Another question about disc brakes & downhill riding

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eyeless
Posts: 2
Joined: Tue Sep 02, 2014 9:56 pm

by eyeless

Seems like everyone is talking about disc brakes these days. Turned up at the club training this evening and others were talking of it while I had read about it on the web before in the day (though of course it has been around for long and some has used it on road bikes for some time now).

At first glance it would seem obvious that I would benefit more than most from these. Esp. as I had two of the typical dreaded failings of standard road brakes in one week this Summer: first the front tube exploded on the downhill because the brake pads had gotten damned muddy in bad weather and I hadn't noticed that as it was wearing down the pads (one of them) had made their way in to the front tyre/tire (did not even realized it until after cycling a bit again after repairing ...). Second time I had the explosion due to overheating the rim, which I had feared many times before and heard about, but it never happened to me until now ... I partly blame the rim tape though -- no one really takes rim tape quality seriously enough!!!! (so much crap sold even by otherwise respected brands)

BUT, I hear that continuous braking down long steep mountain roads could be a problem for disc brakes too and read elsewhere in an old thread here that this is not the fault of disc brakes but of people not knowing how to brake properly - well, I might have forgotten myself and had to hear this argument also from the guys helping me fix a broken spoke ... :? . However if you descend steeper roads than Mortirolo and Monte Zoncolan -- what help is there to brake and let loose and brake again in order to stop build-up of heat when the speed is up to 200 km/h after 3 seconds - well not quite, but ... . Which brakes are most reliable when descending such roads once a day a full month??

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eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
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by eric

Going faster than about 20 mph increases cooling via convection to the passing air (Cycling Science, 3rd ed). And the brakes (pads + rim or disc) won't cool off if you're continually adding heat by braking. So you let off the brakes when you can and brake only when you have to.

But if the road is steep enough you will need to brake most of the time. From my house to the public road it's 1/3 mile and 300' of elevation. There's one section that's a 22% grade and has a tight blind turn at the bottom. I brake most of the way for that. But few roads are that extreme for long. Usually the road levels out enough that you can get off the brakes more often. The Mortirolo is only an average of 10.5%. So while it may have steeper ramps, on the less steep parts you brake only when you have to for corners and let the brakes cool.

On some organized rides like the Markeeville Death Ride I see people who have their brakes clamped on the whole way down a 7% grade with (to me) 30mph+ corners. Someone like that needs to learn how to descend before they ride down steep technical descents.

eyeless
Posts: 2
Joined: Tue Sep 02, 2014 9:56 pm

by eyeless

eric wrote:Going faster than about 20 mph increases cooling via convection to the passing air (Cycling Science, 3rd ed). And the brakes (pads + rim or disc) won't cool off if you're continually adding heat by braking. So you let off the brakes when you can and brake only when you have to.

But if the road is steep enough you will need to brake most of the time. From my house to the public road it's 1/3 mile and 300' of elevation. There's one section that's a 22% grade and has a tight blind turn at the bottom. I brake most of the way for that. But few roads are that extreme for long. Usually the road levels out enough that you can get off the brakes more often. The Mortirolo is only an average of 10.5%. So while it may have steeper ramps, on the less steep parts you brake only when you have to for corners and let the brakes cool.

On some organized rides like the Markeeville Death Ride I see people who have their brakes clamped on the whole way down a 7% grade with (to me) 30mph+ corners. Someone like that needs to learn how to descend before they ride down steep technical descents.


Thanks! Yes, reading a bit more meanwhile, I realize that going down too long/too steep roads will always prove to be a danger no matter what ... . Just feel that some new technology for road bikes is just adapted so that it can be used in ordinary races, but won't hold up in tougher circumstances.

I usually have no problems on mountain descents, but have been exploring some of the most hopeless roads in the Alps lately and it happens that I can hardly let the brakes go for an hour without having an instant crash. Still only had overheating cause a flat once (I have had flats before due to shifting between wet and cold and very hot on descends before, but then it always was down to less than stellar rim tape! The Swiss repair guys had some decent Continental 18 mm rim tape expressly tolerating 18 bars pressure (or what it was) and that held up for the rest of my vacation down there. (Velox typically works most of the time too, but a good idea is using the 18mm and not 16mm as it can glide sideways.)

Yes, obviously it is stupid braking all the time ... unless necessary. I was going down Alpe Galm and it is rather steep, narrow and very twisting road higher up. Zoncolan is steep enough (2 of the three sides) for thinking of the problem (Mortirolo perhaps not as I cannot remember thinking of it there). Also I weigh a bit more than most cyclists adding up to the heat. Cycling down from the top of the Rigi mountain for example will not give you a chance to ease up the brakes early on. Down Alp Anarosa I tried to consciously try and brake and release - maybe it helped but still had to brake more than not for 10 km. Down Rittner Horn on a steep gravel road I also had to brake like 95% of the time. But as you say usually the very steep sections are not so long (still it is a problem for me, so think I will stick with brake pads and good rim tape for now).

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