tankslapper can push back on the brake pads???

S

SkyRider

Well-known member
Forum Sponsor
so watched the japan motogp race. during race stoner had a tank slapper then he had no brakes. he had to jam on the brake lever to get the brakes back and did a little stoppie. announcers said the tankslapper made the rotors push the pads back in.

just curious, i thought, since the rotors are mounted on the wheel, calipers on the forks, wouldn't everything oscillate at the same rate?? so i wonder how the rotors can move more hence pushing the pads back. it's like the rotors are loose or something...

then again it's a slapper at what? 250kph so who knows...
 
caliper pots can get pushed back... u have to pump on the brakes a lil kinda like you do after putting on new pads
 
Okay, first off I don't watch MotoGP and I can't find an image of a stationary Ducati GP12. That said, I still think the carbon rotors are mounted on buttons, therefore they are not rigidly mounted. During a tank slapper the rotors would be able to flail around a bit. I guess it's possible for them to push the pads back, if it was violent enough.
 
SkyRider said:
so watched the japan motogp race. during race stoner had a tank slapper then he had no brakes. he had to jam on the brake lever to get the brakes back and did a little stoppie. announcers said the tankslapper made the rotors push the pads back in.

just curious, i thought, since the rotors are mounted on the wheel, calipers on the forks, wouldn't everything oscillate at the same rate?? so i wonder how the rotors can move more hence pushing the pads back. it's like the rotors are loose or something...

then again it's a slapper at what? 250kph so who knows...
Click to expand...

The rotor can't push the pistons back in. I gather it's the sheer force of the wobble that causes to pads and pistons to recede under their own weight as they get tossed from side to side.
 
SkyRider said:
so watched the japan motogp race. during race stoner had a tank slapper then he had no brakes. he had to jam on the brake lever to get the brakes back and did a little stoppie. announcers said the tankslapper made the rotors push the pads back in.
Click to expand...

Sounds fishy... like the announcers were just filling in time. I highly doubt there is enough force being exerted on the brake pistons to push them back in. I wouldn't think they would have enough mass. Aside from that, for every motion that would tend to push them in, there would probably be an equally forceful move in the opposite direction that would force them back out again. Also, there are two brakes on the front wheel... they would tend to balance each other out, don't you think? (But then again, a tankslapper at 250 km/h - who knows?)
 
well even stoner himself said that's what happened. yeahh... btw what does the duc gp12 have to do with stoner? he's on honda.
 
Nothing fishy at all, speaking from experience it can happen. pump the brakes back up and your good to go.
 
SkyRider said:
well even stoner himself said that's what happened. yeahh... btw what does the duc gp12 have to do with stoner? he's on honda.
Click to expand...

Oh right ... like I said, I don't watch it or keep up with it except for the odd race. Not a judgement of the series, though I do find that the TV coverage I've seen manages to take a lot of the excitement out of it.
 
This is a well-known kinda thing, but until reading this thread it never occured to me to ask how it happens.

Most plausible answer so far seems to be from TwistedKestrel - they are floating rotors, so they can wobble back and forth a few mm - more than the total travel in the pistons duing a normal braking event. So yeah, it seems the rotors could whack the pistons back into the calipers during a tankslapper, enough that the brakes would need a few pumps at the lever to push the pads back out again.
 
fastar1 said:
The rotor can't push the pistons back in. I gather it's the sheer force of the wobble that causes to pads and pistons to recede under their own weight as they get tossed from side to side.
Click to expand...

+ 1 What he said. Watched it happen. Ever seen Mythbusters high speed cam when Adam takes a slap to the face? Just like Fastar wrote, it's the gyrations of the wobble just knocks everything from side-to-side under it's own weight. And a hell of a wobble it was. Scary moment for Stoner. Freakish race with all the errors made. Did they all have radiation on their minds?
 
ike said:
Sounds fishy... like the announcers were just filling in time. I highly doubt there is enough force being exerted on the brake pistons to push them back in. I wouldn't think they would have enough mass. Aside from that, for every motion that would tend to push them in, there would probably be an equally forceful move in the opposite direction that would force them back out again. Also, there are two brakes on the front wheel... they would tend to balance each other out, don't you think? (But then again, a tankslapper at 250 km/h - who knows?)
Click to expand...

Your front wheel is flipping rapidly, from full lock to full lock, with enough force that it can break your steering stops. This can happen at much lower speeds. It can and does smack the pistons back in the brake housing. If it ever happens to you, don't go into that first corner assuming that you've got brakes.
 
It's happens quite often. Newer bikes are more rigid so it takes a more violent event to make it happen, but as we all saw, it still happens.
 
If you get one that is bad enough that your triple clamp slaps from steering stop to steering stop....Then it will force the pistons back into the caliper, and they will need to be pumped back out, until they come in contact with the rotors before you regain brake pressure...Has happened to me before a few times
 
That look violent and scary at the same time ... then it finally bit, rear wheel comes off and he's too late to slow down for the corner. As Stoner said, such a small thing making a huge difference at the end.

When Pedrosa said .... "Stoner made a mistake ..." I kinf of have said ... What??? Well thinking about it more, it was Stoner's fault ... of hitting the nasty bump which did cause the tank slapper in the first place. You could see that for the remainder of the race he was making sure to take the the right line from the bump.
 
I wonder if the slapping forces the fluid back into the resevoir, perhaps forcing minute amounts of air down into the the caliper piston or somewhere in between.
 
promac said:
I wonder if the slapping forces the fluid back into the resevoir, perhaps forcing minute amounts of air down into the the caliper piston or somewhere in between.
Click to expand...

Just inertia. When the steering hammers the stop, the piston keeps moving back.
 
This can happen in cars as well, but the piston seal has to be worn out. Then just add hard cornering and blamo, there go your brakes for the next corner.
 
Stoners bike , RC212V, is running Brembo 320mm hard carbon front rotors on dry tracks. They only weigh 750g each and its hard to imagine they would have enough lateral motion to push back on brake pads. But if a guy the caliber of Stoner says in a post race interview he had to reseat the pads by pumping the brakes, good enough for me.
 
it has nothing to do with the rotors and everything to do with the calipers....

i downloaded the race and watched that part a few times....you see him squeeze the brake and nothing happens, he then lets go and squeezes again and almost loops it. why? cuz he was squeezing fast and hard without knowing where the engagement point was...

go to WERA forums and you'll hear guys talk about this all the time...especially with the zx10's
Forum Sponsor
 
You must log in or register to reply here.
Back
Top Bottom