TT Bike Fit have a great article on the TDF bike tech. I just had to put it in after the team time trial yesterday. I loved watching how awesome the teams looked, all aero and moving SO SO SO fast in unison.

There are some clearly converging trends in aero bike design that were visible to the trained bike-nerd eye on Saturday:

Bayonet-style extended head tubes: Pioneered a few years ago by Felt, we now have extreme versions on the Giant which debuted a year ago, along with the Specialized Shiv and the Trek Speed Concept. The new Scott achieves a similar end by using a fixed but extended head tube. While these designs may improve front end stiffness, the main purpose is likely to increase the airfoil chord length of the head tube, turning it into a broad 8-1 or similar airfoil shape. They also give the ability to blend the front end more smoothly into the front wheel/fork, and in some cases facilitate hiding the front brake and cable. Note that the Look 596 (I didn’t see any of these on the TDF coverage- but they may have been there) also sports it’s own version of this design.

1. The Original Bayonet (Felt) with a modified stem
2. The Giant took the bayonet design to the next level
3. The Giant TT took the bayonet design to the next level – but otherwise looks like a P3 knockoff
4. The Shiv sports a large “nose cone” with integrated bars and brakes

Hidden brakes and cables: Also pioneered by Felt, the behind-the-BB under-inside-over -chainstays rear brake position is becoming standard. The Giant (at least some examples), Trek, Scott, Specialized (Shiv and Transition), and Cervelo P4 all use this design to clean up the trailing edge of their frames. Front brake placement however is still evolving. Some designs mount the brake behind the fork (Giant, Fuji), but the latest designs are embedding them along with their cables within the fork or head tube extension (Trek, Shiv). Notably absent from any front brake innovations are Cervelo (the P4 uses a conventional setup) and Scott.

Fared rear wheel: Pioneered by Cervelo on the P3, most new TT frames now blend the rear wheel tightly into the seat tube.

Low seat stays: Pioneered by Kestrel and QRoo some 20 years ago (and maybe by others even earlier). Seat stays on most of these frames join the seat tube far lower than they would on a standard road design. While this can stiffen up the rear end, it also helps keep the trailing edge clean and narrow, turning the upper half of the trailing edge into a shape similar to a sleek airplane rudder.

Integrated front ends: The new bayonet designs are allowing stemless front end setups with bars being mounted directly on top of the “nose cones”. Trek uses a modified version with a custom stem that blends tightly into the front end faring. While some designers have used this setup to eliminate dead space that occurs behind a standard stem/steerer tube by blending the bars evenly into the top tube, Trek diverges here also, setting the top tube below the bars but providing a smooth transition via the custom stem.

I think you have to give some props to Felt here, as some of these convergent design features were pioneered by Felt a few years ago: Bayonet fork and hidden rear brake. I didn’t notice any major changes to their frames as ridden by Team Garmin though. They did have a modified stem attachment on at least some frames for a smoother shape and lower position.

Another thing that is quickly becoming clear: Pro-Tour riders are demanding different frames than those sold to the mass tri market. Scott’s manager mentioned this potential trend at the Tour of CA, after Team Columbia refused to ride the Plasma 2 in the TT’s. When 1-2 secs over 60 minutes can be crucial, it is no surprise that these guys expect no-holds-barred aero designs that don’t necessarily lend themselves well to the tri market. Many of these riders use massive amounts of front end drop that would be simply unachievable on some “tri frames”. On the flip side, such designs would have limited mass-market appeal. They also have to conform to increasingly draconian UCI rules – tri bikes don’t. Finally, many of these super-aero innovations will be very difficult to build up and maintain, and will be even more difficult (and expensive) to adapt to a wide range of rider sizes and fits due to the broad use of custom parts. And let’s face it, a pro-tour TT and a triathlon bike leg have little in common other than the requirement for some amount of aerodynamic efficiency and aero-position friendliness. With all the other variables in a triathlon you have to admit that splitting these ‘aero hairs” on mass market tri bikes is probably not worth the hassle and expense.

Specialized has made it clear that their Shiv will be sold to the public next Spring, but in a “take it or leave it” manner. The frame will have one stack height, and a few different reaches (likely through swapping out the front end faring attachment in some manner). Essentially, it will be “size M” with a few different “stem lengths” available. If you fit on it and have what is likely to be big bucks, then have at it. If not, too bad. Specialized makes no apologies: the Pro-Tour riders are close enough in size and fit that most will fit on this one-size frame. To compensate the rest of us, they plan to offer 3 more sizes of the Transition – a great idea since the existing frame range is quite narrow fit-wise.

There are also clear signs that the Giant and the Trek will also make it to market in some form (the Trek in 2011). My guess is they will follow Specialized’s lead and offer them on a limited basis. The UCI is having a major influence here, as new rules now state that all race bikes must be “currently marketed” or at least “marketable”. This recalls the ‘homologation specials” in the auto racing world. For example, BMW sold a handful of it’s M1 supercars in street-legal form in the early 80s and E30 M3’s later in the decade so that they could race these designs in touring events.

A few other observations:

The new Trek sports a “Kamm” airfoil design with a squared-off trailing edge, a design used effectively in the auto racing world. This allows a narrower section (i.e. 3-1 fitting the UCI rules) to mimic a broader and more efficient 8-1 airfoil section. If the shape is right, the air flow doesn’t “notice” the squared-off tail and rejoins as if the the tube was a true 8-1 airfoil. Apparently this design works well even in 15 degree yaw situations (thanks to James Huang from cyclingnews.com for a great preview of this frame). I suspect it rapidly stalls at steeper angles of attack, hence you wouldn’t find this airfoil on aircraft. Look for a lot more of this Kamm design on Pro Tour TT bikes if it works as advertised, as it seems to be a way around the UCI’s 3:1 aspect ratio limit.

We finally saw P4’s under the Cervelo Test Team riders. However, at least Sastre didn’t use the P4’s integrated water bottle, and instead had an Arundel-type bottle (made by Elite) mounted in the space. As I have guessed in the past, the UCI “may” not look kindly on the integrated bottle according to a Cervelo Team engineer. Cervelo now stands out as having their Pro-Tour guys on their mass-market frame. Will this be the last Tour without a special Cervelo Pro-Tour TT frame?

TT Bike Fit Blog posted their observations (based on the photo only – Kestrel isn’t talking):

* Center pull cantilever front brake. Eliminates the need for aerodynamically dirty cable housing. Similar to Specialized Transition.

* Broad fork blades incorporating mounting posts for cantilever brakes. There appears to be some slotting or interesting sculpting of the fork blades, and the fork crown fares into the downtube.

* No cables. It may be that this prototype simply doesn’t have the cables routed yet. Or, they could be concealed in the steerer/headtube and exit above the front tire, entering the down tube inside the crown faring. Also, there is no front derailleur (now that would be a trick! – I’m sure it’s just not mounted yet) and an electronic rear Dura-Ace derailleur.

* Concealed rear brake

* Very clean and low seat cluster area. The seat stays join the seat tube very low, similar to the Airfoil. This, along with the relocated rear brake, presents a very clean and thin trailing edge allowing air flow to pass between the rider’s legs easily, and likely helps it to rejoin flow passing over and around the rider, reducing low pressure (and hence drag) behind the rider.

* Seat stays form wings around the rear tire near the seat cluster area.

* Tiny, almost rudimentary seat tube. It fares the rear wheel, yes, but I wonder if it is mainly there to satisfy the UCI “double diamond” requirement. The Airfoil seems to do just fine with no seat tube or rear wheel faring.

* There also appears to be some unusual sculpting or slotting on the seat stays.

* The frame look to incorporate a variation on the integrated seat mast – an extended “seat tube mast” with internal post. My guess is the “seat tube mast” may still need to be trimmed to size, but the internal post should allow more adjustment than the caps used with seat masts. It is unclear how the seat post is fastened, and the post itself looks like it may be just a mock-up (quick prototype). In any case this may provide all of the advantages of an integrated seat mast (lighter weight, stiffer, cleaner interface) with greater adjustability. Or, they may add an extended cap onn the outside similar to the D6.

* The seat mast looks to be built at 75 degrees, although there is some parallax distortion in the photo. This will suit UCI regulations well, but will mean that the final seatpost will need a movable clamp (perhaps like the Fuji D6) to get a steep seat angle.

Nice one. I like it. Very much. Let the aero wars continue…