What's the big deal about Radial mounted brakes?

[Juggler]

I've been seeing a lot of info about radial brakes, and don't know what all the hubbub is about. How are they superior to what's on the Busa? What's on the Busa by the way? Linear brakes? Non-linear, co-linear, hella-linear?

Educate me, Busa people.

--Juggler

 

[stkr00]

Juggler,

Radial brakes typically have a greater stopping power than conventionally mounted brakes.

Both are disc brakes, but the difference comes from the diameter of the rotor. With radially mounted brakes, the rotor is larger, which gives a greater radius (distance from the axle center to the rotor clamping area). Torque is the force multiplied by the radius, so for a given force (brake pads clamping on rotor) the system with the greater radius will have the greater stopping power.

On radial systems the caliper is mounted inside the rotor which allows the rotor to be larger.

Hope that helps.

 

[justintime2]

learned something new thanks!

 

[FLCN72]

During exreme racing conditions, conventionally mounted calipers do twist slightly relative to the axle.  They rely on the rotors themselves for some of their resistance to these twisting forces.  But this causes the rotors to warp slightly (generally not permanently) while braking.  All of which reduces the accuracy of feedback and braking at the very edge of performance.

Radially mounted calipers are far more resistant to twisting during hard braking.  Because their heavy duty brackets come out radially from the forks relative the the axle. Therefore they are far less likely to cause any twisting or warping of the rotors while braking hard.  

These differences aren't dramatic.  And are a result of racing tweeks to shave as little as a half second off of lap times.  

Buell has a radially mounted brake rotor on the front.  This mounts the rotor to the rim instead of the hub and has the caliper mounted to the inside.  Buell calls these ZTL (zero torsional load) brakes.  But these are in no way similar to the brakes I described above.



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[BusaFever]

I understand that the brakes are better.

But...

What about the larger rotor affecting the MOI of the wheel? I mean I have seen these larger rotors, they are farther away from the center of the wheel, which makes the MOI worse. So my Q is, are these brakes a true advantage or a diadvantage? If the MOI is worse, then it affects the corner turn in, and etc. I guess the braking advantage probably outweighs the MOI disadvantage. Your thoughts on the FLCN72?

I have seen those buell rotors, they are HUGE! It has got to affect the performance of the bike.

 

[FLCN72]

It is my understanding that a larger and heavier rotor would have an impact on MOI (moment of inertia), causing a slower turn in and decreased agility, by adding rotational wheel mass. This is assuming that all other factors remain equal.

However, for the radial mounted calipers found on newer sport bikes, this wouldn't be an issue. As their front rotors are generally no larger than is typical of conventional set ups. Or if they are larger in diameter, it is only by a few millimeters and the rotors are made thinner or given wave cuts to negate the effect on mass.

Now the Buell rotors are another matter. They are large and heavy. However there is only one of them, so I am guessing they aren't much heavier than a conventional twin rotor system. But, they carry their weight farther out away from the axis of rotation. So, in theory they would add more MOI than a conventional twin rotor of the same mass. Buell claims that they have made the front wheel lighter though, so we might be back to square one. I honestly don't know.

I suspect that the Buell system is no better than the conventional sport bike brakes of the past five years or so. Both in terms of resistance to fade and effect on MOI. With the right pads, they probably could have good initial bite and feedback. But I doubt they are as good as the new brakes found on current sport bikes (both conventionally mounted calipers and radial mounted calipers.) But I honestly don't know what effect, if any, these brakes have on the total MOI of the Buells or their agility.

 

[BusaFever]

Great, thanks for the answer... I have been thinking about that one for some time now... Whew now I can sleep at night againg!

 

[FLCN72]

 

[Ononewheel]

FLCN pretty good explanation.

Couple points I would like to emphasize.

The biggest advantage radial brakes have over conventional is the flex less, supposedly helping braking feel and ability.

Here is a side pic of radial calipers on an R1. Yes they are superior to whats on a busa. Busa brakes pretty much dissapoint me, but.. they do stop you very well considering there is an extra 100 pounds to slow down.

 

[Ononewheel]

Here is the busa brakes just for reference.

 

[Ononewheel]

Radial mounted calipers mount frm the outside just like conventional ones.

 

[Ononewheel]

The disc diameter is no different for radial brakes. Some manufacturers will very but they are all close to each other. Here is my best attempt to compare an R1's disc to a busas. Excuse the dark pics.

 

[Ononewheel]

Lastly the r1s disc.

 

[busaguy]

interesting

 

[justintime2]

After reading all, I still don't see the difference in the pics?

Thanks for them though!

 

[ohzone]

The Calipers on the radial mounts are supported along their entire length much more than the conventional mounts, The conventional Calipers are solidly mounted to the fork end but the other end is almost swinging in the breeze, this allows flexing and distortions and a vague feeling under heavy braking.

 

[Ononewheel]

The Calipers on the radial mounts are supported along their entire length much more than the conventional mounts, The conventional Calipers are solidly mounted to the fork end but the other end is almost swinging in the breeze, this allows flexing and distortions and a vague feeling under heavy braking.

Exactly!!!! There is a difference with the brake lever too. It's hard to describe but if I get a minute this week I'll get some more pics. As for how the radial brakes work and feel, I got to try em out today. Thats my buds R1. Anywho They are UNBELIEVABLE brakes. One finger will lift one rear tire in a second. The are much better feel, and powerful then any bike I have ever ridden. Including the 954RR which I believe to be the benchmark in brakes.

 

[justintime2]

Now that you have pointed that out I see what you are talking about. The Busa brakes seem to have all the brake pistons below the level of the mounting tabs. The radial's have the brake pistons squarly between the mounting bolt and look much beefier. Thanks !

 

[justintime2]

Also those radials look like they are 4 piston and not 6. They still feel better even with less grab?

or are the pistons on the radial larger?

 

[ohzone]

It's not really the pistons being larger that makes the difference
The R1 is a much lighter bike and does not need as much "brake" as the Busa
The idea of more pistons is to spread the pressure the pistons apply to the brake pads over a larger area, you would probably find the actual pads are quite a bit smaller in the R1.
So many variables, pad area, swept area of the disc, type of pad material, type of disc material, rigidity of the caliper and so on.
If the Hayabusa calipers were mounted on an R1, in just as rigid a manner, they may very well be more powerful than the R1 calipers, who knows

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