How to bypass folding bike weight limits

Innovation

December 27th 2016

By Bob Forgrave

Three times in recent weeks, I’ve gotten questions about weight limits for CHANGE bikes, because folding bikes typically have smaller wheels and frames with built-in stress points. The wheels have to go around faster to go the same distance, they’re working harder, and so is the frame, so every bit of weight matters on a standard folding bike.

The best way to see the difference is to look at a standard bicycle the way engineers do, as a set of forces. Your weight is a force, and the resistance of the ground is a force; both put stresses on the frame. Here are two stress cases, where more stress on the frame shows in red:

This stress case is about rider weight. Look at which bar is red.

This stress case is about a rider hitting something in the road with the front wheel. The force travels up the fork. Look what part of the frame turns red.

A big part of the reliability of a standard bike frame is the triangle design. No matter where a force comes from, there’s always a supporting, resisting tension on a nearby bar. Now look at a common folding bike design.

All forces are concentrated in a single, highly stressed bar. And just for good measure, cut it in half and add a latched hinge, to make it super-stressed!

Same problem. Same limitation.

As a result, folding bikes come with these weight limits:

  • AIRNIMAL JOEY: 225lbs
  • AIRNIMAL CHAMELEON FIXIE: 225lbs
  • AIRNIMAL RHINO: 240lbs
  • BIKE FRIDAY: 220lbs, or 260lbs heavy rider option (beefier bar)
  • BIRDY: 245lbs (incl. luggage)
  • BROMPTON: 242lbs (plus 44lbs of luggage only, NOT EXTRA RIDER WEIGHT)
  • DAHON: 230lbs
  • KANSI: 223lbs (incl. luggage)
  • MEZZO: 242lbs (incl. luggage)
  • MONTAGUE: 250lbs (plus 30 lb luggage)
  • MOULTON: 224lbs
  • PACIFIC CYCLES REACH: 242lbs (incl. luggage)

Nearly all are in the 220-250 pound range. What if that 240-pound rider (or even a lighter rider) hits a speed bump or a pothole like in the stress test above? The two bikes outside of that weight range beef up the same design by adding more metal. Same stress points, heavier bike.

***UPDATE: We recently had the same discussion with the owner of a broken Tern Cargo bike with a stated weight limit of 350 pounds. The frame broke at–you guessed it–the latch. (Although…a failure at the hinge, or at the weld on either side of the hinge/latch unit would have the same effect of a broken top tube.)

Higher weight? No problem!

Meanwhile, a standard, non-folding Trek frame with no special, heavy beefing up has these weight limits:

  • 275 lbs: Road bikes and triathlon bikes.
  • 300 lbs: Hybrid bikes, urban, commuter, mountain bikes.

Note that urban bikes and mountain bikes are at the same weight limit. So what’s the biggest difference between the two weight categories? Racing wheels vs. thick wheels. With a standard triangle frame design, the limiting weight factor for a rider is simply whether you’re riding skinny wheels!

At Flatbike, we’re huge fans of the time-tested diamond frame, where front-wheel forces are distributed between top tube and downtube. And we’ve taken the seat-tube, right below a heavy rider, and made that entire tube the pivot for folding.

CHANGE 812 folding MTB

Now that’s a folding bike designed for hard use.

When there’s no weld-hinge-latch-weld series of failure points, you can handle a lot more weight. It doesn’t matter whether that extra weight is from a Lycra-clad mountain biker landing a jump, or large commercial trucker doing a convenience-store run. Force is force, and a bike like the CHANGE 812 folding mountain bike is designed to handle it.

Modified CHANGE 609 folding mountain bike

Sometimes truckers make CHANGE bikes their own with custom mods.

So what do we recommend at Flatbike for heavier riders?

First, we recognize that the classic diamond frame didn’t get there by accident. It’s the result of 100+ years of weight vs. strength tradeoffs, and we embrace it.

Like Trek, we steer heavier riders (260+) away from the skinny-tire road bikes. With heavier riders, the frame won’t break–it’s still ruggedness-certified–but you’ll be more susceptible to pinch flats from low-pressure tires and rim dents from potholes then the average rider. (Want a road bike anyway? Keep your tires pumped and stay away from potholes.)

For riders over 260 lbs, and we even have riders over 360 lbs, use a bike with at least 1.5″ street tires, like the CHANGE 811 rugged folding hybrid, or CHANGE 812 folding MTB. In our experience, you’ll also likely want a slightly more upright position, with raised bars and a wider seat (like Trucker Paul did in his custom mods above).

And then you’ve got a folding bike for your weight, and your riding style, but that folds in half:

CHANGE 812 folded

Where would you take a bike like this?

 

We’ve got a lot of full-size foldable bikes to choose from. Choose well, ride often, and enjoy the freedom.

 

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11 responses to “How to bypass folding bike weight limits”

  1. Alan says:

    I am 290 lbs and need a folding bike – what can i do?

    • Bob Forgrave says:

      No worries, Alan. We’ve got plenty of truckers over 300lbs.

      The CHANGE folding frame isn’t an issue, as all models are tested to levels well beyond 290 lbs. So focus on the wheels. You’ll want a model that spreads weight across a larger area. The CHANGE 611 and 811 have 1.5″ tires and Mavic wheels, which are super-tough. The CHANGE 612 and 812 bump this up to 2.1″ and add shocks.

      Honestly, if your goal is to ride mostly on roads, I’d recommend the 611 or 811. You’ll have less rolling resistance (no knobby tires) and a bike that can handle whatever you throw at it.

      Bob

  2. Roburt says:

    Hello,
    I thought that higher weight is not good for a folding bike. now i’ve no confusion about this. i’m thinking to gift a folding bike to my brother’s birthday. Thanks for this article. Best Of Luck.

  3. Rahman says:

    Hi, I’m considering a 20″ dahon jetstream which has full suspension and my weight is at 118kg (260 lbs). The max rider weight is 105kg. However will the shocks be able to absorb the additional weight and applying less stress to the frame? Thanks

    • Bob Forgrave says:

      Hi, Rahman. There are multiple levels to this question. Let’s dive into it.

      Dahon max weight of 118kg (260lbs). Engineers typically understate the max limit so their creations will never fail. Marketers typically overstate the maximum so they never lose a sale. Who set this limit? Given the numerous results when Googling “Dahon bike fail”, I’d lean toward the view that this max limit is … aspirational. Expect it to be less.

      Shocks absorbing stress and weight. Stress and weight are different concepts. I weigh 205 lbs; no matter what springs or big pumped-up tiers I put on my bike, I will still exert this weight on the frame. But when I hit a speed bump and high speed and then land, my weight (or mass, in physics terms) is multiplied by my acceleration to exert even more force on the frame–easily 260 lbs or more. That force is temporary, and can be smoothed out a lot by springs and wide tires.

      Ultimately, your answer is No. The shocks will help even out impact stresses, but you will continue to exceed a perhaps dodgy weight limit every time you ride your bike.

      Bob

  4. Gary says:

    I’ve been riding a biria easy boarding with 26″ wheels over summers for 6 yrs. The non-triangular frame hasn’t shown any cracks yet. I used to worry about that. I’ve never found frame fails on internet. I avoid bumps. I’m 300 lbs. Is it going to break?

    • Bob Forgrave says:

      This is a fascinating question, Gary. First, let’s strip out the Biria models OTHER THAN the Easy Boarding that you ride. Those Biria folding MTBs with four points of failure on a single bar? That’s exactly the design that this article was intended to critique as dangerous.

      But your bike isn’t that. It’s a one-piece, solid frame (likely very solid) with a massive U-shape instead of a triangle. So what have they done to counter the forces, besides using a thicker bar? Actually quite a bit. They’ve inserted a triangular metal piece (called a gusset in engineering terms) to reinforce the weld at the base of the front wheel and another one by the pedals. And most ingeniously, they’ve pushed the seat way back, so it’s centered over…a triangle.

      Let’s think about this like a physics forces problem. 300lbs comes down to the triangle, and half goes back to the rear wheel and half goes forward into the frame welds. Will a gusseted design for the U frame handle 150lbs in simple, standard use? Absolutely. The questions are about non-simple or non-standard use, like regularly riding pothole-filled roads, riding the “washboard” bumps on an old gravel road, hitting a speed bump without slowing, or any of those extreme events where you think afterwards, “Wow. That just happened.” That’s the time to check your gusseted welds. Otherwise . . . full speed ahead and enjoy biking!

      Bob

  5. JESUS MARTINEZ says:

    350 lbs trk drvr interested on a folding bike for heavy riding activity like its mentioned above going to the (me adding) convienience store and grab me a snack or two . :7)

    • Bob Forgrave says:

      Then you’re definitely going to be interested in this article, Jesus: https://flatbike.com/truckers-with-bikes/. It was suggested by one of our trucker customers! 350 is not an unusual weight on this bike.

      • Roberto P. Buenaventura says:

        I bought Dahon K3 Plus. In the Dahon website, the maximum rider weight is published at only 85 kilos. I am almost that weight. Will the said bike be a safe bike for me? Thank you.

        • Bob Forgrave says:

          Thanks for the question, Roberto. The answer is “Probably, unless.” That response requires a bit of explanation…

          The published maximum is a legal limit, not an engineering limit. If it fails below that rider weight, Dahon is legally liable for a product failure to achieve stated functionality; above that, they are not.

          The engineering limit will be above that, to keep the company out of trouble. How much above? Nobody knows. It certainly won’t be published anywhere. But it should be enough to cover the additional forces that the maximum weight will generate in typical use–bumpy road, a small pothole, anything with moderate additional up & down movement.

          The “unless” part comes in with unexpected forces. Like… you’re carrying 2 gallons of milk (7 more Kg) AND hit a speed bump. Or you stand up to stretch your legs and then come down card on the seat just as you hit a big pothole. Or maybe the welder simply had a bad day when building your bike. A low weight limit is simply easier to exceed than a high one.

          Bottom line? You’re probably OK. Smooth and safe riding…

          Bob

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