Hot Disc Brake News… Or News About Overheated Disc Brakes, If You Prefer

Photo posted to BikeForums.net by akexpress shows intrepid tandem teams who ascended Mt. Ventoux on August 4th.

A Little Background:

During my Eurobike debrief with Bill McCready of Santana Cycles last week he mentioned that some 17 [sic] tandem teams from Santana’s July 31 through August 8 Burgundy & Provence Tandem Cruise signed-up to participate in an optional ride on August 4: an ascent of  Mt. Ventoux.

Interestingly enough, we’d already heard about the ascent as one of the teams who were on the tour and who made the climb belong to the BikeForums.net discussion forums and contribute under the pen name akexpress penned a post-rally report on the climb back on August 11th.

Based on the report from akexpress, there were apparently as many as 50 tandem teams on the tour who signed-on for the ascent before the rally began.   However, after a week of riding and looking more closely as the climb’s percent grade and total climbing involved, only 15 teams headed up the mountain and of those only 13 completed the entire ride.  As for the logistics, Santana arranged for a bus to transport the riders and their tandems from their 360-foot river cruiser, the Amadeus Symphony, on the Rhone river to the base of Mt. Ventoux.  Quoting from akexpress’ write up:

 Mt Ventoux is one of the classic beyond category climbs in France with about 5400 ft of climbing in 14 miles with not a single ft of level road. The grade averages 6% with some extended pitches at 10%. Many stage rides of the tour de France have included Mt Ventoux. We think it may have been the largest number of tandems on the mt at one time. The professional photographers that are on the side everyday kept commenting every time a tandem went by.

Hot Brakes: And The Winner Is?

OK, now to the crux of this blog entry: how well did the various disc brakes fare on the descent?  Even with Bill’s detailed, pre-ride training session on how to properly use your brakes when descending steep grades on a tandem, the teams running Avid & Winzip disc brakes all had “issues” during the descent ranging from wearing through brake pads to melting the red plastic adjusting wheel on the inboard side of the Avid… noting that all three of the Avids did in fact melt their adjusting knobs.  The only disc brakes that didn’t have any issues were the new Bengal / Santana models mated to the larger 250mm Santana disc rotors.

According to akexpress, it didn’t matter what “technique” was used by the teams with disc brakes that had issue, the descent was just a tremendous challenge that tested the limits of the disc brakes. As for the Avids with the melted inner adjusting knob (#106, below), akexpress had one on their Calfee tandem but the brakes otherwise worked fine throughout the descent.  After the day’s ride they were able to install new brake pads, adjust their caliper sans the plastic wheel using a torx head bit and finish the tour using the knob-less caliper.  They have since acquired a set of the Bengal calipers for their Calfee.

 

One of the other teams with an Avid lost their inboard disc brake pad (#74, above right) and the piston (#156 left, #86 right) while riding the next day, noting that the red adjusting knob on the inboard side of an Avid BB7 is also the part that keeps the piston from moving once the brake pad distance from the rotor is set. In hindsight, it would seem that a spare inner adjusting knob + a spare set of pads would be a good thing to take along when tackling challenging climbs if your tandem is fitted with a set of Avids.  Bill also mentioned that another Avid was of marginal use after the descent but I can’t recall the particulars.  Our BF-brother axexpress mentioned that a third tandem equipped with an Avid (another Calfee) had the same problem that they experienced, e.g., melted adjusting knob but were otherwise able to use their brake throughout the descent and finish the rally by working around the melted part.

Again, with regard to the older Santana tandems equipped with Winzips, the only thing I saw mentioned was brake fade and pad wear but no detailed post-mortem beyond that.  As for the thee (3) newer Santana’s with the Bengal disc brakes, they were apparently not adversely affected by the heat on the descent, which is goodness.  I’m still not a fan of the white color that Santana chose for their brake, but what are you gonna do?

As for drum brakes, there were apparently a few tandems with drums that made the descent and other than a few heating up to the point where they started to glaze and give off some odors, they all worked as designed.

Now, it is worthwhile to note that another BF-brother who did the climb to Mt. Ventoux did so on a tandem that was only fitted with front & rear caliper rim brakes.  Our friend from BF & Hobbes — bikerriderdave — wrote:

We had only standard reach caliper brakes on our Bilenky and experienced no brake-related issues on the descent. We did stop once not far from the top to let the rims cool, because we were stuck behind a line of cars who were all leaving the mountain when we were. Once traffic cleared, we didn’t have to brake very often. Yes, it probably helped that our combined net weight (i.e., buck naked) was/is only about 270 lbs.

So, What To Make Of All This?

As is so often the case with tandems, your results may vary.  It sounds like the same weakness that was noted in the Avid BB7 disc brakes as far back as the late 90’s by the German magazine BIKE.  The disc brake pad falling out was a new twist and something that I’d not heard reported in the past. So, that’s why I might add a spare adjusting knob kit to my tool box, about a $6.00 kit in addition to a spare set of pads.  The Bengal performance is notable in light of Avid’s (owned by SRAM) lack of interest in coming up with a more heat-resistant material for their adjusting knobs given that the Bengal has been somewhat optimized for use on tandems per Santana’s specs.

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About TG

I've been around a bit and done a few things, have a couple kids and a few grandkids. I tend to be curmudgeonly, matter-of-fact and not predisposed to self-serving chit-chat. Thankfully, my wife's as nice as can be otherwise we'd have no friends. My interests are somewhat eclectic, but whose aren't?
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11 Responses to Hot Disc Brake News… Or News About Overheated Disc Brakes, If You Prefer

  1. Were all of the drum brakes Arai? Were any shaved? That old beast sounds like a best buy. What is the status of the Maddox drum brake?

    • TG says:

      I would assume they were Arai just based on what we’ve seen at Santana rallies in terms of rolling stock. As for any details, such as how many may have had the cooling fins shaved-off, no details were offered. Perhaps someone who attended with a drum and who pay attention to what his peers were using will see this and share some details.

      As for the Maddock drag brake, will advise. I’ve sent off a note to Tom to see where they are in the development process.

  2. Andy Kami says:

    My wife and I, 290# buck naked, climbed and descended all the top ten passes in North America in the last 8 weeks, 3,500-5,000 feet, many over featuring 10 mile descents with 8-12% curvy grades (Slumgullion and Guanella were the steepest). Not as steep as some of the harder descents in Italy/France, but at least similar to Mt Ventoux.
    Our Paketa is equipped with rim brakes and we had no problems. It is important to note that the for rim brakes to work, the design has thought though the braking equation with an understanding that deep section metal rims are key to the cooling equation. Ours are 38mm, just a little deeper than the 31mm Rolfs (I don’t have data on the Rolfs which might be sufficient for cooling). I understand the point of failure for clincher tires to be about 400 degrees based on formulas and bench test by our bike designer, and that rim tape is the most susceptible point. For that reason our wheels are built with velo plugs rather than rim tape to better resist heat.
    To back up the formulas and testing I tagged our rims right below the braking surface with 4-position temperature plates to read if the heat exceeds 150-200-250-300 degrees (Palmer Wahl Model Number: 442-151F). For the season of climbing/descending we have tripped 200 degrees but not 250 degrees in front and not quite tripped the rear 200 degrees (even though I brake more on the rear). I should also note that I am a conservative rider on descents, so I sure brake a lot. On some descents I braked pretty much the whole time.

    I would be interested in someone re-counting McCready’s techniques for braking.

    • Christian Bratina says:

      Can you provide more details on the “point of failure for clincher tires to be about 400 degrees based on formulas and bench test by our bike designer”? Is 400 degrees the point tires are likely to blow, how is the rim temperature calculated based on the weight, slope speed, etc.?

      • Andy Kami says:

        For tire pressure, our wheel & tandem designer provided this:
        “the increase in tire pressure goes as PV=nRT, where P=pressure (absolute, that is), V=volume (a constant in this case), n and R are constants (ignore), and T=temperature (absolute; either Kelvin which is metric, or Rankine which is the Fahrenheit equivalent). If the tire pressure starts at, say, 100 psi at room temp (300 K or 74 deg F) and the rim/tire temperature gets as high as 400 K or 254 deg F) then the tire pressure will be 133 psi. Tires are generally rated such that the blow-off pressure is about 2X the rated maximum pressure printed on the sidewall. If the tire says max. 120 psi inflation pressure, then it should hold up to 240 psi. Tubes are good to at least 360 deg F/475 K, provided they’re not defective. 300 deg F is a safe maximum temperature that takes into account the tire, tube, and rim strip/plug, and actually provides a reasonable safety margin, as tires, tubes, and rim strips (conventional rim strips, that is) begin to have problems north of 360 deg F. That’s quite a bit hotter than most people would ever guess, which is why I mentioned that it’s the rim strip that fails first in most cases, since many (not all, but I’d say more than 50%) rim strips fail before 360 deg F. VeloPlugs are good for 400 deg F, and I’ve tested a variety of rim strips and the ONLY one that’s safe for tandem use is Velox cloth, which is good to at least 400 deg F.”

        So 360-400 degrees is when rim plugs or velox tape fail and the tube will blow flat thru the rim tape. The tire should stay on the rim. If you can run the calculation above you could tell me at what temp the pressure reaches 240psi and the tire really would blow off. Next time I wear out a tire I’ll run that bench test myself to see at what temp I get a tire to fail. All that said, I’ve had hidden damage to a tube maybe from installing it and had it blow, I’ve had sidewalls fail due to tire integrity, and other failures. The figures above are just trying to put in perspective the temps, and for me, highlight the importance of aluminum, deep section rims, on a rim brake configuration in mountainous areas.

        Rim temperature can not be reasonably calculated since ambient air temp, wind, braking style, how twisty the road is, and rim section have a significant unpredictable impact. The best way I know of determining the temperature is with the temperature plate “sticker” I mention in my post above. To give you some idea, I can only offer my experience. Rim brakes on a standard Velocity tandem rim will heat to the point it is still safe on steep twisty descents, say 8-10%, up to only 1-2 miles. Maybe less for a heavier team. I base this on my own history having run rim brakes on Velocity rims for many years here in Colorado and not blown a tire in those years. One example is a trip to the 5 mile Palm Springs tramway road which is 10-14% (with the steepest at the top). The tire did not blow in the first mile, nor after a short cool down, did it blow in the second mile. And we’d ridden many Colorado passes and not had a heat failure on those Velocity rims. But don’t use my history as a solid convention!! In comparison, for my team and bike weight, an now running deep section rims (38mm), and my braking style; I have been unable to heat the rims beyond 250 degrees on twisty descents continuously 10% grade for 10 miles. That suggests the rims remain self cooling under these conditions for any mileage.

      • Andy Kami says:

        OK, if that last mathematical posting was not clear, and anyone really wants to wade thru more math, here are some examples of tire pressure relative to rim heat crib’d from the designer who is helping us all with this formula:

        The formula simplifies to PV=T, which can be rewritten as P=T/V. Assuming V=constant (reasonable for bike tires; ignores a little stretching as temperature and pressure increase) this simplifies to “P is proportional to T.” Doesn’t get much simpler than that. The temperature has to be absolute temperature when using the equations; let’s use Kelvin and convert to Fahrenheit after

        Let’s use a typical example as below, with starting tire pressure of 100 psi at 80 deg F or 300 deg K. (ask google to convert it by typing “convert 80 degrees fahrenheit to kelvin”).

        Example 1: Let’s say you want to know what the pressure is when the rim/tire temperature gets hot. Our designer has used temperature-sensing adhesive dots on tandem rims, including a triplet, for many, many years to verify how hot the rim’s getting in different riding conditions. On the triplet, I can tell you the maximum temperature I’ve ever seen was 250 degrees F, which is 394 K. Using the above formula, the tire pressure is P_hot/P_cold=T_hot/T_cold, or P_hot=P_cold*T_hot/T_cold=100*394/300=131 psi. That’s a lot higher than 100 psi, but any decent tire can easily handle that. High-quality tires are usually rated for twice the recommended maximum pressure printed on the sidewall, although that obviously depends on the tire-rim combination you have. Continental tires, in particular, I know are generally good for at least twice the pressure printed on the sidewall when mounted on a high-quality rim with a tight bead seat.

        Example 2: Let’s say you want to know how hot the tire has to be to get to a certain maximum safe tire pressure; in this case, let’s assume you’re running 125 psi on your tandem with a tire that’s rated for 125 psi max and we want to know what temperature will raise that to some presumed “safe” maximum; let’s assume 170 psi to give us a pretty good safety margin from “double the rated pressure,” which would be 250 psi. Rewriting the above equation, T_hot=T_cold*P_hot/P_cold=300*170/125= 408 K=275 F.

        Example 3:
        105PSI rated tire starting at 80 deg F (300 deg k) going to 400 deg F (477 deg K). Tire pressure = 105*477/300 = 167 PSI. That’s 60% higher than the rated pressure.

        As discussed in a prior post, generally the “weak link” in the system is the rim strip. Many materials soften or melt long before the tire or tube rubber–not to mention the pressure–gets close to the failure point. The simplest, safest rim strip is cotton cloth (Velox being the most common brand, but there are others that are comparable), which our designer safe to at least 400 degrees F. Velo-Plugs are also good but not as common.

  3. Fred says:

    I won’t tell you what our team weighs buck naked. I will tell you our Avid BB7 disc brake rotors get very hot. I have a blister on my left index finger to prove it. 😀

  4. Pingback: Bengal MB700T Disc Brake… The Start of a New Product Test « The TandemGeek's Blog

  5. Alex Zucosky says:

    We have had a Santana Team Ti with the 250mm rotor since January 2014. At about 4500 miles (summer 2015) we started to get a lot of noise from the rotor. We did a lot of steep and long descents in NM and CO in that time. I added a 160mm rotor to the outside of the big one(at the suggestion of Jack Goertz Tandems Limited) and that helped some. We finally replaced the rotor at about 4800 miles as the noise got to be too much even on shallow descents and stops. The new Santana rotor (with the 160mm rotor) seems to be working well. At about 5000 miles we replaced the original pads with Hayes MX2?sole brake pads. They seem to be working well but we have only made a few steep or long descent since the 5000 mile mark. I am interested in what anyone would suggest for brake pads as we will probably replace them this summer

    • cbratina says:

      So you replaced the 250 mm rotor with a 160 mm rotor? How is the new Santana 160 mm rotor different? If you were to order one, is there a part number?

      • Alex Zucosky says:

        Sorry. I added a 160mm rotor(cheapest one that I could find at LBS) outside and against the 250mm rotor. used a little silicon sealant on the brake part of the 160 rotor. Seems to help as a stiffener and it does help with noise. Not sure how to add a photo as that would probably make the idea clear.

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