Brake Power Meter Prototype - Interbike 2016

Sep 19, 2016
by Mike Kazimer  
Mountain bike brake power meter
No, that's not a time machine - it's the data gathering unit for a prototype brake power meter.

Matt Miller, a PhD candidate at Massey University in New Zealand, and Dr. Phil Fink, have created a new device that's designed to measure how hard and how often a rider is braking over the course of a ride. Why is this important? Well, think about it – what's the easiest way to go faster? That's right, don't use your brakes. The trouble is, that's easier said than done, especially without being able to figure out exactly where you're braking too much or too little. Miller and the rest of the team working on this project hope that their brake power meter can help make it easier to perfect braking technique, whether that's in order to win on a particular track, or to improve a rider's skills.

Ideally, the data will be able to be displayed in conjunction with helmet cam footage that's gathered at the same time, allowing a rider to see exactly how much power they were applying to the brakes in each section of trail. Imagine pre-riding an enduro or downhill course and then being able to go over the footage later that day to figure out exactly where you could let off the brakes. According to Miller, they've found that braking harder, but less often, leads to faster lap times than more constant, lighter braking, but until now it's been difficult to gather data to prove that theory.

Mountain bike brake power meter
The prototype is a clunky, overbuilt affair, but that's only because...
Mountain bike brake power meter
...the focus was on gathering data, not on looks or counting grams.

How Does It Work?

The first generation of the brake power meter looks like something that Doc Brown could have dreamed up in Back to the Future, with an almost comically large data collection unit mounted to the handlebars. It's an exercise in “Kiwi ingenuity” as Miller put it, a way to test the concept before worrying about things like weight and appearance. On the prototype the front and rear brake calipers are mounted to brackets that allow the caliper to move slightly during braking in order to determine the torque that's being generated. Taking that torque number and multiplying it by the wheel's velocity allows for the amount of watts being generated to be determined. One obstacle that arose was measuring power when the rear wheel was skidding and no longer turning, but Miller said they should be able to overcome that by developing an equation that factors in the velocity of the front wheel.

During testing, which took place on trail bikes, the highest number measured was 10,000 watts, but Miller expects that they'll find even higher numbers once they start getting elite-level downhill racers on the device.

Mountain bike brake power meter
Matt Miller holds version 2.0 of the brake power meter, a much, much sleeker design when compared to that first prototype. Photo: Massey University

Miller also had the second generation of the device on hand, a drastically smaller unit that relies on a strain gauge and an accelerometer encased in carbon fiber and mounted directy to the rotor. The goal is to have the final version available by the middle of next year; a small power meter company called ZWatt will be helping Miller and company with taking the project from the laboratory to the market. No final price has been determined, but it's expected to be in the range of what a typical power meter costs, although the caveat is that two units will be required, one for each wheel.

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Must Read This Week

  • 196 4
 "have created a new device that's designed to measure how hard and how often a rider is braking over the course of a ride"

I'll save a lot of people a lot of money. The answer is too hard and too often.
  • 78 1
 I would say not hard enough and too often for lots of people, myself included.
  • 3 1
 True that brother!
  • 8 52
flag fecalmaster (Sep 19, 2016 at 18:23) (Below Threshold)
 Some would say how hard is too hard. From my own patent pending bonnertonic 3000 device my girlfriend has testiefied it is toooo hard.
  • 39 2
 Biggest breakthrough I've made the last few years was the day I focused on when/how I was braking and realised that half the time I just brake because I'm a pussy. Probably cut my race runs by 10 seconds just from that.
  • 3 1
 Well said!
  • 8 1
 @PhillipJ: One lesson I learnt doing a bit of amateur karting is that short,sharp braking makes you faster as you spend more time at the faster speed so your lap average improves. Plus braking can upset the balance of grip f-r, carrying speed and momentum is the key.
  • 3 1
 except Hart and Hill .. at the moment
  • 2 1
 @Badassbaby: Looks like a flux capacitor for bikes
  • 3 0
 @Satn69: It only works when you brake from 88mph?
  • 3 1
 @fecalmaster: she's not one of the rubber doll things is she?
  • 8 0
 @Satn69: where we're going we don't need brakes.
  • 2 0
 @DaMilkyBarKid: Errr. I assume you mean that short sharp braking is better for weight and grip transfer as an advantage over progressive braking (like left foot braking) in order to maintain balance and stability.
  • 2 0
 @Andy-ap: you can do short, sharp progressive braking, they're not exclusive. You can also do both with left foot braking. I was on about carrying speed through a corner or down straight, the less time you spend braking the more you spend at faster speeds/accelerating so your lap time decreases.
As an aside, in a kart you actually can brake less as the weight shifts forward seeing as most karts only have rear brakes.
  • 3 0
 Riding a single speed has made me learn how to brake efficiently
  • 79 1
 Yea, that first prototype definitely won't add 20 extra pounds to my bike and summon a Soviet Submarine from the depths of the Pacific at the same time.
  • 5 2
 This made me stifle a laugh so hard whilst queuing, tears began to form. Hahaha! You win for today sir!
  • 60 3
 Breaking news.
  • 36 2
 I'm glad I stopped to read it.
  • 22 2
 @JacobKmtb: This is some heavy shit.
  • 18 1
 I need to slow down a moment to take this all in.
  • 43 1
 Articles of this caliper deserve an up vote.
  • 3 9
flag Clarkeh (Sep 19, 2016 at 17:17) (Below Threshold)
 Have to keep revolutionary discoveries of this data testing momentum moving.
  • 11 2
 @VTwintips: There's that word again. "Heavy." Why are things so heavy in the future? Is there a problem with the Earth's gravitational pull?
  • 7 2
 i dont really even care about the meter, i just came here for the puns...
  • 10 0
 I'm looking forward to seeing what data they can squeeze out of this. I just hope they don't pad their numbers or drag their feet on releasing it.
  • 10 1
 This meter is a real drag. I wonder how many people will brake this thing.... Seems to be squeezing the industry for ideas. Maybe it will lead to a brake through?
  • 3 0
 I wonder how long they'll bleed this tech out
  • 31 1
 There is so much ghetto in this article that it resonates very well with me.
  • 20 1
 And your mama cries.
  • 13 0
 ...Cause if there's one thing that she don't need
It's another hungry mouth to feed
In the ghetto (in the ghetto)
  • 20 3
 That seems quite overly complicated, Why not just measure the brake pressure? You could use a sensor like the ones used in motorsport (way less bulky than that) and install it in any point of the brake line.
  • 10 1
 Intersting point! I imagine with all the intermediate steps they would lose the accuracy they're looking for? Pressure to piston force to tangential force to torque to power.

What would be really interesting is to monitor both and see if you can track brake fade as everything heats up.
  • 8 0
 I guess they must see some benefit of knowing the actual brake power over time, as opposed to just the pressure on the line? You'd think they'd be pretty linearly related... but always assuming things to be linear is how I almost failed physics so I'll just stop there.
  • 4 1
 How accurate can it be with all that extra weight on your bike? It will change your braking habits for sure. Brake less. speed more, clear more.

Three things determine if you'll ride that trail/feature:
1) The most critical, balls/kahunas. Braking comes into play here.
2) Skill. Some braking involved.
3) Bike. Brake quality involved here.

You may have the bike to ride the trail/feature, you may also have the skills, however if you lack balls/kahunas, the previous two don't really matter, and you and your badass bike won't ride that trail/feature.
  • 3 1
 @ryetoast: yep, linearly related only works for spherical brakes in a vacuum
  • 3 1
 @unobtrusiveluke: On a frictionless inclined plane, I presume?
  • 9 0
 I think if you used brake pressure and extrapolated to find braking force you would end up with a lot of error. Your calculation would rely on knowing the friction factor between the pads and the rotor, and that's something that is very hard to know accurately since it's a function of temperature, the presence of dust or water, specific brake pad compound, etc. By measuring the torque and wheel velocity directly, there are no approximations in the calculation of brake power. Thus the calculation will be more accurate and reliable.
  • 4 2
 I thought of another reason too. If you are measuring only wheel velocity and brake torque, braking power can be calculated without knowing any of the specifics of the braking system (e.g rotor diameter, piston area, or coefficient of friction).

For example, we know:
(Power) = (Torque) * (Angular Velocity) (1)

We can approximate (Torque) as:

(Torque) = (Brake pressure) * (Piston area) * (Coefficient of Friction) * (Rotor radius) (2)

Then we can plug this equation for torque back into (1) to find power, but then the user needs to know these extra numbers and enter them into a computer or something.

Anyway, I'm done nerding out now.
  • 1 0
Except, energy is also dissipated between the wheel and the ground.
I'd guess that is a significant part of the total, especially for the rear wheel.
  • 2 0
 @SJP: Yeah. I think that's what they were talking about when they mentioned how they can't measure breaking power dissipated when wheels are locked up. I'm interested in how they plan to account for that.

However, when you're breaking without locking wheels, I think it's a safe approximation to assume that whatever energy is dissipated between the wheel and the ground is very small relative to the energy dissipated by the brakes.
  • 8 1
 But but but but the joys of engineering this thing aside, why does the eventual buyer of this device care what the actual brake power at the wheel is? Wouldn't it, for training purposes, be enough to know when you're dragging the brakes, when you're slamming them on and when you're off them? Brake power is a function of how good your brakes are, and this thing is supposed to improve your riding, not your equipment, right? What am I missing?
  • 2 0
 @ryetoast: Good point
  • 1 0
 What about a strain-meter built into the pistons (or sandwiched behind) of a dedicated caliper (perhaps with a thermocouple), in tandem with an accelerometer (or three) in/on the wheel/rim? Make 'em all BT enabled and collect the data on your cell phone with a dedicated app. BTW, don't steal my idea, I want royalties.
  • 1 0
 @ryetoast: that's what I was thinking. I was thinking some sort of small sensor on the lever could do this.
  • 1 0
 Actually, all you would need would be a strain gauge on the brake lever. Then calibrate it on a dyno, add a wheel speed sensor, et voilá, there is your braking power. Of course, this does not consider brake fade etc, but then, you could easily correlate measured brake lever force with measured deceleration - i.e. when the ratio increases, this is your factor of fading. Or, you could apply a second set of strain gauges to the frame&fork, their deflection would be coresponding to the actual braking torque. Calibrate them with the brake torque measured by the brake levers in "cold" condition, and you get brake torque at the wheel.
Anyway, the better metric would be brake force/torque, as the brake power goes to zero when the wheel locks up. Bake power between wheel and ground could only be a rough estimation, as the lateral force and the coefficient of friction is unknown. Of course, one could estimate this from an accelerometer, at which point the whole brake torque measurement becomes redundant.
  • 2 0
 @ryetoast: no reason not to do it simply like all race cars and many other setups I've seen on bikes. Pressure sensor in a T in the brake lines and any of the many data recorders already on the market. Add wheel speed sensors if you want to monitor lockup as well. Most of the units I've seen them use on the bikes are AIM Evo4's.
  • 4 0
 wow I'm impressed with the level of Engineering/Physics around here! Anyway, great points have been made. I agree that if your objective is to measure the braking power, the method described in the article, or the ones in the comments, would be more accurate.
However, if what you are interested in is simply to help the rider get faster, I think that showing him a trace of the braking pressure would be enough. He could know when he is braking, when he isn't, and how hard. And crucially, he could compare between runs.
  • 1 1
 Couldn't you use temperature sensors (disc and fluid), wheel speed and pressure sensor in the bleed port. Those 3 together wouldn't be as accurate as this system but would be much easier to produce at the size/cost needed.
  • 3 0
 Imagine your rotors are full of oil and you brake. That means high pressure, but no braking power. Therefore...braking pressure alone is uselos for braking power. Braking pressure could show you how often you engage brakes which is also interesting.
  • 1 1
 Why not just measure the action of the levers... Force, duration and distance actuated...
  • 2 0
 Using this technology to validate the equipment is exactly what SRAM has been doing. There's a dcrainmaker video with Quarq that mentions it.
That seems like what they're going for here. "One obstacle that arose was measuring power when the rear wheel was skidding and no longer turning, but Miller said they should be able to overcome that by developing an equation that factors in the velocity of the front wheel" - but a rider doesn't care if they're using 5W or 100,000W to make the tyre skid; just the fact that you had too much brake/not enough grip is the important info.
Wouldn't that gen 2 version need to know the orientation and size of the pads? The strain on the rotor at the point of the gauge is going to be a crazy calculatio, as the rotor will not deform uniformly as force is only applied to the part with the pads.
And they have seen 10,000W, well derrrr - that's what happens when you try to slow down the 5000kg of electronics you've strapped on.
  • 2 0
 @arrgh ideally friction is not dependent on surface area and if we assume all pads are created equal, the coefficient of friction is just some constant they could estimate in the lab. F = m*a = u*N, so if the mass of the rider and bike are known, and you estimate 'u' (coeff of friction), the accelerometer gives you 'a' in the direction the wheel is rolling, and the strain gauge tells you whether the rider is braking (to distinguish acceleration due to braking from acceleration due to hitting an obstacle or going uphill), then you can estimate the frictional force slowing the wheel and N, the force of the pistons on the rotor. And good old torque = radius*F if you want that too. Source: my D- understanding of physics

Since this is so much funner to think about than my actual homework I retract my earlier question about the purpose of the project.
  • 1 0
 Totes agree...seems like someone completely lost sight of their supposed objective in engineering this thing. The objective measurement is all relative to itself anyway, no need to try and convert it to a power measurement needlessly and introduce a host of irrelevant problems in doing so. Wish I could short universities somehow...
  • 1 0
 A theory: "late braking" is optimal in mtn biking as in auto racing, so you want to go as fast as possible, then decelerate as quickly as possible at the last second by braking as hard as possible without locking up. If this thing gives you braking force and acceleration, which you could carefully integrate to get speed (or you could add a GPS unit), yeah, I can see how that would be a useful training tool--especially for doing a zillion runs in a row on the same track with the same trail conditions.

*my homework is done and I was never here*
  • 1 0
 @ryetoast: This is pretty fun to think about right? Turns out A is really hard to figure out in the real world on a mountain bike without some serious data crunching. Correlating lever force to braking force can be estimated with some error though, but the u changes quite a bit with heat/cold/dirt/water.. Measuring caliper forces (like he's actually doing here) is the easy way to do it, but isn't as easy as an actual power meter rotor to switch from bike to bike. With braking torque and lever force you can paint a much better picture of the brakes in general!
  • 18 2
 Interesting concept, would be intriguing to see it combined with other telemetry too. Surprised he's from the University of New Zealand - I thought it closed back in 1961!
  • 13 0
 You're right - he's from Massey University. Good catch.
  • 14 1
 "...the focus was on gathering data, not on looks or counting grams."

Very well may be the understatement of the year!
  • 12 2
 I brake short and hard in select places where I expect enough grip and for the rest let it roll most of the time. Last Sunday I decided to take a clinic, you can always learn something. The instructor told me to keep dragging the brakes lightly on the descends and keep pedalling. I didn't believe my ears. He also told me that it is best to have the saddle high and remain seated at all times. I shouldn't jump obstacles and holes on the downhills, only roll them. And I should get some clip in pedals and compatible shoes. That was 26 euros, for those interested. It wasn't quite the right clinic for me Frown .
  • 5 1
 Name and shame. That's rubbish.
  • 6 0
 I'm surprised to read that the benefits of late braking are only a theory in mountain biking! It has been common practice in auto racing for ages. The later you brake, the more speed you have in that zone where you would have been braking early. Definitely a cool advance either way, I'd love to see a DAQ like the Aim SoloDL for bikes.
  • 4 0
 Sometimes if you keep your brakes on,light pressure,maybe you are not pushing the wheels on to the ground to get their maximum grip.
  • 3 2
 When I race bikes this is exactly how I race, brake late and brake hard. I learned it from car racing when I was a teenager. It works really well. I don't ride this way recreationally because it leads to skidding and not so fluid ridding.
  • 8 0
 As an average rider, I already know I use my brakes too much like the big pansy I am.
  • 1 0
  • 4 1
 Why couldn't you just use a pressure transducer? You should be able to calculate brake force from that, or just use the 'ducer measurement instead. Pressure transducer and a datalogger is a much tighter package than that.
  • 2 0
 That's what I expected as well. Magura has a hal sensor in their E-bike brakes to shut off the motor when braking. I don't know if it measures how hard you brake but at least you can connect a device with software counting when and how often you brake. That's the cheapest solution, that pressure transducer you mention should be able to tell how hard you brake. Connect it to a speedometer and maybe some gps logger and you should have a pretty comprehensive and lightweight system.
  • 1 0
 @vinay: I would think with out knowing the torque applied To the wheel/frame you are just guessing. 200mm disc have more stopping power then a 160mm disc with the same line pressure. Pad material, condition of the disc/pads, moisture etc. you can not tell torque with just line pressure alone. . . . . Yet! Give them time. Motor sports have used this info for years! And motorcycles have used a pressure switch in the brake lines to sense pressure (brake lights) for decades, now e-bikes to turn off power.
  • 2 1
 @MX298: I think with some assumptions about power loss in the frame and correlations for pad material and rotor size it's definitely possible to get pretty damn close. There will be error in the measurement, but i'm just saying that a graph of brake pressure over time probably looks reeeaaally similiar to a graph of brake force over time
  • 1 0
 Of course the software needs some input to relate oil pressure to brake force. Rotor size is one. Brakeforce may not be linear with oil pressure so it probably needs a chart to interpolate within and then there may still be uncertainties about the pad and rotor conditions and the weather. But the same goes if they look at stresses at the caliper instead of brake pressure. If they really want to measure brake force accurately, you might have to use those special hubs they also use for pedal power measurements. Or measure spoke tension, but that's going to get you a massive load of data.
  • 2 0
 Very cool!
A big hinderance for me on the trail is braking too much!
But, thats a natural reaction to whats happening, I wonder how possible this is at improving your ride?
Good to know people are testing ideas of new possibilities!
  • 2 0
 ABS for bikes? Traction control for braking? MSC?

It is already all over motorcycles and breaking into MOTO. I would wager it isn't far off. In-fact AMA has banned wheel speed sensors.

That system isn't all that heavy. Can show difference in front VS rear wheel speed.
  • 2 0
 Well, I'm pretty sure on a track like Val di Sole your front and rear wheel is skidding in front of corners... how do you measure that then?
I spent the last two weeks in the alp riding huge trails completely on sight. After a while dragging both wheels in front of corners was quite normal, because I was going so quick and some corners were so tight and surprising.
  • 3 0
 If you are interested in seeing the Brake Power Meter in action and getting on the list to be the first to know when we launch the product go to- Thanks!
  • 2 1
 Interesting tech, but I wonder if it doesn't already exist in compact form for motorcycles. Version 2 looks like it would allow for more normal use situations without adding a few extra lbs to slow down. No point in having telemetry if the sensors changes the ride.
  • 3 0
 Yeah, MotoGP bikes definitely have it--they occasionally show you little real-time metrics on a rider's brake and throttle use during the race, pretty cool. Though I guess this is measuring torque at the wheel, and that might just be measuring the position of the lever or something.
  • 4 1
 Oh man, I wish I could go back in time. This time I'd take states for sure. You guys want to see me throw a football over that mountain?
  • 1 0
 I've always thought I would be cool if in the world cup/championship races if we could see how the riders use their front and rear brakes, similar to what you see in formula 1 racing, of course not with a massive contraption like this.
  • 3 0
 Looks like they strapped an NES console to their bars. Gotta love prototypes.
  • 4 1
 If someone shows up at the trailhead with this on their bike, they're getting sent home.
  • 4 0
 Perfect! I can learn just how much more of a pussy I really am!
  • 3 0
 Man cam; Mount camera on handlebar facing brake lever. Review footage with friends #hecklefest
  • 1 0
  • 1 0
 Is there a social media app that I could sync with this equipment so that I could share and compete with other trail users to see who uses brakes the most on our favorite trail sections?
  • 3 1
 Perfect! Now I can accurately assess my burrito to hot air conversion efficiency!
  • 2 0
 Being a lard-butt, I want a power meter that shows my output as I push my bike up hills.
  • 3 0
 Why can't people just ride their bike
  • 2 1
 Gotta love the nerds. Even if none of us ever see one of these gadgets in person it's technology like this that filters down in some shape or form and makes all bikes better.
  • 3 0
 That's why Sram riders are faster
  • 1 0
 Cool low profile design. Seriously, now the cats out of the bag the race to perfect the design is on. I think the application is totally there.
  • 3 1
 Do my brakes work?
Do I need a big ol box of data acquisition to tell me that
  • 2 0
 Judging by the weight, mass, and bulk of the tool... you infact have changed the results by measuring them...
  • 2 3
 So wait, you're supposed to spend an ooutrageous amount of money on stuff to make your bike lighter, but then spend who knows how much on a 10lb gizmo that tells you when you brake?
  • 1 0
 You think they'd show the sexy prototype first, not the old CNC conglomerate.
  • 2 1
 the biggest Problem here are the sram guide Gadgets..never needed telemetry with saint
  • 3 1
 Welcome to MotoGP, circa 15 years ago.
  • 2 1
 This isn't formula 1,maybe I'm not nerdy enough but I don't see this as relevant for mountain bikes,on any level.
  • 1 0
 I guess if they could test pre production brakes for consistency and how temperature affects them on the fly with data then they could prove their brakes are performing. Also the amount of people that don't know how much they brakes is surprising, when you're coaching people to slow down, then let off the brake for the corner many drag the brakes but swear they aren't. It'll end up in 10 years being technology bedded into top end DH brakes that allow people to analyse their braking on different lines to find the fastest at a world cup.
  • 1 0
 Would be really interesting to know how hard the brakes are being pulled right before crashing.
  • 2 0
 It's not even that noticeable either...
  • 1 0
 What a pimp. I wish I had the skills, and ingenuity to make useful things I wanted.
  • 2 0
 Oh shit....does this mean we're heading for ABS and ride modes?
  • 1 3
 Seriously? Did this guy fall asleep with his 'meter' in 1963 and just wake up now?
If for some reason you're needing to know how much brake pressure you're applying, you can buy a modern data acquisition unit and dedicate a channel to it. I might add that the sensor(s) and 'control unit' is about 1/100th of the size of this thing too.
With the looks of that thing, unless he's looking to PHD in ancient electronic equipment, methinks he's not doing too well.
  • 2 0
 I love Kiwi's, cool innovation!
  • 1 0
 Maybe they should have just modified some powertap hubs
  • 1 0
 Will these fit on a bike with 26 inch wheels?
  • 1 0
 WHO CARES!!!!! The only thing that should matter is can I stop in time
  • 1 0
 I only grab my brakes hard enough to stop
  • 1 0
 Doesn't your finger tell you how often/hard you brake?
  • 1 2
 Did I read that this was a Dr Phil project? Couldnt get past that first line
  • 1 1
 What does it do?
  • 1 2
 Did I fall asleep? 1st April already?
  • 5 8
 Good job it looks so light weight, otherwise Id never put it on my bike.
  • 15 1
 I applaud the fact that they are trying. I don't remember what website I saw it on but there was a timeline of power meters for cranks and it was amazing how far they have come.
  • 7 0
 I'm sure you know that this device is not meant to be affixed to the bike permanently. =P

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