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Are Disc Brakes Faster? Disc Brakes Vs Rim Brakes | GCN Does Science

Are Disc Brakes Faster? Disc Brakes Vs Rim Brakes | GCN Does Science

– We get hit with statements
about the superiority of disc brakes all the time. Bike manufacturers say
that discs are the future. A lot of bike riders, to
be fair, say that discs are the future. And several GCN presenters,
in fact, feel that discs may well be the future. But do we actually know why? We get told that discs give
better braking performance, but then critics will say
we don’t need better brakes on road bikes, you need
better tyres that give you more grip, because you
can lock up your wheels very easily with rim
brakes, should you so wish. Today’s critics oh they say
a-ha, it’s not about power, it’s about modulation. And then I realised I
actually don’t have any facts to back that up, it’s all based on feel, and feel is, of course,
completely subjective. So we wondered whether or
not you can actually analyse the performance of disc
brakes versus rim brakes. Generate some real data for
both wet weather and dry to find out just whether
discs are actually better at braking. So how are we gonna do
a super science, then? Well firstly, the bikes. We’ve got two Orbea Orcas here. One with SRAM RED eTap HRD disc brakes, and one with SRAM RED
mechanical rim brakes. Now, while the bikes aren’t
completely identical, the important points are, so the geometry of the frames is the same. My position on the two
bikes is also the same, and then the contact patch,
the tyres are also the same. They’re Continental GP
4000 IIs, 25mm wide, and run at the same pressures, so 75 PSI. And then, what are we gonna do with them? Well, we brought them
to the Alta Badia region in the Dolomites, and we
are currently stood on top of the incredible Passo Pordoi. Down there in the background
lies nine kilometres of sinuous tarmac. One of the most amazing
descents I have ever ridden, and I’m gonna get to ride
it another four times, twice on each bike. Once in the dry, and then
once again in the wet. Then, in terms of the
data we’re gonna collect, firstly we’ve got our GPS
data that we’re gonna get on our Wahoo ELEMNT. That will be able to tell us,
obviously, our actual time, but then also we have
to drill down and see specific entry and exit speeds on corners. Now so far that might
not sound too sciency, but we’re gonna back it
up with powermeter data. And we have a heart rate
monitor, but I’m not really sure that’s gonna tell us anything. But then, it’s gonna get
really really interesting with this, which may well just be a phone, but it has an app on
there which turns it into a really accurate accelerometer. So all being well, this
will tell us just how hard I can brake on a dicc bike
versus a rim brake bike, and also how hard I can lean into corners. See? Science, big data. Right then, let’s go. Disc bike first, in the dry. Recording, here we go. (dramatic music) So run number two, rim brakes. I’m a bit more familiar with the descent, so that might go in their favour. Right, run number three. Rain with a little bit of snow, on discs. Ready, off we go. Oh God, the things we do for science. Right then, run number four. Rim brakes in the wet. (brakes squeal) Right then, time for some data. And there is quite a lot of it, actually. We logged 688,000 points of data alone from our accelerometer. So it’s take a little
bit of time and more than a lot of help from GCN
team legend and brain, Daffyd Thomas, so thank
you very much to him. Right then, the million dollar question: were disc brakes faster? Yes. And also no. In the dry, there wasn’t much
to separate the two at all, and in fact rim brakes
came out slightly faster, by two seconds, in fact. In the wet, though, results were flipped. Disc brakes were significantly
faster, by eight seconds. If you translate that out into the road, at 50 kilometres an hour,
that works out as about 120 metres of gap between the two. So that’s not to be sniffed at, I think. But, that’s just the top line. Let’s have a closer look
at the data, shall we? We do have enough of it, after all. We’ve isolated a key section of road. It’s 2.2 kilometres long. It’s got 11 corners on it,
some of them super fast and others really tight. If we overlay the speed of
each bike through that section in the dry, then we can again
see that there isn’t much to separate the two. Disc brakes are in blue,
and rim brakes are in red. Now the GPS data is a
little bit patchy in places, but if anything, it does
look like the disc bike goes slightly faster on the straights, but also slightly slower
’round the corners. The power data was the same,
the average was 175 watts for each run, and the maxes
were also about the same, 804 watts with discs and
811 watts with rim brakes. To see whether or not we
really were going fast on the straights and slow on the corners, we’ve taken the velocity data
and plotted it on a histogram. So that is where each bar
represents the number of seconds on each run where the bike
was going a certain speed. So if the bike was consistently
going faster speeds, we expect to see taller
columns on the right-hand side of that graph. And we can see that on that
short twisty section, again, there isn’t really anything
to separate the two. But then, if we look at the
data over the whole run, we can actually see
that the rim brake bike consistently hits much faster speeds. And that’s kind of puzzling. So, we thought about the bigger picture. Although the bikes are almost identical, you can actually guess
that the rim brake bike has the aerodynamic advantage. If nothing else, it’s got the
slightly faster Zipp 404 NSWs, as opposed to 303s. So, potentially then, a significant part of the faster velocities
could actually be down to pure aerodynamics. What about in the wet, then? Well again, disc brakes seem
to go a little bit faster on the straights and
then a little bit slower in the corners. But this time when we
actually plot that data on a histogram, we can
actually see that that is indeed true, disc brakes did
seem to go a little bit faster on the straight. So that’s food for thought,
and we will come back to that in just a moment, after we’ve had a look at our acceleration data. Now I’m not gonna lie,
this was a massive pain in the backside. I was a little bit concerned
initially that the data would simply be too noisy,
given that the top tube of the bike at 70 kilometres
an hour is probably going to be quite bumpy. And sure enough. Not to be deterred, though. We took the data from the
y-axis, which records force in the direction of travel,
and then Daff set about looking into one particular corner
with a super fast entry. Can we see the difference? Eh. One thing, though, those
oscillations at the end of the graph, they were the
only pattern that was repeated throughout the whole of the descent. And we can see it quite frequently. So we plotted that against
GPS data, and it turns out that’s actually me
getting out of the saddle and sprinting back up to speed. Kinda cool. Not very relevant to
braking, but nevertheless, kind of cool. Anyway, through the noise
I think you could argue that actually there is definitely
more pronounced activity on the disc brake bike on
the entry into the corner. It looks like I brake harder
compared to the rim brake bike where there is less activity,
until midway through the corner when I grab a handful of brake. Which is not exactly
textbook stuff, I know. And then those big spikes,
by the way, that is actually bumps in the road, like that one. So if that is the summary
of the data, then, what does it all really mean? Well, there isn’t much
to separate disc brakes and rim brakes when it comes
to performance in the dry. There is nothing from
any of our data, in fact, that can really set them apart, other than perhaps our
rim brake bike performed slightly better aerodynamically. In the wet, though, things
are much more interesting, thanks to the fact that there
is actually a difference between the two, particularly
the faster top speeds on straights, which I think
are probably down to the fact that the braking in the wet on disc brakes is much more controlled. We can see from our accelerometer
data that I was able to brake much harder, and
therefore slow down faster. And given that I obviously
didn’t have any more grip from the tyres, I think
that purely comes down to more predictable braking. Do that for each corner, then,
and you can see where time is really gonna add up. The reason I was going
slow around the corners on the disc bike in the
wet was probably a result of it being my first run down
the mountain in the rain. And therefore in the second
run, I was a bit more familiar with the level of grip
that the road was offering. And actually the same is true in the dry, the disc bike went first
and the rim brake bike went second. Although it wasn’t my first run
down the mountain full stop, I was a little bit more
familiar with the road, particularly on a couple of
key sections where I knew that I could let off
the brakes completely. Now in the intro to this
video I said that anything we ever really talk about in
the disc brake debate is feel. And so having spent ages
collecting data and then going through it, I do feel
slightly sheepish about the fact that we are now gonna come back to feel. But then maybe actually that is one of the most important things
when we ride our bikes. I had more confidence
descending on a disc brake bike in the wet, and actually I had
a little bit more confidence in the dry, as well, if I’m
being completely honest. And clearly I wasn’t making
the most of the bike. I wasn’t pushing the
tyres to their limits. And I think that comes down,
then, to the limitation of the test. I didn’t do enough runs
to remove any kind of bias about run one versus run
two, and being more familiar with the road on that second run. So, more time needed actually doing tests. And then whilst we’re
at it, why not do tests on different descents, as
well, that may well change the results, as would different riders. What happens if you weight 60 kilos, as opposed to my 73 kilos,
and then what happens if you’re 80 kilos, or even 90 kilos? It certainly brings home the
difficulties with actually trying to measure the
differences between bikes. Often what we perceive
as being significant is actually almost impossible
to quantify out on the road. Finally, before I go, there
is one thing that definitely needs to be said, and that
is that our little test track of the top five and a half
kilometres of the descent of the Passo Pordoi in the Dolomites was one of the best
descents I’ve ever ridden. And on each bike regardless of
brakes, it was fantastic fun, and I think that is very
important to mention. Now, obviously we wanna
hear your thoughts on this. Have we missed something from our data? And in fact which side of
the fence do you sit on in this great debate: disc
brakes versus rim brakes. Let us know in the comment
section down below. Also make sure you subscribe to GCN before leaving this video. It’s very simple and free. Just click on the globe,
and then if you want some more content now, we’ve got two old but very good videos about disc brakes. Are they ready for road bikes? That one is just there. And how much faster can
you stop with disc brakes? That one is just there.

100 thoughts on “Are Disc Brakes Faster? Disc Brakes Vs Rim Brakes | GCN Does Science

  1. I have rim brakes….but my nextbike will be hydraulic disc….and it doesn't matter….all big bike manufacturers will go over to disc brakes in the next ten years anyway…

  2. 6:30 "it does look like the disc bike goes slightly faster on the straights, but also slightly slower round the corners"

    perhaps thats because its braking more with the same effort, therefore slowing down more? which, since you then need more effort to recover from the additional braking, would lead to the slightly faster speeds that they saw on the rim bike. this is interesting, but as someone else mentioned, not the best way to test braking ability because there are too many variables. best to do a bunch of straight runs on a flat surface, accelerate to a certain speed compare braking ability.

  3. Disc brakes add weight to bike over rim brakes so I'd expect that to be a slight advantage on descents, and the feel is your confidence in disc over rim in wet weather allowing you to be a bit more aggressive. Cheers!

  4. Wrong!!! Si, we all don’t go riding down mountains and going down is not even comparable to climbing. I’m sure the big bike companies paid for this!! Also, no areo dynamics testing done on the flats with big wind blowing head on or cross winds!!! Really!!! All these years no disk and now they’re just as good!!! No way jose!!!!

  5. Another benefit of disc is you're able to run fancy carbon rims without worry of ruining the braking surface

  6. How about turning it around and climbing the same route with the same two bikes? How would the data look then as far as which bike is faster?

  7. I wonder how many people apply degreaser to their brake pads and rims before a ride. Makes a huge difference.

  8. As scientific and as accurate as cutting bread with a toilet roll. One thing we can be sure of .. that road is SO much more fun in a car

  9. I choose to keep rim brakes. they just perform well, and I like the fact they're reliable and simple to maintain and adjust. I never use my main road/race bike when the wheather is wet, so for me it's a no brainer.

  10. Can you guys measure the force required to squeeze the disk brakes vs. rim brakes in dry and wet conditions? That is one of the largest factors; that when I encounter wet conditions, my rim brakes suddenly require substantial more force. My disk brakes function the same.

  11. I think a key component that is missed for this discussion is the heat that is generated on RIM brakes. The rim is often a compromise between its role for holding the bead of the tire and holding part of the tube and it's aerodynamics vs the need the need to provide a flat friction area for braking. At its worst the heat can cause the tube to pop, and delamination of all carbon rims. Furthermore, the need to brake on the rim hinders the goal of rim aerodynamics. Finally, carbon is a poor braking surface as compared to aluminum, which is becoming more and more of an issue as all carbon rims become more and more prevalent.

    Note, for a while the delamination due to rim braking got so bad on rides with a lot of mountain descends, that ride organizers banned rim braked bikes on all carbon rims.

  12. Coming from the mtb side of things, I like my discs, but tbh, they aren't functionally any better than a good V-brake. Stepping up from cantis to Vs was revelatory; moving from Vs to discs freed up suspension design, and not much else.

    PS I weigh 120kg-ish (235lbs), so I think I have more than a little intimate experience with applied braking power. 🤔😂

  13. THAT is science : test , facts , can be replicated , that i aprouve , …… Big bang theory, evolution , that is belief, that is religion, that i dont !(at least dont say it s science)

  14. Disk should have delayed stopping power due to flex in the spokes when power is being transferred from the diameter of the wheel down to the disk. Whereas the rim brakes are absorbing that power directly. Is this right?

  15. I have both disc & rim brake road bikes. Generally I prefer the disc bike – a Giant Contend SL2 (cable operated disc).

  16. Rim brakes always for me. Flip the bike over & you can true your rim on the road if you hit a nasty hole or something. Plus for me, disc brakes make the ride ugly looking .

  17. I just bought a new city bike with hydrolic disk brakes. It is much higher quality than my old bike with rim brakes. I live in a hilly city and ride down hills every day AROUND TRAFFIC. I really don't care how fast I am, I care how safe I am. There is no comparison. Disc brakes all the way for safety.

  18. It's funny when you see sub 900g frames etc etc and then a load of disk brakes added to make an 8kg "super" bike.

  19. On a mtb it’s no question..I can’t imagine a ride without good hydraulic disk brakes. On my road bike it would be a nice upgrade but the biggest advantage for them in my opinion is the option to run more tire choices. Although after a nasty wreck in the rain I don’t ride road much anymore in heavy rain or snow so maybe that’s where my opinion would change more. I trust Simon on the scientific data lol

  20. too poor for discs – end of debate for me / next time I have the money to buy a new road bike is probably when rim brakes have become extinct anyway. until then, I'll gladly ride my rim brake road bike.

  21. Your "science" videos are kinda useless tbh 1 run for each configuration is as you said not enough for any kind of conclusion… Waste of time to watch.

  22. I know everyone is about performance, but for me disk brakes seem to be just less hassle. Wheel gets a knock, rims start to rub, disks don't. Taking the wheel off, just slides in and out with disks. Pads wear down a bit, rim brakes need an adjust more often. Rim pads can get turned, knocked around as well. Replacing disk pads just slot them in and they are in the right spot (mine have magnetic seats).

    I think they are better too, rims definitely pick up more gunk in nasty conditions and a rim takes longer to clear water as it is more surface area around the whole wheel. I get more feel and feedback with disk brakes. Just seems a no brainer, one less thing to worry about on the road.

  23. The proper sequence should have been: dry-disk, dry-rim, wet-rim, wet-disc then repeated as wet-disc, wet-rim, dry-rim, dry-disc. The sequence used for this test favors the rim brakes because you went with the discs's first and that gave you greater knowledge allowing subsequent runs to be faster — again, favoring the rim brakes. If this test were done as I indicated I'd wager that disc brakes would be faster everywhere. there's no reason corner speed should be faster on either bike so the fact that the corner speed was lower on the disc bike further highlights the advantage rim brakes had by going second — with experience you could take the corners faster. In reality, the test performed as it was is almost useless.

  24. I'm surprised you didn't mention one obvious, visible difference: rim brakes allow for lighter and/or cheaper wheel builds,(note radial front lacing) because the spokes don't have to stop the bike.

  25. This is Rediculous. A guy that's used to rim brakes. Brakes just as efficiently as a guy used to disc. The only thing different is the feel. And the modulation. I can lock up disc. I can lock up rim. I can brake every pressure in between. So what's the difference again besides rider error?

  26. dont rim brakes wear out much faster? I weight 100kg let me descend on that bike and watch them burn with smoke, or attack weights to yourself

  27. I've never had a problem slowing down "fast" with rim brakes
    except when caught in a rainstorm and then I stop riding and look for a highway overpass
    or some sort of shelter so I can sit down and smoke my pipe.

  28. I have plenty of modulation ability on my rim brakes to suit my needs, so the cost of replacement isn't worth it for me, at least. Even for wet scenarios, as I never brake hard in the wet, and I always start early, allowing that layer of water to be quickly wiped off.

  29. The braking load is transferred from the hub thru the spokes and then the rim. Rim brakes don’t cause loading on these components. I maintain extra maintenance is required to keep the rims true and rigid. Pro teams have finances and means to do this on a regular basis.

  30. Or you could just buy a big box store bike that almost always now a days gives you one of each style of brake. Best of both worlds 😉

  31. Rim brakes have suited me fine for the most part, on both trails, mountains and bike paths. If I felt there was a need for better brakes, I would just replace the worn out brake pads. But generally speaking, the less I brake the faster or more speed I gain. So having disc brakes is more or less a non-issue.

  32. Kudos for doing this test, but I can tell that you weren't interested in giving it another go in the cold wet. …can't blame you.

  33. C'mon! Disc brakes are the future. The only reason the industry hasnt fully adapted to it yet is because it would mean less sales on wheelsets in general. Its all about making money for these companies.

  34. Disk brakes are superior to rim brakes. More immediate contact, buckled / out of true wheels are not so much of an issue and in the dry they just give better stopping distances

  35. How about 2 identical bikes (except for the brakes), driving in a flat surface in the same speed and brake at designated point, so we can see the gap between them.

  36. The only reason I prefer hydraulic disc breaks in that they wear slower and at least in my experience seems generally more reliable than than any wire systems

  37. The real question : Are Disc brakes worth all the extra money and effort to maintain them in place of the rim brakes ? As bike manufactures try to push rim brakes out of the sport, they screw themselves out of the business.

  38. My first cars had drum brakes all around. Then front brakes were disc and the rear drums. Now my cars are all disc brakes. Why? Because they are easier to fix and they work better. They same for my bikes.

  39. I hate rim brakes. Commuting and just riding about the cheap shitty rim brakes get damaged, wear out so fast. Disk brakes I can do anything I want leave them for ages. If I crash into another rider or hit something 8/9 times of 10 the rim brakes can damaged/moved around somewhat.

  40. Currently ride a 2018 Trek FX3 with disk breaks and "feel" the break performance is vastly superior to my old Schwinn with rim breaks. Fair comparison(?), maybe not.

  41. You should try Transfăgărășanul road as well from Romania. Great mountain road, similar but more spectacular then this Dolomiti.

  42. Me in 2019 : Im still riding rim brackes, because its lighter and i only right in the dry.
    Every other rider : DISK BRAKES ARE BETTER!?!?!!
    Me : I dont care, they are heavy and not even better in the dry!

  43. Can I put some old rim breaks on a modern rock shok on my old mtb? i dont see anywhere to mount the rim breaks, because i need to replace the old shock (30 years old tange)

  44. Good test. I’d love to ride in a place like that. I don’t really care for the looks of the disc on the front wheel

  45. As a mountain biker, I wouldn't be caught dead on rim brakes (actually, I would, and that is the problem). But I also would never ride anything less than 2.4" tires sooooo shrug. There's a reason the mountain bike industry gave up on rim brakes 20 years ago.

  46. I think drum brakes would be better on a bike. Drum brakes don't care about wet conditions because it is very unlikely that water could get in and brake fade isn't a issue on a bike like it is on a truck.

  47. Which brake needs more maintenance?
    What is the weight penalty with Discs?
    Disc brakes have the side effect of allowing you to play around with wider tires. No?

  48. This is a really well done video. You guys did a great job. Personally, I say get the HED jet black rims with rim brakes and then you’ll get the braking performance you need in the wet.

  49. Must be nice to have access to disc brakes and not need to build custom wheels or source compatible forks. BMX life…

    If anyone argues with this I'd appreciate the corresponding links to the parts supplier?

  50. The comparison between brake systems to me would be the ability to feather the brake, especially on wet pavement. If the brake is applied and feathered differently on wet pavement than dry pavement I think would be the most important. I’ve noticed through the years that I would find different pad material to determine brake performance for my trickiest descents. My choice would be a brake material that would NOT hook up too quickly. This cause the wheel to lock up and slamming you down on the pavement. For instance the difference between Campy brakes and other cantilever brakes. The Campy would let you feather the brake easier from different road conditions, without risk of locking up the wheel, being the most important on various road conditions.

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