The previous stack and reach measurements published for the forthcoming Kestrel 4000 were off in several spots. Steve Harad forwarded me the updated values a few days ago, and it is clear that Kestrel is positioning the 4000 more towards the short-and-high (reach-stack) end of the spectrum in the middle (and most popular) portion of the size range. Steve said they looked at thousands of actual rider setups and decided that this geometry will suit more real-world athletes. It is certainly true that their are way too many Cervelos and Felts (in the long-low category) in the transition area with massive stacks of spacers and upturned stems. I think some of this is due to poor bike fits, not necessarily the wrong frame geometry. That said, many folks simply don’t belong on long-low frames. The 4000 geometry will actually compliment the Airfoil well, as especially in the smaller sizes the Airfoil is the longest-and-lowest frame you can get. And seeing as Kestrel ships the steerers pre-cut to use a maximum of 2cm of spacers, you better be sure you can get the front end high enough, and you better be sure the reach isn’t too long. Remember that ideally you would use 0 spacers and a level stem for both aero and structural reasons. So you don’t want to get too far from that. Here is a table comparing the 4000’s stack and reach with some other popular frames. The Plasma is a short-high design, while the others are long-low:
Note first that the 47cm Airfoil is the low-stack champion of all bikedom. If you are small in stature and/or have very short legs, and you can handle the reach, it may be the only stock frame that will work for you. The 4000 geometry is Cervelo-like in the smallest and largest sizes, but in the middle we can see the stack goes way up into the Scott range. The 52.5cm 4000 will fit like a M Plasma. Note that the 55cm 4000 has the same reach as the 54cm P2 but a 2cm higher stack. It will fit more like the L Plasma. But then in the larger two sizes it drifts back into the longer-lower range. The 59.5cm 4000 will be a good option for 61cm P3c riders who want an even lower front end (me!). Some riders who think they are a “54” might find themselves on a 50-or 52.5 4000 with a longish stem. The bottom line – make sure your fitter-bikeshop etc determines the best stack and reach for you and then looks for frames that fit those specs.