I don't really understand what is the difference? The chinese abs you talk about is a mechanical abs, what is a pressure valve, I think, isn't it..? Why is it so bad?
One reason it is so bad is it is almost always bleeding brake pressure. You virtually never get the braking force you are applying to the brakes in full because in any hard stop it is bleeding pressure. The valve has no idea what the wheel is doing, once the pressure in the system gets to a certain point the valve opens and there goes a percentage of your braking force. REAL ABS has a sensor that can tell when the wheel is spinning and when it locks and adjusts the pressure accordingly. You only will lose the absolute minimum distance to keep the wheel from locking.
The "mechanical" as you call it, just bleeds pressure through a "dumb" valve. In many situations it will increase your stopping distance and get into accidents where you should have been able to stop in time but can't due to the pressure that has been bled off.
The bleed valve just makes the system not strong enough to lock up the wheel anymore and calls it ABS. It should be called "weaker brakes".
Simply put: In panic or emergency situations the mechanical valve does nothing but keep the wheel from locking
by reducing the braking force and adding to the stopping distance. The computer controlled system produces the shortest stopping distance possible in all situations without locking the wheel.
So in theory, a proper computer controlled system will be able to out brake an experienced rider when traction is poor/lost. But an experienced (or perhaps even a novice) rider might be able to out brake the valve system just modulating by feel as long as they don't lock and go down. But humans will often be able to outbrake the valve system as long as they modulate to keep from lock. In that case, the valve system will always produce the worst outcome: longest distance to stop IF the rider good enopugh to avoid lock by modulating the brakes. The fixed object or car you are trying to avoid, you may smack into because the valve has increased the distance to stop. A valve might be superior to a person when say a wet road is the only concern, but if it is a panic stop due to a left turner or something coming into your path, the valve can prove more hazardous than a bike without one. If I had to venture a guess, these "ABS" valves are standard on chinese bikes because they are used in many parts of Asia with poor quality/dusty dirt roads and little training and hard grabs on the front lead to locked wheels and rider going over the bars. IMHO they are far less needed/effective in countries with decent pavement. If I am riding in rural Thailand or China on dirt roads daily, I probably want one, otherwise I don't.
I am kind of a technical guy and a mechanically inclined, but an inexperienced rider. It freaks me out to know that lots of inexperienced riders buy cheap Chinese scooters that say ABS on them and gives them a false sense of security to ride faster or less conscious of conditions and increases the distance they need to stop when they think it will be the opposite. Accidents on motorbikes are not very forgiving.
