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Ciao from sunny Sicily!
With all the marketing mojo devoted to magic chain treatments and the claims of saving of a few watts due to the reduced friction, I wonder if anyone has done any testing on the effect on drivetrain friction losses when cross-chaining?
I can’t help but wonder how many extra watts may be used pedaling a bike (usually uphill) in the big-big combination? Back-in-the-day when there were just 5 or 6 cogs in the back, the chainlines were never as extreme as nowadays, but the coaches used to drill into our heads that drivetrains were much more efficient when the chain was running in a straight line rather than at a big angle. I assume the chains have gotten more efficient and flexible to deal with 11 or 12 cogs back there, but conventional wisdom suggests there’s still a difference? And the spring tensions are certainly higher than the old Campagnolo Nuovo Record days when there was only one spring back there instead of two.
I see this all the time watching pro races on TV – the pros, just like your average weekend rider, seem to shift all the way across the cogset in back while staying in the big ring.
When I try the big-big combo myself it certainly seems to create more resistance, whether it’s the extreme sideload (for lack of a better description) on the chain or the extra spring tension from the pulley cage as it’s maxed out in the big-big combo.
Has anyone tested this? No money to be made telling riders (like they used to tell us back-in-the-day) that a chain running in a straighter line creates less friction, but I’m interested to know if there’s any data to back this up.
Jason Smith, founder of Friction Facts and Chief Technology Officer for CeramicSpeed, answered your question.
Larry: Friction Facts/CeramicSpeed has performed a few tests investigating cross chaining and the effects on drivetrain frictional losses.
You are correct on both accounts; cross-chaining increases frictional losses, and riding in the big ring decreases friction losses. However, as you point out, riding in the big-big combination creates a severe cross chaining angle, which begs the question: Is it more efficient to ride in the big-big, even with the heavy cross-chaining, or is it more efficient to use the small ring and smaller cog (with a similar final gear ratio), which creates less of a cross chaining angle, but we know the small ring consumes more energy?
Does an efficiency crossover occur between big and small rings? If so, where is it?
The answer in this case is: Use the small ring; it is more efficient than big-big. An efficiency crossover does occur with 2x drivetrain.
Testing has shown that optimum (efficiency-wise) big ring-to-small ring shift points exist. Based on lab testing, it was found that the big ring is most efficient when riding from the smallest cog, up to about the 8th (largest) cog on an 11sp drivetrain. After the 8th cog, it is advisable to shift into the smaller front ring, rather than remaining in the big ring and taking the chain up into the larger 9th, 10th, 11th (largest) cogs.
Granted, this optimum shift point can vary slightly depending on the cassette range and ring sizes. It might be the 7th, 8th, or possibly the 9th cog. But in no circumstance would it be more efficient to ride big ring up to the largest cog. To maintain the highest efficiency, a good rule of thumb is when riding the big ring, don’t take the chain past the 8th cog.
How much energy is lost by using the big-big? About 1 to 1.5 watts of loss occurs. Some might view this as inconsequential. Yet for a high-level racer, a ½ percent power output gain to the rear wheel by shifting properly could make a huge difference at the podium. At a minimum, the data exists for the rider to decide if/when to shift.
Two important tests have been performed to prove the 2x efficiency crossover. Both tests involved the drivetrain friction of 2x setups, in which the friction was measured for both the big and small rings with all of the cogs. The ‘crossover point’ of the two friction curves, the curve of the small ring with all cogs vs. the curve of the big ring with all of the cogs, is the optimum shift point.
The original Friction Facts report “Effects of Lateral Chain Misalignment & Chainring Size on Drivetrain Efficiency” is publicly posted on the CeramicSpeed website.
This report fully explains this effect and provides some good data curves.
Additionally, Lennard and I did a comprehensive test to compare the effects of a 1x vs 2x setup. The data from the 2x portion of the test shows the friction curve crossovers and optimum shift points of the 2x.
Jason Smith, Ceramic Speed chief technology officer
Enjoy Sicily, Larry!
― Jason Smith
Regarding the delamination of the friction material from the backing plate on disc brakes, I’m posting a slew of letters refuting my contention that it is vanishingly rare.
In our shop, in about the last year and a half, I’ve seen two disc brake pads that had lost the braking material on one of the pair of pads. In both instances, the remaining pad was extremely worn. In one case the metal spring was wearing off, with very little of the pad left on that side. I had chalked up the pad loss to be uneven brake wear, and the user ignoring the sound of the metal spring wearing against the rotor. Besides those 2 instances, I can recall only seeing a pad delamination once before. That was at least 10-15 years ago, and I saw the same extreme wear on the remaining pad.
Regarding Randy’s brake pad delamination issue. There are a couple of clues in one photo of the pads. Firstly, there is a clear demarcation between the lower half and upper half of the ‘good’ pad. (indicated with red arrows). This may indicate the use of an undersized rotor, excess spacers for caliper mounting, or some other issue with pad-to-rotor contact. Secondly, there are signs that the pad material chipped away, possibly caused during wheel installation (noted in blue circle). This damage lends support to your theory that the ‘bad’ pad was weakened.
Thanks for the very nice analysis. Yes, the nick circled in blue could certainly be explained by banging the rotor into it while installing the wheel. Very interesting about the mark that clearly looks like there was a mismatch in height of the pads and rotor, also possibly indicating using the wrong caliper mounting adaptor for the given rotor. I’m not sure how the rotor being too low on the pad could have contributed to the delamination of the pad. It certainly would result in less effective braking.
I saw your November 3rd post about disc brake pad delamination and wanted to report some more cases of this. I’ve had exactly the same thing happen (pad delaminated, or sheared off the metal backing). In fact, I’ve had it happen twice. They were several months apart a few years ago. I’m pretty certain that my pads were metallic, not resin, as I’ve always preferred that for longevity. I had always assumed it was a bad batch of pads. Anyway, just wanted to let you know that it may not be so rare after all (or maybe I’m just lucky).
Regarding your recent column, you asked if anyone else experienced disc brake pads delaminating. It has happened to both my wife and me, but, happily, we both lived to tell the tale. In our case, the common thread was EBC Gold brake pads and these failures occurred about 5 years ago. We both use TRP brakes, Hy/Rd and Hylex, respectively, but I really don’t see the brakes as a contributing factor. In relation to Shimano’s response in that column, we have been using disc brakes for 20 years and are careful when inserting wheels, so I don’t think the pads were compromised either.
We live in the hills of western Massachusetts and ride year-round, mainly on dirt roads, so our brake pads do experience a tough life. When it first happened — at night, on a steep descent, approaching a hairpin bend — I thought it was a freak occurrence. A second occurrence, as my cheapskate side tried to use up a stash of those pads, suggested otherwise though. Following that, we switched to Kool Stop pads, chiefly, but have also used Swiss Stop and Shimano pads without similar problems.
I’m writing in response to the Tech FAQ posted on VeloNews on November 3rd about disc brake pad delamination.
This happened to me on mountain bike pads in ~2000mi. or so. The brakes at the time were Hope Mini’s. I hit the brakes, heard a “schwing” like a sword being drawn in the movies, and a sudden loss of front braking power. The brake still had a pad backing plate in my front brake, but the actual friction material was gone. Hasn’t happened since, but a spare set of pads has been in my hydration pack ever since along with other key spares (tube, bit of chain, SPD cleat screws)
I had a similar disc brake failure to the one described which occurred while putting my rear wheel on after changing a flat on my commuter, which gets ridden year-round. The rotor got hung up on brake pad material. I had off-brand sintered brake pads, though it’s disconcerting that it happened with genuine Shimano pads…
In response to your letter from Keith and his “lightning only strikes once” brake pad delamination issue, I will chime in to say that this has happened to me I believe a total of 3 times in about a decade, all on the same bike (Bianchi MUSS single speed, Avid BB7 brakes) but I cannot recall if the delaminated pad was always the front or rear pads (although I believe as in your reader’s case, it was always just one pad of the pair).
I do know that it has happened with the original Avid sintered metal pads as well as Avid organic pads and I believe one set of red Kool-Stop pads (cannot recall if those were resin or metal).
In my case(s), I don’t think the issue stems from heat build-up, as I live in Chicago, and this is my winter bike. I also am not sure banging the pad material on the rotor during wheel installation is a possible culprit, as I have 3 other disc brake bikes and have never had the issue occur on any of these bikes. I imagine that like everything else failure-wise on the bike here, it was a result of road salt exposure and time/use.
I just read the article on the brake pad failure. I too experienced this on my XTR front brake. I did find it odd, but I replaced the pad and haven’t experienced it again.
Thanks for the interesting articles!
Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.
Follow @lennardzinn on Twitter.