Known Issues & Problems with Tern Products + Help, Solutions & Fixes

Ann M.

Well-Known Member
No ebike is perfect, this is a thread dedicated to sharing known issues or problems with electric bikes from Tern as well as any help and solutions you know of. Sometimes that means a DIY fix and other times it can mean a recall, software update or part replacement by a dealer.

Please be respectful and constructive with feedback, this is not a space for hate speech. In many cases, representatives from the company will see feedback and use it to improve their product. In the end, the goal is to enjoy riding and help each other go further and be safer.
Hello to Tern users,

I have been asked to look at a quite new GSD S10 regarding drivetrain noise and upon inspection discovered a rather bizarre design decision wrt the chain tensioning wheel. I tried to find information about this but most results are for an earlier version of the GSD.

The short question: is the chain supposed to enter the derailer cage at such an extreme angle? (see photo)

If not, what is the fix?

If this is "normal", how is it possible this passed the design stage? The sideways stress on the chain is unnecessarily extreme, and it is impossible to tune the shifting to achieve quiet operation in the lowest gears (especially first).

In first gear, the chain attempts to ride up off the lower idler wheel of the derailer and then pops back down - the result is rough pedal feel and high noise levels.

Even in other gears, the chain passing over the smooth (non toothed) tensioner wheel creates a vibration that affects pedal feel. It seems like this wheel only exists so that the kickstand design can be accommodated.

It seems to me there are three options here:

1. Use a longer bolt and spacer to move the tensioner closer to centerline
2. Redesign tensioner to use a toothed idler wheel that can slide in and out on a shaft
3. Modify the chainguard and kickstand to make room for the chain to pass straight to the derailer without a tensioner (there should be no need for a tensioner on a longtail with this moderate length chainstay)

I can't believe these folks are the only ones to experience this symptom. I'm interested in others' thoughts and experiences before I make a recommendation to them. They are currently second guessing their investment in this bike.