Anyone know anything about disc brakes?

New pads are en route as the old ones are pretty worn. I ordered a full bleed kit so no harm in doing a whole swap to learn how it all works.

By sanding the rotors do you mean using a 3m pad or a bit of wet n dry paper with the disc cleaning solvent?

I just use a bit of emery cloth and hold it on the rotor as I spin the wheel while trying to retain my fingers, but whatever is good for you, then clean up a few times with your chosen cleaner.

chosen cleaner

Is that the butler or housekeeper?

Chambermaid or valet. The butler would never get involved in cleaning. Not his job.

The batman helps with some cleaning duties

With new SLX braks all assembled straight out of a box, had a good mechanic trim hoses down for me already. Bought TRP rotors with little black diagonal strips across the pad face. Somebody explain what ‘bedding in’ pads actually is? Have already ridden the bike up and down the road to check fit, fix rattles & adjust derailers etc, that’s all. Front is a bit ... scrapy feeling. I’m finding it slightly feels through bike a bit like fingernails on a blackboard - i.e. upsets my spectrumy sensitivity to noises and touched vibrations.

Theoretically, using protracted light-ish braking to heat the pads and distribute material evenly over the rotor, to increase bite and prevent grabby spots/pulsing.

Seems less important with modern pads/brakes, and it should happen under normal riding, but my ancient Hopes were absolutely useless until I'd bedded in the fresh pads.

Basically just ride along at a decent clip, preferably down a hill, and drag the brakes. Don't just yank them and come to a dead stop.

Thanks.

Don't drag, brake hard and often from speed, ideally down a hill, but don't lock up or stop the wheels.

There's a lot of travel in my brake levers before the pads bite the rotor, the levers nearly hit the handlebar when fully compressed.

This is a brand new groupset/ bike so I would be pissed off if I have to bleed it. Is there a simpler method?

rim brakes are so much easier

You can probably solve that by adding a bit more brake fluid to the system. No need for a full bleed.

Thank you I will give this a try

There's a lot of travel in my brake levers before the pads bite the rotor, the levers nearly hit the handlebar when fully compressed.

Road or flat bar?

This is a brand new groupset/ bike so I would be pissed off if I have to bleed it. Is there a simpler method?

If it's new take it back the shop. It should be set up for you. That said depending on your levers there might be bite point adjustment.

rim brakes are so much easier

Cable pull stuff is much easier, yeah.

You can probably solve that by adding a bit more brake fluid to the system. No need for a full bleed.

This shouldn't really work. Or rather, without ninja level bleed tricks I don't understand why it would do anything.

Road bar. I bought it from an online Northern Irish retailer (which was circa 25% cheaper than others) so returning it would be obtuse as I live in Essex.

I hate not knowing what’s wrong with my bike, I need to get my head around all this hydraulic malark. I feel like I’ve entered the jet age.

Well, if it’s shimano is pretty straight forward to add more mineral oil to the top chamber.

If the bike has been out riding I doubt there are any bubbles left in the hose, so it’s just a matter of topping up with mineral oil.

But if there's enough in the reservoir to not pull in air under braking then more fluid won't make a difference, it'll just top up the reservoir which is still useful if there's room, as it'll need the fluid as the pads wear and the system self adjusts.
Either there's a bit of air in the system, in which case the "burping" process I described above should help (and top up the reservoir) or possibly you're not used to hydros just tending to have a bit more lever throw, you rarely actually pull them that hard, so give it a test ride and see.

^ this

It is possible to over fill the system to reduce lever throw - assuming the air comes out first - but it’s unlikely to stay consistent as the system adjusts to pad wear.

“Ninja level bleed trick over fill” needs to be done from the calliper and requires a special bleed block.

And once the pads wear the ninja overfill will stop working anyway.

I've had success dropping the wheel out, giving the lever a little squeeze to over auto adjust and popping the wheel back in (top up reservoir if wanted), but it'll ease back to where it was as the pads wear, was mainly a problem for early shimano road systems.

it’s unlikely to stay consistent as the system adjusts to pad wear.

And once the pads wear the ninja overfill will stop working anyway.

it'll ease back to where it was as the pads wear

Glad we agree on something!

Stupid me, cleaned my chain in the dark yesterday and must have had some chain cleaner spill on the disc brake. No stopping power today. Clean the rotor with isoprop alcohol and sand the pads or should I just bin the pads?

Worth a try cleaning, but might not work. Clean pads and rotor a lot though, doesn't take much to fuck things up, and if you do put new pads in, clean the rotor loads again.

New rotor / pads fitted and bedded in on Sunday. Squealed on Monday in the rain - stupidly loud.
Stripped everything off yesterday, cleaned, refitted, torqued on and lined up.

Still howling. Video with sound...not sure it does the loudness justice.
Could it be that RT-800 Ultegra rotors don't like SRAM (would seem odd) OR perhaps there is a constant stream of sh*t coming off the mudguards OR something else?!
Here is the state of the rotor after a few wet miles.

are you actually getting any braking power out of them?