On Sunday, July 2, 2017 at 3:15:02 PM UTC-6, Patrick Moore wrote: > > Speaking of discs versus calipers, I've read in more than one place that > discs are useful on racing bikes because they stop faster and therefore let > you go faster into a corner before you have to slow down, so that you can > negotiate corners faster than with calipers. > > I daresay that hydraulic discs will jam a wheel still with less finger > pressure than any caliper, but so what -- when you have a tiny rubber > patch, what advantage does a more powerful "squeeze" make? > > Note that I'm not figuring carbon fiber rims into the equation here; i > daresay that, since calipers work less well on cf rims than on aluminum > ones, discs on road bikes with cf rims may well be useful in that regard. > But consider the question asked for bikes with aluminum rims. > > So, is this bogus, or is it true? > > I think discs have advantages over calipers that make them useful for > certain types of riding in certain conditions, but I am very skeptical of > this claim. >
Right, you hope they're not comparing discs to rim-braking on carbon brake tracks where rim-braking is not at it's best. I've noticed I do brake later into steep high speed road turns on my disc road bike, turns that require coming down from 50 mph to 20pmh on my canyon descents, but the biggest difference in late braking is with wider tires. When I compare are tires (41mm Baby Shoe Pass EL) with brazed-on Raids on A23 rims vs. TRP Hy/Rds 160 rotors with Modolo levers on Pacenti TL28 rims, I brake somewhat later with discs. But I noticed braking much later into these high speed turns on my most recent canyon descents on 47-48 Switch Back Hill EL tires. I'm guessing I'd also brake later on rim brakes with SBH tires too--they fit on my bike with Raids but not under the fenders so I may have to remove fenders to try it sometime. In general I don't see a lot of difference in braking quality or power in these two road set-ups, rim vs. disc, except that the same amount of braking requires somewhat less hand effort with discs. Both seem to do really well with high speed descending on pavement with heavy braking for tight switchbacks. Hand effort seems really good to me with the Raids too, much less hand effort than required with the regular old single pivot Record brakes I'm used to. But hand effort is still noticeably less with discs. But the big difference in late braking for me has been with increasing tire width. This surprises me because I was doing these same 50mph to 20mph turns on 25mm tires with no complaints before I started riding fatter tires on the road. I'd hear descending was faster on fat tires and I would think maybe that's just for riders who aren't fast descenders. But I think the difference is there because I brake noticeably laters on 42mm tires compared to 25mm and then on 48mm tires the late braking is really noticeable. I think the reason for the late braking is probably two things (?): there is more grip with the larger contact patch, but also wider tires soak up more road irregularity and surface roughness through the turn and on narrower tires I feel like I need to get speed down a little earlier in preparation so I can manage that roughness leaned over while with the wider tires I'm more ok leaning the bike over and trusting the tires to handle more of that roughness than narrow tires can on their own. The late braking difference in lower hand effort seems to come from the fact that I notice I use progressive stages of hand effort when I scrub a lot of speed (50 down to 20). BTW, all of this braking I do on descents is from the hoods. On rim brake Raids, I squeeze and lose a lot of speed, but then there is a harder squeeze I have to ramp up to with more hand strength to get down to the safe 20mph to go through the sharp sweeper turn. Some people might do this all with one progressively firmer squeeze but for me it does feel like two separate squeeze--one big firm one then a really hard one. On disc Hy/Rds I don't require that second stage of harder. One stage of firm hand pressure on Hy/Rds takes me all the way down to 20mph. This simpler process lets me brake later I think, or at least that seems one likely explanation, all else being equal. (The old school Record single pivots handle the same 50mph down to 20mph turns just fine but it takes noticeably more hand pressure than the Raids.) --Mitch -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at https://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
