Don't know precise width spec, but they'd likely be extremely fast if run with narrow tires. Problem is the fastest tires these days don't come in narrow widths anymore.

Well, conti supersonics are plenty fast, and they come as narrow as 20C ...

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Haven't those been replaced by the GP TT? I can't immediately find SS for sale anywhere.

As far as I know, and I have looked quite recently, multiple online sellers in the EU and Asia sell and ship them in both 20C and 23C. (They're also avail on ebay US from some German merchants, but not super cheap to get them there.)

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Yes, they are slower, and don't handle as well in crosswinds. The FC aero benefit is that the blunter "rear" of the shape is a better leading edge when the air hits the back of the wheel (esp at yaw).


In the chart above, the 2011 is Firecrest, the 2009 is pre-FC.

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What does the C stand for?

Good question, but I haven't the foggiest. Conti lists 'em as 700 x 23C and 700 x 20C ...

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I think 700C means: external diameter is about 700mm (though grossly estimated) and C means the tire is wide enough (on an ABCD scale which is actually obsolete) so that the inner diameter is 622mm.
So basically that means 700C=622.

So you can write a tire dimension as follows:
23-622 (ETRTO and ISO)
700 x 23C (obsolete French designation)
It's the same.

Side note: for a rim, the C in the rim inner width dimension 19C means "crotchet type" (the rim has hooks) as opposed to 19SS "straight side" (hookless)

We have a pre-firecrest Zipp 404 with aluminum brake track hanging up in our basement, hasn't been ridden in a while as I didn't like the looks of some tiny cracks in the rim around the nipples. Probably should just toss it. I measured the external width as 20mm and the internal width as 14mm. Very narrow by today's standards!

I have a set of SRAM S80s (same as pre-FC zipp 808 no dimples) since there have a hybrid toroidal design, the brake track width is 18.7mm if I remember correctly but the rim width is 24mm. I run 20mm GP4000s II's with latex tubes or GP supersonics. Zipp stated in some old literature that 21mm tires work best for the 808 non FC.

typically, real world riding is done with yaw angles that are between 2.5 and 12.5 deg. so optimize for low yaw unless you are riding in a hurricane, Ironically, The 2009 alloy outperformed the FC 808 below 10deg yaw. narrow is aero.