The photo appeared to be his left leg that was injured. I'm not sure how that would happen with the disc's being on the left side of the bike. Maybe if the offending bike was tumbling around or some other way facing the opposite direction, it might possibly happen, but I can't see it.

About 5 years ago, I was rushing to get to work. I jogged my bike from the shed to the driveway and tripped. I had the bike to my right and ended up tripping and landing on the rear wheel/ I drove my knee into the spokes and did a minor version of the accident in question. My right leg, just below the knee, got ripped to shreds by the spoke. It wasn't even a bladed spoke and it was a rim brake bike, with the nearest disc being back in the shed. :-)

Accidents can happen.

I suspect it wasn't the disc at all, but a spoke, and he's just jealous his team doesn't have disc brakes :-). If he had disc brakes, he could have stopped before the pile up. Rim brakes are at fault here, not the disc brakes on someone else's bike.

I hope he recovers fast. (looks like a vet did the staples!)

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

To quote RChung, "Logic isn't your strong suit, huh?

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http://bikeblather.blogspot.com/

Logic is only 3rd on my list of skills. Vain attempts at humour is 1st on the list. Achieving humour is well down on page 2 of my skill set :-)

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

To quote Norm Crosby, "Hey! I resemble that comment!" :-)

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http://bikeblather.blogspot.com/

:-)

Indeed

now, back to our regular program.....

(your seat is too high!)

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

Thanks for lecturing me so politely!
Maybe I didn't express the phenomenon correctly:
Yes, the increased (thank you) trail at the highest brake force applied may be the same.
However, a force applied to the hub directly changes trail not exactly the same way as a force applied indirectly through the wheel.

Can you explain to me how modulation of trail (and the direct versus indirect action of brake force on dropouts) results in the same brake power modulation or power curve?

If we talk about modulation, I do not believe this to be true (spoke flex comes to mind).

Polite response welcome.

Disc brakes are on one side (unless you use two discs on your front wheel.) That twists the fork in addition to the rearward motion, so they do steer different. You can, of course, make the fork stiffer with more material and more weight.

Let's talk asymmetries..

Jump on the brakes hard or maybe ride through a dipsy do and watch your forks as you do this.
They move, they move big time. You will see them flex with what seems to be alarming amounts when you are not used to seeing this.

When you use rim brakes they make use of the already substantial material near the crown of the fork that is required for strength anyways, to mount the brakes.
When you use discs, the disc tries to rotate the axle out of the dropout, hence the need for different dropout angles for disc over rim brake forks.
But this is a moot point now as the new standard is a 12mm through axle, so the wheel is contained and only the fork blades need beefing up on the bottom third to handle the rotational force force of the brake.
This is helped by the through axle which adds total stiffness to the fork.
The asymmetrical bending of the fork are movements that are a tiny, very tiny component of total fork movement. (Like, you know, the fork has been designed to compensate for this. as well.)
The fork is beefed up in the bottom third for the disc, but designers will then thin out further up to bring compliance of the fork back into line with a normal rim braked fork.
I mean nobody wants a rough riding fork.

MTB designs have air spring on side and damping on the other as well as huge discs.
All this mounted to a twisty suspension thing that is alarmingly flexible if you take the through axle out and grab the forks and twist them.
Yet they seem to manage.
Put on some road tyres, lock out the fork and they handle amazingly well on high grip bitumen.
So, worrying about asymmetry in your fork is not really something that should be keeping you up at night.
My disc braked, QR, get around flat bar bike has never let me know in the handling department that there was a disc on there.

A disc fork will be heavier, can't get around that.
But now you can use carbon rims and get that back and still have better brakes.

But that heavy fork will have the same road handling characteristics you are used to.
They are simply designed to feel the way the manufacturer wants them to.
You can lay the things up to do whatever you want.
Look at today's aero forks, the shape is all aero but they still manage to engineer in the required stiffness and compliance they seek.

How much flex will there be in the spokes?
Well just look to your rear wheel to get an idea.
Can you honestly say that you can feel the spoke windup when you stomp on it? When it is blurred by tyre flex, frame flex, axle flex etc?
Even a loosely spoked wheel is amazingly stiff, far, far stiffer than the frame or tyre.(many orders of magnitude in fact)
Spoke windup is a nonevent for discs, spokes will be crossed to counter this, at least on one side and the wheel will be dished, again creating asymmetries, but can you honestly say that you can feel the much greater dish that a rear wheel has when you are bombing down a hill now?

You can't, because each side is as stiff as the other, they have to be because they work in opposition, they are in balance.
The dished side will be weaker, but they are equally stiff.
Just lean hard on your bike with a bias to one side, you will see the wheel sit crooked in the frame, thats frame and axle flex, You will also easily see the tyre deform, but you won't be able to eyeball any wheel flex.
Wheels are far stiffer than frames and tyres.
Your bike is full of asymmetries.
Most rear stays are different drive side to non drive side.
Many BB's are different side to side.
Disc brake asymmetry is a nonstarter in concerns.

Now back to that pesky fork flex with it's corresponding trail changes.
The road contact doesn't change.
The wheel will still try to pull the fork back under the bike and the two operating bits are the fork where the wheel attaches and the tyre where it contacts the road.
It doesn't matter how the wheel is being slowed, the backward force is still applied through the axle to the fork.
A rim brake will be tried to be pried forward out of the crown and the disc brake will twist the fork leg trying to get out of the frame, but the tyre will transmit the retarding force created by braking to the rest of the bike by the axle in both cases.
Imagine if you can, the front wheel rigidly fixed to the ground at the tyre contact point.
Now without using any brakes, try and push the bike forward.
What happens?
The fork bends toward the frame and the bike moves forward the amount it is allowed by the fork flex.
So you can see that the brake is not what causes the flex.
It's the fact that the wheel is being retarded somewhere, doesn't matter how.
In that example, it is being retarded by the link to the ground.
So it doesn't matter if it is at the crown, the lower fork leg or the ground, the position of the retardation will not effect the trail change that the fork causes when the wheel is retarded.

So it is also still transmitted via the spokes in all cases as well.
The force gets from the place of retardation to the axle/fork tip via the spokes, it does however do that twice with disc brakes, but can you feel the spokes wind up now when you use the rim brakes?
It will be double that, minus the quite considerable flex in the rim brake arms.
So probably less really.

Ever noticed that one side of your rim brake pads wears out quicker than the other?
One arm is longer and the force applied is asymmetrical.
Should we worry about this?
It is a pain in the arse if you are using fast wearing carbon wheel pads, but I don't think that I will loose sleep over it.
When you stomp on the pedals, the right side is supported by the chain tension and the other is not.
One stay is compressed, one is not.
Surely that must stuff up the handling.........

In the end. the handling differences you may have felt riding disc braked road bikes is simply a reflection of the current tendency to put discs on to grand fondo type bikes, not racing bikes.
Different geometries from the get go.

Starting to ramble and really I should sit down and write out something more structured, but this way my mumblings will leave a few crumbs for Tom A to try and misinterpret, and that after all is what this thread is all about, keeping Tom active in his vilification of all things disc.