Anyone know anything about disc brakes?

I'm selling a BNIB M7100 rear ...

https://www.lfgss.com/conversations/366703/#comment16129376

As winter approaches I'm thinking of Increasing rotor size. Going from 160 to 180 on the front.

Does this put more strain on the forks?
How can one tell what the limit is for forks?

(these are steel road bike forks)
Thanks for any pointers

180 rotors on a road bike? What kind of mad descending are you doing?

Does this put more strain on the forks?

Yes.

How can one tell what the limit is for forks?

The manufacturer will have tested it, there will be a spec somewhere. Seeing as most MTB forks are 36mm+ diameter and only spec'd to 200mm rotors, I'd be surprised if thin spindly steel forks would be rated for anything past 160 rotors

No. Forks and frames are normally tested with the smallest possible rotor size. Levers innit.

So how has this number been ascertained?

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The caliper won't move far enough out to deal with a bigger rotor?

Continued from here https://www.lfgss.com/comments/16155834/

SRAM Paceline rotors are bad if you're doing the CenterLock thing. The interface is a loose fit on my DT240EXP and no amount of torque fixed it in my case. I've taken them off and mounted DA rotors (from Germany as that's where I could only find stock) instead. Maybe should've stuck with Centerline XRs, but the provided rotors were 160 and not 140.

Turns out the fins on the DA rotors create a problem with the Force callipers and I went through better part of my brake pads in a two day (<200km) Bath trip. It was noisy (gobble sound as the wheel rotates and the pads hit the fins) and squishy. Lightly used DA rotors will go on sale as soon as I find the urge to clean and photograph them.

So instead of faffing with spacers/washers to get the callipers at the right angle (which might've also led to poor brake perf) I had to spend more to get 140mm XR rotors and replace the dead pads also (Swiss Stop this time, not because I like them but because SRAM/Avid was OOS as always...)

Yes, and that's the number he's trying to find out for his forks

I'm saying there is a spec'd maximum size that the manufacturer says you can use, and that they will have tested to make sure that this size is ok to use without tearing the fork apart

A bigger rotor isn’t going to tear the fork apart. It might mean you have to stack 2 adapters which isn’t the wisest idea though. Normally I wouldn’t gor for anything more than whatever is native +20mm.

A bigger rotor may have the possibility of tearing the fork if it's not been designed for a bigger rotor, probably not but the manufacturer won't guarantee against it, maybe it'll just flex a bit much, you can get +40mm adapters too.

well a hybrid I use on roads 😎

Why would a bigger rotor make a fork flex more?

Levers innit.

The tire is always the limiting factor in braking force (or overturning in case of full front brake). So for a given torque, a larger rotor will put less force on the fork.

Indeed. Rotor size has no effect on the maximum loading on the fork, on any bike where the brakes are powerful enough to lock up the front brake. Anyone who disagrees should immediately go out and buy L-shaped cranks. The limiting factor is how big a brake disc you can fit before it hits the inside of the fork leg. It's a geometric limitation, not a strength limit.

What are the current go to cheap decent Shimano hydros for flat bar bikes?

Rotor size has no effect on the maximum loading on the fork

If the caliper is further away, there's more leverage on the mounting post, no? I'm genuinely asking because physics was lost on me at school

The limiting factor is how big a brake disc you can fit before it hits the inside of the fork leg. It's a geometric limitation, not a strength limit.

On fork legs that taper, I get that. But on a straight legged suspension fork, the rotor will never touch no matter how large a rotor. Yet there's a maximum spec'd size from the manufacturer. I appreciate I'm including all forks in this debate, road and MTB

Bigger rotor stops faster, fork bends faster, crack?

If the caliper is further away, there's more leverage on the mounting post, no?

Or is it the same because you’re not changing the force that you’re braking to a halt? You’d still have the same rider + their same velocity, just a longer lever, so the forces farther (further is for metaphorical distance) away from the hinge would decrease, but the same force would be applied to the hinge.

Well now I’m confused and still sober :/

If the caliper is further away, there's more leverage on the mounting post, no? I'm genuinely asking because physics was lost on me at school

The longer lever works both ways. It increases the mechanical lever operating in the caliper mounting points. But it also decreases the force needed to be exerted by the caliper due to the additional mechanical advantage. In the end it all equals itself out.

I was assuming you want a bigger rotor to because you feel the current one isn't giving you enough power and you'll be braking harder with it, if you can already get enough power to lock up the wheel or throw yourself over the front when trying not to be thrown over the front then you don't need to change your brake set up.

There’s more leverage on the adapter if you make the adapter longer, but the torque going into the fork legs is the same. I’ve never seen the mounting points on a fork fail before an adapter.

this is dangerously incorrect. a larger rotor gives more braking power which puts more force on the fork

We need to settle this. Bleed kits at dawn! FIGHT