My first contact with air bleeders was on a friends bike. I liked the little "pfff" sound it makes when you push them. And so did my friend and together we would use them like a button on a slot machine. Whenever we felt like it (and that was several times before during and after the ride) we would push it.
Only years later my dear husband clued me up on the sense and non-sense of those fork bleeders. So let’s have a closer look at those 3 rules:
When there is pressure build up in the forks they feel hard and harsh. So that is why you want to bleed them. How come there is pressure build up in the forks? Well, there shouldn't be except when changing altitude.
It might also happen due to bad seals or poor bush tolerances. A fork service and replacing the bushes and seals can help. But the forks are not normally just building up pressure by riding the bike unless you change altitude or there is a problem with the seals and bushes.
The main reason for using the bleeders is to equalize the pressure in the fork with the outside atmosphere. If the air pressure is higher (in low altitude e.g. at sea level) air will enter the air chamber when bleeders are pushed. If the air pressure is lower (in high altitude e.g. in the mountains) air will exit the air chamber.
Now it also becomes obvious why the wheel has to be off the ground. If you push the air bleeder (as my friend and I often used to do) while the bike is strapped on the trailer, that can have two effects.
You will have similar effects if you push the bleeders while sitting on your bike or riding. So don't do it!
It also becomes obvious why you want to bleed the fork before your ride. We live in South Africa near Johannesburg where the altitude is quite high. If we go to a race in Natal (which is much lower) we will equalize the pressure before we start the ride in order to get the full performance of the fork.
During a race or ride it is only advisable to bleed the fork when there is a lot of change in altitude. The "Roof of Africa" in Lesotho is one of those races. But also then make sure the wheel is of the ground so you will probably have to do it at a service point.
If you can push them while you wheelie that is also an option ;-)
During transport the forks will be upside down at times. If the fork
bleeder gets pushed then all the oil will run out. So if you send your
forks for a service and they come back with the oil all over the courier
truck and your garage you won't have much joy.
I would give them 3 out of 10 "must haves". It is functional and the additional weight is negligible. With a price from around US$ 15 to 34 it is not a huge investment. Now you only have to weigh the risk of losing the bleeder screw against the risk of breaking the air bleeder off when a branch gets stuck.
The Dirt Bike Garage Manual
HOW TO GUIDE for "do it yourself" riders