I’ve been asked to build a cargo fork ala Crust’s Clydesdale (read somewhere about the history of this style once, if anyone got a source I’d love to read it again).
I built a similair style of fork for myself as one of my first bike related projects not knowing anything about how the geometry would affect the riding but it rides really well so I never gave it much thought.
Now that I’m building one for a customer I want to actually understand what would be the best solution for his needs.
The fork’s primary cargo will be his child of about 30 kg - but i assume that weight will increase!
But matching the trail of that setup with a 20" wheel would result in a 670mm a-c with a 43mm rake.
Today I took apart my cargo bike to measure the dimensions of the fork so I could model the bike in bike cad
It appears, according to the bikecad drawing, that I’m riding a bike with 3mm trail and 1mm wheel flop…
This got me even more confused.
Got some numbers from a framebuilder who has experience with building this kind of forks that I could just go with but I kinda want to understand what’s going on here.
Would love any input, experience or thoughts about how the fork geo will affect riding qualities when you swap out the front wheel to a 20"
Made one 3 or 4 years ago to compliment a stunning street find chrome SUNN( they were the s**** back then). I rode it as my messenger bike, so useful during the christmas rush!
Now for some numbers, my main concern was to keep AC similar to the 26" fork, and for the rake I eyeballed 50mm and called it good. The bike tracked very well, was not too twitchy and could handle a lot more weight than the usual porteur rack ( read you could carry a medium size human being no problemo), forks were kinda flexin tho.
Not much help to you but maybe someone with more experience will chime in.
Sidenote : only in Switzerland you could leave a bike loaded with chocolates and champagne freelocked in the street and nothing would happen
Comparing the tire size and front end geo of the original frame, and assuming a 60mm 20" front tire, I get about 13mm of fork offset to give the same trail as the original.
I owned a Clydes for a couple years on a Surly Straggler an it handled about as well as I can imagine a fork like that could handle. The rake of the fork was measured at 44mm for a trail of around 40mm. BikeCAD of the setup below.
Despite handling fine I actually didn’t love this setup. It was ok for lighter loads but when you maximised the room on the fork (15kg+) things got sketchy. If ya going custom I would reccomend a full frame modification that supports/braces the rack/weight back to the frame. This will keep the steering a lot lighter.
I eventually sold the Clydes to a mate and bought an Omnium Mini-Max. And funnily enough my mate is about to make the same move. Worth considering.
I made a cargo fork as well. It was a fun project but not the best cargo bike solution. What annoys me most is when stopped and loading up with goods, the front wheel flops over. This knocks the bike off balance and has landed on the floor. A center kickstand would solve that but I hate the way they look.
What I like most is that the bike unloaded handles the same as it did with the original fork. Math is fun when you get it right. The bike’s overall length is a little shorter which is an added bonus for those in tight spaces.
The geometry of my fork is very similar to the Crust Clydesdale. I used 1” x .035 chromoly for the cargo deck, the lower fork legs are a repurposed set of chainstays, Columbus Unicrown upper fork blades all hanging off a Paragon Machine Works steerer. It’s very stout and has a milk crate attached full time.
I have build a bunch of them. I added 2mm of offset to the original specs if I knew them.
The feedback I got from most is that it handles the same as before
We decided on the front rack secured & supported by the frame to keep the steering light when loaded and to avoid the tendency to dive into the turns.
Not sure how that would work with a childs legs dangling where the wheel turns… ?
But as for geometry we used an off the shelf 20” fork, long head tube, extended the steerer, and kept the HT angle the same as the inspiration (72*, I think, same as a ‘92 Stumpjumper). and the handling is normal, just different for the 20” wheel.
