I called my little imaginary bike brand “Dobro.Velo” because my family name is “Dobrowohl”, and dobro just means “good” in many slavik languages. Going along with this slavik theme, I try to find names for my bikes from that part of the world. My gravel frame from last year is the “gramoz” (just meaning gravel in Slovenian), and this one is the “Planina” which is “Mountain” in croatian/serbian. It is also inspired by a beautiful mountain range I visited a couple of years ago in southern Serbia called the “Suva Planina”
Originally, I started thinking about this design three years ago, when I was toying around the idea to go full commercial and actually have a real brand. The design is essentially a four-bar with one of the links missing, so the rear triangle has to flex a bit to compensate for that. I believe that this arrangement works particularly well in steel, and lends itself quite well to small-scale production since it is quite simple.
The bearing arrangement is inspired by “Last Bikes” in Dortmund, Germany, a business I am friends with. There is no bearing in the main frame, just pieces of solid bar with quite chunky threads in them (M14x1.5 in my case). Six bearings sit in the rocker arm and two in the swingarm. There is no complete axle going through the whole arrangement left to right, which makes manufacturing and assembly really easy.
The kinematics are nothing out of the ordinary, about 100% antisquat on the largest sprocket, 32% progression in a 1:3 leverage ratio (going from 1:36 to 1:24 if I remember correctly…) I can dig out all the linkage plots if anyone is interested
The two most challenging things during this build for me were
making a lot of one-off positioning fixtures. It’s kind of hard to hit the sweet spot of how much effort you want to put into a fixture that you’re probably never going to use again!
And
brazing all those awkward inaccessible different wall thickness acute angle weird spots… I’m definitely not super skilled at the torch, but I can manage a tube joint with some confidence. On this frame though, I struggled a lot with heat mangement, torch control, visibility…
Curious how much flex you expect from the rear triangle. Is the “flex point” on the seat stays near the rear dropouts? Are you using dropouts for the upper seat stay-to-rocker attachment?
Laterally, the rear triangle is surprisingly stiff. The rocker bracing adds a lot of stiffness to the already quite chunky yoke/main pivot area. I did a lot of back and forth on that design, didn’t want to incorporate a seatstay bridge because that would have meant either a different seat tube position or a longer swingarm, neither of which I was a fan of…
The seatstay-to-rocker-attachment is home made on my lathe, it’s essentially just a cup with a thick bottom plate and a little dome in the middle, with a threaded hole, and then I chopped some of it off. Ignore the angle on the drawing, I just eyeballed that…
I would be very interested to hear how it rides. Do you find the shock compression tune too stiff? Especially the low speed compression, because of the flex stays. It should also lower the coil spring stiffness.
Glad there is a mtb build in this forum. Pumps a little more testosterone in here.
right now, the spring stiffness is too soft for my weight, so I can’t really comment on how it rides yet. The force needed to flex the stays is negligible though, without the shock installed I can move the rear axle through the travel with my pinky finger. It only needs to flex +5/-2mm going through the travel at the tip of the seatstay.
I will get a stiffer spring today, hopefully it’s stiff enough so I can start playing around with the damping
Yes I have but I must admit I do like the looks of the bright yellow “Swedish gold” Öhlins spring Haven’t decided yet though… I’ll get a 550lbs/in spring today (currently running a 500)
