Scott unveils new 5.9kg Addict RC road bike... the same weight as the 2008 version

Scott has today unveiled the latest incarnation of the Addict RC, its top-end lightweight road bike, claiming frame weights of just 640g (size medium) and complete bikes starting at 5.9kg.

The updated Addict RC has been spotted before now, but today’s the official launch day and, as you read this, it should be available at Scott dealers. And boy, is it ever light.

The Ultimate build pictured above weighs in at just 5.9kg (13lb) as a full build, so we’re back to the days of the pros having to add some ballast to their rigs to nudge them over the UCI’s 6.8kg minimum weight limit for racing, even with pedals and bottle cages added. The frame is available in two configurations, HMX and HMX-SL, Scott claiming a weight of just 640g for the lighter HMX-SL version in a size medium.

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We haven’t seen weights this low for… well, in Scott’s case, since the first iteration of the Addict, way back in 2008. The top-dollar build of that first frameset, with its mechanical gears, rim brakes, wheels and tubular tyres, tipped the scales at 5.9kg, and the bike has never been that light since. That was the inspiration for the new frame, and the target for the scales at the end of the process.

“We were quite happy when we had developed the Foil RC, our aerodynamic bike, with the results we got,” says Christian Holweck, the product designer of the new Addict. “We wanted to see how much we can differentiate a climbing bike from the Foil. How light can we go with the climbing bike? There was still potential to do a much lighter bike, and we were particularly interested in the sensation you get from a climbing bike: how it feels to ride such a light bike, how nimble it is, how effortless it feels.”

Bike design is an iterative process, and there are plenty of similarities with the outgoing model. But five years is also a long time in bike design (the last Addict RC was announced in June 2019 for model year 2020), and the sub-6kg target – 800g less than the Ultimate build of the previous bike – meant revisiting pretty much everything on the bike and trying to figure out savings. The result is that every single component of the bike is lighter for 2025. 

The Addict RC Ultimate’s HMX SL frame weighs in at a claimed 640g, fully finished in a medium size. Scott had an unfinished frame on the scales at the launch, which was a nudge under 600g; prepping the frame, painting it and adding things like axle inserts adds 40g.

The HMX version of the frame found on the non-Ultimate models (such as the RC10, above) is a little heavier, but Scott still claims complete bike weights as low as 6.5kg.

For comparison, Specialized claims that its S-Works Tarmac SL8 FACT 12r Carbon frame weighs 685g. It also says that its S-Works Aethos frame weighs just 588g (56cm version) with complete bikes from 5.9kg, although it’s always dangerous to compare weights across different brands; they rarely agree.

At the computer modelling stage, it’s easy to try different things, so a lot of work was put into the design before a physical model was ever made.

“Really early in the process, we did a lot of different versions”, says Christian. “Some of them were generated by the computer, some of them were our proposals, driven by aesthetics. We compared all of them and really analysed every tube dimension. And then, obviously, it's all connected. You can’t just say: ‘This is the down tube size.’ You always have to say: ‘Okay, how is the combination of the seat tube together with the down tube working?’ And then, when it comes to transitions, a lot of the stress is in these transition areas, the bottom bracket area and so on.

"We were looking for tailor-made surface solutions to really guide the forces through that frame. The more you can do that, and prevent stress build-up, the less material you need.”

Scott was keen to keep the contact points in the same position as before and to match up with the Foil, but in five years tyres have got bigger; The pros now regularly race on 28mm or 30mm tubeless tyres and the new Addict RC was designed around a 30mm tyre, with clearance for up to 34mm.

That presents challenges with the geometry: a bigger tyre can make the front of the bike feel a bit lazier, and it means adding clearance at the back, which leads to longer chainstays, and the same effect.

To combat this, Scott has tightened the head tube angle a touch and introduced a more offset fork for the smaller sizes to mitigate toe overlap (where the wheel touches your toe when you turn). At the back, the seatpost has been moved, shunted forward 5mm relative to the bottom bracket to keep the chainstays the same length. A 5mm layback has been added to the seatpost to compensate. The bottom bracket has also been dropped very slightly to compensate for the higher tyre profile and keep the centre of gravity the same.

The fork changes are possibly even more significant; Scott is using a completely different process for manufacturing the new Addict RC fork.

“For the last 15 or 20 years, carbon fork manufacturing hasn't really changed much,” says Maximilian Koenen, the lead engineer on the Addict. “It's always been a four-piece approach: the fork blades are pre-formed on a wooden mandrel, and the steerer is rolled on a steel rod, and then everything is puzzled together around a crown piece, which is a glass fibre part that stays in the fork.”

Keeping the glass fibre in the fork, and then combining the four elements, adds weight.

Scott has moved to a new process, which moulds the fork in a single piece. It uses a polypropylene mandrel, which is essentially a smaller version of the fork. The material feels a bit like a water bottle, and the carbon is laid up around it. Then it’s inserted into the mould, and the mandrel is inflated to form the fork. After that the finished fork is heated up; the mandrel material softens and it can be pulled from the middle of the fork.

As you can imagine, there’s a lot of stuff to get through a small hole, so it took a while to perfect the process without the mandrel breaking and wrecking the fork, but the end result is a unit that’s single piece, lighter, and with a much smoother internal cavity.

“Previously, when the fork pieces were fitted together, you always had these areas where you had double the wall thickness because you need some overlaps”, says Max. That’s changed with the new process, so there are savings there. And now, finally, we can have some continuous fibres from the steerer into the fork legs.”

The frame and fork contribute 245g of the 800g weight saving over the previous Addict RC that was needed to hit the 5.9kg target, with 175g of that saving coming from the frame, and 75g from the fork.

There are just under 100g of savings from other frameset bits – seatpost, headset, axles – and the rest of the saving is in the build components. The Addict RC Ultimate isn’t trying that hard: the Syncros Capital SL 40 wheelset is very light but could easily be bettered in terms of weight, and the big tyres aren’t especially light either. You’re getting a 2x (double chainset) transmission, a proper padded saddle, and full bar tape. If you wanted to shave a bit more off for hillclimb season, a 5.5kg build is certainly achievable.

A lot of work has been done to make the frame and fork light, but lightness isn’t the only consideration. Scott is firmly in the two-bike camp for racing – an aero one, and a light one – but aerodynamics has still played a significant part in the design process. It hasn’t obviously been hit with the aero stick, but there is still plenty going on.

“The tubes, even though they look roundish, are actually all following aerodynamic principles,” says Christian. “It's just that mainly the trailing edges of the tubes are more rounded to get a better stiffness-to-weight ratio. But you still get some of the characteristics of an aero bike – how it behaves in crosswinds, and so on.

“I think that a good example is the seat tube area, where it transitions to the seatstays. We identified on the Foil, when you look at the whole system with the rider pedalling, that tilting the seatstays a little bit inward does something to the flow created by the wheel, and we can see drag reductions there. So we said: ‘Okay, maybe we can’t do it to the same extent as on the Foil, but we still like to use that principle.’ So we scaled it accordingly, validated it with our simulations, and then brought it into this bike as well.” 

The last version of the Addict was at the forefront of what brands were doing with full integration at the time, but things were different back then, especially with groupsets: mechanical shifting and wired shifters still needed to be considered. Less so now, with wireless top-end groupsets from all the main players; the new bike is designed exclusively for wireless groupsets.

The Addict RC will be available with a new integrated cockpit, which is going to be made in a pretty wide range of widths and lengths; there are 18 variations in all at launch. The trend in handlebars has been ever narrower over the past few years, and that’s reflected in the choices available. The bar also includes a lightweight tool that slots into the end. It has just a T25 head – all the bolts on the bike are standardised to this head size – and a 6mm Allen key for the through axles.

To complement the new handlebar, there’s a skeletal 3D-printed metal GPS mount available in two lengths, which weighs in at just 10g.

Other tweaks are more aimed at making the bike easy to live with. Scott has built a channel into the seat clamp wedge, and that fits onto a carbon spline in the frame, so that the wedge can’t fall down when you take the seatpost out. It’s a nice touch, as is adding a circlip onto the seatclamp bolt so you can’t accidentally undo it all the way.

There’s also a new integrated rear LED light available, which fits magnetically into a recess in the seatpost. The Ultimate and RC Pro builds don’t have this because it would increase overall weight, but the other bikes in the range get it. The LED seatpost has the dual advantages of adding some neat visibility to the bike, and also dialling in a bit of comfort because the thinner seatpost profile in front of the light unit allows a bit more flex.

Talking of comfort and stiffness, it was refreshing to hear the Scott team say that lobbing a 30mm tyre on a race bike is likely to do more for the comfort than minor changes to the frame characteristics; we already know that, right? Even so, it wouldn’t be new bike day without some manner of percentage or numerical gains claimed, so I’m here to tell you the new frame is “36% more comfortable” than the old one. This means what, exactly?

“There is a testing protocol in the ISO 4210-6 (Section 4.5) to test vertical fatigue loads on the seat post”, says Scott. “This testing setup can be used to determine frame comfort (seat tube compliance). When comparing the MY25 Addict RC equipped with the comfort seatpost against the MY20 Addict RC equipped with the SL seat post (the stock setups of the 10/20/30 model for both bikes), the new version is 36% more compliant.”

So it’s not really comparing eggs with eggs, as the old bike didn’t have the cutout comfort seatpost, and there’s no word on how much of that comfort comes from the seatpost (my guess: a lot of it) rather than the frame, and it’s not a measure of “comfort” per se as it doesn’t take into account front end comfort. But anyway, there’s your number.

The aero claim is more straightforward. Thanks to aero updates that have reduced the frontal area of the bike by 15%, the new Addict RC is “12W quicker” than the outgoing model, by which Scott means that at a VERY brisk 45km/h you’ll need 12W less input to maintain your speed. That testing is done with a dummy rider and averaged over a range of yaw angles (the bike’s angle relative to the wind).

It’s worth noting that Scott says the new Addict is also more aerodynamically efficient than every Foil aero bike up to the current one, which is 9W better at the same speed. So in terms of aerodynamics, it’s no slouch, according to Scott’s figures 

The Addict RC is available in five builds at launch:

Addict RC Ultimate (£12,799 / €12,999 / $14,999)
Frame Addict RC HMX SL
Fork Addict RC HMX SL
Groupset SRAM Red AXS (inc power meter)
Wheels Syncros Capital SL 40mm 
Claimed weight 5.9kg

Addict RC Pro (£8,599 / £8,699 / $8,999)
Frame Addict RC HMX
Fork Addict RC HMX
Groupset Shimano Dura-Ace Di2
Wheels Syncros Capital 1.0S 40mm
Claimed weight 6.5kg

Addict RC 10 (£6,599 / €6,699 / $6,599)
Frame Addict RC HMX
Fork Addict RC HMX
Groupset Shimano Ultegra Di2
Wheels Syncros Capital 1.0S 40mm 
Claimed weight 7.1kg

Addict RC 20 (£5,899 / €5,999 / $5,699)
Frame Addict RC HMX
Fork Addict RC HMX
Groupset Shimano Ultegra Di2
Wheels Syncros Capital 1.0 40mm
Claimed weight 7.4kg

Addict RC 30 (£4,899 / €4,999 / $4,999)
Frame Addict RC HMX
Fork Addict RC HMX 
Groupset Shimano 105 Di2
Wheels Syncros Capital 1.0 40mm
Claimed weight 7.7kg

Go to www.scott-sports.com for more info.