One of the more noticeable differences between the Tarmac SL4 and its predecessor is its internal cable routing. The change in frame design to allow for internal routing isn’t peculiar to Specialized. Many manufacturers are offering frame designs with internal routing options. This has been driven to a great degree by electronic shifting systems, Shimano’s Di2 and Ui2 in particular. Some bikes offer an option for either internal or external routing, depending on whether you plan to use electronic or mechanical shifting systems; some still require mechanical systems to be routed externally. Not so with the Tarmac SL4. All cables get routed internally, whether the bike is spec’d with a mechanical or electronic shifting system.
Internally routed cables clean up the look of the bike, there’s no doubt. That said, I need to make a small declaration: Internally routed cables may look nice, but the bike suffers in almost every other way if you’re using mechanical shifting.
The first issue is assembly. Now, this doesn’t affect you as a consumer right off the bat, but it affects the shop you do business with because it can double the amount of time required to build a new bike. That slows down the productivity of the wrenches, thereby driving up the owner’s cost to build the bikes, and that’s a cost he has to figure into his bottom line. Where it affects you is any time you take the bike in for any service that requires replacing a cable. I’ve built a lot of bikes over the years and while I’m not as quick as I used to be, I can do a very thorough build on an ordinary road bike from the box in two hours. My initial build of the S-Works Tarmac SL4 took me six freaking hours. Now I’ll admit, had I been able to attend a tech presentation that went over the assembly procedure on the bike beforehand, I suspect that could have shaved as much as two hours off the assembly. I could have watched Avatar during the time I wasted just trying to figure out where each of the ferrules and cable guides went.
Even once I knew how everything fit together, when I swapped out the parts for SRAM’s new Red group, the tear-down took more than an hour and the assembly of the new parts took three full hours. Working on this bike will never, ever be speedy and you’re going to pay for it by being charged more in labor. And in the event you’re not, you ought to be concerned about your retailer taking a hit on his bottom line by not making enough on the labor. I know everyone wants a deal on parts and labor, but your local shop needs to make a profit so they can keep being your local shop. End of sermon.
The other problem that internal routing causes is a degradation in shift quality. I haven’t noticed a problem with rear braking, but I did notice that the Dura-Ace 7900 I first built the Tarmac SL4 with didn’t shift as well as it did on the Tarmac SL3, which had externally routed cables. Given that the group was fresher than sushi, there shouldn’t have been anything wrong with the shifting that wasn’t already an inherent problem in the group—which mostly boils down to high shift force. I consistently had a problem with either the rear shifting hesitating on downshifts, but if I increased cable tension, it would hesitate on upshifts. The sweet-spot in shifting proved to be nearly as elusive as the Snuffleupagus. I did manage to get the shifting to work with 7900, but it took a great deal of fiddling. With SRAM Red the dial-in of the shifting was a good deal simpler.
I’d like to go back to the seemingly incompatible goals of torsional stiffness combined with vertical compliance. If you’ve ever seen a modern helicopter on the ground with the engines off, then you’ve probably noticed how the rotor blades sag while at rest. Those rotor blades are made from carbon fiber and they are stiffer than a murder one sentence in rotation, but vertically they aren’t made for stiffness; they achieve their proper straight attitude thanks to centrifugal force.
Now, no bicycle frame is ever going to flex visibly under its own weight, but carbon fiber layup technology has come a long way since the original Kestrel 4000. Today, there’s software available that allows engineers to simulate particular layup schedules. They can specify the dimensions of the structure, the size and shape of each sheet and the orientation of the fibers. Following a set of calculations that make differential calculus look like long division the workstation yields feedback on how stiff that structure will be under a given load. The upshot is that we’re now seeing frames that are hundreds of percent more flexible vertically than they are torsionally.
I think it’s with observing that what carbon fiber allows a manufacturer to do is control the entire fabrication process from the shape of each tube to the material used as well as where it’s placed. As much as I love steel frame building, there’s not a builder out there who has as much control over their fabrication. After all, they aren’t creating their own tubing, specifying the tube shapes before they are drawn and then also dictating the butt lengths. Previous history has shown that the stiffer a steel frame is in torsion, the stiffer it will be vertically. The only steel frame I ever rode that is as stiff as today’s carbon fiber beauties was an Eddy Merckx made with Columbus’ stouter-than-a-Cuban-cigar Max tube set. I’ve ridden only a handful of bikes that bucked more on a bump than that bike; most memorable among them was Cervelo’s SLC-SL.
There’s a huge mitigating factor to this phenomenon: frame weight. While there was a time when a lighter frame deserved to be an end in itself because shaving more than a pound off a frame’s weight was a pound you could lose forever, shaving an additional 100 grams off a frame’s weight won’t give a rider much in terms of better acceleration or speedier climbing, but if you can starve an additional 100g off a frame, especially if you can do it without sacrificing torsional stiffness, the result is a bike with a livelier ride.
I’ve long held both fascination and admiration for the work that goes into laying up a carbon fiber frame. Never have I been more impressed than when I was laying on the ground in Tuna Canyon and my buddy unclipped my shoes from the pedals and picked up an intact bicycle. It became the only topic of conversation that could distract everyone from just how messed up my face was. It’s remarkable to me that I could render the frame useless with one firm swing of a hammer and yet it came through a 30 mph impact ready to ride. Holy Indian cow. My regard only increased when the recall was recently issued for the Tarmac SL4′s fork. Here’s a link to information about the recall.
For the most part, the geometry remains unchanged from the inception of the Tarmac straight through to the Tarmac SL4. The head tube angle, seat tube angle, fork rake, BB drop and wheelbase remain exactly the same between the various iterations. If yo’ve previously ridden a Tarmac and liked it, you’ll like this bike. I went into the geometry of the six sizes in some depth in my review of the SL3. You can check that out here.
The only difference between the SL3 and the SL4 is in the head tube length on the four largest sizes. The two smallest sizes (the 49 and the 52) remain unchanged. In the other sizes, the head tube has been shortened; I’m told this was to respond to requests by pros so they could position the bar lower. On the 54, the head tube has been shortened by 5mm, from 145mm to 140mm. On the 56, it’s been cut from 170 to 160. The 58 was chopped from 205 to 190, while the 61 got a haircut from 230 to 210. I’m of the opinion that head tubes are too short in general and that most riders, when properly sized will never wind up with a no-spacer fit. I’m also of the opinion that the majority of all pros are on bikes with ridiculous fits—no spacers, minus-17-degree stem that’s a centimeter (if not two) too long. What’s most surprising about this is that Specialized has taken a very proactive role in making sure the riders of the teams they sponsor are on bikes that fit them, thanks in no small degree to having one of the best fitters on the planet—Scott Holz—on staff. So it’s a bit surprising to me that their bikes would still have such short head tubes.
As I mentioned in a comment in response to Part I of the review, I went through a fitting recently, one that was exceedingly thorough and pinpointed some issues I’ve been wrestling with, but hadn’t been able to properly diagnose. And I write that with the acknowledgement that I’ve been through five or six fittings in the last eight years. The upshot is the realization that aging has resulted in more spinal compression than I had previously understood. I stand 5′ 11″ these days but still possess a 6-foot wingspan. Compounding matters is that I have a 34 1/2-inch inseam. While I want to have a chance to do a fitting with a 56cm Tarmac before I commit to it, on paper it looks like it’s time for me to drop down a size.
Ride Quality and Handling
What separates the Tarmac from many other bikes on the market is its combination of crisp handling, high stiffness, low weight and sensitive road feel. you can find bikes that are as stiff, but most are heavier and don’t have the road feel. There are bikes that beat it on weight, but most of those aren’t as stiff and as a result don’t offer the precise handling. Broadly speaking, I consider the sub-kilo frames in a class apart from all of the frames weighing 1000g or more. They have a liveliness all their own. You can go on a date with anyone who seems attractive, but when you’ve got chemistry it makes all the difference. Most of those kilo-plus frames are as fun as dinner with someone on Lithium.
It’s been interesting to watch the geometry of other bikes follow suit on the aggressive trail numbers of the Tarmac (62mm for the 49cm frame, 57mm for the 52 and 54cm frames, 56mm for the 56 and 58cm frames, and 53mm for the 61cm frame). What we’ve come to appreciate is that the stiffer the frame the sharper the handling can be. The inverse is also true though: If a bike isn’t super-stiff, you need to relax the handling so that the bike isn’t twitchy to the point of being difficult to control. I can say that with every steel bike I ever rode that posted numbers this aggressive, I didn’t like how they handled but with carbon fiber, it’s a very different story. Let’s put it this way: Steel is to stiffness what slapstick is to comedy, while carbon fiber is to stiffness what satire is to comedy—subtler and more calculated; it rewards skill.
I can come up with a dozen solid, objective reasons why this is a great bike, why the sheer ubiquity of Specialized dealers pumping these things into the market is a good thing for cycling. That still doesn’t seem to be a good enough reason to consider purchasing one. What separates the Tarmac SL4 from some of the more rudimentary expression of carbon fiber bicycles is the difference between an Arabian horse and the plastic variety you find on a carousel. Is this the greatest carbon fiber bike going? Ahh, that’s like asking if Mozart is the greatest composer. He’s on everyone’s short list—and with good reason.
I’m going to start this post in a way that you’re not supposed to start a review—on a sour note. I didn’t see the need for this bike. Initially, it struck me as the inevitable result of the Specialized product machine. The template was struck some years back following the introduction of the Roubaix. The company alternates between a new Tarmac and a new Roubaix each year. In odd-numbered years Specialized introduces a new Tarmac, while there’s a new Roubaix in even-numbered years. Fall of 2011 required a new Tarmac.
When I first rode the Tarmac SL, I was not particularly enamored of the bike. I was a bigger fan of the Roubaix. I still think the Roubaix is the better bike for most non-racing riders. The issue for me was that I was accustomed to grand touring bikes; the two bikes I’d spent most of my miles on prior to first riding a Tarmac had relatively low bottom brackets and longish wheelbases. The Tarmac was a big change; the Roubaix less so.
It wasn’t until I began reviewing the Tarmac SL and the Roubaix SL back to back that I really acquired a taste for the Tarmac’s handling. I’d ridden plenty of bikes with handling as sharp as the Tarmac, and had disliked plenty of bikes with such quick handling. Well, “dislike” might be a bit harsh; they wouldn’t have been my first choice. The Tarmac showed me that with adequate stiffness (particularly in the fork and at the head tube) sharp handling needn’t make you nervous. By the end of the review I’d come to the conclusion I actually liked the Tarmac better in my favorite terrain—the canyon roads above Malibu. Here’s the post where I changed my tune.
Next, Specialized came out with the Tarmac SL2. I didn’t like that bike. It was okay on smooth roads, but anything rougher than a chick flick would rattle you like a paint shaker. It made chip-and-seal feel like the Arenberg Forest. That said, I know plenty of people who liked that bike.
Two years later Specialized came out with the S-Works Tarmac SL3. The biggest difference between those two bikes was in the rear end. The seatstays were flattened and reduced in diameter. And while I was told there were some changes in the layup of that frame, the folks I talked to didn’t go into too much detail. Broadly speaking, I was told that the layup was changed to permit more flex vertically while keeping the bike as rigid as possible torsionally.
So here’s where I have to address that trope of “vertically compliant but torsionally stiff.” It’s become a joke because some of the publications out there use it as a crutch to convince you that a Toyota Camry is a BMW M3. There’s nothing wrong with a Camry, but very few autos can provide the performance of an M3. That line about ”vertically compliant but torsionally stiff” rings hollow because at a certain point, if all bikes have that quality, then it ceases to be a way to distinguish bikes. And we know they aren’t all that way. There are real differences.
When I say I liked the SL3, I mean I loved that bike. Here’s that review: part 1 and part 2. It was one of my two or three favorite bikes I’ve ever ridden due to its particular constellation of road feel, performance, handling and weight. It didn’t need improving. When you’re putting out one of the best bikes on the market there’s a risk in trying to improve upon your work; there’s a real chance that no one will notice the difference. And the risk there is that if consumers can’t tell the difference between the old product and the new, improved one, they will begin to think what you’re selling is smoke and mirrors.
After assembling the S-Works Tarmac SL4 (and I’ll come back to the assembly in a bit), I went for a ride on the SL3. It was a short ride in my neighborhood, less than two miles. Then I jumped on the SL4, and did the same circuit again. I took care to make sure the tires were pumped up to the same pressure. The difference was not night-and-day, but the bikes were unmistakably different.
It’s common for fans of handmade steel and titanium bicycles to deride carbon fiber bikes for lacking personality, or sometimes it’s phrased as soul. When you’ve got a one-man shop, the marketing effort is pretty obvious. Land Shark begins and ends at John Slawta. As it should. But with a bike like the Tarmac, there’s quite a team involved and it’s not exactly possible to market a bike around every engineer and layup craftsperson who worked on the bike. And believe me, if you’ve ever seen someone doing layup, you begin understand that it really is a craft, just like brazing or welding.
The team responsible for the Tarmac includes some of the most knowledgeable people within their respective fields that I’ve met in the bike industry. And the resources that Specialized put into the bike are staggering. I was surprised to learn that each iteration of the Tarmac, from the original SL up to the current SL4, received its own set of molds. That’s a new set of molds every two years. That’s a lot of tooling. Consider that some Italian bike companies are still using the same frame shapes from six years ago.
So why new molds every two years? Easy. With each iteration of the Tarmac, Specialized has altered the frame shapes, slimming seatstays here, swelling the down tube and growing the bottom bracket there. Like other carbon fiber frames, the Tarmac is made from several monocoque sections that are joined after molding. With each new iteration, the locations of some of these joints have shifted based on what the engineering team has learned about the previous bike.
In talking with members of Specialized’s engineering team, they revealed that feedback from riders on the HTC-Highroad team indicated they needed to increase vertical compliance without sacrificing overall torsional stiffness. While riders said they liked the S-Works Tarmac SL3, the front end was a bit harsh for a 200k day. To that end, Specialized replaced the 1 1/2-inch lower headset bearing with a 1 3/8-inch bearing and decreased the diameter of both the fork steerer and the head tube. Another important evolution in the Tarmac is the move to Specialized’s OSBB design, which is essentially a press-fit 30. Such a large bottom bracket structure—and similar ones by other manufacturers—has eliminated bottom bracket flex that I once used to take as a given in all bikes.
Aside from the desire for a more gentle front end, one of the few criticisms sponsored pros had for the S-Works Tarmac SL3 was that the rear brake bridge wasn’t stiff enough, that the rear brake would chatter and squeal. To correct that, the brake bridge was beefed up and right at the brake bridge the seatstays were also beefed up.
I could tell you that the bike uses Specialized’s FACT IS 11r carbon—okay, I have told you that it has the FACT IS 11r carbon. But that didn’t help, did it? Information ought to answer questions, not raise them and while all that stuff signifies that the carbon fiber material and layup that Specialized is using is more sophisticated than anything they used in the past, it really doesn’t tell the consumer anything objective. Not a crime, but not nearly as helpful as they’d like us to think. The upshot—the part that matters—is that the S-Works Tarmac SL4 is the lightest frame Specialized has ever produced, that is, with the exception of the women’s Amira frame. My 58cm frame weighed in at 898 grams and likely came in a few grams heavier than the matte carbon version due to the number of coats of paint necessary to generate that bright arterial red.
Up next: the build, the ride, the bottom line.