Set-up & adjustments · 79Bike · Sur-Ron · Talaria
How to adjust chain tension on an electric dirt bike (79Bike, Sur-Ron, Talaria)
A loose chain jumps under the instant torque of an electric motor; a tight one wears the sprocket, front sprocket and bearings within a few hundred kilometres. Adjusting it takes 20 minutes with basic tools. Here is the method we use in our workshop.
Why tension matters more on an electric bike
An electric motor delivers full torque from the first turn of the wheel (up to 410 N·m at the wheel on a Falcon Pro or Lynx in off-road mode, 610 N·m on a Falcon GT). Every hard launch snaps the chain. Too much slack and it slaps the swingarm, skips teeth out of corners and can derail. Too little and it goes tight as the suspension compresses, hammering the wheel and motor output bearings.
How much slack?
On electric off-road bikes of this size, the usual working range is 20 to 35 mm of vertical play, measured halfway along the bottom run, bike on its stand, rear wheel on the ground, no rider. Your owner's manual always takes priority: if it gives a value, use it.
- Under 20 mm: too tight — accelerated wear and tight spots.
- Over 40 mm: too loose — risk of the chain jumping.
Find the tightest spot
Chains and sprockets never wear perfectly evenly. Turn the rear wheel by hand and measure in three or four positions: always adjust at the tightest spot. If the difference between the tightest and loosest spot is over 10 mm, the sprocket is probably bent or worn — see our guide on replacing the chain kit.
Alignment: the step everyone skips
Left and right adjusters must be moved by exactly the same amount. A misaligned wheel wears one side of the chain, heats the sprocket and hurts handling. Check the marks on the swingarm, then sight from behind the wheel that the chain runs straight onto the sprocket.
Tools you need
- Spanners or sockets (model-dependent, often 10, 13 and 22/24 mm for the axle)
- Ruler or tape measure
- Torque wrench
- Chain lube
- Rag and degreaser
Step-by-step procedure
- 1
Prepare the bike
Bike switched off, battery disconnected if your model allows it, on its stand with the rear wheel on the ground. Clean the chain so you can see the links.
- 2
Measure the slack
Halfway along the bottom run, push the chain up then down and measure the total movement. Repeat in 3 to 4 wheel positions and use the tightest reading.
- 3
Loosen the axle
Loosen the rear axle nut just enough for the wheel to slide, without removing it.
- 4
Turn the adjusters
Turn the left and right adjuster bolts by the same amount (a quarter turn at a time) to pull the wheel back and tighten the chain, or the opposite to loosen it.
- 5
Check alignment
Make sure the marks are identical on both sides and the chain runs straight onto the sprocket.
- 6
Tighten and re-check
Torque the axle nut to the manufacturer's value, lock the adjuster nuts, then measure again: tightening the axle often changes slack by a few millimetres.
- 7
Lubricate
Lube the bottom run while turning the wheel by hand, then wipe off the excess after a few minutes.
Useful genuine parts
In stock, shipped in 3–10 business days.
FAQ
How often should I check chain tension?+
A 30-second visual check before every off-road ride, and a proper measurement every 2–3 rides or roughly every 150 km. A new chain stretches faster during its first 100–200 km.
My chain goes slack quickly after adjusting. Why?+
Usually an under-torqued axle nut or adjuster lock nuts left loose. If everything is tight, the chain is probably worn out (stretched): measure it or replace the chain kit.
Can I set the tension with a rider on the bike?+
No — always measure with the bike unloaded. With a rider, the suspension compresses and the chain tightens, which is exactly why it needs slack at rest.
Key takeaways
Adjust at the tightest spot, move both adjusters equally, torque the axle and measure again. If slack varies a lot over one wheel turn, it is no longer an adjustment issue but a worn chain kit.
Need a hand?
Our workshop in Toulouse Sud (France) services 79Bike, Sur-Ron and Talaria. Send us a photo or video of the problem.
Related guides
These guides are for information only. If in doubt about a safety-critical part (brakes, steering, wheels), have a professional do the work. Always follow the manufacturer's manual.