This article was produced in association with Scott
‘It’s what’s inside that counts’ is a maxim rarely applied to bicycles, but in the case of the new Scott Addict RC, the flawless inner surfaces of the tubes are a crucial part of a new method that has allowed the brand to make the lightest production race bike on the market.
The new Addict RC weighs an unbelievably light 5.9 kilos with a raw frame weight of just 600g achieved thanks to Scott’s innovative PP mandrel manufacturing process. A high-precision moulding of inner surfaces and transition zones leaves the inside of the frame super clean without voids, wrinkles or excess resin, leaving only what’s necessary for stiffness and strength. Paired with optimised tube shapes that eliminate additional reinforcements and unnecessary filler material, the result is an ultra-light frame without compromise.
As well as reducing the frame weight in order to bring the new bike in under six kilos, Scott worked to shave grammes from other areas of the frame kit – the frame, fork, seatpost and hardware required for assembly – and claims a 300g reduction in weight compared to the frame kit of its predecessor.
Scott’s lead road bike engineer, Max Koenen, explains how his team pushed the boundaries of modern carbon manufacturing, but also why 5.9 kilogrammes is an auspicious number in the Swiss brand’s story.
“We were digging into the history of Scott’s road bikes, the Addict, and we found the original Addict Limited from 2008, which came in at 5.9 kilogrammes. This was a frame with an integrated seat mast which had a weight of 790g – pretty spectacular back then. It also had a nice racing history: Mark Cavendish used it for his Tour de France final stage win on the Champs-Elysées in 2010. So we had our target right there.”
However, Koenen continues, despite 16 years of road bike evolution, it would be a challenge to make a modern bike as light as that. “This original 2008 bike was mostly determined by its components, which are outdated by modern standards. It had tubular rim brake wheels, rim brakes, no electronic shifting or integration... In 2024 bikes have specifications that are a must- have, but which add weight.”
Koenen continues: “So we defined our development targets for this bike. Number one was clearly the weight. We calculated that to achieve this goal of under six kilogrammes we needed a frame under 600g in the top version. Among our competitors there is barely anyone under 600g and certainly with a frame which is racing compatible in terms of stiffness, so it would be a challenge.
“The Addict RC is also a race bike used by pros in the WorldTour, which means we cannot fully ignore aerodynamics [Scott also has the Foil RC aero bike]. Aerodynamic improvement was clearly also one of our top targets compared to the previous generation.
“The comfort topic is everywhere at the moment, driven by bigger tyres as well, so we wanted to increase tyre clearance to 34mm. We’ve seen the trend among pro racers to go wider in the tyres but also the normal user goes to at least 30mm. So we wanted to be future proof. The comfort of the frame also plays a role, so it should be increased, too.
“Last but not least, the geometry has to be racing. RC stands for ‘Racing Concept’ so that means the bike-fitting geometry for the rider should be very aggressive, low and long, as our pro riders request, but also the bike should be agile and nimble. With the bigger tyre clearance we would have to make some adaptations to avoid it becoming too lazy or sluggish. The goal was that the new bike should feel similar in handling to the old bike but with increased comfort and lower rolling resistance and better grip of the bigger tyres.”
Next, Koenen and his team had to decide how to actually achieve their aims. “Often when we develop new bikes there are some restrictions: we need to use the same axles or the same steerer diameter or the old bar and stem needs to fit... but it became pretty clear early on that if we wanted to achieve this goal of getting a bike under six kilogrammes we needed to start thinking everything from zero and not in terms of backwards compatibility.”
First came the geometry – adapting the frame so that with bigger tyres it would still handle like a race bike with the rider contact points in the same place.
“We had to drop the BB because the centre of gravity is increased when you put on 30mm tyres. The other effect of big tyres is to increase the trail. A longer trail makes it more lazy or stable if you like, but that’s not what we want for a snappy racing bike. So to compensate we increased the fork rake to get back to similar trail values as before. We also had a challenge with the rear tyre – we needed to make some space behind the seat tube. We did it by shifting the seat tube 5mm in parallel forwards, and compensated with a 5mm offset seatpost so that the saddle would be at the same spot in the triangle of contact points as before. We managed to get to the same bike fitting position as the old model, and with the Foil RC. This was requested by the pro racers: sometimes they switch between the Foil RC and the Addict RC so they want similar geometry on all their bikes.”
Then came the weight. “So we took our time to go to the factory, observe the way the previous Addict RC was produced, searching for possibilities to get rid of everything that was there just as a filling material, design edges or features and sometimes manufacturing methods that were costing us weight because we weren’t achieving a high enough precision”.
Koenen uses the new fork to illustrate how the manufacturing method that they used, called PP mandrel, works. “The PP mandrel process is used in the bicycle industry mostly by e-bikes where you want to have a very precise inner shape of the frame because there’s the motor and the battery inside, and it’s also used on our high-end mountain bikes to get as much resin out of the frame as possible and only leave behind what is needed,” he explains.
“The moulding core inside, the mandrel, is made from poly- propylene [PP] and it makes everything precise. For years forks have been produced with a kind of tube-to-tube approach: a small glass-fibre mandrel for the crown section and then tubes for the legs and steerer and then you have some layers of pre-preg on top that are connecting them all. The glass-fibre piece stays inside the fork crown. After the production process you can’t get it out and it weighs around nine grammes. We identified this as something that’s not there for a structural purpose, just for the layup procedure. We tried to use the process on forks for quite a while, but the problem is that the crown is quite voluminous and the only exit where you can get the PP core out after moulding is the steerer. Often it would rip apart at the steerer so the lower part of the moulding core would stay inside, you cannot route cables and it’s a waste of a fork in your production if this happens. It took us a while to figure out how we could tweak the thickness of the moulding core so that it was stable enough to not rip apart, but another way was to tweak the design of the fork itself. If you design it to have a minimal crown volume and smaller step to the steerer you can get the moulding core out. This kind of strategy for design went not only into the fork but into the other parts of the bike as well.”
It’s clear the new fork is a highlight for Koenen from an engineering perspective. “If we made a frame that looked the same but without the PP mandrel it would be at least 50 to 100g heavier. But on the fork it’s certain that we saved around 40g and for sure it’s the reason why we have the lightest fork on the market. The fork of the new Addict RC weighs 270g, even though our fork has aerodynamic blades and much more volume. And we still have a high wall thickness for safety where the bearing seat is and also where the hole where the cable passes through.”
So, with the new Addict RC weighing 5.9kg in its top spec with SRAM Red AXS and Syncos Capital SL wheels, there’s no redundant resin left inside the tubes, but there’s just one very lightweight elephant left in the room: the UCI minimum weight limit is 6.8kg.
“Yes,” laughs Koenen. “We’ve already had phone calls because the teams have received the first new bikes for training. ‘Hey guys, we’ve built it up and it’s only 6.5kg with deep rims and all the stuff we want to put on, so what should we do?’ Usually you aim for a low centre of gravity so you put extra weights in the BB area. Or a more comfortable saddle or another layer of bar tape, or use tyres which have more puncture resistance or larger for better grip. So we would suggest adding it where you can get some benefit but failing that, in the BB area.”
For the professional teams it will indeed be a case of ‘it’s what’s inside that counts’ if they’re not to contravene the UCI’s rules, but, says Koenen, the Addict RC was not designed only for racing by WorldTour teams.
“It’s slightly unique what we’re doing now. Most of our competitors are unifying their competition race bikes but we decided not to – and one of the reasons was because the Foil RC is pretty light, close to the 6.8kg UCI rule, so the pro teams on flat stages will always go for the aerodynamic bike. But we saw room to make a lightweight bike that is a bit more for the consumer and the people not bound by the 6.8kg rule, so that’s why we went spectacular with the weight numbers.”
