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Radially mounted calipers......what's the advantage?


Guest Speedy23
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Radial brakes seem to be all the rage among the sportbike crowd, right? What are they? What's the fuss? Why are they in use? What else is there? Let's "brake" it down! OK, I'll stop.

When you hear someone talking about radial brakes, they may be talking about radial-mounted calipers or radial master cylinders. Let’s look at both, and discuss why they are gradually replacing their conventional counterparts on high-performance bikes.


Radial master cylinders

For as long as there have been juice brakes (that's Uncle Loomis talk for hydraulic brake systems), there have been axial master cylinders. In an axial master setup, the master cylinder's bore runs perpendicular to the lever travel. A protrusion on the lever pushes the plunger in the cylinder to force fluid to the calipers, which squeeze the pads and make you stop. Axial master cylinders are still in use on all but the highest-performance bikes. How come? They work well and have been in use for decades. Why reinvent the wheel?

But this section is called radial master cylinders, so let's talk about those. Radial cylinders move the piston in the master cylinder in a direction parallel to the lever travel. That's it. That’s the big difference.

So in practical terms, what does a radial master cylinder get us? Quite simply, improved feel through parts with more rigidity. Rigidity is key to obtaining consistent, crisp braking feel. Many riders say a radial master gives more precise feel through the feedback the rider gets.

Many brake levers allow for lever position adjustment, but a few aftermarket units also allow adjustments in the linkage to give greater or lesser mechanical advantage to the lever. This allows fine tuning of the feel. Some riders, like Showroom Expert Bob, prefer a linear feel the whole way through the lever's travel. Others, like our Training Sensei Eric, prefer a big hit of stoppin’ juice right up front and then modulate that big dose of brakes after the initial bite.


Radial-mount brake calipers

When someone mentions "radial brakes," they’re usually talking about radial-mount calipers. For the longest time, calipers have been mounted to bosses that were cast into the lower fork tubes using bolts that run parallel with the axle. Radial calipers have similar bosses cast into the stanchions, but they are cast so that the caliper mounting bolts run perpendicular to the axle.

What does this mean? Well, as you can see in the illustration above, the braking forces transmitted are all in line with the direction of wheel rotation. There is no opportunity for deflection because the braking forces are on the exact same plane as the rotational forces.

There is no increase in braking power with a radial setup versus a conventional rig. Rather, the lack of torsional flexing (lateral movement) means crisper-feeling brakes at the lever. Although it may seem nearly imperceptible, that tenth of a millimeter or so that the calipers are allowed to deflect simply feels to the rider like a mushy brake lever.

The other benefit to these systems is that larger rotors can typically be fitted simply by spacing the caliper farther from its mounts. A traditional setup requires a custom mounting bracket, at a bare minimum, to make such a change. Larger rotors increase the mechanical advantage the caliper has on the rotor, which typically yields (you guessed it!) better braking feedback.

Why do we have this radial stuff?

These days, improvements in braking are subtle. The transition, say, from drum to disc brakes, or from cable to juice setups, was certainly noticeable to riders who experienced them, but we are reaching a point where improvements in sportbike braking are becoming sublime. Most bikes stop plenty fast for most riders, so the current focus is on making the brake system provide better feel for improved modulation.

Until recently, feel was really only altered through pad and rotor composition, rotor size, and brake line material. In the quest for superlative braking feedback, enterprising engineers began tweaking the moving parts of the hydraulic system.

Do we need all this just to come to a stop on a streetbike? Didn't axial master cylinders and traditional calipers do that just fine for years? Sure they did. But in the racing world, where maximum braking happens several times a lap and feel and feedback make the difference between victory and disaster, the tiny advantages of radial brakes add up. Since today's sportbikes reflect the technology honed in racing, you can find radial brakes right on your dealer's showroom floor.

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When it comes to engineering you need a damn good reason not to stick to the KISS principle. In terms of the forces involved I see no advantage.

 


so, you are saying that radial brakes are unnecessarily complicated for the rather subtle improvements they provide?


My Africa Twin has them.. on the list of reasons for buying the bike the brakes didn't even figure. I didn't even notice that they were radial until I got the bike home, paid an extra degree of attention to my bright and sparkly bike and noticed they were of this recent(ish) design. All i had to compare it with was my other bike. The new bike as well as being "new" is only really a fairly subtle upgrade.. obviously there are a lot of aspects to the bike that are not even remotely subtle. In many ways its radically different. but the brakes? They work. They work rather well. The two bikes have fairly similar weights. The brake discs on the new bike are 5% bigger. This slight increase is in line with the other improvements which are similarly slight. power. torque etc. The brakes "feel" really good. sharp, linear. and they stop the bike. Ive yet to test the ABS in anger.. but the brakes definitely have been. once. when i made a fairly crass mistake. But.. hey ho. I survived intact. the bike lost enough speed in a hurry to spare me.


Have these brakes added unnecessarily to the cost of the bike? probably not, as this design is widespread and the numbers Nissin in particular produce and Honda buy. has likely offset this considerably.


Maybe the design.. because its positive effects are so subtle is used for purely aesthetic reasons. or, its now 'expected'. Its the first bike I have even owned that had them. I could care less. brakes have just one function and they fulfil that more than adequately. for me, that is all I need to know.

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When it comes to engineering you need a damn good reason not to stick to the KISS principle. In terms of the forces involved I see no advantage.

 

If there was no advantage then why does pretty much every race bike for the last 10+ years have them??

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When it comes to engineering you need a damn good reason not to stick to the KISS principle. In terms of the forces involved I see no advantage.

 

If there was no advantage then why does pretty much every race bike for the last 10+ years have them??

 

I have absolutely no idea, as I said, I see no advantage. What difference does the direction of the caliper bolts make? So long as the caliper is mounted securely the simpler the better.


If there is a clear advantage that justifies the added complexity then fine...I'm just saying it isn't immediately apparent to me.

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From my understanding the bolt holes on a normal caliper can expand when very hot, allowing play... it can't on radials.

Unless your on a nurburg time attack I doubt it makes any difference.

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From my understanding the bolt holes on a normal caliper can expand when very hot, allowing play... it can't on radials.

Unless your on a nurburg time attack I doubt it makes any difference.

 

Thats been the case for a lot of developments over the years that began on the race track and ended up in showrooms later. And.. unless (or until) motorcycle racing ends it will continue to to happen... first these things appear on top of the range super sports bikes and then filter down. So.. here we are all these years later and a bike like the CB300 naked has them. So, the racers found an advantage in them.. we may or we may not. The problem is there is no way to find out because they do not offer these brakes as an option so you cannot compare identical bikes with or without.


the only problem with this trickle down effect for ordinary users is if it adds significantly to the cost of maintenance. do they? I don't see why they should.


When looking at high end sports bikes. "race proven" means a lot for buyers. and for a time there is an exclusivity. but soon.. after a few years once it proves itself on the roads it becomes 'normal' and 'everyday'. I haven't looked.. but i wouldn't be surprised if there weren't scooters that had them. Bikes where the original advantage that lead to their development no longer applies aside from what is described in the articles posted, larger discs, better 'feel', a subtle improvement in braking. But, they're now normal.

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From what I can gather it's more to do with vibration and flexing of the feeble front forks, brake force is no better it's just a engineered solution to problems most of us never encountered, one of the early advantages in early race days was the ability to fit bigger disks by just adding spacers to the radial caliper.


I guess if your bike has them and it's an improvement on what went before well it's all good.

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Radial calipers tend to have the bolts spaced far apart at each end of the caliper whereas non-radial calipers have them closer to the middle.

With conventional brakes having the bolts mounted parallel to the wheel axis there is a shearing force generated which could easily result in vibration or twisting.


With radial brakes having the bolts mounted perpendicularly to the axle it means the shearing force is eliminated so no flex if vibration will occur. And because there is no flexing it mean calipers can be spaced further away from the axle allowing for larger brake discs.


Thats my thoughts on it anyway. It's all to do with the distribution of forces through the mounts.

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I spent some time on the race track as I lived just few miles from, and I had zx6r 1995 model with normal mount calliper, than I got zx6r model 2005 with radial mounted callipers and honestly I did not feel so much difference. Maybe I wasn’t fast enough or didn’t squeeze that brake so hard. Only difference I could notice when changing brake pads with some race stile pads and of course with right breake lines.

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Maybe I'm old and cynical but I tend to think that the primary objective of many innovations is to extract cash from the gullible (which I have certainly fallen for many times).


I remember spending a significant sum of money converting my car from drum brakes to discs and then being sad when the braking force measured at the MOT station was actually less than I had started with.

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The difference is, this isn't something you can choose. It comes with the bike. If you specifically don't want radial brakes or any other innovation. Buy a different bike.


It's a bit like ABS, there are people who just don't ever want it. The time is fast approaching where any nearly new bike is going to have it and it won't always be possible to remove. So... If you want a new.. Or nearly new bike you get ABS too.

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The difference is, this isn't something you can choose. It comes with the bike. If you specifically don't want radial brakes or any other innovation. Buy a different bike.


It's a bit like ABS, there are people who just don't ever want it. The time is fast approaching where any nearly new bike is going to have it and it won't always be possible to remove. So... If you want a new.. Or nearly new bike you get ABS too.

 

Very true of course. But I know several folk who have to have the latest thing so as soon as something new comes out they have to buy it. They are the marketing department's dream customers.

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