Anyone know anything about disc brakes?

If you can lock up the front wheel with both sizes of rotor this is not correct.

I think let's just all agree that disc brakes are witchcraft, and it's absolutely fine to put 246mm rotors on any bike.

Until it's not fine.

go ahead, be my guest. Try it

Depends how quickly it locks up. If it happens quicker then you're exerting more force.

Then why aren’t rim brakes the most powerful and snapping fork all over the place?

because rim brakes are very weak. the reason they stop the wheel successfully is because they are on the widest part of the wheel and therefore the maximum leverage is gained. If the rim brake was on a small disc like a rotor you would never stop.

Learn some physics dude

Plus those top bits of fork are right up by the crown and not putting the force at one side of the bottom of the legs or trying to drag out the wheel if it's not a through axle. Are DBAD?

Such sass in here ritenow

Then why aren’t rim brakes the most powerful and snapping fork all over the place?

Checkmate atheists.

Depends how quickly it locks up

It really doesn't. Maximum deceleration, and hence maximum loading on the mounts, will occur before the front wheel locks up and the front tyre is right at the extreme of its grip circle before locking up. But any braking system which is powerful enough to lock up the front wheel will by definition be sufficient to reach maximum deceleration and hence maximum loading in the brake mounts.

go ahead, be my guest. Try it

If I felt the need for rotors larger than 160mm I'd be happy to do so. I'd be more concerned about the caliper adaptors failing than the fork if I was fitting silly large rotors.

I have a masters in physics.

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Learn some physics dude

I've got some Savlon if you need it.

Can't believe people is arguing about bigger rotors stopping better. Riding bikes>science

The tire is always the limiting factor in braking force

lol what

bigger rotors stopping better.

But probably not in use on bicycles. As Brommers was saying, the very maximum stopping you can do occurs just before the wheels lock, hence ABS as you'll know. So if you can lock the wheels with a 140mm rotor, a 203mm aint gonna stop you any quicker

Don't ask me about forks tho

I've put a 203mm on the front of my cargo bike because there's no chance of me doing an endo on that and with a 2.1" slick tyre, losing grip either

So if you can lock the wheels with a 140mm rotor, a 203mm aint gonna stop you any quicker

exactly. bigger rotors achieve more stopping power given the increased mechanical leverage, but there is often diminishing returns in going for bigger rotors if you can lock up the wheel perfectly easily in all conditions with a smaller rotor

the issue with running bigger than suggested rotors is that they may put force through the frame/fork/adapter where it can't be handled.... this will hugely depend on fork/frame/adapter though of course

anyone that thinks rotor size doesn't impact stopping force is completely clueless. there is a reason we dont all just run discs the same diamater as the hub flanges

the issue with running bigger than suggested rotors is that they may put force through the frame/fork/adapter where it can't be handled.... this will depend on fork/frame/adapter though of course

I think this is the only thing that was originally asked isn't it. We've all just been mansplaining to each other about stopping power rather than force through the fork

Brommers was saying, the very maximum stopping you can do occurs just before the wheels lock

Yeah this is the point that a lot of folk miss.
In the Mtb side of things, people seem to think that the post mount will rip off a fork if you go one rotor size above what’s recommended.

I challenge anyone to show me a post mount fail on a fork or frame due to the forces in using a larger rotor. I’ve never seen it happen.

Cargo bikes are actually one of the most interesting instances of this issue because the short fork, and large mass meaning you can put some serious stress into the whole front end. With a road bike, meh, stick whatever you can fit you’ll be grand.

Can't believe that despite all this physics arguing no-one thought to ask, what fork is it?

Sorry if this is a stupid question. Just picked up a new bike with Ultegra discs and it’s my first disc brake bike. Also been sitting brand new and boxed in a garage since July.

On a quick test ride, it felt like the bite point of the brakes was really “far”, and I had to squeeze for a while before getting any stopping power, which then came quite quickly.

I’m used to rim brakes biting immediately… so is this normal, or do I need to do something?

It sound like you like your rims brake to bite at the slightest squeeze of levers (do not recommend).

Is the lever touching the bar when you finally got it to engage?

And lastly, have you done a proper test ride? The brakes might have a big throw at first before settling down after a ride.