Clever Engineering from Felt
Written by: Dan Empfield
Date: Mon Oct 29 2012
Last week I wrote about Felt’s new B12 and I like that bike a lot. I’ll be writing more about Felt’s bikes over the next few weeks because once I get up a head of steam on a brand’s bikes I like to plow right through them, before I forget about what I learned.
The impression I may have left you with about the B12 and that new mold may not be entirely correct. So I thought I’d stop here and talk a little bit about that mold. What I wrote in the B12 article is this: “[Felt] came out with an entirely new mold for the B series, and this upcoming 2013 season is this mold’s debut.” Yes, what I wrote is true. But it’s not the entire story.
Felt spent a lot of time working on the DA it introduced two seasons prior to this new B series motif. Most companies downstream their upper end technologies. For example, Shimano’s electronic shifting started as a Dura Ace product, then went to Ultegra, and will probably end up as a 105 product as well. SRAM has introduced its yaw front derailleur as a Red product, but I would guess it’ll be a Force and then Rival technology in years to come.
What I wrote was, “Not to worry (thought I), Felt will downstream this DA mold in upcoming seasons... But Felt did not do that.”
May I revise and extend my comments?
“Wait! Wait!” you say. “What about the fact that the stack and reach of these series is so much different?” Yup. And it took me a good while to figure out what I think is going on. Felt did something sort of like what Cervelo did several years ago. If you’ll remember, Cervelo’s P2 geometry was more conservative than its P3. However, the bikes were really geometrically very similar.
Here’s what Cervelo did. Imagine taking a P3, adding a couple of centimeters of spacers, and then slapping the stem on and out the door you go. Quite a few tens of thousands of people did just that. Imagine just building the frame up to the point where those spacers topped out. Just extend the head tube up to that point (an extra 2cm or so), then raise the top tube to the point where it intersects with the top of the head tube and, presto, you’ve made a bike that is geometrically identical to the more aggressive model, however it isn’t geometrically identical in terms of how it fits. If you add head tube, you’re adding that head tube not vertically, but tilted back at 72 (or so) degrees. So, the top of the head tube—where stack and reach are measured—sits both further above the bottom bracket (the frame has more stack), and a bit further back toward the BB (the frame has slightly less reach).
These Felt B series bikes do not require that the headset top cap be all of 20mm in height. They also come with a 9mm tall headset top cap, and you can use whichever one you want. But you must use one of them.
What does all this mean, in terms of fit? In my size, 58cm, the DA has a stack of 536mm, and the B series has a stack of 576mm. That’s a whopping 4cm of height difference. But that’s not all. The bar bore (center of the pursuit bar) on the DA can sit as low as 30mm above the stack/reach point on the head tube top. The B series, with the lower (9mm) headset top cap, and a –17° stem (stem extension parallel to the horizon) sits exactly 30mm above the head tube top. So, if you want the difference in the height of the bike to be only that same 30mm of “Y” axis above the bottom bracket that you get from the lower of Felt’s available one-piece DA stems, you must use both that lower 9mm headset top cap and the –17° stem.
In other words, the B12 is the same geometry as the DA, it’s just that the B12 has its head tube extended up. Why do this? Because you’re spending good money on a bike, and you ought to be getting bike for your money, not headset spacers. The new B series is a clever way to get you a bike that fits you nicely without all those spacers, but also preserves the good geometry and the good aerodynamics of the DA.
However, what if you want a DA, but you need the bike to fit like the B series? Felt offers two kinds of one-piece stems for the DA, and one of these stems is in a lower motif, with both 70mm and 100mm of extension and 30mm of elevation. Then there is the taller motif, with both these extension lengths and a 60mm rise. The DA with the taller, 60mm-rise, stem gets you 30mm of that height difference back between the DA series and the B series.
The DA also comes with the option of a hinged stem, and then the geometric world is your oyster—you can stick the bars wherever you want.
We examine the particulars of rear dropout and derailleur hanger design. Do you want horizontal or vertical? Replaceable or non-replaceable? For the ins and outs of each, read on. 1.30.13
Felt has been skating along on its flagship B series mold for 5 years. Rather than downscale its newer DA mold, Felt chose to built a new B series mold from the ground up. Here's the B12 built on that chassis. 10.24.12
It's been just 3.5 years since Felt remade its tri line-up, top to bottom. But you can't stand pat these days. Here's Felt's new mold, the DA for 2011. Felt's stab at a superbike hits its mark. 8.03.10