.
