Bike Check: Isak Leivsson's Homemade Steel Downhill Bike
Photos: Logan Mulally
As the test pilot for the wild Pole downhill bike a couple of years ago, Isak Leivsson is no stranger to out-there geometries. In the two years since then, he's been eager to put some of his own experiments to the test and has now decided the best way to do that was to build his own downhill bike. The result is this steel sled that looks like it would be at home on Fury Road as much as it would on a downhill World Cup track.
The bike was built as a geometry experiment as Isak noticed that the trend for longer front end bikes has led to more stability in a straight line, but he found them much more difficult to corner. Isak believes that the ratio of front center to rear center is skewed too heavily forwards on these bikes, so he's tried to bring it back in line and create a bike that shares the same stability as modern bikes but that can also corner easier.
He has used two main methods of achieving this. Firstly, he has much longer chainstays - they measure 490mm on this bike, dwarfing the 27.5" wheel in the rear end, restoring that ratio to something a bit more balanced. He admits that the numbers are a bit of a guess on this first go, but he has based them on the ratio from Sam Hill's bikes from his golden era and transposed that onto the bigger bikes we all ride today.
The 490mm chainstays really jump out on the geometry sheet, but the wheelbase is a not-too-radical 1319mm. This makes it just 4mm longer than, for example, an XL Santa Cruz V10, but it's more than 40mm shorter than the Pole downhill bike he has ridden in the past.
Secondly is a short cockpit, built around a 10mm stem, which allows him to have a big range of movement around the bike and keeps him in a central position while still having the wheels far away from him. Isak mentioned he could have slackened the head angle to achieve the same thing, but feels that it doesn't work as well as his current method. The short stem is combined with a 470mm reach as Leivsson says he was looking for a feeling that was similar to his trail bike that has a 430mm reach and 50mm stem.
Full geometry
As this is mainly a geometry experiment, Isak hasn't spent too much time worrying about suspension kinematics. He went with a single pivot design loosely based on the Kona bike he was already riding as an ambassador because it was simpler to get right and allowed him to get the bike rolling without too much faff. Isak built the bike from straight gauge 4130 Chromoly steel - 0.035”(0.9mm) for downtube, top tube and rear end, and 0.049” (1.2mm) for seat tube and tubes surrounding link.
A closer look at Isak's handiwork. Steel was the material of choice purely for practical reasons. Isak was fabricating the bike himself and didn't have access to the facilities to build a bike in any other material.
So has the experiment worked? Early indications from Isak are good. He says that he likes how the front wheel is constantly weighted without him ever having to consciously think about it, making the bike much easier to ride.
These kinks allow room for the shock piggyback and front wheel. It may look like a weak point, but considering Isak has already tested this bike on the biggest jumps at Windrock and hucked the bike off his roof, it seems to be holding up ok so far. He hopes to replace this with a properly curved downtube on the next iteration of the bike.
The linkage designed is inspired by a Kona Operator as Isak is an ambassador for them. He wanted to keep it simple so he could focus on the geometry changes instead.
This is version one of the bike and Isak is already working on a second version that will take on board some lessons from this bike. Isak inadvertently welded the BB the wrong way round on this version, which he admits means he has to bodge the cups, so that will be the first change. The V2 will also have a properly bent downtube and some improvements like ISCG mounts, better cable routing and a lighter weight. Isak will be riding that bike until something goes wrong, although he is also interested in trying a different wheelsize in the future. Isak is now hoping to earn a spot at Worlds at Leogang this year and will be bringing his steel bike with him if it goes ahead.
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Steel is real, love it to bits, but it isn't for weight.
Megatower isn't a competitively light frame. Go look at Scott's weight and prepare to drop something.
the lightest steel road bike I know of is a Rodriguez Outlaw and at 14 pounds it is a very light weight bike. Not sure what the frame weight is, but I would guess that it is under 1.5 lbs based on the weight of my road bike and how much less the components on the outlaw weigh.
Its just effing expensive to do, effing hard to have good consistency and quality control from frame to frame, and the cycling industry still doesn't fully utilize FEA or generative design yet.
And that's only when looking at a straight tube/beam. Full suspension frame structures are quite complex with all their mounts etc. This is why Robotbike/Atherton works with titanium in those areas and only uses the carbon tubes in the straight connections between those nodes. In my mind this still seems like the best application of the material though obviously it isn't necessarily a cheap way to go. And I'll forgive the guy for not going down this route, considering this is a homemade bike meant to experiment with geometries.
Fwiw, I know steel frames don't have to be heavy. I'd much rather own a quality steel hardtail or road frame than aluminum or carbon. All I said was sub 1.5 lbs seems unreasonable, and I'll stand behind that.
I rode a 26” one (which weighed 4.4lbs) for thousands of miles, had it for four years, did uplift days on it, 140mm fork, dropper post, big tyres, got crashed plenty. After all that I only lost £200 in depreciation when I sold the frame!
Love the chainstay experiment. Makes perfect sense to me: front-centers have been steadily increasing, but rear-centers have remained almost as short as possible, which is just weird. Just look at Minnaar's custom dropout extenders for more evidence that it's a good thing. Plus a handful of manufacturers are finally starting to increase chainstay length on larger frame sizes. Makes sense.
Would build some thing like this, if my welding did not look like it was spat on?
Weird.
ie: cdn.instructables.com/FEU/QCKW/J1WEQTVI/FEUQCKWJ1WEQTVI.LARGE.jpg
m.pinkbike.com/photo/5815923
Mandrel bends only.
cdn.thefabricator.com/a/press-brake-bending-basics-going-old-school-with-notch-layout-1512054636.jpg?size=1000x
21 year old me. BMX is life.
Tuck no-hander out of the big hip. Landing deep. Landing really deep.
Bike returns to earth with meteoric impact. No suspension. 20" wheels. Ear shattering crack resounds.
Ride away clean.
Dudes asking if I'm okay.
I was fine. Teeth kinda hurt, headache coming on and my arms are going numb but I'm 21 so that's not gonna slow me down.
Pushing bike up roll in when some little punk is like, "Your bike is broken."
f*ck off kid, it is not. I look where he's pointing.
Top tube and down tube both cracked the entire way around just behind the weld. Frame had a gusset on both tubes and that's all that held the headtube to the bike. Kid noticed a bit of light flickering through the frame as I went up the ramp.
Thank you gussets and random 10 year old loitering at the jumps. Saved me from financing some dentists 3rd Yeti.
Well the denim destroyer and the leather lunatic would make one hell of a team
Anyone remember this video? Steve from Vorsprung basically recommended the same ratio and Leo from Pole disagreed in the comments. Now a former test rider of his is running the Vorsprung ratios and loving them.
Through the mud and the sand,
let’s go.
Siphon high, squirt it out,
swivel all about,
let it all hang out.
Go, Geoducks go,
Stretch your necks when the tide
is low
Siphon high, squirt it out,
swivel all about,
let it all hang out.
Can we get around this petition to show worldwide interest! Legends
www.change.org/p/kate-jones-lets-use-cairns-skyrail-as-mtb-uplift-facility-to-access-tracks-and-smithfield-mtb-park?recruiter=908681578&recruited_by_id=9e227230-db59-11e8-b8c3-cf1b1ae9a449&utm_source=share_petition&utm_medium=copylink&utm_campaign=psf_combo_share_initial
Neither. They're both going to end up with their center of mass in roughly the same place relative to the front contact patch because they both want to resist going over the bars and they both want to be in a centered/neutral position with their weight balanced between both contact patches.
The benefit of the longer wheelbase is that, even though both riders have an even weight distribution between front and rear wheels, the rider on the longer wheel base is more stable. Bumps, compressions, and impacts shift his COM less relative to the two contact patches.
Out of reach, so far
I never had your heart
Out of reach
Couldn't see
We were never
Meant to be
Du
Du hast
Du hast mich
Du hast mich gefraght
Mama, just killed a man
Called his Yeti shyte from shed
Jumped from clinics roof, now he’s dead
Mamaaa, trolling has just begun
But now it’s time to send it sidewaaaaays
Mammaaa didn’t mean to make him die
But if I’m not back on Pinkbike for 5 hours in a row
Carry ooon, carry ooon, cause wheelbase doesn’t matter
What sucks, is i bet we'd be good friends in real life. I feel like I could talk shit to you(if you ever stopped talking) tell you how wrong you are,and you wouldnt get butt-hurt.
Then, youd ride my bike and have a spiritual awakening and would have to humbly repent and grovel to aaaallll of Pinkbike .
That would be fun to watch
Fun to do it yourself, no doubt, I love welding
I know because of the fab I've done. I have a hydraulic pipe bender and a tubing roller, but they just don't cut it with the thin stuff. I'm still glad I have the tools for other applications tho. I utilized the technique this guy did for my bikes because I had no other way. I would love to have friends at a company that has that equipment. Booze bribes and donuts go a long way.
Once knew a pro who wouldn't bother to put a derailleur on his bike for his race run if it broke in practice. Watching him in the gate, touching his bike, asking people how to use a thru axle....yeah.
Also, not saying anything about Isak.
This is best the reply I’ve read all day, thank you.
I think it looks rad as hell.
But everyone propping up how light it is and how steel is real etc: it's pretty minamalist as it's not for riding but checking the angles. It needs about 7lbs worth of gussetting to ensure that frame downtube and headtube stays in tact. Well actually, every tube.
After gussetting to actually function as a DH bike steel would then truly be steel and not so real anymore. And it would no longer look rad but like something a country with no military budget might bolt an m-30 to.