The only bit of theory is inferring that shorter head tubes mean more load on the bearing assemblies, which is pretty damn elementary; if you can't imagine the difference changing the head tube length makes to that picture, that's no skin off my nose. I'm sure many others aren't so challenged by simple concepts of leverage.

And as for the actual experiential bits of reality I mentioned, do you have any response beyond willful ignorance?

I've worked as a mechanic on and off since 1990 and ride 50cm road frames. I've never seen anything like what you're describing.

Are you familiar with BMX bikes and their short head tubes? Have you seen what people do with them?

Willful ignorance, indeed.

Also some physics involved in two aspects:

1. static weight loads (weight distribution). If you've got 40/60 F/R distribution and you bring in head-tube to get say... 50/50 F/R. How much extra is that? If you've got say... 200-lbs total weight, initial balance is 80/120lbs which changed to 100/100. How much worse is that extra 20lbs on front-end bearings? Especially compared to hundreds of lbs impacts from hitting bumps.

2. dynamic loading. As mentioned, hitting bumps puts way, way more load on front-end bearings than any amount of weight-distribution can do. Braking is also a dynamic event that puts more load on front-end. Say you've got 40/60 F/R distribution and at maximum braking, what's the load? It's 100/0 F/R with back-end skimming the ground. With 200-lb load and 1G braking, you're looking at 400 lbs on front wheel.

Let's change head-tube angle and modified weight-distribution to 50/50. What's the load on front-end at max-braking? Exact same 100/0 with exact same 400-lb load on front wheel!


You also have to separate force-vectors on headset bearings into vertical and horizontal components. Head-tube length only affects horizontal loads, which is minor compared to vertical loading from weight and bumps. Unless you're rear-ending parked cars on regular basis...

On a bike with a fixed gear and substantial toe overlap (proper track bikes have it in spades) you learn to tilt your toes up or down when manoeuvring at low speeds. That is usually enough to avoid contact.