2015 Specialized Tarmac: Adventures in Redefining Limits

Published May 10, 2014 01:05AM

Did you know you rode a 56cm? It doesn’t matter if you are 5’3” or 6’3”, you’ve been riding a 56cm frame, it may have been scaled up or down to fit you, but it is based on performance targets created around a 56cm.

When Specialized began designing a Tarmac to replace the all-conquering SL4 they decided to create performance targets based on data collected while riding, not on a static test bench and they learned something startling, scaling a 56cm to fit taller or shorter riders was missing the mark dramatically. Quite simply, the way designing bikes has been done since the beginning of time doesn’t work – unless you ride a 56cm.

The launch of this new Specialized – it’s just a Tarmac, no more SL designations – is more than the launch of a new bike, it’s the launch of a new way to design a bike. Specialized calls it ‘Rider-First Engineered’, a cute phrase to be sure, but thankfully it is the only one. This 2015 Tarmac is refreshingly devoid of marketing slogans. There are no ‘power transfer thing-ama-jigs’ or ‘optimally compacted smooth wall do-hickeys’. Specialized measured rider induced forces with on bike data points for every single size they make, from 49cm to 64cm. This created a discrete set of performance targets for each and every size. Gone were the days of just making the tubes a bit bigger or smaller and hoping they reflected the performance of the 56cm. This new Tarmac is essentially seven new Tarmacs to ensure each handles like the new 56cm Tarmac, which had performance targets well beyond the old SL4.

Understanding Center of Gravity’s Influence
It was during high speed cornering that Specialized first understood the different demands rider size put on a frame. They found riders on the 56cm SL4 could turn in and hit their line with perfection while riders on the 58cm or 61cm would turn in but then make corrections to find the apex as the frame deflected, loading and unloading the frame during the corner. Interestingly, riders on the big sizes still equated this with cornering well, they didn’t realize what they were missing. Specialized looked closely at what a bike actually does to help you corner and found it destabilizes you, allowing you to fall into the corner, then catches you with the front wheel creating the apex. This motion puts loads on the frame a simple, static torsion test never reveals and it’s all due to the rider’s center of gravity. For every 10% your center of gravity rises, loads increase 18%. The exact demands a big rider puts on a bike were truly understood for the first time. Conversely Specialized knew the small bikes were stiffer than necessary, and they could create an even better handling experience.

While this example uses the forces created while cornering the new Tarmacs, all seven of them, were created from unique performance targets for power transfer, compliance and everything else an all-around race bike needs to do. Using ride quality, handling and power transfer as your only barometer resulted in the 56cm and smaller bikes getting lighter, but the 58cm and larger are actually heavier than the SL4, 81grams heavier for the 61cm. Of course, only in the rabbit hole of cycling marketing and media is 81grams, the weight of an empty water bottle, a big deal. A 61cm 2015 Tarmac can still easily break the 15lb barrier.

There are many more details associated with the new bike beyond the ‘Rider First Engineering’ marching orders. While the geometry is identical to the SL4 the new head tube features size specific headset tapers. The SL4’s seat collar is gone, in place of an integrated binder, which exposes 3.5cm more seat post to help compliance in the saddle with more seat post deflection. The bottom bracket is still 68mm wide. Specialized has found while going wider may be a strategy for increased frame stiffness, all those improvements and more are lost by leaving the crank spindle unsupported by bearings for such a large span. The bottom bracket and stays are molded together to eliminate a bond joint in that critical area and the rear dropouts are molded as a single piece within the stays improving stiffness dramatically, a feature they use to full effect with the new disc Tarmac.

Yes, the 2015 Specialized Tarmac has a disc option, and unlike many disc options, Specialized managed to keep the geometry identical to the rim brake version. With the 135mm rear dropout spacing this requires a disc specific derailleur hanger, which slides the derailleur inboard 2.5mm to ensure optimal chain line even with the tight rear stays. What this means is for the first time a bike with the incredible modulation of discs actually has the tight geometry to take full advantage of it on a descent.

First Ride
While two rides over new terrain are typically insufficient to make many definitive statements about a bike, the two rides we enjoyed on the new Tarmac were long, hilly and very challenging. We did over 190 miles in two days, up and down some of the most scenic roads in Northern California. While we will wait for a long-term test bike’s arrival at our Ojai Test HQ for detailed rider feedback we feel qualified to share some educated impressions.

First off the bike is stiff, the size 61cm we rode feels stiff vertically, at least as stiff as the 58cm SL4 we tested previously. After 6hour days in the saddle we weren’t beaten up, but it communicates with the road very directly. In terms of pure power transfer it feels a hint livelier, which is incredible, since the SL4 was the benchmark rocket ship, but more testing is necessary to say this with true conviction.

What we can say, unequivocally, is the bike is faster in the corners and downhill than the SL4, and faster than anything we have ever ridden. The 61cm, a size typically associated with sluggish downhill performance, corners on rails. Countersteer, set your line with the front wheel and rocket through the corner with total confidence. Day one on the bike took some getting used to as we cut apexes too tight. It was then we realized that our other bikes, SL4 included, required us to hunt for the line a second time as the frame loaded and unloaded. Both the 58cm and 61cm hit the target immediately and stay locked on. If this is how the 56cm’s have been cornering we finally know what we have been missing. Bike handling is the single area of bike performance where we can push the bike as hard as the pros. You don’t need to be a genetic freak to go downhill fast, so focusing on the Tarmac’s handling means more of its improved performance is available for mortals.

For reference, here’s the second day’s Strava file – 105.8miles, with over 9k feet of climbing if the iPhone is to be believed. We rode a segment called the West Alpine Descent , ridden by 2315 people. It’s a tree covered, snaking, rollercoaster of a descent. On the first trip down following a rider who knew the road and staying well within the comfort zone we posted a top ten result. The only conclusion we can draw from this is the 2015 Tarmac has taken what was the ragged edge and moved it well within our comfort zone meaning the new edge, the new line, has been moved much faster and farther away. We can’t wait to explore our new limits with the 2015 Tarmac just as soon as we get our hands on a long-term loaner. We’ll share that experience and more details about the bike in an upcoming issue of peloton magazine.