The Scott Addict RC all-rounder race bike has had a workover, with the new bike in top spec dropping a claimed 800g from its predecessor. 170g of that comes from the new frame, the fork drops 75g and there are an additional 86g of weight decreases in other parts including the bar/stem and the seatpost.
Scott has bolted the flashiest wheelset from its Syncros component brand onto the halo bike, as well as other top-drawer components to achieve the headline weight of 5.9kg for a size medium (or 5.87kg to be exact – we’ve weighed it). That’s despite an increase in tyre clearance to 34mm and the inclusion of a Torx T25 and 6mm hex wrench in the bar end. Scott also claims to have improved the bike’s aerodynamics by 12 watts.
UK prices for the five available specs range from £4,899 to £12,799.
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Back to 5.9kg
‘The 2008 Addict frame weighed 790g and the Limited build weighed just 5.9kg, which was pretty spectacular in 2008,’ says Scott product designer Christian Holweck. ‘But when you’re judging the weight of a complete bike, you have to look at all the parts. Back then we had rim brakes, very thin tubular tyres and rims, mechanical gearing and light but ridiculous gear ratios: 11-23t. Who would ride this now except down a hill?
‘Today we’re starting on the back foot because we’re dealing with components that are heavier, but that was the challenge we set ourselves. Could we accommodate these modern constraints and get back to this magic number of 5.9kg?’
The answer is here, 16 years, ten engineers and a four-year product cycle later: the Scott Addict RC Ultimate. You don’t need to ask the weight, but you might want to ask how Scott got there.
In pursuing overall lightness, the problem for most manufacturers is (A) there’s a huge amount of the bike that isn’t made by you, and (B) there’s a very good chance the last time you made a bike you shaved off as much weight as you could, so where to next?
Problem A doesn’t exist for Scott in quite the same way as it does for many brands thanks to in-house component arm Syncros, which lends its Capital SL wheels – 40mm deep, 25mm wide internally, hookless and just 1,170g (claimed) – and also makes pretty much every component except the groupset and tyres, giving Scott control to shave weight across the board. Yet even then Scott is not immune to problem B.
The outgoing Addict RC Ultimate was also developed to be as light as possible, coming in at 6.7kg, hence savings in the new Addict’s components are pretty tiny. Thru-axles drop 12g to 44g, headset 16g to 42g, the one-piece bars 45g to 285g and seatpost 13g to 85g. Laudable, but some way off saving the total 800g needed to take the new Addict to 5.9kg.
‘What we had to do was work backwards from all these components and calculate the maximum an unpainted frame could weigh. No more than 600g,’ says Holweck. ‘This is very light when you consider the last frame weighed 810g, and this is very hard as now riders are asking for wider tyre clearances and more aerodynamic shapes, things that make frames heavier, not lighter.’
The frame conundrum
The heart of Project 5.9kg, then, is the Addict’s new frame, which came in tenths of grams under 600g when Scott placed a raw size medium on the scales in front of Cyclist, and a claimed 640g when painted and furnished with hardware such as bottle bosses.
It’s a miraculous feat for a bike that’s 12 watts faster aerodynamically than its predecessor and has room for 34mm tyres, says Holweck.
‘The thing is, there are so many constraints. Take the tyres. To create bigger clearances you usually elongate the stays so the tyre doesn’t rub on the back of the seat tube. But this adds weight, reduces stiffness and affects handling, as now you have a longer rear triangle and wheelbase. RC means “racing concept” and this is a race bike so it needed to be built on racing geometry and stiffness.’
Scott’s answer was a canny one: push the seat tube away from the tyre.
‘The chainstays are still 410mm – the shortest Shimano recommendation for good chainlines – but the seat tube doesn’t end up in the centre of the bottom bracket anymore, but 5mm further forward.’
Helping make such decisions is the type of computing power that Holweck says ‘you leave on overnight to run simulations’, meaning instead of this bike having the usual 20-25 working prototypes before being committed to moulds, it had five.
‘The simulations helped us make decisions like the position of the seatstays. The UCI rules say they can be so low, but if they are dropped too low there isn’t enough space for the brake calliper [as the angle at the dropout becomes too acute to fit it in], but if they are too high it reduces stiffness and increases weight. So we ran a computer simulation changing the seatstay angle in 0.5° increments until we found the ideal placement for stiffness to weight.’
Still, for all the computing power in the world, the key to unlocking the frame weight conundrum was developing smarter manufacturing techniques.
‘The usual way to make a fork is to mould the crown around a fibreglass mandrel, which because of its material and shape has to stay inside the fork afterwards, but that’s just redundant material,’ says Holweck. ‘The traditional way to mould a frame is around air bladders, but these are like plastic bags; they wrinkle when inflated inside the frame and the wrinkles fill with resin. This is not a structural problem but it is more needless weight.’
Scott’s solution is to form the Addict around ‘PP mandrels’, short for polypropylene, a material that has the look and feel of very thin milk bottle plastic. The mandrel for the fork, for example, looks like a smooth, hollow, semi-rigid version of the fork itself, just thinner.
‘You still inflate the PP mandrel but unlike the air bladder it gives even compression across all the layers of carbon and you are left with a perfectly smooth inside shape where only the material needed for structural purposes is left. The mandrel itself becomes very flexible when it’s heated, meaning we can pull it out, even through the fork steerer, which is very narrow.’
It’s all marginal, it’s all way more detail than the average rider needs, but there’s no denying it has made for one exceptionally light bike. Pity the engineers who need to make the next one.
Scott Addict RC geometry
Scott Addict RC specs and prices
Scott will offer the new Addict RC at five spec levels, with the Ultimate the only variant to use its HMX SL carbon. Other specs are built on the HMX carbon frameset.
Scott Addict RC Ultimate
- Frame/fork: Addict RC HMX SL
- Groupset SRAM Red AXS with power meter, 46/33 10-33t
- Wheels: Syncros Capital SL
- Tyres: Schwalbe Aerothan TL 28mm with Schwalbe Aerothan inner tubes
- Bar/Stem: Syncros IC-R100-SL
- Seatpost: Syncros SP-R100 SL
- Saddle: Syncros Belcarra Regular SL
- Claimed weight: 5.9kg
- Price: £12,799 / $14,999.99 / €12,999
Scott Addict RC Pro
- Frame/fork: Addict RC HMX
- Groupset Shimano Dura-Ace, 52/36 11-34t
- Wheels: Syncros Capital 1.0S
- Tyres: Schwalbe Pro One TL-Easy 30mm with Schwalbe Aerothan inner tubes
- Bar/Stem: Syncros IC-R100-SL
- Seatpost: Syncros SP-R100 SL
- Saddle: Syncros Belcarra Regular 1.0
- Claimed weight: 6.5kg
- Price: £8,599 / $8,999.99 / €8,699
Scott Addict RC 10
- Frame/fork: Addict RC HMX
- Groupset Shimano Ultegra, 52/36 11-34t
- Wheels: Syncros Capital 1.0S
- Tyres: Schwalbe One TLE 30mm
- Bar/Stem: Syncros IC-R100-SL
- Seatpost: Syncros SP-R101-CF
- Saddle: Syncros Belcarra Regular 2.0
- Claimed weight: 7.1kg
- Price: £6,599 / $6,599.99 / €6,699
Scott Addict RC 20
- Frame/fork: Addict RC HMX
- Groupset Shimano Ultegra, 52/36 11-34t
- Wheels: Syncros Capital 1.0
- Tyres: Schwalbe One TLE 30mm
- Bars: Syncros HB-R100-CF
- Stem: Syncros ST-R100-AL
- Seatpost: Syncros SP-R101-CF
- Saddle: Syncros Belcarra Regular 2.0
- Claimed weight: 7.4kg
- Price: £5,899 / $5,699.99 / €5,999
Scott Addict RC 30
- Frame/fork: Addict RC HMX
- Groupset Shimano 105 Di2, 52/36 11-34t
- Wheels: Syncros Capital 1.0
- Tyres: Schwalbe One TLE 30mm
- Bars: Syncros HB-R100-AL
- Stem: Syncros ST-R100-AL
- Seatpost: Syncros SP-R101-CF
- Saddle: Syncros Belcarra Regular 2.0
- Claimed weight: 7.7kg
- Price: £4,899 / $4,999.99 / €4,999
