Yeah she just walked off of the pavement into the flow of traffic while the red man was on. Aliston shouted at her and since she was already a few m into the road, he continued cycling close to the kerb, but when she heard him shout, she tried to jump back onto the pavement and ended up going in front of him.
The stopping distance of a vehicle at 30mph would have been double that of Aliston at 18mph, so if a vehicle had hit her she would have probably died as well. And just been a statistic, due to Alisotns comments on social media on the evening after the incident, the courts decided to make an example of him. A valuble lesson here for other cyclists, if you hit somebody, get back on the bike and disappear quickly.
The limiting factor is not grip unless there is very little grip such as on wet grass. As the brakes are applied, the equal and opposite force is for the rider and frame to try to rotate forward to counter the fact the wheel is decreasing in speed. This then means more and more load is on the front tyre, until the rear tyre lifts from the road. A rider will naturally push against on the bars and lower there bum to move weight rearwards to counter the force. There is a sweet spot with the riders weight pushed back and low, with the rear tyre about 3" off the road at which the maximum retardation of speed will occur. Brake any harder at this point and the rider will go over the bars. This point of maximum speed retardation was studied by MIT, and using the calculation they dervived, at 18mph Aliston would have needed 6.25m to stop at an absolute minimum, so the coppers with 3m were miles off.
An MTB with disc brakes actually is worse at stopping because when the suspension fork compresses the sweet spot for going over the bars arrives sooner, plus with some of the 203mm rotors on the front of MTBs, the power of the brakes mean this can be achieved with a single finger on the brake lever. The reason MTBs have such big brakes is for longevity on big descents, so that the brakes don't over heat from prolonged use. This is why the recent trend for road bikes to have tiny disc brakes instead of using rim brakes has its pros and cons. The biggest con being if you are cycling in winter down a long hill and need to drag a brake to prevent going to fast, the brake heats up to soon and melts the brake piston seals, been there done that.
You sound like a pukka cyclist Mr. Sub
Re: your comment about riding off after an incident lest you should be unfairly blamed, I'm not sure whether you were joking? But that's never a good idea IMO, apart from being immoral you'd likely be caught anyway if the accident proved to be serious, and leaving the scene of an accident would make matters worse. And if you'd done nothing wrong, surely better to stand your ground than run? And obviously, assist with the aftermath if required!
In Alliston's case he was knowingly (I think?) riding an illegal bike because it was 'cool', and I would wager that although he'd still have hit the woman who stepped out in front of him had he correctly had a front brake, I think he'd have theoretically been able to reduce his speed slightly better than simply backpedalling. Whether this would have had any real effect on the tragic outcome is a moot point, but the fact of the illegal bike, spouting his mouth off on social media, and his apparent initial cavalier attitude and overall appearance as a gobby young twat, won't have done his case any good at all.
I get your point about going over the handlebars if braking hard, but in my personal experience the brakes on my bike aren't aggressive enough to achieve that if I'm sitting down, and even with sitting down the rear brake will lose grip and lock out on the road quite early, even on a dry road. The MIT calculation you quote seems intuitively about right, about a stopping distance of 6.25m at 18mph.
Your point about the front suspension on a MTB is totally valid but of course if you were on a road or hard/smooth surface and had the suspension locked then the bike would behave more akin to a standard roadbike?
The overall point in all of this though I think, is that being on a bike you should be just as responsible a road user as if you were in a car. Your bike should be legal and properly maintained, and you should be alert to other roadusers and even pavement-bound pedestrians, because they are liable to do something silly in front of you, especially if you're travelling fast. I see a lot of pedestrians underestimating the speed of pushbikes, on the occasions I've been in London just walking along, it's apparent that being part of a stream of motor traffic means you get swept along, and speeds of 20mph+ are commonplace. It's as if you're riding with a big tailwind, as a pedestrian you can actually feel the 'whoosh' of passing traffic.
