Monday, October 13, 2008

Interbike - Felt AR

One of the things I looked forward to at Interbike was a look at all of the aero road bikes out there. I figured that there had to be a bunch introduced. With the announcement of the Felt AR, I thought that other companies would follow suit. With the AR introduced so late in the season, it would make sense for competitors to unveil similar framesets at the fall season IB.

Alas there were no framesets out there that met my criteria for an "aero road bike" - wind tunnel tested framesets designed to give an advantage to racers at any speed where wind resistance became a factor. I looked to a couple places to "judge" a frame - the fork/downtube area, the seat tube, and the downtube. All of these areas receive a lot of attention with TT bikes, so it follows that they should receive attention on aero road bikes.

Felt, it seems, is the only one out there with a truly aero road frame. I'd judge some other frames to be close, but not with the most up to date aero refinements.

Without further ado, my take on the Felt AR.

Rear quarter shot. Frame looks squashed from this angle.

I took this picture to capture just how thin the bike is when viewed as the wind sees it. The downtube especially loses a lot of width, something not obvious in the normal profile shots.

Bottom bracket. Cables run inside the frame.

The bottom bracket area has to retain some stiffness, so Felt increases the width of the frame until it appears pretty much normal just above the BB shell. A friend rode this bike (with the new mechanical Dura Ace) and raved about everything. Even on a very large size (he rode some enormous size - like a Magnus size) the frame exhibits adequate stiffness. I'd want to try one too, just to see, but if the rigidity is there, I wouldn't see any compelling functional reason not to use the frame. Yes, cost, yes, sponsorship, but any "logical" reason?


To run the cables inside, you have to insert them somewhere.

The top tube, just behind the head tube, is a popular spot to insert cables. With the stem already disrupting airflow, this is a great spot to stick vertical, unaerodynamic cable housing. It has to be a low stress area too - I don't recall manufacturers welding reinforcements to the top of the top tubes on BMX bikes, for example.

Fork to downtube relationship.

One of the areas pinpointed in time trial frames is the fork-downtube area. Trek came out and declared it relatively important in their latest TT frameset design. Felt deals with it by dropping the downtube so that it allows airflow to smoothly come off the fork crown.

The downtube - tire detail. The tubing is so smoothly seductive.

The downtube continues its air flow smoothing effects by following the front wheel profile. Apparently this spot is where the air really separates from the tire, and the little notch helps pick up the turbulence and gives it a smooth surface to follow.

A blurry rear stay.

Although not a clear picture (a problem apparently occured with the nut that holds the camera), it's apparent that the rear seat stay is faired in pretty well. No lumps presented to the wind. Well, not until you install the rear brake.

And there's the problem.

With all this aero frame stuff, suddenly the components look, well, un-aerodynamic.

I think that'll be the next component group thing - more aero brakes, more aero derailleurs. With normal road frames going aero, there'll be demand for more aerodynamic components. Hanging a big lunky brake on a smooth, sleek fork simply won't cut it anymore. Nor will the big, lunky bottles.

Here's my prediction for today:

I figure in the next few years we'll see a lot of aero bottles (with a somewhat standard cage shape for versatility) and narrow profile major brand (Shimano, Campy, SRAM, FSA) brakes on aero road bikes in mass start road races. Think of a reincarnation of DuraAce AX, but this time the components will be light, functional, and stiff.


Anonymous said...

I love the look of that frame. Probably one of my favorite frames right now.

Now if they only made it with Al and made it affordable on a college student's negative income!

-Young rider.

Mike said...

With all these frame posts it sounds like you're on the market for a new one already!

After watching cervelo's little slide show about aero vs. weight, I ran a few numbers in kreuzotter. Cervelo claimed a 1.5% reduction in their Cda values, so I lowered my height until the kreuzotter number was 1.5% lower.

A 1500 watt sprint had 43.2 mph, 43.6 mph with the aero frame. Not that I could touch 1500 watts, but even at those kinds of speed it's a pretty tiny difference.

Aki said...

YR - I like that frame too, and I was really, really disappointed not to see any more (signifcantly) aero road bikes. I think an aero frame will have to be carbon to be both aero and stiff. I think that aluminum will be too heavy, too stiff. Just a guess.

hocam - No way I can afford a frame right now. But I can still observe, and since frames differentiate bikes ( group components are unto themselves, and the rest is so personal it's hard to quantify which is better), I've focused on frames. I think that frames will converge on a certain type of look and design, adapting as the rules evolve.

It's like cars - they all got sort of jelly bean shaped, but with recent mandatory design features like higher hoods (for pedestrian strike survival), higher shoulders (for passenger protection), certain static design limitations (legal light height from pavement), and market tastes, designers are pretty constrained as far as what they can do. If you get a Mazda6, Camry, Accord, whatever the Lexus is, Acura, etc, and line them up, they have very similar profiles, very similar shapes. 10 years ago that wasn't the case (okay, except for sister cars like Acura/Honda, Lexus/Toyota).

The bike industry seems a bit less constraining so the frames are a bit more different, but part of it is that non-functional features don't get penalized.

A frame that looks aero is no different from an actual aero frame because no one knows the difference (me included). But I was really disappointed to see the limited evolution of the frame in the 2008 show - I really expected some radical developments to pop up, accompanied by statistics that support their new ideas (wind tunnel data, efficiency/rigidity data and the like).

I also think that aero frames will beget aero bottles etc, and that as an overall package, the bike will become somewhat significant (frame/fork, components, bottles, wheels, etc) in the aero equation. I'd expect someone to set a standard for aero bottle cage shapes, and lots of companies to then design their frame to fit this bottle perfectly. Think Cervelo P4 but industry wide. Ditto tool bags, brakes, even bars and seats.

I think the benefit will be not just in top speed but in breaks, chases, leadouts, etc. And right now, since I kill myself to break 1500 watts, to be able to go the same speed at "only" 1480 watts (~1.5% less) would be nice because that's much more within the realm of possibility. Sort of. lol.

Unknown said...

A question about aero components... is there any compelling reason not to hide the brakes as they are on TT bikes for an Aero Road design? Regulations I'm not aware of, or any such thing?

Aki said...

I don't know the rules regarding brakes (other than no disc brakes). A brake mounted in odd places (like under the BB) would make for an interesting "on the bike adjustment" in pro races, especially after an inopportune crash in the last 10-20k of a race. I think there'd be a huge increase in rear derailleur adjustments and such if brakes went to under the BB.

On the fork it's just awkward - you lose some potential steering angle, albeit useful only when riding at slow speeds, and the fork is probably heavier than not. Still, though, an aero brake like the Specialized one (on the Transition) wouldn't be a handicap as far as I know.