Probably not your target market since I already have the bike I want--but building a gravel race frame is tricky because there are so many different kinds of gravel race courses. I think the ideal bike for the old SBT GRVL Black course would have been something like a Specialized Crux, but for a not-muddy Unbound 200 it would be something like the BMC Kaius. From experience in those events, the challenge is focusing the design on the use case that matters. IMO, there are fewer bikes made for the 200+ mile type race event, though that is starting to change. On the other side, it's harder to sell a bike designed for a use case built around an event; only a fraction of people will try and attempt, and only half will finish.
If it were me, I would still pattern the bike after the BMC Kaius in terms of non-custom geometries. To me, a gravel bike focused on racers means:
1. Long reach--about 10mm-20mm longer than bikes like the Specialized Crux. This is needed for FC length as well as toe clearance, but the measure of a good gravel race bike is how well it can take going 40mph on a descent and needing to change lines mid-corner on a loose surface.
2. Tire clearance for 700c x 55mm (29x2.1" MTB) and if possible 650b x 60mm+ (27.5x2.4"). I expect 700c x 50mm to be a widespread size i see at events going forward, so a little wider for those that want it
3. Low BB: Given the wide tire preference, I would consider an 85mm or even 90mm BB drop to really design the bike's handling around a 700c x 50mm tire. This is a big change from many current designs that are designed around a 700c x 35mm or 40mm tire size.
4. UDH
5. I don't think 2x should be an important part of the design. I am currently a 2x rider, but designing for 2x would likely conflict with the tire clearance, which will likely be a more significant consideration and differentiator going forward. I would think of 2x as an option at most, but I would design the bike with the intent of 1x. I would also consider shipping the frame with a chain catcher for 1x rather than a cover if you are making a frame with bosses for an FD mount.
5. Aero frame shapes don't seem to matter as much as aero position on the bike, so I would focus on stem compatibility and consider the integrated bars to be similar dimensions to what BMC offers for the Kaius. Also, people are going to be riding these with pumps, bags, and tools strapped to the bike, as well as a number plate likely in front, so even optimizing for bottles is unlikely to matter when you load it up for racing. Mud clearance is also important, so aero features that require the frame to hug the wheel will probably not work well. Don't be 3T.
6. Avoid the deep aero fork. I really like the feel of the Enve and Open gravel forks, and I would be hesitant to build too stiff a front end on a gravel bike.
7. Mounts: 2 bottles in the frame, one under the DT. Top tube bag bolts. No more. No dynamo wiring. No internal storage. You cant use that in a race and it just adds complexity, weight, and something else that will rattle. Just stick to the essentials.
8. FSA or Deda headsets. I would also use genuine ones or source high-quality stainless bearings because this is a problem area for gravel bikes.
9. Round 27.2mm seat post. Just don't bother with D-shaped. If you race it on gravel, you will break stuff, including saddles and seat post-mounting hardware, so avoiding proprietary parts is essential.
10. Don't bother with comfort gimmicks. If you ride for 12-15 hours at a time, you will probably find that very little of that stuff works.
11. BB should be t47 68mm for ease of access, compatibility, and reliability.
12. Care should be taken to think about how the bike can be assembled/disassembled for travel and cleaning, as a gravel bike that sees even five tough events a year is going to need a lot of cleaning and will probably rack up 10K+km/year in training.
