"Fastest road bike in the world": First test of the new Specialized Tarmac SL8

The competition bike from the Americans, which came onto the market in 2005 in the form of the S-Works E5, has been one of the best racing bikes in the world for years. In the TOUR test, the S-Works Tarmac SL7 one of only four models to earn the top score of 1.4 to date. Thanks to top performance in the four most important categories: Weight, aerodynamics, comfort and stiffness. Specialized wants to top it all off with its successor: The new Specialized Tarmac SL8 is said to be "the fastest road bike in the world". Although we have not yet been able to verify this in the test lab and wind tunnel, the new bike already gave an impressive indication of its potential on our first test ride in Glasgow.

Specialised Tarmac SL8: The most important facts at a glance

• Weight of complete wheel: 6.6 to 7.8 kilogrammes
• Frame weight: 685 grams (S-Works) or 780 grams
• Fork weight: 358 grams (S-Works) or 371 grams
• Aerodynamics: 16.6 seconds faster than Tarmac SL7 (40 kilometres)
• Stack/Reach/STR: 555/398 millimetres/1.40
• Maximum tyre clearance: 32 millimetres
• Frame sizes: 44, 49, 52, 54, 56, 58, 61
• Prices: 6500 to 14000 Euro

As with its three-year-old predecessor, the bike manufacturer from Morgan Hill/California took a holistic approach when developing the latest generation of the Tarmac. This means that the Specialized Tarmac SL8 remains a race all-rounder that combines low weight and the best possible aerodynamics. Like the SL7, the most ridden model in the professional peloton, it is designed to tackle both fast flat stages and steep mountain passes. Specialized was the pioneer in the industry with this strategy. However, because the competition is not sleeping either and has caught up in recent years, the original has lost some of its unique selling point.

Record-breaking frame weight

To restore the old hierarchy, Specialized took its cue from the lightweight Aethos model and put the Specialized Tarmac SL8 on a diet. For the S-Works frame (size 56), the US company claims a weight of just 685 grams. That's around 100 grams less than the SL7. The simpler version of the carbon frame is also remarkably light at 780 grams - and could also easily compete with professional material from other manufacturers. Cannondale, for example, specifies a weight of 770 grams for the high-end frame of the new SuperSix Evo Lab71. In total, the lightest version of the S-Works Tarmac SL8 should be under the UCI weight limit and weigh 6.6 kilos. According to the manufacturer, the "heaviest" version is around 1200 grams heavier.

"The steeper the climb, the more important it is to have a light bike. You can really feel it," says top star Remco Evenepoel about his new tool: "It can make a difference of one or two seconds - that can be enough to win a race," adds the Belgian, who, like his Danish Quickstep team-mate Kasper Asgreen, was closely involved in the development process. "We now have a platform that we know works on many terrains," says Asgreen. The duo started the World Championship road race on the new Specialized Tarmac SL8, as did Julian Alaphilippe (France), Sam Bennett (Ireland) and Peter Sagan (Slovakia).

Detailed aero optimisation

In addition to a lightweight road bike, aerodynamic performance is also important on the mountain. This is shown by simulations based on our wind tunnel tests in Immenstaad - and Specialized also demonstrates this with the new Tarmac. Overall, the Specialized Tarmac SL8 is said to be almost 17 seconds faster over 40 kilometres than its predecessor. The new Specialized should need 20 seconds less for the average 7.3 percent gradient and 17.1 kilometre long climb to the Col du Tourmalet. According to the manufacturer, the SL8 takes more than two minutes off its predecessor on the 294-kilometre Milan-San-Remo course with its undulating finish. In short: the new racing machine is the fastest Specialized ever developed in California. Even before the Venge aero model, which was built until 2018 and achieved 207 watts at 45 km/h in the TOUR test.

The US manufacturer wants to narrow the gap to the top material again, which would be tantamount to a return to the top ten of the fastest production bikes in the TOUR test. With 210 watts at 45 km/h, the SL7 has not only lost ground to aero specialists such as the Canyon Aeroad or Cervélo S5 (both 202 watts) in recent months, but has also been beaten by comparable race all-rounders such as the Cannondale SuperSix Evo Hi-Mod 2 (207 watts) or the Van Rysel RCR Dura-Ace Di2 (207 watts) tested in TOUR 7/2023.

Specialised Tarmac SL8: "Rocket tip" on the head tube

Specialized deliberately avoided the flat tube shapes that are now permitted by the new UCI regulations when it came to aero tuning: "A deep down tube and seat tube may look aerodynamic. However, due to the air turbulence at these points of the frame, they only bring negligible aerodynamic advantages, but significantly impair weight and ride quality." Instead, the Americans focussed on the details. "We wanted to combine the characteristics of the SL7 and Aethos in a new, great model," says chief engineer Peter Denk from Freiburg.

>> More details of the development process: How the Specialized Tarmac SL8 became the best road bike in the world

The new aero cockpit from in-house component specialist Roval alone is said to save four watts compared to the handlebar-stem combination of the predecessor. The most striking component is the head tube, which the Americans whimsically refer to as the "speed sniffer" or "nose cone". The physical explanation behind the unusual shape: The bulge at the front of the steering head is intended to channel the airflow more effectively around the frame and rider. The filigree aero seat post and the slim seat tube should also help to reduce the air resistance of the racing bike.

Because tuning the weight and aerodynamics is not worth much if the Tarmac rides as hard as a rock, the US company has - of course - also thought about comfort and stiffness and, according to its own statement, has made significant progress. Especially the Stiffness-to-weight factor (STW)which puts steering head stiffness in relation to weight, is said to be more than 30 per cent better than the SL7. The newly designed aero seatpost is responsible for more suspension comfort, which Specialized claims is an increase of six per cent. The SL7 was already extremely stable on the road and had above-average suspension for a competition bike.

First ride impression of the Specialized Tarmac SL8

After information was leaked shortly before the official presentation, we couldn't wait for our first test ride around Glasgow. Specialized provided us with the top model S-Works Tarmac SL8 Di2 with Shimano's Dura-Ace and fast Roval wheels, on which you sit just as race-like as on its predecessor. At first glance, however, it doesn't look particularly fast. This is because the Specialized Tarmac SL8 does not have the flat tube shapes familiar from streamlined aero specialists. Instead, we are looking at a racing bike that impresses with its restrained and elegant design language without a lot of frills.

Speaking of convincing: The new bike from California delivered what the development department promised in advance on our ride around Glasgow. The Specialized Tarmac SL8 is very responsive both on the climbs and on the flats and steers corners precisely. The flat aero handlebar sits comfortably in the hand and puts the rider in an aero position - without having to sit extremely stretched out on the bike. Only on longer climbs could the wide contact surface on the upper handlebar be slightly oversized. The high level of rear-end comfort was surprising: on the very rough Scottish roads, the Tarmac's suspension was excellent for a competition bike. In addition to the carbon seat post, this is also thanks to the comfortable Power Pro saddle from the 3D printer. Will the SL8 once again achieve the TOUR top score of 1.4 or possibly even be the first road bike to achieve 1.3? Our test in the lab and GST wind tunnel will find out.

Specialised Tarmac SL8: Equipment and prices

Touted by Specialized as the "fastest road bike in the world", the Tarmac SL8 will be available in five equipment variants and various paint finishes. The two S-Works models are based on the lightweight carbon frame (Fact 12r), are equipped with a one-piece cockpit and aero wheelset from Roval and cost €14,000 with Shimano Dura-Ace Di2 or SRAM Red AXS. A small, not entirely serious side note: this makes the top versions 500 euros "cheaper" than the Tarmac SL7. The other versions with a carbon frame weighing around 100 grams more (Fact 10r) have a handlebar/stem unit, with the basic Expert model coming with aluminium handlebars. With Ultegra Di2, Force AXS or Rival AXS, the price is between 6500 and 9000.

All models are equipped with a power meter (4iiii or Quarq). The maximum tyre clearance is 32 millimetres; 26 millimetre wide tyres from Specialized are fitted ex works. Thanks to the removable front derailleur, the Tarmac can be ridden or set up with a single drivetrain. The US manufacturer offers the basic frame set for 4000 and 5500 euros.

S-Works Tarmac SL8 Di2

• Weight: 6.62 kilogrammes (size 56)
• Price: 14000 Euro
• Frame: Fact 12r Carbon (685 grams)
• Switching group: Shimano Dura-Ace (2x12; 52/36, 11-30 t.)
• Impellers: Roval Rapide CLX II
• Tyres: S-Works Turbo RapidAir (26 millimetres)
• Cockpit: Roval Rapide (integrated)

S-Works Tarmac SL8 eTap

• Weight: 6.85 kilogrammes (size 56)
• Price: 14000 Euro
• Frame: Fact 12r Carbon (685 grams)
• Switching group: SRAM Red AXS (2x12; 48/35, 10-33 t.)
• Impellers: Roval Rapide CLX II
• Tyres: S-Works Turbo RapidAir (26 millimetres)
• Cockpit: Roval Rapide (integrated)

Tarmac SL8 Pro UDi2

• Weight: 7.16 kilogrammes (size 56)
• Price: 9000 Euro
• Frame: Fact 10r Carbon (780 grams)
• Switching group: Shimano Ultegra Di2 (2x12; 52/36, 11-30 t.)
• Impellers: Roval Rapide CL II
• Tyres: S-Works Turbo (26 millimetres)
• Cockpit: Roval Rapide (semi-integrated)

Tarmac SL8 Pro eTap

• Weight: 7.44 kilogrammes (size 56)
• Price: 9000 Euro
• Frame: Fact 10r Carbon (780 grams)
• Switching group: SRAM Force AXS (2x12; 48/35, 10-33 t.)
• Impellers: Roval Rapide CL II
• Tyres: S-Works Turbo (26 millimetres)
• Cockpit: Roval Rapide (semi-integrated)

Tarmac SL8 Expert

• Weight: 7.77 kilogrammes (size 56)
• Price: 6500 Euro
• Frame: Fact 10r Carbon (780 grams)
• Switching group: SRAM Rival AXS (2x12; 48/35, 10-36 t.)
• Impellers: Roval C38
• Tyres: S-Works Turbo (26 millimetres)
• Cockpit: Specialised Expert Alloy (semi-integrated)