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Racing Brake XT910 vs XT970
- Thread starter beastmode13
- Start date
Knightshade
Well-Known Member
For stopping distance? No, they really don't. They can't. That's not how physics works.
Guy in video appears to be "testing" by just hitting the brakes at what he visually thinks is the same speed/spot every time and then sticking a flag in the ground where he stops.
Real stopping distance tests are done with calibrated electronic devices that don't rely on "guessing" if you hit the brakes at the right time or speed to do apples to apples comparisons.
Anyway, if you want to know more about the physics of why brake pads can't shorter your OEM stopping distance, read this:
GRM Pulp Friction
Author designs braking systems for major OEMs, teaches SAE master classes on brake systems, and has literally written books on the subject.
I can also quote you technical white papers from Stoptech or the FAQ from Brembo all telling you brake upgrades don't reduce stopping distance if you're still unsure.
I suspect (or hope anyway) even MPP would confirm their pads won't (and physically can't) knock 12 feet off a normal 45 mph stop as that video claims.
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Sorry for the late reply. RB 380mm BBK in front. RB 335x21mm directional vein rotor in rear. It is all documented in my other thread P3 Break Job.
Only if if the brake system is already designed from the factory to reach the absolute maximum stopping power the tires are capable of as fast as possible. Which I doubt it is.
But no matter. You can theorize all you want and share your internet links. I prefer to rely on my years of experience in racing and testing many different pads on the track.
Knightshade
Well-Known Member
Then you'd be wrong, again.
If the car can engage ABS then MOAR BRAKES don't help. Can't help.
And every car I'm aware of made in the last decade or two can do that with factory brakes.
I bet you prefer the butt dyno to a real one too
The author of the link I gave you that you clearly didn't read has a lot more racing experience than you do.
Plus literally designs braking systems for a living for major OEMs.
And both teaches SAE master classes on the topic, and writes books on the topic.
He also says you're wrong.
Seriously dude, even the biggest folks who sell brake upgrades for a living say you're wrong- including Brembo and Stoptech.
If their kits could actually stop you shorter they'd be screaming that from the mountains
Instead, Brembo doesn't even bother to measure stopping distance, and they tell you why in their FAQ-
Brembo said:
Anyway, back in reality, the brakes do not stop the car. The tires do.
The only way to reduce your normal stopping distance is stickier tires.
See also the porsche guys who drop $10,000 on PCCB kits and don't stop any shorter either.
In fact- Road and Track did a big test on this a while back
The Power to Stop
So, first, they tell you straight up that for a normal single stop-
Car and Driver said:
Which is why brake upgrades don't help there. At all.
Where they do help is fade resistance- the ability to not stop any longer on the 10th back to back high speed stop than it did on the first.
That's vital on the track, but useless in normal street driving unless you're Jason Bourne.
And second- they actually tested two Porsche 911 Carrera S vehicles...one with stock brakes, and one with the $10,000 PCCB upgrade. Their findings?
Car and Driver said:
A $10,000 brake upgrade, and no improvement in stopping distance.
Because again, the brakes don't stop the car. The tires do.
Again the entire point of a big brake kit is never to stop the car shorter- and especially not on a normal street panic stop.
It's so that your tenth stop from 100 mph without giving the brakes time to cool isn't any longer than the first stop was. (they can also customize the "feel" of the brakes and other things all explained in detail in the original GRM link you didn't read...but twhat they can't do is stop the car any shorter the first time)
THAT is why brake upgrades are useful when tracking a car, but not for normal street driving.
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They can engage ABS at some speed, yes. But it won't engage immediately at high speeds, because there is too much motion energy for the brakes to engage ABS. The ABS will only engage once the speed has reduced enough.
By your internet wisdom the brakes can't be made worse by pads either, no matter how bad the quality.
Have you ever compared different pads?
As long as we are sharing links, here is one for a brake pad comparison: https://www.google.com/url?sa=t&sou...WMAJ6BAgHEAE&usg=AOvVaw3GnZeuxZtCNHlJerZtxuSF
For some reason the stopping distace is not the same for all pads.
For some reason the stopping distace is not the same for all pads.
Knightshade
Well-Known Member
This is a nonsensical sentence.
"too much motion energy for the brakes to engage ABS"?
Uh... no. I suggest you look into a book on how ABS works. ABS engages when the system detects slippage (ie the sensors, which are taking readings every few miliseconds, say a given wheel is decelerating more quickly than it's actually possible for the car to decelerate for example)
Nope- you've once again totally failed to understand how any of this works.
There's lots of ways to make stopping distance worse with aftermarket parts.
You just can't make it better.
In fact- here's a link that both explains ABS to you in simple terms AND gives an example of how an aftermarket brake upgrade can actually make things worse in some cases-
ABS and Brake Kit fundamentals
it's from Stoptech... who again:
A) Knows more about brakes than you
B) Also says the tires, not the brakes, stop the car
C) Sells BBKs so would be highly motivated to publish data showing their brakes stop you shorter if they actually did- but they don't do any such thing.
If you're still not sure, here's car and driver also telling you you're wrong (and also quoting a Brembo brake engineer ALSO telling you you're wrong!)
Shedding Light on Fading Brakes
Car and Driver said:
Of course it's not- they're testing brake fade- that's why they do 10 stops back to back from speed. Notice how the distances (with the SAME pads) get longer after repeated stops? And some pads resist than fade better than others?
Which is exactly the one thing I mentioned pads can change. And why on a TRACK car this is pretty important.
As opposed to street driving where they make no difference because you aren't panic braking from high speed over and over and over again back to back to back.
Interestingly though- even THEN if you look at say the phase one 60mph data, none of the tested pads
In fact- I'm glad you mentioned this report, since the 2000 version explained why they stopped testing for single panic-stop braking distance in normal driving-
Link-
https://www.justnet.org/pdf/EvaluationBrakePads2000.pdf
You know- just like I (and Brembo, Stoptech, and more) have all told you.
That fact is why they changed their testing to instead focus on things like pedal force, brake fade from heating over repeated heavy stops in a short time, and pad life.
It's the same reason Brembo explicitly tells you they don't even bother testing or reporting stopping distance- because a brake upgrade doesn't make any difference to it (unless it's a really crap brake kit that actually makes things worse... THAT is certainly possible for a few reasons... but they can't make it better)
Don't you think if their BBKS actually stop you shorter they'd advertise that? Instead they clearly tell you they don't...and instead focus on how they do handling brake fade and other things that brake upgrades can actually do and are typically only relevant on a race track.
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Indeed. Slippage happens, when there is enough braking force fo break the traction. Not before.
Well, at least we can agree it's possible to change the performance. Kind of like Tesla did with their OTA update.
Notice how there are differences in the braking distances between first tries. By your theory they all should stop at the same distance. Yet somehow some are better than others. Even better than OEM. See page 61.
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PSA. Racing Brake XT970 for P3 rear is available now. I'll be running XT970 both front and back at the next track day.
Front - RB 380x32mm BBK with RB460 4 pot caliper. Rear - RB 335x21mm two-piece direction rotors. I documented my brake upgrades in the P3 Brake Job thread.
destructure00
Active Member
I'm really curious to hear your opinion on the difference between the 910 and 970. If the 910s are not enough I may pair the RB rotors with the 970s for track days and run 910s with stock rotors on the street.
For track I would recommend having at least 970 for the front. It is rotor friendly but with higher temperature limit than 910, with the tradeoff of more noise. However, on my drive home from track with 970 front, my brake stayed quiet the entire 60miles home. So the noise might not as bed as people said.
I am running on XT970 for the past two weeks of street driving. After a proper bedding process, the brake is almost completely silent in street driving. The only time it squeaked a few times was braking while going backwards. Let’s see if this setup stays quiet after Laguna this Friday.
Braking power wise, I’m 95% confident this will be sufficient for my driving. I do have a backup full race pad for the front if the situation calls for it.
Braking power wise, I’m 95% confident this will be sufficient for my driving. I do have a backup full race pad for the front if the situation calls for it.
destructure00
Active Member
As you recall I ran 970 front at Laguna Seca in June. The front looks good, with very little sign of wear.
destructure00
Active Member
Hey @beastmode13 , how are your XT970s holding up? I'm on my second track day with the XT910s and getting poor performance from them. Pulled them after first session and they are totally glazed over. Clearly not enough, wondering if I should get the 970s or go a different direction.
970 is doing fine after two days at BRP and one day at LS. In between I drove it on street for two months, which caused more wear on the pads than the 3 track days combine. XT970 provides huge amount of bite and progressively increases as the pad heats up into a braking zone. Its not as linear as I expected and experienced from other pads. So I end up over braking at end of long straights. With XT970 you can go a lot deeper into the braking zone before braking. The pad also has a soft feel at the pedal, but the stopping force is there. I attribute the soft pedal to slight brake fluid boil from the rear calipers, a bit disappointed at 3 month old Motul 660. I had rear caliper boil at end of the track days I had so far in M3. I think it’s just the way I use or over use the brakes. I will switch to Castro before Laguna in December. If I still get fluid boil issue with Castro, I will consider to upgrade the rear to one of the RB rear BBK.
@mcbarnet007 drove a few BRP laps in my car. Perhaps he can chime in on a comparison of XT970 with Endless EX90 pad on his car. Not quite Apple to Apple, as my pedal was already soft from fluid boil, and my car was around 60-50% SOC.
2 months of street driving with XT970. No visible wear on rotor, but 2.5mm off the pads.
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