If filtering in the UK is illegal, why does the Highway Code caution road users to watch out for bikes filtering?
It *is* legal.
There is a line between legally filtering and careless riding, though. It's subjective too, which doesn't help and a lot depends on how you're doing it. If you are straddling the white line, keeping within about a foot either side of it, that's okay.
If you're completely switching from lane to lane all the time, that is weaving, NOT filtering.
In an incident, liability *used* to be automatic 50/50 at best, but that is changing. A lot of it depends on witnesses. If you've just ridden like a cock, expect to get dumped on by anyone nearby.
Personally, anyone who moves aside, even a touch, I like to thank as I go past. Quick wave, hand up or whatever. Costs nothing, good manners and might even perk the miserable buggers up a bit.
To help avoid incidents, try and keep one of your brakes covered as you go.
Watch people's mirrors (space gauge) and keep an eye out for indicators (early warning), as well as their front wheels starting to turn (earlier warning).
Also, there is no set speed limit for filtering, but that still means you have to obey the speed limit of the road you're on - No filtering at 40 through a 30 zone!!
General guide is the 20:20 rule...
1/. Not more than 20mph above the speed of the traffic you're filtering past and
2/. Not filtering if the traffic is going faster than 20mph.
Note that this is given as a ratio. This means you can feasibly do 30mph past traffic that's going 10mph, or go 10mph faster than traffic that's doing 30mph. Just watch your spacing and keep thinking, "What If...".
Be ready to rejoin your lane when you can.
The aim is to keep you from doing anything faster than 40mph - If you find yourself exceeding that, it's time to find a gap and rejoin your lane.
A good trick for rejoining is to see when cars start to move off or pick up speed - You're watching their wheels, remember - As the line of traffic starts to expand and space out, there will come a point where this 'caterpillar effect' reaches you. Cars pull away slower than bikes, so as car A pulls off, you can merge into the gap before car B really gets going. Slow down, maybe whack your indicator on and make SURE you've been seen approaching by car B. Be ready to drop in front of car C or even D, if they haven't.
Once you merge in, be nice and wave a thank-you or give a thumbs-up to the vehicle behind!!
Other general guides:
Single lane of traffic - 2 way traffic: Go down the right hand side, remembering that you're essentially overtaking, so watch your solid white lines and so on. Watch for oncoming traffic especially and fucking well give way to any, since you're occupying *their* lane!
One lane traffic: Don't. Just DON'T!
Two lanes of traffic - Head up the middle, between the two. Left side would be undertaking and right side would be just insane.
Three lanes - Motorways!! Filter between lanes 2 and 3. Cars swapping lanes are less frequent, vision is better and people do often expect to see you there.
When going past HGVs especialy, watch for vehicles pulling in front of them, or into your lane from in front - HGVs create a blind corner and hide views of other vehicles from each other.
Do NOT pull directly in front of HGVs either, even if there is a gap. The front is a large blind spot for the driver and even a Range Rover can hide in them, so you definitely won't be seen. If you have to brake when you're in that blind spot, you are likely fucked!! Instead, wait until the HGV is at least central in your left mirror, if not further, before pulling in front of them.