Comparing the braking needs of a 400-800lb motorcycle that has a 50,000-150,000 watt motor to a 20lb bicycle with a +/- 300 watt "motor" is kinda ridiculous. Kinetic energy increases with the square of speed. Motorcycles can go much faster than bicycles, and can power themselves to high speeds even on flats or up hills. Even a moderately powered motorcycle can tango with 130 mph, while 1-Liter Super Sports are capable of 180+.

A sport bike's brakes a built to withstand the repeated heavy braking one might encounter on a race track. A mid-level cafe racer (something like a Ninja 650) would need to convert something in the range of 2000 kilojoules of kinetic energy to heat every two minutes lapping Laguna Seca. Even with a clydesdale rider up top, a 20 lb bicycle braking from 50 to 10 mph for a hairpin is a ~25kj event. Without 50-150 kilowatts of power to re-accelerate, a bicycle isn't going to get to the next extreme braking event nearly as soon as a motorcycle, giving the brake rotors more time to cool. How many times in two minutes are you likely to go from 50-10 mph, even in the most technical descent? Three times, maybe?

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"They're made of latex, not nitroglycerin"

Here's just one example of the type of descent I have around me. This is nearly 7 miles of hairpins, mostly 6-10% grade. There's actually a LOT of accelerating/decelerating on that descent, and it's by no means the longest one around here. The climb from San Jose to the the Lick Observatory on Mt. Hamilton is 19 miles of hairpins. Being able to modulate the brakes effectively going into corners and not have your brakes fade on you is just as critical on a bike as on a motorcycle.

Since most of my outdoor riding involves this sort of climbing/descending to some degree, I do most of my offseason riding on the C5, but as i get into the final 12 weeks before my A race and I'm on the tri bike exclusively, I end up severely limited on the routes I can ride if I have to stick to flatter ground.

Right and your unique circumstances represent probably less than 1% of the riding population.

Once I realized I do 90% of my rides indoors, almost never (intentionally) bike in rain, and don’t live in an area like you described I found myself wondering why I would need disc brakes even assuming for the sake of argument they offer better performance. My circumstances are probably far more common than yours.

Good braking isn't just for technical descending.

let me give you another real-world example. You're cruising along a dead-flat suburban area and a car pulls out of a driveway in front of you or a driver makes a left turn in front of you. With good brakes that I can modulate well, I can make a solid panic stop competently. On the P4 it's probably 50/50 that I'll lock up the brakes and eat shit and end up under the car. That's a real situation that 100% of riders face. The few times that I almost died on my motorcycle were all from people making left turns in front of me.

Agreed. That is more like what I may face. Brakes don’t matter until they do. I weighed all of that and I’m confident in the braking performance I will get from Omega X with kool stop salmon pads and HED Blacks.

I found the best wheel for either Diablo or Hamilton is c24. Light, stiff, smooth and rim brake.

The Salmons might be slightly soft for the Blacks (and turn the brake track orange)...I mostly run just plain Kool Stop black pads with my Blacks. Work VERY well.

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http://bikeblather.blogspot.com/

Thanks for the tip!

You mean this segment? https://www.strava.com/...analysis/12688/13398

Doesn't really look that taxing on brakes, honestly. One ~45-30 decel, and another 40-25, with a handful of 10mph scrub-offs over ~7 miles/12 minutes. I can't imagine a bicycle with a pair of 160mm rotors (or even 160F/140R) and the right pads couldn't do that kind of work all day, every day, without overheating.

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"They're made of latex, not nitroglycerin"

Whoever that is has way bigger cajones than me through some of those turns.

Quite. Two weeks into my new job back to cycle commuting, I had my first collision in many years - guy turned right across the oncoming traffic (UK) didn't see me in the cycle lane. Fortunately I managed to scrub off a bit of speed with my discs and steered into his direction of travel to avoid a 90 deg impact. Hopefully his passenger door needed an expensive repair. Apart from a my finger I got away quite lightly.

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29 years and counting

I guess the point is, if you have the best brakes in the world, you can still ride on a trainer and not use them. But if you do find yourself riding in the hills in the rain, you'd be covered there too.

How often will that situation arise? I don't know, but it's nice to have your bases covered. I take a spare tube, money, my phone, a mini pump and a co2 canister even for short road rides. How often do I need them? almost never, it doesn't mean they aren't nice to have if I puncture or get stuck a fair distance from home though.

Agreed. I said above that Brakes don’t matter until they do. For me, I just realized that necessary hard braking occurs in far less than .01% of my rides (hasn’t happened once this entire year). With good brakes and good braking wheels (ie not carbon) I will get very close if not equal stopping power in the event it does ever matter and save hundreds on costs. I can certainly understand others who swing the other way as I was very close to a disc purchase recently but ultimately decided the cons outweighed the pros.

Threads like these always remind me of Brexit & Trump discussions on social media. I want to just post...

Look you lost, discs are coming, accept it and stop whining.

;-)

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29 years and counting

Ummm...yeah...with those 2 examples, sounds like an apt analogy :-/

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http://bikeblather.blogspot.com/

but like brexit, discs breaks cost people money lol ( i wanted to just post ...),
but i feel like iam wining as i will get a cheap non disc break disc soon lol

It wasn't an analogy though was it Tom; I just wanted to post that paraphrased response. Lighten up.

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29 years and counting

I think Julian Alaphilippe would disagree with “ you can’t get down a mountain pass with any speed on a rim brake bike with that have carbon brake track wheels “

whereas i believe sagan was on discs when he crashed so case closed ;)


oh, but then yates was on rim brakes... oh no, what to do!

i do believe discs brake better, whatever this test says... i'm just not sure that in the (dry) road context it makes enough of a real difference to justify the downsides (including new bike and wheels cost). everyone i've spoken to who has them loves them but how many people don't gush about their latest bike upgrade, whatever it might be?

This might not be the best place to ask, but what is the current thinking on buying cheap chinese carbon clinchers with disc brakes?
In the past people were worried about rim blow outs and poor braking, that 'shouldn't' be an issue with discs, are they now a better proposition?

Needing discs for riding in the rain is my justification for getting an additional road bike. Unfortunately my cross bike has cantis, and in the wet it is easily the worst braking bike i have so that isn't an option. My rim brake tarmac is unpredictable braking in the wet on descents, and on the days i get stuck in the rain i will change my route to avoid steep descents where i either have to turn or stop. I'm hoping discs and 28s will be much better on those wet, hilly rides.

Sounds like your brakes aren't set up correctly. (Cantilever brakes are common on tandems for very good reason.)

Canti brakes on cross bikes were (are?) traditionally set up to maximize pad travel for mud clearance as opposed to stopping power. Definitely isn't common knowledge that you can go the other way with 'em. But you do pretty much have to pick one or the other.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

If only there was a type of brake that allowed for both large pad clearance AND high leverage (AKA "stopping power") once the pads came close to the braking surface <cough...cam actuated center-pull...cough> ;-)

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http://bikeblather.blogspot.com/

The constraints that they are given is that they need to feed their family (even if that is just themselves). These constraints may (and sometimes do) diverge from what a performance data driven focus would be.

Stephen J

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I believe my local reality has been violated.
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Happiness = Results / (Expectations)^2