Scott has unveiled the new Addict RC, which weighs less than 6kg in its top-flight build, matching the weight of the original Addict Limited from 2008.
It does this with all the weight penalties of modern bikes, such as disc brakes, wider tyres and larger cassettes.
The brand says its road bike has “always been about shedding grams” and after four years of development, the new £12,799 / $14,500 Addict RC Ultimate weighs 800g less than the previous generation.
Speaking to BikeRadar, Christian Holweck, product designer for the new Scott Addict RC, says: “We wanted to see how far we could go with a light bike with modern restrictions – still thinking about aerodynamics, still integrating everything and with modern specs.”
How light is lightweight?
The team of 10 behind the new bike had to decide what lightweight meant for them at the beginning of the design process. The answer came from the original Addict Limited from 2008.
Maximilian Koenen, lead engineer on the project, says: “It was the first bike named Addict in the Scott universe and it came in at 5.9kg for the complete bike and 790g just for the frame, including the seat mast.”
Mark Cavendish raced the Addict Limited to victory on the Champs-Élysées at the 2010 Tour de France, but the 5.9kg weight became a suitable target for Scott’s latest climbing bike.
Holweck and Koenen knew that for the new Addict RC to hit 5.9kg, the frame would have to be around 600g because of the extra weight of modern bikes.
The new Addict RC Ultimate’s frame – the only one in the new range to use Scott’s HMX SL carbon – isn’t far off that 600g figure at a claimed 640g.
“The Ultimate build in a size medium, painted, with 28mm tyres and tubes, complete with pedals and saddle, comes in at 5.9kg,” says Koenen. The bike has 40mm-deep Syncros Capital SL wheels wrapped in the unreleased Schwalbe Aerothan tyres and a SRAM Red AXS groupset.
Koenen adds that all five models in the new range are under 8kg. This includes the cheapest Addict RC 30, which comes with a Shimano 105 Di2 groupset and costs £4,899 / $5,000.
Learning from mountain bikes
One significant way Scott achieved the Addict RC’s low weight was by using a new carbon moulding technique called PP Mandrel.
This process, which it says is unique in the cycling industry, involves wrapping carbon fibre around inflatable polypropylene (PP) mandrels. The mandrels are then deflated and removed, leaving behind a smooth interior, which avoids the build-up of unnecessary resin and material, therefore saving weight.
Scott already uses the process on ebikes and mountain bikes for moulding the frame around internal shocks, and it now uses the technique for the Addict RC.
It’s easier to use inflatable mandrels for frames, but it’s harder for forks. The shape of a fork’s PP mandrel, with a voluminous crown, is difficult to extract through the bottleneck of the steerer tube without it ripping and staying inside.
But Koenen says that after much testing, “We were finally able to tweak the material composition of the PP mandrel and the thickness in some areas to get it out of the forks.”
The result is the inside of the Addict RC’s new fork has less excess material and resin than before. Comparing cross-sections of the old and new Addict RC forks, you can see how there are wrinkles of resin in the older design, whereas the new fork is completely smooth on the inside.
Eliminating this unnecessary material means the new fork weighs 270g with a cut steerer for a size-medium bike.
“To our knowledge this is the lightest fork on the market,” says Holweck.
Starting with the thru-axles
Scott paid particular attention to the number of carbon layers it needed in the frame to achieve its desired weight of 5.9kg.
Holweck jokes that when designing the frame the team behind the bike started with the thru-axles. Beyond designing new, lighter axles, the team determined the number of carbon layers they needed around the axle before moving onto the tubes.
The same is true at the headset. “We checked out how many layers we needed to make a strong bearing seat before moving onto the tubes,” says Koenen.
The widespread adoption of electronic groupsets gave the team one easy win. The new Scott Addict RC has a smaller and therefore lighter headset than the previous model because it no longer needs to fit internally routed gear cables for mechanical groupsets.
This also opened up an aerodynamic advantage. The smaller bearing meant Scott could reduce the size of the steerer tube and consequently the frontal area of the bike by 15 per cent.
The choice of carbon layup, paired with the PP Mandrel technique, also means the Addict RC’s frame is only 0.6mm thick in some places.
From 25 to 5 prototypes
Holweck and Koenen say the research and development facilities the brand has developed in recent years also played a huge role in designing the Scott Addict RC.
Scott is now able to create digital prototypes and put the simulated designs on a “digital workbench” to estimate the real stiffness, weight and strength values with up to 3 per cent accuracy.
“We can adapt the design and the layup before we build the first prototypes,” says Koenen.
The engineer says Scott developed five real prototypes to hit its desired goals for the new Addict RC, which is 20 fewer than with the previous generation of the bike, saving plenty of time, energy and money. “It’s just a better approach if you start your real prototype building from a good basis,” Koenen says.
The development of the Addict RC’s design wasn’t driven solely by performance insights gleaned from the digital prototypes.
Scott looked at the constraints posed on the dropped seatstay design – including creating room for a brake caliper in the rear triangle and the UCI’s restrictions – to then create a stiffness-to-weight ratio bell curve. But after that, it came down to a more intuitive approach.
“I looked at it from a purely aesthetic perspective and said ‘Ok, this is the sweet spot to get the silhouette right,’” Holweck says.
This is an approach taken across the bike. Holweck says the bike almost has “hidden aero” because the tubes are designed following aerodynamic principles but have softer, rounder profiles than aero bikes. In fact, Holweck says that at 45kph and with the same setup, there is only a 9-watt difference between the new Addict RC and the Scott Foil.
Wider tyres and geometry tweaks
The previous Scott Addict RC had a maximum tyre clearance of 28mm, but the updated race bike can accommodate 34mm tyres.
Holweck says this is to “future proof” the bike now consumers and professionals are opting for wider rubber. “But what happens when you increase the tyre size of the bike is it affects the handling,” he adds.
“One example is the fork trail will get longer so the bike will get lazier,” says Koenen.
Koenen explains the new Addict RC has a steeper head tube angle to compensate for this. To mitigate the potential toe overlap that comes with a steep head tube, the smaller Scott Addict RC sizes have a different fork with a longer offset to reduce the trail and increase the toe clearance.
Increasing tyre size can create another problem at the back of the bike, where the tyre ends up touching the seat tube. One solution is to extend the chainstays, but Scott wanted to keep them short, specifically 410mm, which is the shortest length Shimano specifies for effective shifting with its groupsets.
“To compensate for this issue, we offset the seat tube forward by 5mm,” says Koenen.
Scott Addict RC geometry
| XXS | XS | S | M | L | XL | XXL | |
|---|---|---|---|---|---|---|---|
| Seat tube length (mm) | 422.5 | 442.5 | 462.1 | 482 | 502.2 | 522.3 | 542.4 |
| Top tube length (mm) | 519 | 528 | 542 | 555 | 572 | 586 | 602 |
| Head tube length (mm) | 90 | 100 | 113 | 130 | 150 | 170 | 190 |
| Head tube angle (degrees) | 71.3 | 71.8 | 72.3 | 72.8 | 73.4 | 73.6 | 73.8 |
| Seat tube angle (degrees) | 74.5 | 74.5 | 74 | 73.6 | 73.3 | 72.8 | 72.5 |
| Chainstay length (mm) | 410 | 410 | 410 | 410 | 410 | 410 | 410 |
| Wheelbase (mm) | 977 | 983 | 989 | 991 | 999 | 1,006 | 1,015 |
| Stack (mm) | 501.3 | 512.5 | 525.5 | 543.3 | 564.5 | 584.3 | 604.2 |
| Reach (mm) | 379.4 | 386.3 | 391.6 | 395.2 | 402.6 | 406.1 | 411.3 |
Syncros integration
All five models in the new Addict RC range use parts from Scott’s component sub-brand Syncros.
The road bike will be available with either a Syncros SL or Comfort seatpost.
Thanks to the bike’s revised seatpost clamp design, the SL seatpost is 10 per cent lighter than the previous version and is more flexible for greater comfort.
The Comfort seatpost, available on the Addict RC 10, is said to increase the bike’s comfort by another 30 per cent compared to the SL version. The post also has a magnetic cover on the back, which you can swap for a Syncros rear bike light.
The Addict RC Ultimate, Pro and 10 also feature the new Syncros cockpit, the IC-R100-SL. Scott says its goal was to create an aerodynamic handlebar and it also responds to changes in groupset design.
“We brought the drops in line with modern shifters, which are all angled slightly outward. For instance, a 38cm bar on the top translates to a 41cm bar in the drops,” says Holweck.
The cockpit is said to be 40g lighter than its predecessor thanks to a new stem clamping design and carbon layup that retains the same strength and stiffness.
Scott went as far as developing a new computer mount for the bike, which weighs 12g.
The only arguable concession to weight on the bike is the inclusion of a tool in the handlebar end with a 6mm Allen key for the thru-axles and a T25 bit for other bolts on the bike. But you’d probably take a multi-tool with you anyway.
