Specialized Tarmac SL8: Resolving Design Issues for a Smoother Ride
The release of the Specialized Tarmac SL8 has grabbed masses of media attention for its seemingly impressive updates and improvements over the earlier Tarmac SL7, a bike I considered buying. Whilst you’ve no doubt heard about its impressive weight weenie credentials and seen its aero pointy nose, you might not be quite so aware of some notable design issues that had surfaced with the previous model and that needed to be resolved.
Steering System Overhaul
A concern with the earlier Tarmac SL7 was steering tube failure, which was acknowledged by Specialized. In a bid to improve this, the company has taken a comprehensive approach to redesigning the steering system. The Tarmac SL8 features a ‘thicker’ head tube, ensuring enhanced durability and resilience. A notable addition is an unusual-looking nose which at first you might think offers aero benefits, which it might, however, its purpose is to provide additional reinforcement to the steering mechanism and prevent issues that led to the recall of its predecessor (links to recall notice). So, despite the much lower overall weight, Specialized have creditably boosted the strength of the headset. #Kudos
Aerodynamics make a massive difference to your speed. However, the benefits that are possible from minor bike frame changes alone are very minimal, simply slamming your bars and riding on the drops more often is more likely to make you faster than switching frames. That said, at the elite end of sport the genuine single-digit watts that a frame like this might save are worthy of note.
According to Specialized, the Tarmac SL8 can save 16.6 seconds over a 40km course compared to the Tarmac SL7 [no speed claimed]. Most of the aero savings come from the new one-piece bar-stem combo, which accounts for 80% of the improvement. The rest of the savings come from the nose cone, fork legs, and seatpost/seat tube.
In fact, the aero savings at the front end of the bike include thinner handlebars, which are separately claimed to save 4 watts at 45km/h. I have doubts that the nose cone contributes significantly to the overall aerodynamics – if at all.
The rear end of the frame is slightly more interesting, although its aero improvements become more impressive given the requirement to handle dirty air, making their relative importance to the claimed overall performance gains less significant.
The new seat tube is wider and offers less clearance to the wheel, which should result in improved aerodynamics, as might the seemingly thinner stays.
In reality, this frame might only save you or me 1 watt.
Take Out: Specialized’s aero claims may not hold much weight, aside from the fact that the SL8 exhibits superior aerodynamics compared to the SL7 by some seemingly ‘magical’ factor.”
Enhanced Structural Integrity: Learning from Failures
A notable portion of the design improvements in the Tarmac SL8 appears to be directed towards enhancing structural integrity and addressing earlier steering failures. The new model incorporates hidden cable/hose routing and an almost over-engineered nose cone design choice aimed at preventing steering-related failures.
The SL8 also boasts notably increased rigidity in the region of 10%. If true this is a fantastic achievement as the thinner stays are surely less rigid.
Additionally, Specialized has taken measures to improve the durability of the bottom bracket area. The 68mm standard BSA threaded BB is tightly engineered but some key structural elements remain thin and could be prone to flexing; so careful choice should be given to changing brands away from the manufacturer-supplied crankset.
The front end of the model shown offers a very restrictive scope for adjustments to suit the rider’s optimal position. Unoptimal ride positions will certainly wipe out the aero gains from the frame.
Conclusion: Is it really one bike for all rides?
This is a necessary move for Specialized to address engineering concerns. Simultaneously, it provides us with an exceptionally lightweight bike suitable for nearly all types of road riding, except for time trial (TT) cycling.
Despite my current investment in Cervelo bikes, I have previously owned an older model Tarmac and loved it, along with a couple of Specialized off-road bikes. I had contemplated the SL7 until I became aware of the steering issues, but I would certainly consider the SL8 if I were to transition to disc brakes – which is probably a wise move.
I heard believable opinions from several sources that the SL7 was ‘the best road bike‘ maybe it was, maybe it wasn’t. It was certainly up there with the very best and now the SL8 is almost certainly better.
While I doubt that the aero gains or slight weight improvements translate to significant real-world benefits for real-world cyclists, there’s no denying it looks great!
If this was my only bike I would be extremely happy. And if you are upgrading from a 10-year old bike the SL8 will be worlds apart in terms of superior performance in every detail.
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