I have no idea, I don’t do 20mph on a unicycle. Which is an important point – the lack of need for a brake is speed related (my top speed on the giraffe is ~6mph). I’m still betting I can stop quicker than you from 12mph, which is about my top speed on a “normal” 29er unicycle – go and read the discussion in the Charlie Alliston thread about the difference not having a front brake makes. Yes, I am just stopping using back pressure with my legs, but the difference is there is no gearing so the leg force required is much lower than with a fixie.
The only unicycle I’d do 15mph on is my geared 29er, which I mentioned above. That’s not strictly speaking legal in high gear (though I’m sure if I ended up in court – which isn’t going to happen – I’d just argue that it was in low gear which is direct drive, hence completely legal, though I doubt anybody normal would ever realise it has gears). I do keep meaning to put a brake on that, but the thing is it would make no difference to my stopping distance – brakes on unicycles are only really used as a drag brake on downhills, the brake I have on one of my unicycles I don’t use to stop. Again it comes down to gearing – high gear on that is only 1.5x geared up (as opposed to at least 2.5x on a typical fixie) so leg back pressure cuts it just fine.
BTW I also own a fixie (one with a front brake), so I have experience of the difference.
