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Gustav “Dangerholm” Gullholm is a fixture of the mountain bike scene, best known for his heavily customised and extremely lightweight builds. Here he shares the details of his latest weight weenie outing – a jawdroppingly lightweight Scott Spark full suspension mountain bike.
Numbers can be a funny thing. They don’t need to have any significant meaning to our lives, yet they can serve as significant motivation. Maybe it’s a time you really want to beat on a trail section or maybe you’ve set a goal to one day lift a certain amount of weight at the gym. Maybe you want your savings account to one day display a certain figure or maybe you really look forward to that 6-pack of (non alcoholic, right?) beer this weekend.
Either way, we tend to set a number as a goal and it gives us a little extra drive and meaning to work towards something.
In this case it’s about building a 29″ XC/Marathon bike with a total weight below 8 kg – or 17.64 lbs if you prefer the imperial system.
To put this number in perspective it’s around 15-20% lighter than most XC full suspension bikes that you see under World Cup riders. The same goes for complete stock bikes with price tags that would make even your favorite dentist think twice before buying. Going from 10 kg to 9 kg is quite alright, but if you want to have a bike weighing 8.5 kg you really need to put some thought into it. To push it below 8kg, on the other hand, is downright difficult. At least if you want it to actually ride well, and to me there’s no point otherwise.
So that meant a no-cheating and no-shortcuts approach. The weight had to include pedals, GPS mount, bottle cage and not to forget – proper tires. It won’t matter how light your bike is if you have zero grip or get a flat from looking at your tires the wrong way.
But we’re getting all technical here. It’s not all about numbers – the bike had to look great as well. Truly super light bikes tend to have a literally raw and stripped down look. They’re minimalistic to the extreme and to see paint on one is not something you can expect. I know better than most since I’ve been there myself with my World’s Lightest 29ers a few years back. So this time I wanted to go for a more normal appearance with a full paint job and no custom integrated parts. Part of the goal was to make the people see right away that it’s a special bike, without really being able to see what makes it so special before taking a closer look.
And it sure is worth taking that closer look because there are interesting details in abundance. You have everything from textile spokes to an 8 gram bottle cage made out of hollow carbon tubes. And if synthetic fiber cables for the suspension remote isn’t enough to grab your attention, how about a titanium shift cable?
Frame and fork
The Rosso Corsa painted frame is a Scott Spark RC SL featuring 100 mm of remote controlled travel. This is the lightest version, which more specifically is called HMX SL in Scott’s carbon fiber hierarchy. Designing and building a lightweight yet strong carbon frame is of course a science in itself, but the short version is that a higher quality carbon fiber means less material/resin and combined with a good layup design it results in a top level frame. This specific frame weighs 1,761.9 g including the rear shock and all the hardware. Also, that includes some 70 grams of beautiful red paint. Except for a lighter axle, the only changes made are a carbon fiber derailleur hanger and cable insert from Hopp Carbon Parts.
Up front is a matching Fox 32 SC Factory that has seen a little bit of weight shaving via a new axle and carbon air cap. Running no quick release I could also remove the little plate and screw that holds the threaded axle insert in place, saving a couple of grams while also making it look a lot cleaner.
What first catches your eyes is perhaps the quite massive looking stem. It’s a Schmolke TLO in 80 mm and its box section design helps the stiffness to weight ratio. Despite its looks the weight is just 80.3 g and I can tell you it feels quite ridiculous when you hold it in your hand. Along with the carbon design and production method, part of the low weight is thanks to the very trick titanium hardware. You may think you’re seeing regular screws holding that face plate in place, but actually you have threaded pins sitting hinged and molded into the stem section. Then you use titanium torx nuts when tightening the handlebars down. An efficient and durable method because this way they don’t have to mold threaded inserts into the stem.
On top there’s a sleek looking plug instead of a traditional top cap. To save weight a regular expander and top cap is used for installation and to preload the headset. They’re then removed and replaced with the plug that weighs just a single gram.
Please note that this is a custom setup that is not generally recommended. A standard top cap can sometimes help prevent headset play, and some manufacturers specifically state that a spacer of at least 1-3 mm must be installed on top of the stem. This goes for the Schmolke stem used here, so please don’t follow my lead and always read and go by the installation manual.
The handlebars are Schmolke TLO as well, in 720mm width coming in at 105.3 g. At the ends there are foam grips from Extralite, who also make the headset.
Matching the carbon cockpit is a Schmolke TLO seat post with a TLO 55 seat. As the name suggests the latter weighs just 55.2 g while having a 100 kg rider weight limit. Remember that for XC/Marathon riding, padding doesn’t necessarily equal comfort. The important thing is to find the right shell shape for you, and a carbon seat has the benefit of way less friction between your bibs and the seat itself. If the pointy looking rear end scares you off, they do also have a much rounder design model as long as you can live with that one being 20 grams heavier. It can even be had with padding, but we shall not speak about such blasphemous things in this weight weenie feature.
While you may think the seat post puts the seat halfway to the moon it’s actually a standard 400 mm in length. It’s held in place by a Tune Würger Skyline seat clamp, unfortunately not in production anymore, but one of my favorite components of all time.
Why no dropper? While dropper seat posts can be both practical and fun to ride with, they’re not really a must for every kind of riding or every track. The bike is of course prepared to run one though, and while the rigid Schmolke post will be used most of the time the bike would still be very lightweight with one. For example, using a BikeYoke Divine SL dropper would put it at around 8.4 kg or 18.52 lbs.
Trickstuff Piccola has been the lightest brakes on the market for several years now while still delivering a surprising amount of stopping power. But true to the spirit of the often detail obsessed (no wonder I like them) high-end section of the German bike industry there’s always room for improvement. The latest version has Carbon added to the name which of course means new lighter lever blades. The brake caliper has also been redesigned for weight savings and performance improvements. They still keep their trademark smooth and light lever feel and with carbon clamps from Hopp the set weighs a mere 323.2g.
All screws are titanium Extralite and the wispy looking brake discs are an old set of Ashima Ai2. Certainly not the most performance oriented discs, I haven’t had any luck together with other brakes, but they do actually work very well with the Piccola’s. You have a lot of initial punch, but to no big surprise they heat up quickly so if you plan on doing some really long descents you better not drag your brakes.
At the front of this very special drivetrain there is a THM Clavicula M3 crankset. THM is not yet a common sight on mountain bikes, but the company, which was founded in 1996, is quite legendary in the road bike world especially for their state of the art carbon cranksets. The left side crank arm interface especially is a personal favorite aesthetic detail on the bike. This Clavicula M3 (yes, they name their products after bones in the human body) weighs 334.3 g and it has a 36T Garbaruk chainring attached. There’s an optional 38T too for when the pedal pistons need a challenge.
The cassette is an 11-speed 10-46T also from Garbaruk. While 12-speed is quite standard these days and is of course a nice thing, 11-speed still works great and is obviously a bit lighter.
A lot of time was spent on tuning the SRAM XX1 derailleur. Stock it weighs around 245 g, but after a lot of work it came in at 179.9 g. The pulley wheels were changed to Extralite, but most of the weight savings needs to be credited to carbon upgrades. Both the B-knuckle and parallelogram come from Hopp, as do the carbon fiber pins replacing the steel pins usually holding the parallelogram itself together.
It really was a fight to drop the last few grams to bring the bike down below 8kg, and as a final resort I brought out the titanium shift cable. The cost to weight saving ratio is probably even worse than you can imagine, but it does save a few grams. Cable housing can also be a hidden weight saver, and here I use a version with an aluminum core instead of steel.
Wheels and tires
A highlight on the bike is the textile spokes of the PiRope Sub 1.1 wheels. Developed in Germany, and not to be confused with other fiber spokes, they are made from Vectran and use a proprietary fastening system. Not only are they lightweight, they are actually extremely strong and provide enough wheel stiffness to make them suitable for enduro wheels too. At one end they are threaded into the hub shell and at the other a threaded section goes through the rim and a nut sits on the inside of the rim to allow the spokes to be tensioned.
The rims are also made in Germany by Bike Ahead Composites. With a 24 mm inner width, which is just enough for XC tires they weigh an incredible 265 g per rim. All in all the complete wheelset weighs 1020.9 g with a 100 kg max rider weight limit.
As mentioned earlier the bike needed good tires and the choice fell on the trusty Schwalbe Racing Ray and Racing Ralph combo in 2.25″ width. The front- and rear-specific treads give good traction and cornering grip for most conditions and they have been setup tubeless with Syncros sealant.
The suspension remote is a standard Scott Twinloc but it’s running with the aluminum cable housing and synthetic fiber cables. The cables are PowerCordz, which are not in production anymore, but I had one last set to use for this bike. These cables have a plastic surface sheath that would be damaged if you try to fasten it as you would a regular steel cable. So a bit of extra plastic and a knot at the end allows for less screw pressure while still keeping it in place.
Since I had decided that the total weight must include a GPS mount and a bottle cage there were of course grams to be saved in that area too. Another German specialist is CarbonWorks who introduced their incredibly light bottle cage a few years back. It weighs just 8.0 g including the screws. The trick to it is that it’s made with hollow carbon tubes which makes it surprisingly strong and stiff. Another one of those things that feels just ridiculous to hold in your hand. They also make super light GPS mounts for various stems, including the Schmolke stem used here.
Why build such a bike?
I once let a good friend of mine who’s a national level racer take my old super light Spark for a quick spin. He came back just shaking his head, saying “It was like accelerating on a road bike”. And that is a big part of what makes a bike like this both extremely fun and fast in certain situations. The bike becomes so responsive and quick feeling, which is especially noticeable in technical climbs. The bike climbs with minimal effort and you can move it around super easily.
With that said, it’s probably not a bike for everyone. While being very durable for what it is, the bike still comes with a few rider weight limitations. The titanium pedal spindles have a 85 kg limit, the wheel set 95 kg and the seat a 100 kg limit for example. But even if certain components were to be changed or reinforced for say a 110 kg all around limit, it would still be a very lightweight bike. And technical things like that aside, perhaps you prefer a heavier bike. But either way I still wish you all could test ride a bike this light because it sure doesn’t really compare to anything else.
So why did I personally build it? Simple – a bike like this is a ton of fun to ride. It inspires you to do climbs and go for long fast rides or races. And while I’m no contender for the Olympics who really needs such a super bike, having fun riding a great bike is something for everyone. Also, being a bike enthusiast at heart, once I’ve forgotten about all the work hours that went into building it I will enjoy just seeing it parked at home looking fast.
There are plenty more builds to come, so feel free to keep up with them all via my Instagram.