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.
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.
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.
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.