Are Big Disc Brakes REALLY Better?

We know that bigger brakes can stop you faster, but what about their efficiency? We went to Girona to find out whether a bigger disc brake rotor will not only have a lower peak temperature, but also dissipate heat faster than a smaller disc brake rotor. It's time for some GCN Science!
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[@gcntech]

What did you think of the results?

[@kevinomeley3043]

You came to the same conclusions as I gave when selecting rotor size for the weight.

[@12Burton24]

.....not really a scientific test.....you have to measure it permanently and you also have to know the speed, weight, energy which got transfered into heat for one ride and so on.

[@danc1829]

should try it with an alloy rim brake wheel 😉

[@jonnythelegs2597]

Being a mtber and roadie id say fairly predictable, good to see some peak torque recognition tho. Yeah come on let's test some stuff to destruction, get the lathe out. Big brakes are great if you're an aggressive decender theyre always good to go - fade is a thing of the past and in 24hr races having more than enough power is a bonus with tired cold hands. If you're a bit of a panic braker tho good luck, best thing you can do is work on your spacial awareness so things don't suprize you.

[@frankeeeej]

The 55ish degrees across the board shows that the experiment probably isn't hard enough to show any difference between the rotors. (Although the faster heat dissapation of the 180mm is a hint at potential superior performance) Would love to see some more experimentation on the subject :)

[@wawarrior101]

Would love to see a weight based experiment between a 60kg rider and a 100kg rider descending

[@ericpmoss]

I can verify that on steep, loose gravel paths with high consequences for sliding, small rotors fade for Clydesdale riders, and are fatiguing.

[@AiharaKenshi]

Yes please

[@andymonks7126]

Should do heavier and less confident at descending.

[@Rose.Of.Hizaki]

(if all else being equal) Gravity. Means fatties should be faster at descending. Bigger discs will be king as it has enough surface area to handle and dissipate the heat from braking. You could also toast your brake pads as well but even a lot of those come with heatsinks or made with better materials like aluminium on the back of the pad to help remove the heat these days so its not as much of an issue as it used to be unless youre on a super super long descent then brake discipline is key to not cooking your brakes.

[@quartzdonkey]

Agree. Do it!

[@Hambini]

If in doubt, ALWAYS get the biggest.

[@mondoabz]

I’ve got a 622mm disc. It’s called rim brakes 😂

[@Hambini]

@@mondoabz pmsl brilliant

[@coldforgedcowboy]

@@mondoabz ... Eroding the structural strength of a rim to us as braking surface is one of the more moronic things the cycling industry has come up with. Thankfully it is going away.

[@bikeindustryshill]

Is the extra stress from a larger rotor on the fork a concern?

[@coldforgedcowboy]

As long you don't use Titanium bolts you should be okay.

[@AnvilAirsoftTV]

All for fire and flames! I use a 160mm on the front at 100kg. Would think about going to a 180mm next time I change the rotor. Nice to see Peak Torque getting some love on GCN

[@teknonmy7210]

How are you getting on with the longevity of the rotors themselves? I'm much lighter, but Peak Torque saying his pair only lasts ~6 months is scaring me.

[@michaelmechex]

@@teknonmy7210 That was specifically about Shimano icetech rotors because they have aluminium in the middle. Get some cheaper full steel rotors and they will last ages.

[@veganpotterthevegan]

Funny thing is that he hates gcn😅

[@akaraikiriakatsuki3157]

​@@teknonmy7210xD yeah fuck the icetech. If you're going to race icetech is fine. For daily driver normal rotors are better

[@Benagiser]

Love to see this explored more. I built an adapter back in the early 2000s to mount 8" rotors to my MTB as there wasn't anything available at the time and discs were so new. Ran 9" up front and 8" at the rear for literally 20 years now. Love it. Keen to see how a bigger disc works on road bikes as I find my 5" fronts lacking in stopping power to be honest.

[@creative907]

Love the comparison and breakdown of each of the rotor sizes. I currently have the Shimano SM-MT800 140/140 and as a weekend/casual groupride cyclist 140s are good enough for me. I did however, swapped out my stock SM-RT800 (Ultegra road) for their MTB equvailent.

[@andrewdibb3825]

Definitely keen to see glowing rotors! Perhaps you could talk to some motorsports people - they have different sized rotors for different tracks in some series.

[@kramrenrut950]

Depending where you live, in Lincolnshire hardly touch the brakes apart from reaching the cafe, vive the rim

[@billmccaffrey1977]

You touched on the real benefit, but wasn't the focus of your test. The biggest benefit is heat recovery in a situation where you have to brake on a continuous basis (same on a car/truck). A long technical descent where you are breaking hard on and off for 10 to 20 mins would be a better test.Also at what temperature do you start to loose breaking power? You could use a lath to perform both test.

[@steverhysjenks]

Would love to see a comparison of rotor size and rider weight (light vs heavy rider) - Heat, stopping distance, feel

[@DanTuber]

Peak torque has gone mainstream

[@stephenmorris6202]

Follow Peak Torque and have been impressed by his analysis and ingenuity. Plus the pros have complained about distortion of rotors 0on descents. A 180 (or larger) seems to be the way to go, particularly as the weight difference is marginal. Yes, please investigate further.

[@tmswfrk]

I wish they had discussed about the warping being often more prevalent on the larger rotors by comparison (usually due to just larger distance from the center axis). My front 160mm Shimano definitely causes me considerably more grief than my rear 140mm.

[@SMlFFY85]

Wouldn't that be down to using the front brake more?

[@tmswfrk]

@@SMlFFY85 how much you use the rotor, at least theoretically, shouldn't affect how much the rotor warps. It mainly warps (in the real world) because of the tight spacing along with the regular heat increase and decrease as materials expand and contract (particularly when it comes to bonded materials of different varieties like steel and aluminum). They inevitably tend to not always go back to normal dimensions (when we're talking sub-millimeter) because of these things. From what I've read, the 140mm rotor is technically thicker by a hair than the 160mm. And since the length of the radius on the 160mm rotor is more, there's more potential for that material to get "out of true" to borrow the phrase, especially given the reduced thickness of the rotor. I'm luckily a smaller rider, so which diameter I use seems to largely be inconsequential, but I've considered running dual 140's to specifically avoid this issue. I pretty much never have rotor rub on my rear 140mm rotor when I have constant squealing and rub on my front 160mm rotor. It would have been nice to see some of this mentioned in the video!

[@thedownunderverse]

@@tmswfrkdid you ever try 140/140? How did it go?

[@tmswfrk]

@@thedownunderverse yeah it’s what I run now. I’m a lightweight rider, so weight isn’t an issue and I haven’t really experienced any fading. So far my choice of SRAM rotors has been working without too much squealing, as long as they aren’t contaminated and have been bed in properly. I’ve also started using resin pads again, which I think can quiet things down a bit in some cases.

[@thedownunderverse]

@@tmswfrk cheers for that! I’m 72kg and considering trying 140/140. Expensive test though

[@djbayr9516]

I run a gravel bike with mountain bike brakes, using a 180mm rotor upfront and 160 in the back. No stopping issues. Sometimes too much. I love it.

[@a1white]

I have a disc(160) and rim brake bike and never really had an issue with my rim brake set-up compared to the disc brake bike. However, recently going out to Spain at Christmas and using a hired (Orbea) rim braked (105) carbon bike, I had less confidence in the brakes. Even though it was alloy rimmed with decent tyres. Granted I got mixed up with front and rear brakes early on (swapped over on bikes on the continent), I either locked up the rear too easily or didn’t feel I had enough stopping power on the steepest descents. Not sure if I was the pads or what, but my own rim brakes bike has much more modulation and control. Maybe I’m just used to the setup more. But it did make me appreciate the arguments for discs more.

[@stephensaines7100]

The pads and rims make a huge difference, as they would on any vehicle, as they do on discs. With the right pads and rim surface, you'll get as much stopping power as discs if your calipers meet a given standard.

[@Aashiek]

Would love to see a graph of the rate of cool down for each disc size. Great video!

[@vulpesinculta7074]

In my cause change front disc from 160 to 180mm was perfect decision. It cost me around 20usd for disc and adapter. Also when i had in one season Giant Fastroad i changed front one from 140 to 160 and i had not regret it I weight around 95 kilograms so it is very efficient

[@joekawasaki]

I'd love to see the test done again with someone who IS in that 90kg range & 50 - 65kmph speeds! (I'm currently about to make the switch to discs)

[@mscbijles1256]

I would like to see you try a descent with a very fit tower of the described length/mass. He’ll maybe have a bigger impact on the rotor differences as well, as there is more energy to dissipate.

[@alterrex4463]

Would love to see a weight based experiment. Would like to see some lathe action too!

[@waynebrowne4383]

MTB is my first sport and mixed disk brake rotor size has been around for a couple of years, however I did own a road bike as my 2nd bike (sorry GCN I flipped to a gravel bike recently) so I was really intrigued by the content of the disk brake on road bikes, maybe the pro teams will consider mixed disk brake rotors on their heavier riders or the fast descender. I think this opens a valid question in the future of the sport

[@slowcyclist4324]

Gives you better disc cooling for long descents, and less lever force needed to slow the bike down

[@kevinomeley3043]

On racing tandems you need the large disc brakes to cope with the extra weight like Ollie saw on my tandem submitted to Nice/Super nice. My rider/bike weight is 172kg and we have blued the disc’s on a mountain descent.

[@PrzemyslawSliwinski]

On our (non-racing) tandem we use either 203mm XT(R) rotors front/rear from spring to fall or 160mm (Ultegra) during winter.

[@gcntech]

What size rotors do you use?

[@rider65]

Correct, weight and load will be affecting factors on the conversion of kinetic to thermal energy. Increased weight and higher load transfers will require the highest efficient transfer anticipation mediums.

[@kevinomeley3043]

@@gcntech 200mm front 180mm rear

[@SeeYouUpTheRoad]

Captain/Stoker combined weight 270 lbs 123 kg we used 203mm rotors and metal pads on my road racing tandem (200 milers- 500 milers) - but I would never ride disc brakes on my solo road bike.

[@seattlegrrlie]

I grew up in Washington in the 90s riding both road and mtn. Could never figure out why road took so long to adapt. I run a 160 on my road bike and 180 on my mtn.

[@ericrickert3045]

This was interesting since I currently have rim brakes and did not know about options for various-size rotors. My riding has lots of hills, so when I do upgrade to a carbon bike with disc brakes, I would want the largest diameter rotor that can fit on my bike. This was a valuable video!

[@lincolnlu9869]

The biggest rotor you can get are rim brakes. 622mm > 160mm

[@simonm1447]

@@lincolnlu9869 220 mm Dh rotors combined with 4 pot brakes will stop every road bike

[@jesmondo5785]

@@lincolnlu9869 luckily it's not 1986 anymore and we can use discs instead 👍

[@macvos]

@@lincolnlu9869 true, but don't confuse that statement with having the most stopping power.

[@asams7255]

@@simonm1447 overkill really, a bikes brakes are only as good as the grip of the tyres, for MTB it makes sense but for a road bike you'd rarely be able to utilise the full power

[@axelschneider1678]

I ride a very roadbike-esque city bike (700C, no suspension, Tiagra all around) and I regularly tow my twins in a trailer. About 45kg for the whole lot (trailer and kids) switching from 140 to 160 made a significant feelable differece. At least in terms of stopping power and distance.

[@pawel8365]

Depends on the bike really. I've got a touring bike, 160mm is good, but later 200mm might be better. Better heat dissipation when speeding downhill with a heavy load.

[@Pillokun]

I am no road bike cyclist, because I am stuck in the past(xc biker) and I use my old school ht from 2003 or 2005 with xt br785 brakes with 203 up front as ac commuter. swtiched to 203mm rotor up front because I could not stand how bad discbrakes actually were. 160mm rotors glazed my brake-pads very often, even at 203 it was quite common. So I switched to sintered pads and it actually did make a difference but still not as good braking perf as old school v-brakes, especially in combination with ceramic coated rims. My work college is still a proper xc biker and tested my bike and said it had the best brakes he ever tried, well I have to say that bikers know absolutely nothing about brakes in that case. I still consider my brakes to perform very poorly. Try a motorcycle and see how good they brake or simply a bike with v-brakes :P to get proper disc brakes we need thicker rotors.

[@PereAndreuUbachdeFuentes]

Please, please, make an experiment indoors monitoring how the temperature builds up in the disc rotor, in the brake pads and in the oil with different setups: a) standard 160mm rotors, 2-pot calipers and a fan blowing on the setup b) standard 160mm rotors, 2-pot calipers and finned brake pads with the fan blowing c) and d): repeat a) and b) with 180mm rotors e) and f): repeat a) and b) with 4-pot calipers Maybe you can do the experiment in association with GMBN for the 4-pot calipers. And make sure that in all cases you are dissipating the same power turning the wheel at the same speed.

[@Barryens]

If you want to get disks really hot go and visit Hope Technology. They have all the kit for testing their own brakes. BTW the hill you were using wasn't nearly steep enough to get the rotors hot. You need an extended section >10%, then use one brake to hold a constant speed.

[@peterhehn9511]

140 front & rear on my Ritchey Outback. Looks sweet, have Klamper brakes so no issues! Well proportioned with my 10-42 cassette. I learned how to brake on a Beetle with 4 drum brakes😜

[@gordongilbertson943]

A group of us road across Switzerland in rainy weather, 2016 specialized Diverge/Dolce. My 130lb + 25lb rear panniers rides aggressively and had pristine rotors. I"m 200lb + 10 on the back and 20 in lowriders on the front, I returned with a smoked front rotor. Other lady at just slightly more weight than my wife was one model downspec with a hybrid cable/hydraulic TRP brake, she over braked and boiled the fluid off on both brakes. I upsized my front Rotor when we arrived home, Have not toured on anything like the scale of Switzerland since, but I was happy with the change.

[@slowiss]

Important factors to consider are 'brake fade' with prolonged use and whether emergency braking is limited by other factors such as tyre/road grip rather than disc/brake efficiency.

[@pablodiaz6130]

Less heat, more surface to stop, strong enought, durable, less problems, less noises and lighter. In 2020 tour the france the 1st and 2nd were Tadej and roglic whom used rim brake.

[@Fire-Expert]

If the heat dissipation is so quick as your temperature readings suggested, does the similarity in final temperature not suggest it was related to the final braking effort? In other words the heat from the heavier braking effort earlier in the descent would already have been dissipated

[@847165nw]

I have a rotor that is about 700c--rim brakes are state of the art tech.

[@JamesSmith-qs4hx]

Rim brakes for the win.

[@rider65]

Another silly remark by somebody who is completely uninformed. A 700c rim is not a brake rotor. You're breaking surface is limited to the breaking track not the entire wheel. There is no swept area on a spoked rim. The spokes and the Hub are unable to absorb and dissipate any energy and heat. Whereas a disc rotor it's absolutely designed to do that. And is much more efficient. Physics does not care about your opinion or your feelings the fact is that a disc rotor is far more efficient and has far more performance than any rim brake. If you understood the basics of physics then you wouldn't make such a silly statements. Again the mechanical laws of physics do not care about your opinion or your feelings Fozzie Bear. Now do us a favor and pull your thumb out

[@matthewlewis2072]

...in 1980

[@andredegraaf1643]

Agree. A rim brake is after all a disc brake that uses the rim as the rotor. A rim brake probably never gets to 54C.

[@SeeYouUpTheRoad]

@@andredegraaf1643 I love rim brake! But I am curious for this experiment!

[@pasti67]

Please do more disc brake rotor experiments! 👍

[@peatfitzpatrick4998]

My experience from MTBs is that discs heat up most on steep descents where they are used for an extended period. The descent on the video looked like one where braking was only needed at each corner giving the rotors time to cool down between them

[@Qsi1969]

I agree. A very steep descent at low speed would be a better test. And I would like to know the pad or the caliper temperature as well, as the disc temperature doesn't matter that much in my opinion.

[@ravennexusmh]

my gravel thing has 203/185mm rotors. hope m4 calipers mated to srram apex levers. the lever feel is very light weight and super powerful due to the calipers being bigger surface area then the levers are made for, the pad area being much bigger and obviously the leverage. braking is a no thought thing,

[@PopEmUpChem]

Good to see PT getting some love from the adverts.

[@visjenl]

The weight of the rider and a more controlled scenario of constant breaking would give a better result. Also using a FLIR camera would give a good insight of the heat buildup and heat disapation

[@brianwoods2998]

I don't have the science, but I can tell you my weight plus the weight my propel is 115kg, and washing off speed say from 80km/hr just before I enter a corner can result in being able to smell the brakes pads cooking and once my rotors go blue from the heat it's pretty much game over for them. Unless you like your brakes sounding like the mating call of a Lamma. I'm running 160's front and back and it took a while to master how to wash off speed quickly without cooking them. I have also blown out a front tyre from heat build-up on rim brakes. Yep, I need to lose a few kgs.

[@NeilSnapePhotography]

I switched from the supplied 140mm front disc Ultegra R8000, to the same in 160mm. I need much less force to brake equally, hence your idea of less wear is justified. Where I ride there are often stop lights on hills so coming to a complete stop from 70km/h was taxing on a 140mm front rotor, now seems to be less stressful!

[@yute-hube779]

12.5%

[@rider65]

Much less force is merely a perception, your initial input of Force to the brake lever will be the same no matter what size rotor. Larger rotors can transfer & dissipate thermal energy. There is less fade with larger rotors thereby creating the perception that you need less force on the lever. After initial pull of the lever you need less Force to maintain the same braking power.

[@Digi20]

@@rider65 of course you need less force with a bigger rotor for the same braking power. its simple physics - bigger lever, less force required.

[@JayLato]

Bombed a hill at 113kg / 52mph. My rotors smelled funny and now have a nice blue color to them 🥵

[@rider65]

Probably because you don't have a good understanding of proper breaking technique with regards to lever pressure. Something worth practicing

[@JayLato]

@@rider65 maybe, but it was also the T junction at the bottom of the hill.

[@trent7919]

A big takeaway for me is how quickly they cool down. Good to know that if you are on a long descent, and you feel the brakes are getting too hot, just not braking for a relatively short period of time, of just switching back and forth between applying front and rear braking, can quickly bring the temp down considerably.

[@luke_crip]

You need to test some MTB 220mm rotors

[@billinhouston3291]

That 180 looks sooooo good! Put on a 203!!! When a loaded tandem could easily go 200kg, it makes sense to make larger discs for road groupsets.

[@nsjohnston]

I'm not sure how accurate an IR thermometer will be on a reflective surface.

[@Alex-wg1mb]

Thermal couple will be a greater choice + recording temperature all through descent and plot the graph. True science.

[@EatMyPropwash]

I’d love to see GCN/GTN get an electric motorcycle for the camera crew so we don’t hear the exhaust noises. 👌👍

[@SeeYouUpTheRoad]

Or the riders have to smell the fumes

[@hockysa]

we’ll see bigger disparity if we were operating at the end of the rotors limitations. Within regular operating temps would be marginal gains. But if it’s a heavier rider or a steeper descent the benefit of the larger rotors would be more apparent.

[@humpy125]

The problem with a large rotor is the extra force going through the fork, which could potentially make it fail.

[@charliedillon1400]

They'll just make the fork heavier to compensate. People think the brakes are where the weight gain is but there is also a beefier carbon layup in the disc forks to compensate for the flex at the end where the rotors are.

[@humpy125]

@@charliedillon1400 doesn't help for an existing fork though

[@magnuspym]

"leverage"! Thank you ...makes perfect sense.

[@darrenhitchcox6345]

The other consideration is pad compound. I have recently swapped to ceramic compound on 160mm front and rear and I have best road brakes I have ever use. They are silent and work much better in the wet

[@larrylem3582]

What brand and model?

[@darrenhitchcox6345]

@@larrylem3582 I used Gorilla ceramic pro. I have a Roubaix with Dura Ace 9100 calipers and ultegra 160mm rotors. I also have a Creo and use Hope Rx4+ with same pads. Both sets of brakes are phenomenal.

[@stephensaines7100]

And ditto on rim brakes, very much so.

[@alexanderstephens9368]

I'm surprised the change in modulation between rotor size was not discussed more. It is my understanding that is a big reason for selecting one size rotor over another, since a smaller rotor has more modulation than a larger one - that's the "less input" feeling that was mentioned by Alex. 180mm might not be the best for every situation. In cyclocross, most pros (under 80 kg) use a 140mm to have better modulation and control of the grip their tires have with the ground. The same can be said for an lighter rider on the road too: a larger rotor could be harder to control and make it easier to slide out. SRAM takes this into account in their rotor recommendations chart.

[@Digi20]

From my experience you won't slide out at the front even with a 180 rotor (in the dry, with good tires), the tire always has so much grip that the bike will want to somersault if you overdo it, but not slide. In the rear though there is really no need for more than 140/160mm on a road bike because you simply can't transfer much energy there without locking the wheel.

[@w.trunks2472]

Having crashed and breaking my collarbone descending a hill and using 140 mm discs and 115kg I have little confidence descending hills now so on the brakes a lot more. On my new bike I wanted bigger discs but could only get 140 at time of purchase so am on the brakes a lot more due to confidence. I will definitely put bigger discs on when showing signs of wear because I worry that being a heavier rider the heat builds up quicker as braking more and will get brake fade. But I’m also 101kg now but still worry.

[@archivesburning2071]

Yes, let’s get some glowing rotors please! Great video. I hope you had a great time in Spain!

[@gcntech]

Glad you enjoyed it!

[@ejpauld3207]

#askgcntech. Hey guys (and Manon), do saddles “wear out”? I’ve had the same one on my bike for 5 years/30k+ km, but it looks the same as ever. I’m spending a lot of time this winter on the trainer and I’m finding it quite uncomfortable. Is it the style of riding I’m doing (ie trainer trekking v out on the road), or do I need to spend some money on a new one?

[@wildsurfer12]

13:06 Glowing Rotors sounds like the name of a band. I wonder if they can get a No.1 single one day?

[@DarkstarDarth]

The rear brake is used more consistently than the front especially downhill, washing out the front wheel is the cause of eay more accidents. Bigger thicker roters on rrar is best

[@aerobrain2001]

Definitely do the lathe experiment, because why not 😂😂 also, definitely do comparisons based on rider weight

[@Cs-ng9qx]

How Ollie said ,,we are talking about discbreakrouters,, in the Intro, so sweet

[@ndennan67]

Like rim brakes because it’s a cheaper option but I’ve noticed over the last week due to an awful lot of rain I’ve been breaking much earlier and been a lot more careful than other riders I’ve been cycling with who have disk breaks

[@charliedillon1400]

No big deal. Seriously, how often are you descending, in the rain, under race conditions? Almost never? Then just anticipate early braking like you just described. No need to add a squealing kilo to your bike for the maybe what if moments.

[@SeeYouUpTheRoad]

I think I’m going to steal that from you. “squealing kilo” 😂 and don’t forget the additional cost of buying a disc brake equipped bike

[@bhismarjalilul4410]

🤘🤘 cool bike nice channel watching from Philippines

[@gcntech]

Thanks for watching!

[@jamesmckenzie3532]

I've noticed that 160 mm disc's work better than 140 mm. However a 700mm disc works better. All are aluminum. Carbon doesn't work anywhere near as good. There's nothing on that run needs braking unless you are trying to keep below the speed limit.

[@whirving]

Certainly for mountain and other offroad bikes I will always stay with disc brakes. There is just not substitute in my experience. I rode with rim brakes for YEARS and the first time I rode with a disc it was a revelation. The bike actually stopped in the heavy rain/mud and the front end felt more controllable. Not to mention my hands wouldn't tire after a long technical and cold/wet decent. For road it isn't as important but in the rain coming downhill on a long ride I'm sure it makes a difference.

[@lesleyrobertson]

I use a 180mm rotor on the front of my touring bicycle. The combined weight of the bicycle and me is around 150kg. The 180 gives me a lot more stopping power but it is always the 160 on the rear which wears out first. TRP has a video of glowing rotors with their HY/RD brake.

[@kidkarbon4775]

Shame you did not discuss the impact of the greater leverage from increasing disc size on the hubs and spokes.

[@rider65]

You do not have greater leverage with increase in rotor size that is merely a false narrative. Roller size has nothing to do with leverage and ratio at the master cylinder. The cylinder the hose and the caliper are the same size no matter what rotor is installed. It is merely a perception or a feel that braking force is less. Larger rotors have more swept area and are able to convert and dissipate thermal energy much more efficiently. This results in little to no fade compared to smaller rotors.

[@thomasoei7089]

So, if we make the rotors large enough, they become rim brakes. 😄

[@_Zane__]

Don't give canyon any ideas

[@pgn666]

thats a good one! :D

[@simonvanpraet6543]

I weigh a 100kg and the stopping power is very noticable for a 180mm disc. For comparison i did the test on a roadbike(140,160,180) and my downhill bike(160,180,203), both in Belgium and the alps.

[@ianiscaratti4924]

got 240mm prototype rotors last week and can't wait to test them

[@simonm1447]

Try a Tektro Auriga Twin (a disc brake with 2 calipers on one lever, made for 3 wheel recumbent bikes) with a hub made for a rotor on each side with 220 mm rotors each

[@billkallas1762]

There are only a few locations in the US where it might be advantageous to have a bike that uses disc brakes. I would guess that it is the same in the UK.

[@stephensaines7100]

Yeah, in the sales department.

[@charliedillon1400]

I live and ride in mountainous Colorado and have no desire to use road disc brakes because it's so very rare you're riding in the rain here. Steep descents at high speed are no problemo with good rim brakes, just gotta not ride like a noob.

[@SeeYouUpTheRoad]

Correct Stephen

[@SeeYouUpTheRoad]

@@charliedillon1400 correct Charlie

[@SeeYouUpTheRoad]

Bill you are partially correct. In the middle of the country and place like Florida - sure flat AF. But if you live in either seaboard, western or eastern, we a lot of mountains and rolling terrain. However, even though I climb AND descend 1,000,000 ft per year I would never ride a disc brake bike. I own one full Dura-Ace disc bike and never ride it.

[@Fugitive_8]

Yes, bigger and thicker rotors means more stopping power and more heat dissipation/absorption *(BUT)* for road bikes the maximum rotor size is 160mm if you can get a special adapter you can use 180mm but often being too big for the tire itself the default standard for mtbs are 180mm and for roadies its 140mm people tend to upgrade these and switch to 160mm and for mtbs 203mm rotors

[@1xXNimrodXx1]

now I want a video where you test how much decending is required to delaminate carbon rims with rimbreaks

[@stephensaines7100]

The secret is not to have carbon rims. Gee, d'ya think perhaps a metal layer could be bonded to carbon? Think about it...

[@yonglingng5640]

@@stephensaines7100 It'd be better to have an actual aluminium rim with a carbon fairing (like how HED does it), but at the cost of weight.

[@BLAKEISHart]

put a heavy guy and a light guy on the same rotors and see the difference at the bottom of the hill. make it a big enough hill so you can push the limits of heating up.

[@adversarius]

Thanks, good video, i am thinking about 203mm or 200mm rotors

[@woolychewbakker5277]

Make them really big. In fact, make them so big that they have the same diameter as the wheel. Ah, they’ve already done that and made them a lot lighter and much easier to service - they call them “Rim Brakes” 🎉😂😮😅😊

[@stephensaines7100]

Ah, but you see, these folks worship at the Church of Fiber, and He has deemed eternal complication for straying from the belief in metal. I'm a Born Again Heretic myself, willing to see their church topple and burn along with the canary outfits that are essential to their religion. Even as a Heretic, I'm a firm believer in returning to the roots: Affordable Fun and Health.

[@SeatSniffer2000]

160mm is adequate for a 160kg total system weight on steep 8-10% descents but needs good rotors with good coolings and finned pads.

[@mrmustard1193]

Love your vids

[@gcntech]

Thanks, glad you're enjoying them!

[@stevenpike7530]

Best upgrade by streets (daylight second) for SRAM/Shimano disc is to fit Campagnolo rotors…

[@stevemclean7473]

Can't agree more! So much more feeling and stopping powers with the Campag rotors 👍

[@jrgenstutemeyer9185]

What about different discs and pads, eg. EBC discs and pads (instead of stock ones). Will they also help reduce the stopping distance…???

[@stephensaines7100]

Short answer: Yes, with massive caveats.

[@DenzCasuela]

I really hope I can easily buy those adapters

[@savagepro9060]

Happy New Year you disc-loving For Cars!!!

[@frankeeeej]

All rotor sizes are probably totally safe and functional when it comes to stopping performance, but as a 90ish kg rider myself I'd probably go with a 180 mm just to avoid disc warp/rub. Disc rub is the most disappointing sound and I hate it

[@raff5604]

Happy New Year!!!

[@nceebee6859]

Riding in uncontrolled environments and competing for far less than ego, I'm more than satisfied with disc. Rain, hail or shine.

[@markvanlintel]

#askgcntech Hey Guys. Nice little test. as a bigger rider myself i wonder what the impact on the fork is? Can it take the extra leverage from bigger disks?

[@mriguy3202]

the limiting factor, even with rim brakes, is the 'reverse wheelie' when the rear wheel lifts. Most riders will lift off the front brake when that happens because you're pretty sure to crash when balanced on just the front wheel as you're decelerating. So the fork can probably handle anything the brakes can dish out.

[@WouterZee]

Look like you were testing on Dels Angles near Girona, which is not that steep. Maybe redo the test on Rocacorba....?

[@letheal]

I've got a gravel bike with 160mm rotors and an xc hard tail that's basically set up as a slightly more hardy gravel bike up with 180mm rotors and fast tires. Descending on the 180 rotors feels so much better. The 160s start to noticeably fade on high gradients and I have to be mindful of how much I'm riding them. Both are using shimano resin pads, and both rotors are shimano rotors. I'm 88kg. if I was 60kg I'm sure the 160s would feel fine :D

[@TecraX2]

Swapped from resin to metallic pads while keeping the 160mm diameter, the difference is like night and day!

[@roypennock8046]

Just a heads up that IR thermometers don't give accurate readings on shiny/reflective surfaces like brake rotors... They emit less IR radiation relative to their true temperature than do other surfaces... The relative readings between the rotor sizes would still be consistent but the absolute temperature readings would skew lower than actual.

[@gagann1091]

What is the difference between Shimano RT-MT800 and RT-CL800 as they both seem to fall under the Ultegra category.

[@tomcrigstar]

Makes sense that all the rotors reached the same peak temperature. regardless of the rotor size the brake is transferring your momentum into heat so if you are braking from the same speed and weight the same then the same amount of heat will be generated. the advantage as you discovered is the rate that the rotors cool, allowing you to brake again sooner with a larger rotor. this is why you don't drag brakes, but gently "pulse" them, brake hard for a few seconds then off for a few seconds repeated on steep descents.

[@rider65]

Finally somebody who understands physics and thermodynamics! 😄👍

[@stephensaines7100]

Close, but there's a problem with what you claim for 'pulsing' (Yes it improves things, but not for the reason you state). If the relationship between heat generated (express it in Watts...kW) is the same as energy lost from braking, then pulsed or not, for the same braking power, you must dissipate the same amount of energy (and Watts is a linear and used way to express this, as it is for electricity to heat in a resistive element). The advantages of pulsing are manifest in a different way that I won't go into here, but pulsing certainly does work advantageously in many ways...

[@ltrtg13]

In my opinion. Which is the most important opinion. The Only good rim brakes. Have been melted down and recycled into baked been tins. I have always had a passionate hatred of rim brakes. Even that substandard tat was the only brakes you could get. As for disc size. Both my 27.5" full sus and my 29er mountain bikes have 203mm front and 180mm rear. Both have 4 pot calipers. As my hybrid on had 32mm tyres. Not the 2.3" on the full sus and 2.6" on the hard tail. My hybrid only has 180mm front and 160 rear. With 2 pot calipers.

[@Mclovinthedank]

I have a 180 in the front on my gravel bike. Mechanical disc brakes, When I had the 160 rotor only half of the pad would contact my rotor.

[@larrylem3582]

I'd like to see a test on a 15% downhill with sharp turns where you have to repeatedly brake hard with little time for brakes to cool. Doesn't even need to be a heavy rider but that would make it a tougher test. I get brake fade with a front 180 mm ice rotor on my local hill.

[@SeeYouUpTheRoad]

Ha ha hello Larry I know you’re describing a local mountain (Baldy ski lifts) to us but that’s not what the rest world has available to them. We are spoiled in Southern California with our mountains. If they performed the test as you outlined there would be barely 5% of the cycling population that would encounter that scenario

[@larrylem3582]

@@SeeYouUpTheRoad haha, I was actually thinking of Crownview Dr in Palos Verdes, but Baldy descent from the ski lift parking lot is nasty, too. It's amazing how quickly you pick up speed before hitting the brakes at Mankar Flat.

[@SeeYouUpTheRoad]

@@larrylem3582 I’ll have to come up and climb that one sounds fun!

[@neelsahay5227]

you guys should do a bike check of your camera motos, that would be really interesting.

[@ericsleeth]

the part where this test fell short was not measuring the rear rotors. On a long decent, you tend to hold the rear.

[@sepg5084]

"better"? At what metric? "Small" discs have enough leverage to lock the brakes. Bigger discs can carry more heat because it has more material and can dissipate it easier by having more surface area. The same is true for car brakes: big brake kits are used to stave off brake fade not for stopping power, stock brakes are sized to be able to lock the brakes (hence why ABS is needed).

[@JoaoPedro-en7kz]

Force required at the lever and modulation. Softer levers are way better to use and allow way more control, allowing to get closer to the locking up point without crossing it.

[@leisterj]

I would like to see a 15-20% decend with 250lb rider. I agree that for light/ moderate riders going down moderate declines, it doesn't matter. But i recently did the tripple bypass in colorado. And 20 mile 10-15% declines at 30-40 and sometimes 50mph decents scared me to death. What would also be nice is to know how things go bad. Do the brakes fade. Do they make sounds then warp. Or do they break and bind. I mean, if you have to push them, then they will rub a little thats one thing. If they lock up at 40mph on the side of a mountain thats another story.

[@twatts4436]

Even as a light-ish rider, I use 160mm front and rear for two reasons. 1) easy to swap wheels between bikes by having consistent across all bikes. 2) reduced leverage. I've not got massively strong hands sue to injury. If I. Can reduce the strength needed to achieve adequate braking.