When Karl Groetzinger set out to design his first fully built frame design, he had one goal in mind - make it different from everything out there. Karl first began designing bikes 10 years ago, but didn't have the facilities to build them. Now, as a 26-year-old, he's finished his degree in mechanical engineering at the University of Stuttgart, taught himself aluminum welding, and has been able to make his visions come to life.
DetailsFrame Material Aluminium
Intended Use All Mountain
Intended Travel 140-150mm fork
Wheel Size: 27.5" front/rear
Frame Size: Large
Geometry: N/A
Price: One-off frame, not for sale.
More info: @karlgroetzinger While most manufacturers use metal tubes for the chainstays and join these to a gearbox housing with a weld, Karl uses folded sheet metal all the way along the chainstay and into the BB/mount for the gearbox.
The first question anyone will surely ask is, "Won't that break?" Well, that was the big challenge for Karl; if he was going to make something unique he was going to make sure it worked too. By using sheet metal to integrate the Pinion box, he was able to spread the loads and not have a weak join between the stays and the BB area. Alongside this unique construction method, he's also making sure the area around the gearbox and the chainstays have plenty of metal keeping everything pointing the way it should be. The folded metal cuboids he has used for the stays are 50x20mm in profile plus have a 3mm wall thickness thick, which is about twice the thickness of conventional aluminum tubes used on mountain bike chainstays.
To prove his design, Karl has been using a frame-mounted strain gauge and a 3D scanner to measure how the lack of a seat stay affects the bike. He has concluded that there are "only slight plastic deformations" but this is something he intends to remedy in the next model by using an even stronger 7000 series aluminum alloy, which has an almost 2 times higher yield stress. Also on the next version will be a belt drive instead of a chain and potentially a gusset between the seat tube and top tube.
The attention to detail is incredible, including machining these brake mounts after welding to ensure they were perfectly aligned.
Karl is using a strain gauge with measuring sensors on the cantilever to learn more about his design and how it can be improved for version 2.
So what will the disadvantages of this design? Well, the extra material needed to reinforce the chainstays doesn't come without a weight penalty. The frame currently weighs 2.5 kg (5.5 lb), which puts it about 200 grams (0.5 lb) heavier than, for example, Nicolai's Argon AM Pinion. The full прототип build Karl has selected here tips the scales at around 15kg (33lb). We're also not yet sure how the design will react to torsional forces as the bike is cornered hard. Really though, none of that matters. This wasn't a performance-driven design - Karl set out to create a bike, unlike any that had been seen before and it only takes one look to know that he has succeeded.
Karl is gaining further insight on the physics of the bike from a GOM 3D scanner.
The bike is currently a one-off design exercise although Karl has been surprised at the amount of interest and could consider making a production run if it continues. He currently has designed the frame around his own large proportions with the intention of fitting it with a 140-150mm fork and using it as an all-mountain bike. No geometry info is currently available. The best way to keep up with the project is to
follow Karl on Instagram.
OK Boomer
Uh... put seat stays on it.
Great work!
Don't think I could take the pain (Stay now)
Won't you stay another day? (Stay now)
Oh don't leave me alone in this pit
Don't you say it's the final sit (Stay now)
Won't you stay another day? (Stay now)
The song was a big Christmas UK hit in the mid 90s. I know it is objectively bad but I still kind of love it
Reality is, the market for hardtails is very niche, and ultimately I believe this design would actually gain some popularity among that crowd.
Yes I will agree this design will also have defletion under torsional loading.
Reality is this, in my opinion hardtails are best suited for dirt jumping. They will never measure up to a proper full suspention design, no matter now you stack it.
Done. But why? Is this a sensibel goal.
As I don't sit much on my bike but do value a low top tube, I'd actually be more interested if they'd make one with a bulky downtube (like the older Orange bikes), remove the top tube and do with a super short seattube (so that indeed you'd have a low monocoque rear "triangle" too). That would make actually be fun. But removing the seatstay but still have a conventionally high top tube, I don't see what you're gaining there other than maybe some mud clearance and maybe easier transportation with the rear wheel removed.
PS - I've never hited on the seat stays!
I would say, the rim is loaded like a beam, unrestricted, and that will translate into compression and tensil force accross it's walls
Curious to see how strange it looks from the other side!
And he's using a racing ralph on the front with his fox 36, so you just know he's really putting this thing through the paces.
This design could be used like a softtail, but aluminum is the wrong material for that. He has to add so much material to keep it from yielding (which puts the material in a low-cycle fatigue range where it will fail after tens of thousands of cycles instead of a million-plus where it should be) that there's no weight savings. Yes, 7000-series should help, but if that was the goal, then he should just go to 6/4 Ti and get double the strength of the 7000-series AND still likely get better ductility and fatigue all at a lower weight.
If it does have that vertical compliance--which would be good--I doubt it would have torsional stiffness, meaning you can probably watch the top of the back wheel move excessively right/left, not to mention lateral bending like a fish tail. I can't believe this thing handles well at all except for the mildest of riding.
So for a cruiser--sure, why not. For a mountain bike? I wouldn't bother.
I know this has never been done before because PB says... pretty sure millard racing might disagree though.
Maybe a HT is more complicated to do this with than a FS, who knows. But the millard bike was raced and never snapped, even though the forces would be reduced due to the suspension in theory, or are they higher as you go faster...
I like the design, looks really cool.
but cool design ! looks like a mix of nicolai and zonenschein
I wanna know more about the gearbox !! Gearboxes = the NEXT dimension beyond AXS wireless shifting (made from titanium
www.theproscloset.com/blogs/news/five-vintage-full-suspension-bikes
I don't think I've ever read anything so heartbreaking on this page and that's f*cking saying something. You literally wouldn't have -anything- if somebody somewhere didn't try to do something different, just because.