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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: Grant Peterson's Thoughts on Disc Brakes
Date: Wed, 25 Sep 2024 16:34:56 -0400
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On 9/25/2024 4:20 PM, AMuzi wrote:
> On 9/25/2024 2:58 PM, sms wrote:
>> <https://bikeretrogrouch.blogspot.com/2016/06/gps-thoughts- on-disc- 
>> brakes.html>
>>
>> If I could summarize Petersen's view on disc brakes, it is that 
>> there's nothing exactly wrong with them, but they aren't the vast and 
>> remarkable improvement over good rim brakes that the industry has been 
>> pushing for the last few years. In other words, they don't make bikes 
>> with rim brakes obsolete, and shouldn't.
>>
>> Petersen points out some of the benefits of disc brakes -- notably the 
>> fact that they are less affected by mud and water, and that they don't 
>> heat up rims to the point of tire blowout on scary-fast descents.  
>> Then again, for the majority of cyclists and conditions, those 
>> benefits are over-sold. And on the down-side, as he adds, the leverage 
>> of a disc brake concentrates a lot of force near the hub, putting a 
>> lot more stress on seat-stays, and on fork blades far from the crown. 
>> As a result, frames need to be beefed up in those areas, which can 
>> affect compliance and comfort. He also mentions how those braking 
>> forces concentrated out at the frame ends have been enough to 
>> overwhelm quick releases and even "lawyer tabs" on front forks, 
>> necessitating the move to through-axles. To wit, he asks the question, 
>> "Which is better -- a mechanical system that localizes stress on a 
>> small area, then bullies it into submission with bulk and beef, or one 
>> that disperses stress and spreads it out?"
>>
>> He goes on to say, "Disc brakes are fine, but if the bike could speak 
>> for itself, it might request a rim brake. . . The fact is, rim brakes 
>> are getting pounded these days, but it's a kind of artificial pounding 
>> by fashion and commerce."
>>
>> I would have to agree with that. I mean, if I were looking at a new 
>> bike on the showroom floor and the bike I wanted came with disc 
>> brakes, I certainly wouldn't reject it for that reason. But at the 
>> same time, I wouldn't be drawn to a particular bike because it had 
>> discs. And if there were another bike basically the same but with rim 
>> brakes, and selling for a lower price, I'd probably choose to save the 
>> money.
>>
>> But there's another point to be made that resonates with me. And that 
>> is regarding the simplicity of a traditional rim brake. Everything is 
>> out in the open, easy to see and easy to maintain, while potential 
>> problems are easy to diagnose and solve. Some would likely point out 
>> that once a modern hydraulic disc brake system is set up properly, it 
>> needs little maintenance. To which I would respond that getting it set 
>> up properly is a lot more likely to be something that requires an 
>> experienced mechanic, and if something actually goes wrong (and things 
>> do, indeed, go wrong - even on the best of systems) it can be a lot 
>> harder to diagnose or solve. This is something I wrote about last year 
>> when a bike reviewer for BikeRadar had a pretty scary disc brake 
>> failure on a test ride. In that case, the brake components were sent 
>> back to Shimano for inspection, but ultimately, even they couldn't 
>> adequately explain how or why the failure occurred.
>>
>> Petersen describes it like this: "Ultimately, you can expect the 
>> bicycle of the immediate future to become more of a high tech black 
>> box, with cables being replaced by hydraulics, and the visible levers 
>> and pulleys and other simple machines that combine into bicycle magic 
>> being hidden or replaced by electronics. The bicycle of the future 
>> will, absolutely, be shrouded in mystery and sold on reputation and 
>> faith, like a Samsung flat-screen TV."
>>
>> He continues, "There's a tendency to trust mechanisms you can't see 
>> more than those you can, because when you see how something works, you 
>> see also the potential for failure. . . If you're mechanically adept 
>> you might be more attracted to something you can figure out and fix, 
>> but more people aren't that than are."
>>
>> That really nails it for me, and it's something I've touched on again 
>> and again in this blog - whether it's electronic shifting, or disc 
>> brakes, or integrated/connected dashboards and other electronic 
>> gewgaws -- all that stuff makes the bike more of a "black box" (I like 
>> that description, so I'm using it) and takes it further from the 
>> simplicity that I value in a bicycle. Fly-by-wire electronic and 
>> hydraulic systems, for efficiency, comfort, and safety, all controlled 
>> by a state-of-the-art computer is fine for my car. But what makes a 
>> bicycle special is that it demonstrably doesn't need any of that to 
>> make it any better.
>>
>> People do seem to like push-button/touch-screen convenience, which 
>> oddly enough seems so simple, but only because the far greater 
>> complexity is kept hidden, and only accessible by those who are 
>> specially trained and certified to look behind the plastic covers. 
>> That illusory simplicity is great when everything works as it should, 
>> but vanishes into the ether when something goes wrong. It's like a 
>> microwave oven. If something goes wrong, it ends up costing more to 
>> fix it than to just scrap it and buy a new one. Bikes and bike 
>> components shouldn't be that.
>>
>> In the end of Petersen's blug post, he concludes by saying "Don't dis 
>> the rim brake. It's beautiful and it works, and today's rim brakes are 
>> better than ever."
>>
>> Couldn't agree more.
> 
> I'm OK with most of that.
> 
> But braking force against the hub is the same, AEBE.  Any increase is at 
> the margin, when a disc generates more braking force than a rim brake- a 
> rare event given rear wheel lift.

Braking force against the hub is the same, but the force that fights the 
twisting moment is, for a front disc brake, applied at the bottom of the 
fork. There's greater stress on the fork, so it has to be beefier. Same 
thing at the rear stays, although I don't think it's as critical there.


-- 
- Frank Krygowski