How do you build the world’s lightest 29er mountain bikes? Gustav Gullholm from a bike shop in Mora, Sweden decided to take a couple of already light new Scott bikes – a hardtail Scale RC 900 SL & a full-suspension Spark RC 900 SL – and shed more, apparently unnecessary, weight than you could probably imagine. The result is two incredibly light mountain bikes that he thrashes on real trails regularly. No showroom-only bikes here.

First, all that heavy paint had to go. 1x drivetrains needed to go on a diet. Swap in some machined alloy from Extralite, Garbaruk & Trickstuff. Then, add in plenty of trick custom carbon parts from Berk, Hopp, Schmolke, Tune, and more. We caught up with Gustav in Berlin, where he was showcasing some of the Schmolke Carbon goodies for the company who is supporting him on his next weight weenie project – and upcoming Scott Genius.

Scale RC 900 SL hardtail mountain bike – 6.22kg

Just for frame of reference, the stock Scott Scale RC 900 SL hardtail build is claimed at 8.70kg. But Gustav has trimmed his back to just 6.22kg (13.71lb).

He picked Schmolke Carbon for the cockpit from the start for a balance of light weight and reliability. Only after the complete builds did the German überlight carbon component maker join in his quest for light project bikes. But even the 720mm wide Schmolke TLO bar paired to a stock light stem wasn’t light & stiff enough for Gustav, so he turned to Mattias Hellöre to craft a one piece bar+stem combo with a MCFK stem.

Once you strip back all the paint and unneeded cable stops, there are plenty of little patches needed. Hopp Carbon Parts provided a ton of little trick bits. Frame inserts and fork controls shed a tiny fraction of a gram here and there, and complete that deeply custom look at the same time.

One of the lightest ways to shift – a 1x setup with an Acros AGE hydraulic system. Pair that to some Trickstuff Piccola brakes with a single customized matchmaker-style mount.

Extralite HyperBoost hubs are some of the lightest out there. They also provide the full range of lightweight bolts, plus thru-axles, and the headset. Of course the hubs get custom polished as well, just like that Fox 32 Step Cast fork. Ashima Ai2 rotors are silly light and have just enough brake surface to still work.

Tune takes care of the cranks with their carbon BlackFoot, and are mounted up with a set of Eggbeater 11 Ti pedals and a custom-made 36T alloy direct mount chainring from Garbaruk.

The polished Acros AGE derailleur spins a PYC SL 11-speed chain. Hopp also handles the carbon cable port here to shed a few more milligrams.

Another Extralite HyperBoost hub out back, and what’s that? Yes, a Hopp carbon derailleur hanger, because why not? I hope that is still designed to fail before the frame gets damaged in a crash!

It’s hard to beat an XX1 cassette for lightweight performance. This one still gets the polished to its bare metal treatment for consistency.

What’s lighter than a bare carbon saddle & seatpost? A one piece combo custom-made for the bike by Berk Composites.

At least with the Tune Würger Skyline carbon seatpost clamp, you can still adjust the saddle height (if not tilt or setback).

The complete 6.22kg bike is set up here in its lightest iteration with 77Composites rims and Furious Fred tubeless tires. Gustav readily admits that they are a bit sketchy on his home trails, and he often will step up to a set of 2.25″ Rocket Rons that add about 370g but a lot more trail versatility. A rider weight limit of 85kg is dictated by each the pedals, saddle, and handlebar, with every other component rated for 100kg or more making for a relatively robust build at such a low weight.

Spark RC 900 SL full-suspension mountain bike – 7.86kg

For Gustav’s lightest full-suspension 29er, he again starts with a reliable base bike – the Scott Spark RC 900 SL. That’s the same ride we’ve seen multi-time XCO World Champ Nino Schurter riding, which weighed in on our scale at 9.8kg after winning races. There’s few build similarities between Nino & Gustav’s builds.

But while Gustav has got the bike down as low as 7.33kg with the same light and sketchy wheel setup as on the hardtail, the complete build here uses some DT Swiss rims & Dugast tubulars for a more race-ready 7.86kg (17.33lb) complete weight.

Another Schmolke TLO bar gets bonded to a MCFK stem by Mattias Hellöre. Gustav told us that after building these two super light project bikes for the last year or so, this was about the first time both bikes have been totally complete at the same time. Sharing some similar parts, for a while he was swapping back and forth to race them.

More Extralite Hyperlite foam grips, another set of Trickstuff Piccola brakes, this time mated to a slightly modified SRAM XX1 trigger shifter.

More Trickstuff Piccola brakes with their newer, lighter C21 calipers, plus another set of Ashima Ai2 rotors.

This bike gets a tuned set of RaceFace Next Sl cranks, this time with a stock Garbaruk 36T alloy direct mount chainring, and a set of Xpedo M-Force 8 Ti pedals.

There are more Hopp carbon bits to be found on the Spark’s 1x drivetrain with carbon replacement bits hopping up the XX1 derailleur, along with an Extralite lightweight bolt kit. There’s another Hopp carbon hanger here too, plus carbon frame ports too.

The 50mm tubeless Dugast Fast Bird Flying Doctor Ori cotton tubulars are what give this bike the grip and control of a proper XC or marathon race weapon. They are the same tires that Schurter rode to his Worlds title back in 2015, before going tubeless clincher. These are glued up onto DT Swiss XRC 950 T carbon rims, again laced to Extralite HyperBoost hubs with Sapim CX Super spokes.

The Spark gets another Tune Würger Skyline seatpost clamp, this time clamping down a Schmolke TLO seatpost and a Berk Composites saddle joined in a more traditional two-bolt manner.

Actual weights

Gustav – aka @dangerholm – gave us the full breakdown of the actual weights of both bikes. As we saw them, the Scale was in its super light wheel/tire combo at 6222.7g. The Spark was setup at 7862.1g in its marathon race mode. He said both can go lighter, but is always about keeping them rideable and reliable. He regularly races both bikes, and is looking forward to the snow melt so he can get his spring race season fully underway.

Feel free to follow Gustav on Instagram. We’ll be keeping an eye on his projects, and can’t wait to see what will become of his Scott Genius, already in tuning progress.


  1. terp on

    I’ve heard of light, and I’ve heard of lite, but I’ve never heard of anything that light. I am beyond a blown away man. Montana all the way

  2. js on

    This is top-end ww stuff, in that it’s crazy light and just beautiful. But that polished fork for me is just beyond anything else. SOOOO nice!! Chapeau sir.

  3. Rusty on

    Garbaruk always looks nice, but man, it wears out fast. I got 3 muddy CX races on one of their rings before it was completely toast, and that was hard ano (allegedly).

  4. cousin it on

    I am not really into the weight war thing, but I give this guy credit for running 6 bolts per rotor and not resorting to unrideable DT Swiss suspension just to save weight. You can see that the bikes are actually ridden.

  5. jxjjd on

    am not sure id trust the hard tail for actual trail duty but the fs seems alright. a few sketchy parts but somewhat ridable on real terrain

      • wally on

        That’s absolutely impressive. Still, as a stage racer, I would maybe want to built a little lower risk.
        (I admit to being a weightweenie myself)
        Yet, for example handlebars. Watch this years Cape Epic videos. It’s not the first time I see people riding with half a bar. This seriously ruins your day/overall result.
        No doubt, less weight makes one faster. But technicals don’t help.

        My serious question to Gustav:
        Would you seriously ride that full-sus in any stage race?
        If yes: have you ever had any issues?
        If no: what parts do you swap before riding?

        Best regards and many thanks!

        • Dangerholm on

          So far I’ve never done a stage race, just marathons. But I understand your point, especially if you also travel far and get the trip ruined by a mechanical. Except for switching tires and perhaps use other grips this is how I plan to ride the bikes for training as well as racing.
          The handlebar combos and seats are the only things I’ve not tested yet (was finished after the 2017 season), but for example the Spark has already seen almost 2000km of riding with nothing broken.

          So knowing myself, as long as I trust the bikes for my training and regular riding I’d trust them for racing as well. But cool thing is that even if you change to a heavier handlebar combo and perhaps a more crash resistant seat – it’d still be just above 8kg.

          • wally on

            Many thanks for your answer. I suppose those were the parts I was thinking of.
            The bar would be a definite for me. I’d say it’s worth a thought to ride your seat post in “over dimension”: just ask Schmolke to put your body weight times 1,5 in the dimensioning tool.
            Have you checked out the Bontrager Carbon XXX saddle? If you made such a seat post seat combi, you’d be incredibly light whilst at the same time durable.
            (I ride an AX lightness post, combined with a Selle San Marco Aspide, or SLR flow carbonio. Worked great so far.)
            Then the only open item would be, wheels and tires. 😉

            Enjoy your cycling!

            Best regards

  6. O. Tan on

    I’m just amazed that the weight of these bikes rivals road bikes and gravel bikes. Think about it, most gravel bikes is in the range of 10kg and you can get a full-sus MTB for under 8kg, that’s just crazy.

    • Bill Morris on

      I’d like to see you do a build of the lightest hardtail and full sus xc bikes using only non “one-off items”. That is, using only stuff everyone can buy on the internet, and no painting or polishing trickery required. . Just bolt on weight saving items on the lightest frames you can buy . That would be way more practical for the average guy who doesn’t have the time, machinist skills, or deep wallet these babies take. It would also open up eyes about just how many super light components there are already at anyone’s disposal and if they can be expected to hold up under race/average riding conditions by various sized people. I’m 170 cm and 68 kilos,so I don’t stress a bike as much as some with my sheer weight, but I think many out there would like to know they could lighten their bikes significantly and not worry about failures when choosing online products or stuff from their local shops.

  7. Flatbiller on

    Cool. As a 230-pound, 5’7″ American, I am going to buy one of these instead of hitting the gym to help me KOM a local 300-yard, 19% climb near my house.

    My point being it’s funny seeing dudes having ww wars in the parking lot after a ride as they eat tri-tip sandwiches, potato salad, and slam 4 bottles of some overly-hoppy IPA.

  8. Chris on

    Their so light because of all the energy and MONEY he wasted putting these together. Polished…for real! Have fun keeping that looking “clean”. Not for me, to each his own I guess. I would have bought more stock bikes, I used the extra time to ride them.

  9. Craig Webb on

    Stripping the paint saves how many grams? How do you strip the paint on the frame/fork? How did you determine Scott was the lightest FS frame? What is the current lightest FS frame?

  10. Gabe Ramos on

    Just got a used 2013 Spark for cheap (for carbon anyway) and started in sanding it: looks like it’s gonna take 100+ hours of careful sanding to get down to raw carbon. Using these setups as a basic blueprint for a build. Granted, I won’t be able to afford the 200 gram one-piece carbon stem and handle bars (500 Euro – Experimental Prototype) or 160 gram brakes (750 Euro – Trickstuff) , but there is still a lot that can be done weight-wise with less expensive products. Thanks Dangerholm for sharing these awesome builds, really cool!


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