My custom frame full suspension long tail dual hub cargo bike

frk1206 · Sep 15, 2022

I couldn't find anything on the market that didn't suck so like a true engineer I decided to build my own. This is my long tail full suspension cargo bike cad model for a custom frame. This is going to be a 20" GMAC rear hub, 26" grin all axle front, 72V 2kwh custom battery. Why? because carrying kids/groceries should be comfortable, safe and fun! Slowly coming together, hopefully should have something usable in a month or so!

Ps: While I'm working with a group of awesome mechanical engineers to design / fabricate this bike - but still looking for help specially if you can weld/bend frames and machine parts on a ongoing basis. Please DM if you are interested in some fabrication work or the project as a whole. The closer to California the better (I'm in Oakland, CA)

john61ct · Sep 15, 2022

Once you get past testing prototypes, China will be the way to go

LewTwo · Sep 15, 2022

Is that a rigid fork?

frk1206 · Sep 15, 2022

john61ct said:
Once you get past testing prototypes, China will be the way to go

Yeah - I don't think I want to get into mass manufacturing or anything. Mostly just building one for myself and some low volume hand production for people that want them.

frk1206 · Sep 15, 2022

LewTwo said:
Is that a rigid fork?

Full suspension. Still figuring out the exact components but most likely a Fox / rockshox downhill front fork.

LewTwo · Sep 15, 2022

frk1206 said:
Full suspension. Still figuring out the exact components but most likely a Fox / rockshox downhill front fork.

I would not think that you would need a 'long travel' downhill fork unless you are planning on riding some very rough terrain.

frk1206 · Sep 15, 2022

LewTwo said:
frk1206 said:

Full suspension. Still figuring out the exact components but most likely a Fox / rockshox downhill front fork.

Click to expand...

I would not think that you would need a 'long travel' downhill fork unless you are planning on riding some very rough terrain.

SF Bay area roads can get as knarly as some trails, maybe even worse

. Long travel + linkage in the rear means I can use a DH shock for much more weight since this bike is gonna be way heavier fully loaded than most DH bikes. On the front you are right probably a XC "ebike" shock which gives us 100mm of travel.

maiz · Sep 15, 2022

frk1206 said:
LewTwo said:

frk1206 said:

Full suspension. Still figuring out the exact components but most likely a Fox / rockshox downhill front fork.

Click to expand...

I would not think that you would need a 'long travel' downhill fork unless you are planning on riding some very rough terrain.

Click to expand...

SF Bay area roads can get as knarly as some trails, maybe even worse . Long travel + linkage in the rear means I can use a DH shock for much more weight since this bike is gonna be way heavier fully loaded than most DH bikes. On the front you are right probably a XC "ebike" shock which gives us 100mm of travel.

marzocchi 58 is the fork I'm looking at for a townie grocery-getter. might be overkill but I want plush. I'm also in Oakland, I imagine a robust mid drive would fare better in the hills. something like an HV modded BBSHD or a lightning rod short block. then the front hub could help maintain speed on the flats or regen on the downhill segments. also I would suggest slackening the seat and head tube angles a bit. get close to dutch bike geometry, 68° ish for both. when bolt upright, it is so easy to assess surrounding traffic vs even a slight hunch. especially if the cargo is kids and especially on some of these Oakland corridors. I like the thinking, rooting for you! please post progress.

frk1206 · Sep 15, 2022

maiz said:
marzocchi 58 is the fork I'm looking at for a townie grocery-getter. might be overkill but I want plush. I'm also in Oakland, I imagine a robust mid drive would fare better in the hills. something like an HV modded BBSHD or a lightning rod short block. then the front hub could help maintain speed on the flats or regen on the downhill segments. also I would suggest slackening the seat and head tube angles a bit. get close to dutch bike geometry, 68° ish for both. when bolt upright, it is so easy to assess surrounding traffic vs even a slight hunch. especially if the cargo is kids and especially on some of these Oakland corridors. I like the thinking, rooting for you! please post progress.

Thanks for that tip! I'll look into those forks! Overkill is totally fine - Oakland roads are sometimes worse than the trails at JMP

I used to be a mid drive guy (BBSHD) but the buttery smooth power delivery of the hub motors has me sold. The BBSHD was too much maintenance tbh - internal gears, chains, derailleurs and cassettes were basically consumables when climbing hills. The whole PAS thing also works way better with a hub mentally (the power is predictable and PAS torque sensors are light years ahead of BBSHD cadence sensing). I've seen people push more amps into their BBSHDs with BAC controllers but the end result is always a short life

Interesting about the seat and head tube angles - I'm basically heavily inspired by my yuba kombi and for the most part have copied that bike in geometry. A yuba kombi is what I ride right now. Interesting that you like yours that slack - is that mostly to slow down the steering or just how you sit on the bike?

Fun bit: my gmac actually climbs snake road as well as the BBSHD without the need to change gears. With a dual hub I'm guessing it would fly if I can get enough traction on the front.

What bike do you have? Do you use it for mostly groceries or kids or both?

vanturion · Sep 17, 2022

Looks neat, I hope you post a build thread (or update here if this is it).

I ride a somewhat longer-framed full suspension frame up to 50 mph with 120mm travel in the front after removing internal fork spacers. The setup works well enough to suppress any errant thoughts of suspension upgrades. Biggest downside is the brakes are a little under-powered due to fork manufacture's rating, so perhaps something to give some attention to since you'll likely be carrying a bit more momentum to slow down.

I somewhat mitigate the under-powered brake risks by limiting my time at speed as much as I can depending on the route. More fun to cruise and take in the sights at 20 mph anyway.

frk1206 · Sep 18, 2022

vanturion said:
Looks neat, I hope you post a build thread (or update here if this is it).

I ride a somewhat longer-framed full suspension frame up to 50 mph with 120mm travel in the front after removing internal fork spacers. The setup works well enough to suppress any errant thoughts of suspension upgrades. Biggest downside is the brakes are a little under-powered due to fork manufacture's rating, so perhaps something to give some attention to since you'll likely be carrying a bit more momentum to slow down.

I somewhat mitigate the under-powered brake risks by limiting my time at speed as much as I can depending on the route. More fun to cruise and take in the sights at 20 mph anyway.

What do you ride and how did you build it l? Looking for tips on the rear suspension since it seems to be voodoo more than science. I’m with you on the 20mph - This bike isn’t designed to go much more than that but I definitely want a lot of torque to get to 20 quickly

SlowCo · Sep 18, 2022

Why such a complex rear suspension design for a cargo bicycle? And not just two simple shocks on a swing arm like an old motorcycle?

Chalo · Sep 18, 2022

frk1206 said:
LewTwo said:

frk1206 said:

Full suspension. Still figuring out the exact components but most likely a Fox / rockshox downhill front fork.

Click to expand...

I would not think that you would need a 'long travel' downhill fork unless you are planning on riding some very rough terrain.

Click to expand...

SF Bay area roads can get as knarly as some trails, maybe even worse . Long travel + linkage in the rear means I can use a DH shock for much more weight since this bike is gonna be way heavier fully loaded than most DH bikes. On the front you are right probably a XC "ebike" shock which gives us 100mm of travel.

Suspension is always a letdown when the gross weight and weight distribution of the bike can vary wildly depending on load. You can only tune it to work effectively in a narrow range of weight. The rest of the time it's either too hard and bouncy or too deeply sagged and prone to bottoming out.

Cargo bikes do best with fat tires on wide rims, but no monkey motion.

frk1206 · Sep 18, 2022

SlowCo said:
Why such a complex rear suspension design for a cargo bicycle? And not just two simple shocks on a swing arm like an old motorcycle?

Because I was able work with some experienced mechanical engineers

A link type suspension will almost always be superior (even though require more work). Also it allows much neater inline packaging of the shock so can kids can sit peacefully and full side bags can be mounted.

frk1206 · Sep 18, 2022

Chalo said:
Cargo bikes do best with fat tires on wide rims, but no monkey motion.

This is what I’ve had for a long time and it’s not enough for me. If lightweight dirt bikes can do I don’t understand why cargo bikes cannot. The weight isn’t that variable since unless you are actually hauling very heavy cargo the target weight is mostly known (you and maybe a small child or you and groceries) just like on a motorcycle. Target that weight and eventually allow for some easy way to adjust preload / damping (high end dh shock).

On bad roads (city roads) the safety / comfort gain from a full suspension is very hard to ignore for me - so trying this experiment which very well might fail!!

SlowCo · Sep 18, 2022

frk1206 said:
Because I was able work with some experienced mechanical engineers

I highly doubt that because then the triangulation of the frame would have been much better...

frk1206 · Sep 18, 2022

SlowCo said:
I highly doubt that because then the triangulation of the frame would have been much better...

It’s a work in progress didn’t mean it as a smart ass comment just that if you have access to resources why not do the hard work. How would you design the rear?

AdR · Sep 18, 2022

Carrying weight beyond the rear axle on steep inclines can be a problem,

SlowCo · Sep 18, 2022

frk1206 said:
How would you design?

At least use some triangulation (red) in the frame where the weight will be. Now it looks like a folding mechanism without the hinges. And use bolt in triangulation where the battery pack is situated or make the battery box a stressed member. The swing arm can be a simple, old fashioned motorcycle style design with a shock on each side that is easily adjusted for preload. I don't think you'll need MTB cantilever rear end unless you will downhill the bike in a cargo bike downhill competition. :wink:

vanturion · Sep 18, 2022

frk1206 said:
What do you ride and how did you build it l? Looking for tips on the rear suspension since it seems to be voodoo more than science. I’m with you on the 20mph - This bike isn’t designed to go much more than that but I definitely want a lot of torque to get to 20 quickly

I ride the infamous V2100 walmart special frame with the Farfle (RIP) swingarm upgrade. Build and mods were a very long iterative process to achieve satisfaction, but eventually got there. You may not use it often, but having torque on tap to get over 20 mph and in great excess too is a worthwhile goal IMO. Never hurts to have options to deal with changing conditions and traffic that power affords. I have nearly 9KW peak on tap these days whether I use it or not.

Since the convo is on rear suspension design, if you look up the V2100 rear link suspension, it's noticeably not optimized and results in some degree of pedal-bob. This doesn't bother me though since my goal was never exercise on this bike, pedaling accounts for knee-joint lubrication and blood circulation more than a power-adder at most times now LOL.

SlowCo said:
Why such a complex rear suspension design for a cargo bicycle? And not just two simple shocks on a swing arm like an old motorcycle?

Actually, I think frk1206 is still a bit shy of what can be achieved here. To really channel the inner engineering spirit, I think he should mount a mini air-compressor with shut-off valves and in-line gauges to both front and rear air forks. That way he can dial up his suspension as needed for anticipated cargo loads. Not even joking. :thumb: 8)

PS: Bonus points for powering it off the main battery pack.

LewTwo · Sep 18, 2022

The advantage of a single shock swing arm is cost (one vs two). Spring shocks are cheaper and with limited options for preload. The springs also inevitably rust regardless of the paint, coating, plating or other surface treatment used. A single high quality air-shock will likely be more expensive (than a single spring shock) but will last longer and provide a greater preload range.

Another advantage is that only one device has to be adjusted.

frk1206 · Sep 18, 2022

LewTwo said:
The advantage of a single shock swing arm is cost (one vs two). Spring shocks are cheaper and with limited options for preload. The springs also inevitably rust regardless of the paint, coating, plating or other surface treatment used. A single high quality air-shock will likely be more expensive (than a single spring shock) but will last longer and provide a greater preload range.

Another advantage is that only one device has to be adjusted.

Our thinking was that with a single big spring shock - we would have a lot more flexibility in choosing the right spring after the fact. You think an air shock would actually be better if we can get the load range right? I was under the impression that spring (downhill) shocks would be best to use due to high load. Any air shock in particular? Most air shocks I’ve seen top out at 250-300lbs.

E-HP · Sep 18, 2022

Try Pacific E-Bike in Berkeley;
https://endless-sphere.com/forums/viewtopic.php?f=3&t=116714

I see some of their custom bikes around.

LewTwo · Sep 18, 2022

frk1206 said:
Most air shocks I’ve seen top out at 250-300 lbs.

That is PSI .... now multiply that by the area of the piston.

frk1206 · Sep 18, 2022

SlowCo said:
Triangulation.jpg

Interesting - I'm not a mechanical guy so can't speak for much about the design. Will ask the folks who are! Thanks for your input! Do you think the original design isn't going to be sturdy enough?

Complex swing arm was a design choice - wanted to package the shock nicely inside the frame so its out of the way of children / bags etc. Link gives leverage which lets you trade shock travel with weight limit (so can use socks spec'd for less than the bike)

My custom frame full suspension long tail dual hub cargo bike

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