How HOT Do Bicycle Disc Rotors Get? // Temperatures Measured!

[@calvinmiguel4405]

Wow, who would have thought that when I graduated 2 years ago with a degree in CE the first time I’d hear the words Matlab again would be in a cycling video...😂.

[@TheBikeSauce]

Yea.. I can’t help myself.

[@wsnx_]

European potatoe here, it's kind of frustrating to watch the video when the results are only in Fahrenheit. Ofc I could convert everything while watching but it's kind of annoying. I'd advice to present the results also in metric. All the best for your channel!

[@TheBikeSauce]

Thanks. So many have issues with F, but that’s our intuition here. Future science type videos will probably be in C

[@Pr0hunt3r18]

I was looking for this kind of a vid many years ago. Cool to see someone eventually did exactly the type of vid I wanted. Great vid.

[@TheBikeSauce]

Nice! It was crude, but a good starting point

[@criticalthought7527]

@@TheBikeSauce , Not crude IMHO, just a modest start!

[@omarlanda7]

jesus christ, this is some next level bike nerdom. kudos.

[@TheBikeSauce]

😆

[@johnlong6796]

I would love to see the same test done but with measuring the caliper temperatures which is more important than the rotor temperature esp. on a hydraulic system. I'm going to look at more of your videos. This was very informative.

[@daseishorn1863]

I love this video! A comparison between the RT-MT800 (XT ice tech) and the SM-RT800 (Ultegra) in terms of convective cooling would be amazing! The difference in terms of fins is quite big. I´m very curious how big the difference is.

[@TheBikeSauce]

Yup! Another great comparison. Would love to test them

[@nicholasthiery9542]

I agree!

[@ducatiparts110mb]

Brilliant video. Science rather than speculation.

[@jaspreetsidhu5708]

Bare bones=still better than all the data the bike industry shares about disc brakes.

[@TheBikeSauce]

Ha! I feel this. thanks.

[@bunnyadrian]

Once again, excellent video. Nice to see Turnbull, even though I've gone the other way on my rides!

[@TheBikeSauce]

Nice! I like going down the other side, but it’s more technical. I thought I could get higher temperatures this way. 🤷‍♂️

[@Beefypvp]

Such amazing nerdy scientific analysis and then you measure temps in freedom units!! Arghh!!

[@TheBikeSauce]

Lol I appear to have triggered the entire world with this one. Don’t worry, more sciencey videos are in the works

[@zzzwillzzz]

good start, but you definitely need to test a much longer run off road. longer dirt downhills are when my rotors get the hottest when i have to ride the brakes to control speed.

[@TheBikeSauce]

Sounds like a round 2 is in order

[@josephphillips865]

I think braking technique could make a big difference in these tests. Dragging the brakes the entire way down a very long and steep descent for example can really heat up rotors possibly leading to brake fade. I had this happen to me once to the point I could smell something burning and just barely had enough power left to stop at the very bottom of the descent. Obviously this requires specific conditions and I only had this ever happen on one ride. Another variable to consider would be brake pad material such as resin and metallic.

[@TheBikeSauce]

Totally agree. This and the other suggestions in the comments are exactly what I had in mind for a series of tests adjusting different variables.

[@steveedwards5280]

Thanks for putting this together, really interesting. Agree with the above, I'm not sure stronger riders are what this experiment needs. However, a more cautious rider would certainly challenge the brakes more.

[@TheBikeSauce]

Right, skittish riders would probably yield higher temps. And steeper terrain, regardless of surface type.

[@steveedwards5280]

I think so. Dragging the brakes would cause a higher max temp as the brakes are released less often and speeds are lower so less cooling effect.

[@Swoonorama]

This is a very insightful video and I love your scientific videos! Have you seen Froomey's video of his thoughts on disc brakes? Would love to hear your thoughts on it!

[@TheBikeSauce]

Saw it, but didn’t watch yet.

[@davegieger5560]

Seriously great analysis. Other interesting factors are rider+bike+gear weight and road/trail conditions. I was on a bikepacking trip (GDMBR northbound) and my riding companion boiled his front brake fluid on a 25 mile, 4000 ft forest road switchback-y descent. Boiling point of shimano mineral oil is 536F! He was a little guy - certainly under 150lbs - but carried 95lbs of bike+gear+trailer. I wonder if that amount of weight, 160/160 rotors, and especially constantly braking to keep speeds safe caused some amount of heat stacking. Could pads/calipers be more susceptible to heat stacking under such extreme conditions given less surface area to dissipate heat? I'd be interested to see tests related to how far you need to push it (speed, weight, braking style) to reach "unsafe" temperatures. For the metrics: 40km 1200m descent 280C boiling point 110kg total weight

[@TheBikeSauce]

Yes, I’d love to do another video or series testing different variables. I’m certain the weight is a big factor, but would need to test

[@TheBikeSauce]

Maybe just strap a bunch of weight to my bike next time 😆

[@rgefryer]

Great video. I'd like to see a similar test on a properly steep descent, maybe 20% with regular right corners. It's at times like that where you expect that dragging the brake will cause issues, but allowing 10 seconds of cooling off means that you're breaking from 40mph into the next corner. (All numbers made up - but faintly plausible, I think!)

[@TheBikeSauce]

Yea I’d like to test more extreme conditions too. I think steeper grade can be replicated by adding weight (but I’d have to do the math). No 20% grades in my immediate area unfortunately!

[@rgefryer]

@@TheBikeSauce I just checked an old Strava segment, and that showed me braking from 35mph to 15mph twice in 60s. But I think that I was also dragging the brakes in between (alternating front/rear).

[@criticalthought7527]

@@TheBikeSauce , Do you think that you can add enough weight to safely to cause you to need constant braking on your steepest test course? j

[@kristian.madsen]

Excellent setup & presentation. Thanks for sharing this, I too have shared the heat packing concern as well as wondered what the actual operating temperature of my brakes would be. Only one thing, it would have been nice to have had the temperature presented in Celsius as well, especially as you teased us with the sensor accuracy only to proceed to present the results in those arcane Fahrenheits ;)

[@kristian.madsen]

Also, the caliper temperature remains unexplored, I don't see it being 1:1 w/the rotor, given heat transfer, the different caliper mass/surface ratio, as well as it being the actual component to induce brake fade?

[@TheBikeSauce]

great points all around. Next temp video will be in C since many viewers had complained about it. I just have no intuition for C living in the states. I joked that I'd do the next one in K, so no one's happy 😆

[@criticalthought7527]

@@TheBikeSauce , I'd be happy with Kelvin. but I'm also happy with Fahrenheit even though he was a narcissist with scientific blinders to the natural world effects of the most important molecule on the planet. At least F offers about twice the granularity in whole numbers. ;-) j

[@oldanslo]

Appropriately enough, you've earned a 'C' on your lab report.

[@TheBikeSauce]

Well I am Extra Average

[@mtbphd]

Awesome video mate

[@TheBikeSauce]

Thx! Rudimentary compared to your tech

[@pawanv86]

Great video! The 50s vs 20s difference is because your delta T isn’t the same on the way down. I’d say the time would be a little less on decent but by not that much.

[@PaulBeiser]

Wow, great episode, and analysis. Really also enjoyed your conclusions / assessments. THanks!

[@TheBikeSauce]

Thx for watching as always!

[@do-ineedtosay723]

Excellent video! In a future experiment, I'd like to see the rider dragging the brakes to the point where brake fade is perceived. Be safe, of course. *

[@TheBikeSauce]

That’s a great idea. Conducting it safely is the concern 😆

[@criticalthought7527]

Paul B sent me, nicely done. The question for me as a bike mechanic is what is the threshold for brake warpage due to thermal effects and how can we translate this to real world concerns. This is a very large can of worms due to the large number of variables involved. As someone who has seen several warped straw and blue colored brake discs, I wonder if there is a practical way to predict what size and/or type of rotor is needed for a given application. So far we are stuck in trial and error territory, I suppose A B testing between plain and fancy discs, and plain and finned pads, would be a good place to start gathering data. I don't need to tell you how deep of a rabbit hole this could become. ;-) May you and yours be well, j

[@TheBikeSauce]

Dang. All good points. I will run this by my students and maybe they can structure a test plan to address some of these.

[@criticalthought7527]

​@@TheBikeSauce​, Sounds good, looking forward to any results you and your students can come up with. Subscribed for more. Peace and Love, j

[@morelife9103]

Amazing content!!!!! I cannot recommend this enough to my friends!!

[@TheBikeSauce]

Thx Mo

[@feliperenaultcsp]

amazing ideia and original/instructive video. keep up the good work!

[@TheBikeSauce]

Will do!

[@polyacanthus]

Interesting. I'm actually considering downgrading in rotor size. What came on my bike may be a little more extreme than my riding style.

[@fa1coner]

Just wondering if youre still running the stock shimano brake pads or if you've replaced them with the L03A pads with the cooling fins on them. Would be interesting to see if this actually makes any difference to temperature at the rotors.

[@TheBikeSauce]

All stock. Yes! I’d like to explore different variables in subsequent videos

[@IonMudreac]

would be nice to see for diff rotors sizes and brands

[@TheBikeSauce]

Definitely. Depending on if people seem interested, I might do a short series playing with different variables (like rotor brand)

[@criticalthought7527]

@@TheBikeSauce , That might get too far, into the expensive woods, too soon. Maybe plain vs vented/laminated rotors, and metallic vs finned metallic pads before brand comparisons? Just a thought...

[@kidShibuya]

I have all the gear needed to conduct this test... yet I haven't. You are putting me to shame...

[@TheBikeSauce]

Ha. Probably because you’ve got better things to do

[@criticalthought7527]

Yet... ;-)

[@DrewsterRacing]

Cool experiment! Thanks for the always great content!

[@TheBikeSauce]

Much appreciated! Thx for tuning in

[@curtmccurry72]

Awesome video! I’d love to see this kind of data from a mountain bike! Would have to get very creative for mounting the electronics 🤔

[@TheBikeSauce]

Ha true. Vibration isolation

[@aznwierdone]

Super Minor nitpick, 4:55 temps probably shouldn't be described as "twice as hot", since I think it's safe to assume from context that the temp measured is in farenheit and not in kelvin or Rankine, and 180f to 360f is about 355k to 455k, not 2x the temp. Perhaps if the measurements were made with the context of a deltaT, then the change in energy or temp could be more accurately described as "X times". I've been binging your vids, and have enjoyed them greatly. You are an ordinary content creator on an ordinary topic making videos that are extraordinary. ;P

[@TheBikeSauce]

Agreed. Thai video should get a redo at some point. It was kind of rushed, but the concept is there

[@testdirver]

average pads so resin without fins, right?

[@jacobclark89]

Looking at some of the brakes disk I'm wondering if they are engineered to break ,do to metal removal in high stress points. I hope people know to check the disc thickness often !

[@froggy0162]

What will really get them hot is dragging the brakes - light application but kept on constantly for a few minutes straight.

[@TheBikeSauce]

It’s a theory

[@delavan9141]

Nice setup, but I think you stopped a bit short of providing something really useful by simply doing an experiment that represents "an average bike, average grade/descent" etc. We can assume that good bikes are sufficiently engineered to handle your "average" conditions!!! The value-added you could provide is to test a more extreme situation, such as a long steep descent that requires a moderate yet constant braking, i.e., no let-up to allow components any cooling opportunity. Such as a mt. bike might need to do on occasion. Or simply people who don't like to fly downhill who tend to brake a lot. My question is, HOW hot a temperature can my brakes withstand? Also I noted the almost vertical spike up to 180 on one of your very brief braking events. How high would that spike go if the braking was sustained for 15 sec, 30, a minute, etc?

[@KabirBindra]

Nap time is the best time to get work done

[@TheBikeSauce]

Ha, the only time!

[@Beardcoreguy]

You should do science stuff in Celsius!

[@TheBikeSauce]

Yes you’re not the first to comment on units. I just have no intuition for C. I’ll do future videos in K, so no one’s happy 😂

[@kristian.madsen]

@@TheBikeSauce Please do, addition of 273 is much easier than subtracting 28, and dividing by 9/5 :)

[@criticalthought7527]

@@kristian.madsen , I suspect that you have a super computer in your pocket, or close by. ;-) Having said that I'm sure that he will have to present both scales in order to keep everybody from complaining. Peace and Love, j

[@KabirBindra]

All the bottle cage brackets work so well to mount equipment, can’t the diverge fit a 180 in the front out of the box ?

[@TheBikeSauce]

I think you can flip the mount and use a 180mm front, yea. I didn’t have one, but that could be a cool test too (160 vs 180)

[@thecappy]

I would love to be part of the test, but I live in PA. I have the Hope RX4 4 pot calipers. I'm not sure if they would produce more or less heat.

[@TheBikeSauce]

In theory, they’d produce more (better braking), but then dissipate it faster.

[@thecappy]

@@TheBikeSauce I originally had the ceramic shimano caliper but, coming down a fire break and riding the rear brake the ceramic piston cracked.

[@TheBikeSauce]

Dam! Hardcore.

[@peterho3299]

Great video. Love the data. I’m still running rim brakes, but this will come in handy for the next bike which will be disk. If everyone could do as much as you do at home during kids’ nap times, then we’d probably have solved global warming by now. 😄

[@TheBikeSauce]

Ha. I often nap on the couch too

[@allseasons765]

pleaseee include metric units and celsius. Not all your viewers are from US, you know

[@TheBikeSauce]

It’s just a conversion and I am from The US. Still, yes future sciencey videos will probably use different units. Kelvin perhaps 😆

[@akanoob2072]

I burned my damn finger after accidentaly touching 1 of them after a heavy brake.

[@TheBikeSauce]

Sorry to hear. They certainly do get pretty hot

[@adambarlev8992]

DUUUUDE RECORD SAFA BRIAN

[@TheBikeSauce]

Ha! That’s what I was thinking. Although something tells me he doesn’t use his brakes very much 🤣

[@LDima]

if you count temperature in fahrenheit, can you count distance in bananas? stop it. just tell us celcius.

[@TheBikeSauce]

☹️

[@criticalthought7527]

Only if you tell him what banana unit the world prefers, Cavendish, Plantain, Lady Finger etc... ;-)