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I would like to build a heavy duty cargo bike. Heavy = approx 200Kg of load on the front rack.

I want 2 front wheels.

Basically, there are 2 options that I know of:

  1. the front wheels are fixed to the front rack/ load and the whole part is moving when I want to turn. This uses a single pivot. This seems appropriate, but I'm worried about the single pivot and the tube size (regarding the tube between the bottom bracket and the pivot)

  2. The rack is fixed with the chassis, everything including the wheels can move without moving the rack/load. This includes the whole load is not always in the same plan, and it worries me because i'm not sure it's a good idea to move 200kg, it is a lot of inertia

What's your opinion?

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  • $\begingroup$ What research have you done into existing designs? Option 1 seems more common for 'heavy duty' cargo bikes: catalogo.cargobikesystem.it/WebRoot/ce_it/Shops/990535225/… $\endgroup$ – Jonathan R Swift Jan 24 '18 at 16:53
  • $\begingroup$ Several years ago while traveling in China, I saw very large loads over the rear wheel, on what appeared to be regular bicycles. Things like coal ; formed into cylinders that could be stacked, as an engineer I would estimate close to 300 kg. Maybe you are over thinking this. $\endgroup$ – blacksmith37 Jan 25 '18 at 17:18
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You shouldn't put the load on the front, above the front wheel(s). That's the worst possible location for multiple reasons.

  1. It'll get you smacked on the road:
    200kg located above the front wheel sure will be heavy enough to pull you over for a nice face-plant on the road upon braking. The inertia will 'pull you over' when you brake. The higher you place it, the worse it gets. You get a bonus at that when leaning in on a corner, worsening it even further.
  2. Steering will be heavy:
    The rotational inertia means a large mass can be hard to rotate. In other words. It'll be much heavier to turn your steerer with a heavy load attached to it.
  3. The front tyre(s) already gets the most abuse upon breaking, putting a load on it worsens that.
  4. Steering behaviour such as turning-radius, or minimum speed required to make a turn may get worse.

I'd make a three-wheeler with two wheels at the rear, and a load space between them, just in front of the rear axle, close to the ground. This will give you the a good result because:

  1. Your steering can remain as simple and lightweight as that of a normal bike. You won't have to take into account Ackermann. The steering like on old horse carriages would also eliminate the need for that, but it would create an awful ride experience.
  2. Mass is located close to ground, keeping its negative effect upon steering and 'leaning in' to a minimum.
  3. Mass is located at the rear, preventing it from causing unexpected effects upon braking and steering, which are hard to counter yourself.
  4. You can easily create more space there for cargo than on a rack on your steerer.
  5. You can access the cargo easily with eg. a handtruck. You'll save your back/spine and energy.

In short, I recommend to design it like this, preferable i'd be locating the mass closer to the ground though: bikeGood Rather than this: bikeBad

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  • $\begingroup$ The second picture is not 2 front wheels. With 2 wheels you don't put the load above the wheels. You put the load between the wheels just as you have it in the rear design. $\endgroup$ – paparazzo Jan 25 '18 at 15:40
  • $\begingroup$ As here gastro-bike.com/wp-content/uploads/2017/07/CA2.jpg $\endgroup$ – Jonathan R Swift Jan 25 '18 at 16:04
  • $\begingroup$ @Paparazzi That matches more with OP's idea, but it wouldn't really matter. The load will be low, which is nice, but due to yaw moment of both the load and the entire bicycle, it'll be really heavy to steer with a construction like commented by Jonathan. $\endgroup$ – Bart Jan 26 '18 at 10:04
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You will probably be much better off not having the load directly attached to the steering as this will put a lot of load on the steering linkage and probably make the steering very heavy and it will be heavy enough as it is.

You also need to consider steering geometry. As soon as you have a pair or steered wheels you need to look at Ackerman steering which steers the inner wheel more than the outer one. Without this you are forcing one or both of the steered tyres to slip which is wasting a lot of energy and will make the steering heavier still.

With a single pivot you are essentially attempting to drag the wheels across the direction of travel without any mechanical advantage. Indeed what is more likely to happen in practice is that you end up with rear wheel steering

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2nd is a bad design in my opinion

  • The load is higher has it must be above the wheels (less stable)

  • Load is transferred via the head set

  • When you turn the stance is not as wide so easy to tip

I suggest you draw up the 2 designs to get more input.

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