Sentinel1

That was a typo should have been 15,000 miles. Per bike across the 3 terns I have owned. So about 45,000 miles.

The design isn't floored. It's as good as it gets So let's say there were some duds. That doesn't represent the experience of tens of thousands of other riders. That own Tern verges. You can find a bad batch in many products in the commercial world. But I will stand by my previous statement. Alot of riders abuse their bikes and do zero maintainance on them. And then will be surprised when something goes wrong. And you cannot argue that point. It's a fact. You look after your bike. And it will look after you. If a rider does a bike check before they set out. Any structural damage would be identified. Then it's on them to ride the bike or not ride the bike. And obviously anyone with any sense wouldn't ride the bike.

A frame that has no previous damage. Doesn't just SUDDENLY snap in two. Unless its weight limit is abused. Or it's been improperly used like jumping ramps steep curbs etc. That's a fact no one can refute.

Fentuz

10 years ago tern was known for frame cracking due to poor weld and heat affected zone. Admittedly dahon Mu SL had similar issues but in smaller proportions.

ultimately the curved frame design from the late 2000’s (dahon curve, dahon mus, tern verge) is mechanically compromised as it has a beam going into a single hinge. Things like the helios are a bit better because of the small bar that takes some of the load.

ultimately, one of the best folding bike from a mechanical rigidity point of view is the dahon dash/hammerhead etc. Because it is a diamond shape but the foldability is not great.
the dahon clint showed in another thread is best as it is a diamond shape with a foldable TT handlebar post that fold like a MUsl.

Shame Dahon is not selling as well as it used to and shame that Tern does not make one of them with kinetix comp pro and ultegra like groupset…

Duragrouch

So, there's quality, and safety. On safety issues, generally, manufacturers try to have a margin of safety at least 2X max load or 2X max fatigue strength before failure. Aircraft may have only 1.5X margin due to critical weight issues. Load test is straightforward, fatigue is different as it involves different loads at different occurances; Usually the manufacturer will instrument a product with strain gages and accelerometers and then run it on a durability test course, then use that data to devise a fatigue test. With many years experience, they can sometimes distill that info into one loading magnitude, over a certain number of cycles with no failure, if it passes that, they have confidence. This also allows a much faster fatigue test. This is known as a "bench" test, versus on-vehicle.

IIRC, Tern has touted their GSD meeting stringent European strength standards for utility bikes (I think, if my memory is correct). Prior to Tern going all-in on premier electric bikes, I don't know their level of testing on prior models. Many have spoken of weld-quality issues identified in past. I have no specific knowledge of this, but I think this was confirmed with regard to a past recall. But a used Tern that was for sale at a LBS, I did my homework, saw reported problems (was supposed to be recalled), and went back to look the bike over, and it seemed clear to me a design deficiency, it was a very similar frame style to Dahon Mariner, but lacked a gusset(?) in a critical area that the Mariner had and the Tern didn't (an additional layer of aluminum welded over the tube, at the bottom of where the front tube connects to the hinge).

So, my point is, I don't know the test specs on Tern models, and neither do you. All the time you see on aftermarket automotive parts packaging, "Meets or exceeds OEM (Original Equipment Manufacturer) specifications!" No it doesn't. Those test specs are closely guarded proprietary secrets. The OEM would not give an aftermarket supplier those specs.

So I think it is risky for anyone to make claims, positive or negative about Terns in the absence of data. Riding multiple examples of the same frame design over years, 15,000 miles each (that's about 2-3 years riding for me at my peak), is not really a valid fatigue test, especially if the rider weight is well below max specs and not hammering the pedals like a racer. So this is anecdotal; To quote Jackson Browne, "Don't believe that it won't happen just because it hasn't happened, yet." Failures, on the other hand, are a different story; A couple Boeings fall out of the sky, another blows a door plug off at altitude, and it is clear there is a design or process quality issue or both. Tern is like that. They've made some good bikes. They've made bikes with problems. I think they are getting better. I would feel better if I knew they were doing cyclic fatigue tests on all designs, do destructive weld tests or section and examination on first and last frame of each shift or lot, statistical process control, etc, all marks of modern competent companies. Plus ISO 9000 (or whatever version it's called now) quality certification.

The above is said without malice. I worked in engineering. And as an engineer and later manager, I encouraged debate and critical analysis and openness to the ideas of others. But equally important, I *required* of all staff that they "play well with others", meaning no anger, no intimidation, let's listen and all work together to produce the best product possible.

Of late, I'm seeing more intervention from the forum moderators. I'd expected it sooner. I was active on a different forum online and would see flame wars, usually the same person or persons, and it didn't take long for a time-out suspension, they came back, flamed again, and they were sent to banned camp (a pun in the USA). I hope that doesn't happen here. Most of my friends have died or moved away. I wasn't active on BF until I saw the folding group, and that sucked me in deep. It's now an important social contact for me. I really enjoy being here. I hope you folks all do too.

Duragrouch

All valid points. But Deltech helps the Dahon (and any hinged monobeam) designs a lot. Enough for them to increase max load from 231 lbs to 300 lbs, and, double the warranty to 10 years, both of those are huge from an engineering standpoint. Looks like they are putting this on most models now. I didn't wait until Dahon releases an aftermarket version of Deltech (shown online), I made my own from a double-run of kevlar line. Big reduction in frame flex, both bending and torsion, and I haven't had to adjust the hinge since, over a year now.

Sentinel1

Good post all you say is true. And I can only go on my personal experiences with the Tern Verge bikes I own. They supposedly have weight limits of around 105 to 110kg. Ive weighed between 85 to 92kg in the time I've ridden them. So they wouldnt have been put under any great stress in that area.

I also primarily ride on paved roads. So no extreme stresses there either. A bike like the X11 will go forever. Its immaculate. I haven't had to touch the hydraulic brakes in 7 years. Or tune the gears. They are insane quality. But that frame is immaculate too. And there's no give even in the handle bar stem after 7 years. This is why I am so passionate and defensive about the Verge model. I cannot see how it could fail unless abused. A moderate cyclist like myself averaging 12 miles a day. The bikes gonna last a lifetime.

I have Friends who do mountain biking. And they've broken 2 grand mountain bikes in a week. Because of the extreme uneven stresses they put the bike through. Bike riding is not a level playing field. Constantly banging the frame from a height onto hard ground and rocks. Is a whole other ball game.

Duragrouch

Good post. Well-reasoned.

It reminds me, a friend of mine, I think 6 years ago, built up an electric bike for his wife to commute long distances, before a bike with that capability was common or moderately priced. He used as a foundation, a downhill mountain race bike, mega-travel suspension front and rear due to expected road speeds, in good condition. I asked why. (New Zealand accent): "Uh... because you can drop it off a 5-story building and it'll be unscathed."

Sentinel1

Yes Electric bikes. I borrowed a Fiido M1 pro from a friend once to try commuting to work. And the engine cut out half way there. I tried to ride that 60lb bike manually up my normal hills. Omg nearly killed me.

Duragrouch

Well this is especially fun to read, only to me. In boating, people are constantly referring to the motor, when it's an engine. You're referring to an engine, when it's a motor, completes the circle, we have a moment of Zen.

Due to my bifold frame shape, people are always asking if my bike is electric. I tell them no, I ride for the exercise, and an electric would be an even worse lug up my apartment stairs, no elevator. My bike is ridiculously heavy, 28 lbs new, but with front and rear racks and panniers, trunk bag full of tools and spares, aero bars and bar-ends, backup warm clothing and water bottle, it's 55 lbs I need to lug up and down stairs, which I do unfolded. Even harder back up with groceries. Electric motor and battery, it would be too much.

Fentuz

yes, the line is a good patch to add mechanical integrity but still a “add on”.

ultimately, with the given set of “design input”, easy foldability and weight were more important than rigidity which makes sense as these are commuter rather than race machine.

Duragrouch

The problem is, I'm using my folder as my daily townie, lots of miles. First frame broke at seat tube due to plastic bushing and slot on front of tube. Second frame may hold up, slot still in front but aluminum bushing. Later frames put the slot in back.

If the hinge fails, next folder will have a solid monobeam and swinging rear triangle, a messier fold, but I don't fold mine often. Possible bike friday, but I'd put a hinged folding stem on it instead of their removing one.

Folding mine twice a day for commute would be a drag; I need to keep the hinge and stem latches pretty tight to prevent movement, which makes them a bit of effort to unlatch. Mine is an occasional folder, not a daily. For a daily folder, it would be a Brompton or Helix, Brompton if I needed to roll it folded. Or a Curl D9.

Sentinel1

All I can say is I'm glad my X10 only weighs 21lbs. And my X11 23lbs and I only live on the first floor. Carrying these bikes is very easy for me even at 60.

Fentuz

The hinge pivot axle of my jetstream broke because, I could not help myself and kept jumping curbs etc. and after 10years, it was well out of warranty.
A subcontractor of mine did me a favor a turned a ne axle out of custom 455 H900 and he electropolished it for good measure... perfect but I will have to admit that it is likely to have move the potential failure towards the cast aluminium part of the hinge.