Intial thoughts on road discs -- Specialized Tarmac

[Keith A]

On my recent trip to Utah, I rented a Specialized Tarmac from Bountiful Bicycle. I was a little nervous about riding a completely unfamiliar bike down the canyon roads at 40+ mph, but the Tarmac handling was just fine and very predictable. Overall this was a completely capable bike, but I'm not a fan of the owner of this company.

The one thing that I really didn't like about the bike was an issue with the front rotor. The first time I had to brake heavily going downhill into a corner, when I released the brake lever there was pinging coming from the front wheel. It sounded just like a broken spoke, so I stopped to see what was going on. There wasn't anything obviously wrong, so I hopped back on and continued to descend down the mountain. But every time after heavy braking, the noise would return for a short period of time. It was obvious there was an issue with the front brake and it was a bit unnerving not knowing what was going on.

When I returned the bike to shop and explained the problem, their was response was...yes they were aware of this issue and the disc will warp when heated. I thought the best thing about road disks was being able to go downhill and not worry about overheating, but yet this particular setup couldn't handle the heat.

BTW, I really liked the handlebars on this bike. Not sure the exact model (Specialized), but I thought the shape was very good.

[KidWok]

hmm...interesting...never had any overheating issues with my 622mm rotors.

Tai

[2LeftCleats]

I've been on this bike for the last 6 months and really like the ride/handling. I've experienced the same front disc issue with hard or prolonged braking. My googling suggests it's common. The reasons postulated are temporary heat-related disc warping or overheating brake fluid causing the pistons to protrude farther. A bit annoying and frustrating. I chose discs because the wheels are carbon and hills here are steep and sometimes wet. I'm happy with how they perform otherwise and if anyone has a fix, please post. Thanks.

[Keith A]

hmm...interesting...never had any overheating issues with my 622mm rotors.

TaiI didn't even feel like I was braking very hard.

The other thing I wanted to mentioned...and this is completely a personal opinion, but I've never been a fan of the matte finish and after riding a bike with this type of finish and cleaning it up afterwards, I'm still not a fan of the matte finish.

[weisan]

keith pal, was it the hover bar that you experienced?
https://www.specialized.com/us/en/equipment/components/hover-expert-alloy-handlebars-15mm-rise/118174

[KidWok]

Utah also isn't that hot. Lived there when I was a kid. Begs the question: How would these brakes handle 120+ degree heat radiating off blacktop?

Let's ask this guy what he thinks:

http://autobus.cyclingnews.com/photos/2003/tour03/stage9/olympia/S-CADUTA-BELOKI-.jpg

Tai

[Mark McM]

In my opinion, many, if not most, road disc brake bikes use undersized rotors. There seems to be a mistaken impression that road bikes can use smaller rotors than MTBs. Just the opposite is the case: Road bikes travel at higher energies (speeds) and can brake with higher torque (better tire traction) than MTBs, so road bikes can generate far more heat. Road bikes should really be using larger rotors than MTBs.

If you look at the motorcycle world, you'll see that most road motorcycles (particularly racing motorcycles) use larger disc rotors than off-road motorcycles - especially on the front. Why do people believe that road bicycles can get away with smaller rotors than MTBs?

[oldpotatoe]

In my opinion, many, if not most, road disc brake bikes use undersized rotors. There seems to be a mistaken impression that road bikes can use smaller rotors than MTBs. Just the opposite is the case: Road bikes travel at higher energies (speeds) and can brake with higher torque (better tire traction) than MTBs, so road bikes can generate far more heat. Road bikes should really be using larger rotors than MTBs.

If you look at the motorcycle world, you'll see that most road motorcycles (particularly racing motorcycles) use larger disc rotors than off-road motorcycles - especially on the front. Why do people believe that road bicycles can get away with smaller rotors than MTBs?

All true sir but the marketeers have an input and increased weight is the bogey-man of road discs. Road discs frames/forks and hubs are already heavier but unfortunately weight-less of it, drives this train even if it does translate into poorer performance. Seems Campag's new discs have used heavier, more durable materials....like all steel rotor.

[MaraudingWalrus]

hmm...interesting...never had any overheating issues with my 622mm rotors.

Tai

So, there are what, about six or seven examples people point to on the internet about over heating discs to complete failure compared to how many examples of people completely cooking rim brakes? :confused:

A very small number of issues with discs doesn't negate the overwhelming, objective facts that disc brakes do actually perform better at stopping a thing, especially when the alternative being clung to has the issue more so.

People can argue that they don't want or need them, that's fine. But I do not understand the arguing with objective, widely accepted facts

I'm a huge fat lump of a human, and would I want a single 140mm rotor, without any cooling technology on the rotor or pad to try and stop me at 187mph in before the road leads to a brick wall of spikes? No, I wouldn't. But a Paul Racer - that looks so classic and beautiful - on a carbon rim wouldn't stop me either.

Discs have their limitations and failure points, nobody would argue against that...they're just a bit further than the limits of rim brakes.

All things assuming competent operators...

[KidWok]

A very small number of issues with discs doesn't negate the overwhelming, objective facts that disc brakes do actually perform better at stopping a thing, especially when the alternative being clung to has the issue more so.

But a Paul Racer - that looks so classic and beautiful - on a carbon rim wouldn't stop me either.

Discs have their limitations and failure points, nobody would argue against that...they're just a bit further than the limits of rim brakes.



Okay...let me rephrase that. My 622mm ALUMINUM rims using well-regarded dual caliper DURA-ACE (or comparable) brakes and KOOL STOP SALMON (or comparable) brake pads have never had any overheating issues. I'll also add that rims are covered in a nice rubbery material that won't cut flesh.

If you add carbon rims and other brakes that might not stop as well into the argument, well of course disc brakes work "better".

ALL braking systems already have a pretty well established limitation...the contact patch of the tire touching the surface. I've had no problems getting tires to lock up and skid using dual caliper, canti, mini-v, v, cable actuated, and hydraulic discs.

But the argument I'm hinting at really has nothing to do with the performance of the brakes. It has everything to do with bike industry leaning heavy on perceived obsolescence (and compulsory obsolescence as they stop supporting older standards they've conjured) to sell us stuff that doesn't work that much better.

Tai

[FlashUNC]

On my recent trip to Utah, I rented a Specialized Tarmac from Bountiful Bicycle. I was a little nervous about riding a completely unfamiliar bike down the canyon roads at 40+ mph, but the Tarmac handling was just fine and very predictable. Overall this was a completely capable bike, but I'm not a fan of the owner of this company.

The one thing that I really didn't like about the bike was an issue with the front rotor. The first time I had to brake heavily going downhill into a corner, when I released the brake lever there was pinging coming from the front wheel. It sounded just like a broken spoke, so I stopped to see what was going on. There wasn't anything obviously wrong, so I hopped back on and continued to descend down the mountain. But every time after heavy braking, the noise would return for a short period of time. It was obvious there was an issue with the front brake and it was a bit unnerving not knowing what was going on.

When I returned the bike to shop and explained the problem, their was response was...yes they were aware of this issue and the disc will warp when heated. I thought the best thing about road disks was being able to go downhill and not worry about overheating, but yet this particular setup couldn't handle the heat.

BTW, I really liked the handlebars on this bike. Not sure the exact model (Specialized), but I thought the shape was very good.

The overheating issue to worry about is boiling fluid in your line, not the pinging of a rotor. If the lever went soft after hard braking or you lost brakes entirely, that's an issue with heat dissipation. A pinging rotor? Ain't no big thing.

Fwiw I've seen guys descend some pretty hairy, steep, long stuff on 140 and 160 rotors with no problems. Eating through organic pads? Yeah, totally. But too small a rotor? I dunno about that one.

As somebody who rides both on a regular basis now, with a hydro groad bike and a caliper road bike, hands down the hydro discs are better.

[Keith A]

keith pal, was it the hover bar that you experienced?
https://www.specialized.com/us/en/equipment/components/hover-expert-alloy-handlebars-15mm-rise/118174Weisan pal, I think it was these...
https://www.specialized.com/us/en/equipment/components/expert-alloy-shallow-bend-handlebar/116799

Nothing fancy, just liked the shape.

https://1554652485.rsc.cdn77.org/i/p/8/3/147338_00_c.jpg

[cachagua]

The argument I'm hinting at really has nothing to do with the performance of the brakes. It has everything to do with bike industry [trying] to sell us stuff that doesn't work that much better...

Nicely put. That is the heart of my irritation right there: every couple months there's a GAME-CHANGER!! A revolutionary new breakthrough that turns the whole sport on its head and transforms your riding experience into something you've never imagined before! And when you manage to clear your vision and look around, everything's still... pretty much the same as before. Only it costs twice as much, lasts half as long, and you can't fix it when it goes wrong.

That's marketing. Always has been, always will be. Three cheers for free enterprise. But what would reassure me is if people were a little more resistant to it. The idiotic nonsense that the bike-buying public uncritically gobbles up is just embarrassing.

[p nut]

As somebody who rides both on a regular basis now, with a hydro groad bike and a caliper road bike, hands down the hydro discs are better.

My experience as well. Even the now archaic BB7's on 160/140, I can brake much harder from the hoods and they don't fade as easy as rim brakes. Shimano hydraulics are even better.

That said, I am in the process of building up a dirt cruiser with v-brakes. With good pads (KS), they will work well enough.

[dustyrider]

Every mtb I've owned gets a 203mm rotor on the front and either a 160 or 180 on the rear. I'm sure road will follow along eventually!

[donevwil]

Anyone know why 203mm? 140mm, 160mm, 180mm & 8" ??

[p nut]

In my opinion, many, if not most, road disc brake bikes use undersized rotors. There seems to be a mistaken impression that road bikes can use smaller rotors than MTBs. Just the opposite is the case: Road bikes travel at higher energies (speeds) and can brake with higher torque (better tire traction) than MTBs, so road bikes can generate far more heat. Road bikes should really be using larger rotors than MTBs.

If you look at the motorcycle world, you'll see that most road motorcycles (particularly racing motorcycles) use larger disc rotors than off-road motorcycles - especially on the front. Why do people believe that road bicycles can get away with smaller rotors than MTBs?

I brake much harder on my MTB than road bike. Road descents usually aren't littered with switchbacks, obstacles, etc. to warrant the braking power from big rotors. On most of the canyon road descents around here, it's usually just tapping the brakes a few times. Where on a MTB ride, brakes are used much more aggressively. I like the better modulation from a smaller rotor on a road bike as well.

[dustyrider]

Anyone know why 203mm? 140mm, 160mm, 180mm & 8" ??

Not sure why the 203 and not 200. I've also been out of the mtb game for quite a few years now. It may be down to 200... I know my 26" wheeled 9 speed hardtail has a 203 on the front. Through axles/dropout spacing and wheel size made me lose most of my interest, since I don't typically buy complete bikes and try to reuse parts as much as possible.

[Kirk007]

We have an old 84 Datsun pick up truck: two wheel drive, drum rear brake, tin car body, no airbags, yada yada. It has always gotten me where I want to go when I venture out in it. I'm still alive. Do I prefer a four wheel drive with disc brakes, crumple zones etc, particularly when conditions are crappy out. You bet. Better tool for the job in those circumstances, no question.

I've ridden bikes since 1964. Coaster brakes to start, then centerpull, then sidepull, cantis, v-brakes, cable actuated discs and hydro discs. I'm still alive. Never had a serious accident from not being able to stop. Are hydro brakes better on wet, steep roads - yes. Just as good if not better elsewhere - yes. I like to bomb descents and carve turns. Do discs let me feel more confident braking later and keep more speed, yes. But did I survive descending the Alp d'Huez, Madeleine etc. with Campy record side pull - yep.

It's not just marketing and its not just planned obsolescence. Technology marches on. You may not need it; you may not want it but it just may be better. Who here still uses a Motorola mobile phone that resembled a world war II walkie talkie (what a name by the way - walkie talkie).

[David Kirk]

I've got $100 that says it was not related directly to the brakes nor to heat.

If it made the noise just after releasing the brake and it sounded like spokes plinking it was most likely spokes plinking. When you hit the brakes hard the rim winds up slightly relative to the hub and the "pulling" spokes and the "drag" spokes will rub across each other where they cross in the process. When you release the brake torque from the system the spoke tension will equalize and the rim will move back relative to the hub and you will get that spoke plinking noise you heard.

This means that the wheel either didn't have enough spokes for the purpose or that the spokes were not properly tensioned....or both. This is not at all uncommon FWIW.

This has zero to do with heat, or rotor size and everything to do with a torque being applied to the hub that then needs to be transferred to the rim. Powerful sprinters will get the same thing on their rear wheel after a massive effort sprint for just same but opposite reason.....torque is being applied to the hub and has to transfer from the hub to the rim through the spokes. Rim brakes don't cause this because they don't put a twisting load on the wheel.

dave

[2LeftCleats]

If this is spoke noise, how long should it last? The noise on mine lasts 15-20 sec. it also is more of a scraping sound that is metronomic in time with the wheel spin. To me it sounds a bit like an out-of-true wheel rubbing a rim break.

[David Kirk]

If this is spoke noise, how long should it last? The noise on mine lasts 15-20 sec. it also is more of a scraping sound that is metronomic in time with the wheel spin. To me it sounds a bit like an out-of-true wheel rubbing a rim break.

If you brake hard and long and get the rotor hot it can come out of true and make the noise you are speaking of. This will typically last for a very short time until the heat disapates and the rotor goes back to true.

This is different than the spoke noise that the OP was talking about.

You can make the spoke noise happen just by standing on the floor behind the bike and putting your chest on the seat....now squeeze the brake very hard and push forward very hard. This will wind up the front wheel. Now let off and you'll hear the spoke go back to normal with the plinking noise as a result.

dave

[Keith A]

Dave -- This was a weird noise to be associated with an out of true rotor from the heat. It sounded just like there was something hitting the spokes, but as soon as the rotor cooled, the sound was gone.

[David Kirk]

Dave -- This was a weird noise to be associated with an out of true rotor from the heat. It sounded just like there was something hitting the spokes, but as soon as the rotor cooled, the sound was gone.

Cool - my bad.

dave

[Mark McM]

I brake much harder on my MTB than road bike. Road descents usually aren't littered with switchbacks, obstacles, etc. to warrant the braking power from big rotors. On most of the canyon road descents around here, it's usually just tapping the brakes a few times. Where on a MTB ride, brakes are used much more aggressively. I like the better modulation from a smaller rotor on a road bike as well.

This is an illustration of the erroneous thinking that leads people to believe that road bikes can use smaller rotors.

When riding in a straight line off-road on an MTB, have you ever braked hard enough to skid the front wheel? I have. This shows that the limit of brake force off-road is tire traction. When riding in a straight line on (clean) pavement on a road bike, have you ever braked hard enought to skid the front wheel? No you have not. I have tried many times, and never been able to - before the front wheel will skid, the rear wheel lifts off the ground and the bike would do an endo if I did not reduce braking. This shows that you can brake much harder on a road bike, because the tire traction is much greater.

Although you may brake more often on an MTB, that doesn't mean that you generate more heat. The heat of braking isn't simply linear with speed, it is proportional to the square of speed. For example, if you brake from 45 mph to 35 mph, you generate twice as much heat as you do when braking from 25 mph to 15 mph, even though the speed change (10 mph) is the same. Since typical road speeds are higher than MTB speeds, braking heat will be much larger on the road.

[Mark McM]

If it made the noise just after releasing the brake and it sounded like spokes plinking it was most likely spokes plinking. When you hit the brakes hard the rim winds up slightly relative to the hub and the "pulling" spokes and the "drag" spokes will rub across each other where they cross in the process. When you release the brake torque from the system the spoke tension will equalize and the rim will move back relative to the hub and you will get that spoke plinking noise you heard.

Have you ever measured the spoke loads from disc brakes? If you did, I think you'll find that they are lower than you might think. There is no appreciable "wind-up" of a cross-laced wheel due to torque loads. This was covered in The Bicycle Wheel (http://caravan.hobby.ru/materiel/Bicycle_Wheel_-_Jobst_Brandt.pdf) by Jobst brandt, which includes FEM analyses of different loading showing their relative magnitudes.

The reason that disc brake spoke loading is relatively small is because torque loads are distributed uniformly to all the cross-laced spokes. In contrast, vertical (weight bearing) loads are concentrated on just a few spokes in the LAZ (Load Affected Zone) near the ground contact point. The peak spoke loads due to vertical loads are much higher than the spoke loads due to braking torque.

As it turns out, there actually can be large spoke loads during braking - but these spoke loads are primarily due to the weight shift caused by braking, not the wheel torque. At the maximum braking limit, the forward weight shift can cause the vertical load on the front wheel to increase by 250% - 300%.

I've only used disc brakes on an MTB, but I've never heard the spoke sounds you describe. But if they are happening, they are more likely due to the huge weight shifts that braking can induce.

[MikeD]

Although you may brake more often on an MTB, that doesn't mean that you generate more heat. The heat of braking isn't simply linear with speed, it is proportional to the square of speed. For example, if you brake from 45 mph to 35 mph, you generate twice as much heat as you do when braking from 25 mph to 15 mph, even though the speed change (10 mph) is the same. Since typical road speeds are higher than MTB speeds, braking heat will be much larger on the road.


Speeds on the road are faster and thus more convective cooling on the rotors. Hills are steeper off road and brakes are held on for much longer instead of short intervals of braking while on road. But that being said, I think that 160mm rotors should be used on a road bike, at least on the front.

[Mark McM]

Speeds on the road are faster and thus more convective cooling on the rotors.

That is true. But brake heat increases with the square of speed, while convective cooling increases less than proportionally with speed (from http://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html):

http://docs.engineeringtoolbox.com/documents/430/air_heat_transfer_coefficient.png

So, ratio of heating to cooling is much higher on the road.

Hills are steeper off road and brakes are held on for much longer instead of short intervals of braking while on road.

Yes, but the brakes are typically held on at much lower speeds, so there may be much less energy transfer (energy transfer is proportional to the square of speed). Also, other drag forces (especially rolling resistance & suspension losses) are higher off-road, so braking energy needs to be less.

This is totally anecdotal, but I've heard of far more braking heat issues (disc brake failures or tires blowing off) on road descents than off-road descents.

[dgauthier]

Facinating thread. Whether the sounds came from a warped rotor or spoke windup, it's interesting to hear about new experiences with road disc brakes.

I would encourage people not to get so opinionated about rim vs. disc brakes. With the mantras of low overall bike weight and radially laced, low spoke count wheels so thoroughly baked into road biking, rim brakes will never go away. Disc brakes will simply be an *option*. If all your riding is in the flats, you'll choose rim brakes and your brakes will be simpler and cheaper and your bike lighter. If your riding involves steep climbs and fast descents, you'll be *crazy* not to choose disc brakes, even though that means your brakes will be more complex and expensive and your bike heavier.

Carbon frames and components didn't eliminate steel and alloy. Disc brakes won't eliminate rim brakes.

[Red Tornado]

In my opinion, many, if not most, road disc brake bikes use undersized rotors. There seems to be a mistaken impression that road bikes can use smaller rotors than MTBs. Just the opposite is the case: Road bikes travel at higher energies (speeds) and can brake with higher torque (better tire traction) than MTBs, so road bikes can generate far more heat. Road bikes should really be using larger rotors than MTBs.

If you look at the motorcycle world, you'll see that most road motorcycles (particularly racing motorcycles) use larger disc rotors than off-road motorcycles - especially on the front. Why do people believe that road bicycles can get away with smaller rotors than MTBs?

There are a lot of motorcycles that have two disc brakes in front, but that would add more weight = bad. I agree with larger rotors on road bikes.

[Mark McM]

Carbon frames and components didn't eliminate steel and alloy. Disc brakes won't eliminate rim brakes.

You're right - but carbon frames have largely marginalized steel and alloy frames (at least at the high end). This reduces choices and options, and raises costs, for those who wish to choose steel or alloy.

Likewise, if disc brakes gain large popularity, it may marginalize rim brakes, reducing options and raising prices for those that want to use them.

In this way, it is not true to say, "my choice to use disc brakes doesn't affect those who want to use rim brakes," because the way the market works, it does in fact reduce the choices left for those who want to use rim brakes.

[benb]

I just went to the Specialized site and the first Tarmac with discs I found had a 160mm rotor in the front.

I've never run anything bigger than 160mm on my MTB.. never even come close to fading any set of hydro discs on my MTB, and I have actually taken it up and down some of the big New England paved mountain climbs like Ascutney, Pack Monadnock, stuff like that where the average grade is > 10% for miles and there are lots of dangerous switchbacks. (I often did this just cause it was the easiest thing to do when I wanted the low gearing and/or I wanted the safety for the descent due to bad weather.) I have just about never been able to go down any of those roads on a rim brake bike without managing significant brake fade and often having to let air out of my tires. (Maybe once when there was still snow on the ground) One of the stupidest things I ever did was climb Mt. Caddilac in Acadia NP with a front disc pad that was almost toast on my MTB... it basically gave out the ghost on the way up, and I kept climbing. I came back down on the rear brake alone and it was more than enough to come down without any fade.

It sure sounds like the pinging sound spokes make like Dave K mentioned. I get that on my MTB, both under braking loads and much more frequently under hard climbing offroad on very steep grades where I'm putting out a lot of power in a low gear.

I have taken my MTB in to more than one shop to try and get the spoke pinging addressed... In my experience this is beyond the technical capabilities of a lot of shops/employees. I could very easily see this issue not being the disc and a semi-clueless employee at the rental shop thinks it is and keeps spreading a story. Since it seemingly requires a skilled wheel smith to fix and a lot of shops don't often have someone like that, AND it's a rental bike, it's easy see how this wouldn't get fixed and the guy at the shop might incorrectly blame it on the brake.

In my case (once I found a good mechanic) it's spokes that are subtly unevenly tensioned.. my wheels are on their dying gasp. I can't really get it fixed cause some of the nipples are frozen/corroded. (Wish it had brass nipples) If/When the wheel goes out of true/dish/round enough to matter they're going to have to be replaced.

I have been underwhelmed with the performance of the road hydro disc setups I tried on test rides. I would support the idea of upsizing the rotor compared to MTBs. The Motorcycle example is really compelling.. High performance motos have almost as much front brake as small cars that weight 10x what the motorcycle does due to having 2 huge discs up front.

[Kirk007]

You're right - but carbon frames have largely marginalized steel and alloy frames (at least at the high end). This reduces choices and options, and raises costs, for those who wish to choose steel or alloy.



Only at the mass production level. I'd submit that a Pegoretti is as fine a high end road bike as has ever been produced with steel, with stock sizes (and there are others obviously of this character) and these frames are less expensive that "high end" carbon. Ditto with Gaulzetti and aluminum. Ditto with all the frame builders who participate here like Dave Kirk. Bespoke in the same price range as a stock S Roubaix frame. Fewer options? Perhaps, but not lesser. And I doubt the big three component makers will ever not offer a high end rim brake (not to mention that these components will last for a very long time).

[Charles M]

On my recent trip to Utah, I rented a Specialized Tarmac from Bountiful Bicycle. I was a little nervous about riding a completely unfamiliar bike down the canyon roads at 40+ mph, but the Tarmac handling was just fine and very predictable. Overall this was a completely capable bike, but I'm not a fan of the owner of this company.

The one thing that I really didn't like about the bike was an issue with the front rotor. The first time I had to brake heavily going downhill into a corner, when I released the brake lever there was pinging coming from the front wheel. It sounded just like a broken spoke, so I stopped to see what was going on. There wasn't anything obviously wrong, so I hopped back on and continued to descend down the mountain. But every time after heavy braking, the noise would return for a short period of time. It was obvious there was an issue with the front brake and it was a bit unnerving not knowing what was going on.

When I returned the bike to shop and explained the problem, their was response was...yes they were aware of this issue and the disc will warp when heated. I thought the best thing about road disks was being able to go downhill and not worry about overheating, but yet this particular setup couldn't handle the heat.

BTW, I really liked the handlebars on this bike. Not sure the exact model (Specialized), but I thought the shape was very good.



The shop should true the rotors once the bikes been used a bit...

You and I are different size, but "warping" isn't as big a deal as simply not building it right in the first place.

I have 4 disc bikes, and they've all come off south mountain in 100+ degrees with scorching braking and I have no rub... none.

[Keith A]

The shop should true the rotors once the bikes been used a bit...

You and I are different size, but "warping" isn't as big a deal as simply not building it right in the first place.

I have 4 disc bikes, and they've all come off south mountain in 100+ degrees with scorching braking and I have no rub... none.What is interesting was that I wasn't even braking that hard...and I'm not a big guy either, only 155 lbs.

[benb]

One thing I noticed looking at Specialized's pictures of the Tarmac is the rotors are machined away to almost nothing, probably in a weight weenie effort.

While you want some of the material cut away for cooling if you cut away enough of it you get to a point where there is not enough mass in the rotor to absorb much heat and you probably hit diminishing returns.

If you cut away enough of the "swept area" you also lose power... road discs seem to have the largest portion of swept area cut away of any discs I've seen. The SRAM ones look ridiculous, the Shimano ones look better but they've still cut away way more of the area than MTB brakes, Moto brakes, or car brakes ever seem to.

[zap]

edit

...yes they were aware of this issue and the disc will warp when heated. I thought the best thing about road disks was being able to go downhill and not worry about overheating, but yet this particular setup couldn't handle the heat.


Our disc equipped tandem will do this. The 203 ICE rotor will get out of true after hitting the brakes hard (say for a ss) at a bottom of a steep hill. Tink tink for 1-2 miles until the disc cools and contract enough to clear the pads.

I never worried about overheating the ice discs.......no al alloy has ozzed out.

[dgauthier]

You're right - but carbon frames have largely marginalized steel and alloy frames (at least at the high end). This reduces choices and options, and raises costs, for those who wish to choose steel or alloy.

Likewise, if disc brakes gain large popularity, it may marginalize rim brakes, reducing options and raising prices for those that want to use them.

In this way, it is not true to say, "my choice to use disc brakes doesn't affect those who want to use rim brakes," because the way the market works, it does in fact reduce the choices left for those who want to use rim brakes.

But carbon frames are lighter too. There's no performance downside to carbon. Part of my point was disc brakes are heavier, and require heavier and less aerodynamic cross-laced wheels. They'll never be the slam dunk carbon was, and even then carbon didn't obliterate everything else.

[PeregrineA1]

WRT to the pinging after use. Are the rotor and hat (the portion which affixes to the hub) two pieces?

If so they may expand and contract differentially. My Hope rotors on my last MTB pinged and popped after anything more than mild use.

[rkhatibi]

High performance motos have almost as much front brake as small cars that weight 10x what the motorcycle does due to having 2 huge discs up front.

Hard to compare both on total weight. A motorcycle will derive 95-100% of its braking from the front wheel. Also needs to dissipate the heat in a much smaller disc. Motorcycle discs are around 1.5 kg each vs 9 kg in a car. Assuming a car brakes evenly after the initial bite that's 1400 kg over 36kg of discs vs 300kg (rider included) with 3kg in a dual front brake system.

[Mark McM]

Hard to compare both on total weight. A motorcycle will derive 95-100% of its braking from the front wheel. Also needs to dissipate the heat in a much smaller disc. Motorcycle discs are around 1.5 kg each vs 9 kg in a car. Assuming a car brakes evenly after the initial bite that's 1400 kg over 36kg of discs vs 300kg (rider included) with 3kg in a dual front brake system.

Likewise, a bicycle also derives the majority of its braking with the front wheel, because like a motorcycle, a bicycle has a relatively high CG and short wheelbase. But a bicycle might have a total mass of 80 kg, but a total rotor mass of only 0.1 kg. True, a bicycle typically doesn't go as fast as a motorcycle, but while a motorcycle's rotors might be 1% of its total mass, a bicycle's front rotor are barely more than 0.1% of its total mass. Compared to its mass, the bicycle's disc brake rotors are undersized.

[benb]

But carbon frames are lighter too. There's no performance downside to carbon. Part of my point was disc brakes are heavier, and require heavier and less aerodynamic cross-laced wheels. They'll never be the slam dunk carbon was, and even then carbon didn't obliterate everything else.

The weight of the disc setups is a total non-factor to the manufacturers once carbon frames are a given for racing. Their top tier customers are having to put ballast in the bikes right now with the rim brakes to make the minimum weight requirement from the UCI... every year they are probably having to add more ballast as they keep finding ways to make everything lighter. There is plenty of weight available on carbon frames to give up a few grams for disc brakes.

That AFAICT is totally different than steel frames, maybe not as much for aluminum. The weight delta between the carbon frame and the steel frame is almost always bigger than delta between disc brake setups and rim brake setups isn't it?

[Mark McM]

The weight of the disc setups is a total non-factor to the manufacturers once carbon frames are a given for racing. Their top tier customers are having to put ballast in the bikes right now with the rim brakes to make the minimum weight requirement from the UCI... every year they are probably having to add more ballast as they keep finding ways to make everything lighter. There is plenty of weight available on carbon frames to give up a few grams for disc brakes.

Currently, this is often the case. However, there have been rumors that the UCI may lift the minimum weight limit, perhaps by replacing it with more directly bicycle strength testing.

That AFAICT is totally different than steel frames, maybe not as much for aluminum. The weight delta between the carbon frame and the steel frame is almost always bigger than delta between disc brake setups and rim brake setups isn't it?

It's about a wash. Although a bit of an apples-and-oranges comparison, current high end carbon frames weights are in the region of 2 to 2 1/2 lb, while high end steel frames can be in the 3 to 3 1/2 lb. range, or about a 1 lb. difference. It is generally agreed that disc brakes add about 1 lb. to a bike (compared to rim brakes), so steel bike with rim brakes can weight just about the same as a carbon bike with disc brakes.