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.