Friday, October 25, 2013

Aero Tuneup

by Jack Mott

Some of us get attached to our older bikes and, happy in our long-term relationship, see no need to spend thousands of dollars on a newer and more expensive model. One can get very envious, though, of contemporary super bikes like the Fuji Norcom Straight and Cervelo P5their sleek shapes make our tried-and-true race steed look like it's ready to be put out to pasture. The Norcom Straight and P5 can offer up to a second per kilometer of aero savings, boasting beautiful front ends that hide the cables and brakes from the wind. Fortunately, with a bit of cleverness and careful part selection, you can update the bike you know and love to bridge that aerodynamic and aesthetic gap, giving it a new lease on life.

For our test case we used a Cervelo P2 ridden by Kat Hunter, editor of this blog and ATC Racing TT specialist. The P2 is a great bike, with real aerodynamic engineering, good handling, and a good fit for Kat. However, as you can see in this photo below, compared to a modern super bike, the front end presents all kinds of bolts, cables, and surface area to the wind.




Aerobar
The most important thing to address here is the aerobar. Aerobars must, first and foremost, support your ideal position. After that, pick one that presents the least frontal area to the wind and that keeps cables internal and tidy. Newer versions of the 3T Aura, pictured above to the left, have improved their cable routing so they stay in the bar all the way to the stem, exiting out the back. Look for bars that keep the mounting hardware as minimal and out of the wind as possible. A great budget option is the older aluminum Vision base bar and clip-ons. They use a very aero shape and a smaller stem clamp diameter for reduced surface area. Fancier options with integrated stems include the 3T Ventus II and the Zipp Vuka Stealth.

For Kat's bike we had to stick with UCI-legal options and went with the HED Corsair, which offers a nice integrated brake lever with built-in return spring. We paired it with Vision clip-ons, which are comfortable for her and present minimal mounting hardware to the wind.

Cables
Hiding the cables from the wind offers a fairly small aero advantage, but a huge aesthetic one, and is often easy to do. You can do a pretty thorough job just by putting some thought into your cable routing. Experiment with different routes and find one that keeps the cables hidden from view. Often a zip tie or some electrical tape can work wonders to keep the cables tidy.

We went a step further with Kat's P2 and got out a drill. In standard form the P2 shifter cables enter at the down tube, while most newer bikes have them enter at the top tube. We found this handy tutorial from TriRig on how to modify your P2 to accept top tube cables. The procedure is relatively simple, but be warned that this could void your warranty, and this is in no way officially sanctioned by Cervelo or ATC. The same procedure works on both the older P3 and P2, and may work on other bikes as well.

Stem
Another neat trick in lieu of zip ties to keep the cables tidy is the TriRig Sigma stem, which offers some great aero features. It helps route the cables cleanly, exposes no bolts to the wind, and has a small, smooth frontal area. It has an optional bottle cage mount, so you can throw away a few more zip ties if you use a between-the-arms bottle, and, lastly, it offers a cable stop for center pull brakes. The catch is that it is only available in 90mm length and two different rises, and you have to cut your steerer tube to the exact height. You can't put any spacers above the stem, so you can always go lower, but never higher.

Installation is not difficult. You cut the steerer tube of your fork to a few millimeters below the top of the stem, mount it with the included top cap, and run your cables over the top of it. If you have a center pull brake, you run the front brake cable into the cable stop in the middle of the stem, as shown below.

Sigma stem, with cover off

Once the cables are routed, you then squeeze the cables together and bolt the cover on. If you have Di2, you can mount the control box inside the cover, facing up through the slot so you can see and operate it.

Sigma stem, with cover on

On the left we also mounted an additional piece that allows you to bolt a bottle cage directly to the stem. If you won't be doing that, you can leave that piece off. The finished product with bottle cage mounted looks like this:




Brakes
Tektro Center Pull
Retrofitting the integrated brakes of bikes like the Fuji Norcom Straight onto an older P2 or Slice isn't quite possible, but you can get very nearly the same aero advantage with careful part selection.

Magura Hydraulic
A normal brake up front is only about an 8 second per 40k disadvantage compared to no brake at all, and some of the center pull options get very close to eliminating all of that drag. One option is a standard Tektro or Campy center pull caliper. These mount easily, brake well, and are affordable. You will need to add a cable stop or use the Sigma stem to get them working since you can't run cable housing to them.

Another great option is the Magura hydraulic brake. They have top-notch aerodynamics and better braking power than standard calipers. You may be able to find good deals on these at your local bike shop from people who didn't want to go hydraulic on their P5s and new P3s. If you don't want to go hydraulic either, you can use the TriRig Omega brake. It can accept either cable housing or bare cable, so you don't have to mount a cable stop if you don't want to. The Omega has a wind-tunnel-tested shape that, along with the Magura, makes it one of the most aero brakes you can buy today. TriRig was a sponsor for ATC Racing this past year, so of course we went with the Omega.

Fork
A bike's fork is one of the most critical aero parts of the bike. Like the aerobar, it is up front hitting clean air, and it affects how air flows around the bike and front wheel. Over time, many bike companies have tweaked and improved their forks. If you have an older model year P2 or P3, an easy upgrade is the latest Cervelo fork. Cervelo claims this fork is about a 1.5 watt, or 6 seconds per 40k, advantage over the best previous generation forks. In fact, any bike with a standard 1 1/8" head tube could upgrade to this fork. Kat's bike had the previous generation 3T fork, so we swapped it out for the new model. If you sell the old fork, this upgrade isn't even very expensive overall.

Final Result
With modified cable routing and brakes, a trick stem, and the latest fork, we have managed to achieve many of the aesthetic and aerodynamic features of much more expensive bikes with integrated front ends. Kat will put the new setup to the test this weekend at the Austin 70.3 triathlon as she competes in the relay category hoping to set a screaming fast bike split. UPDATE: 56 miles in 2:21:21 on 221 normalized watts. Fastest relay split by 6 minutes. Congrats Kat!