Jim’s Tech Talk
By Jim Langley
Let me start by thanking all of you for the thoughtful, helpful and entertaining comments in response to last week’s column about the problems with Shimano going all in on electric shifting. As of this morning, the letters are still coming in. I have read and enjoyed every one. I was a little surprised there weren’t more dissing me for underappreciating electric shifting.
Over on my Facebook page, some of my industry friends did. If you’re interested in those comments, I believe this link will get you there: https://tinyurl.com/2s3p8bnw. I don’t know if it’s required to have a Facebook account in order to view a page. If it doesn’t open for you I apologize. I think you’ll enjoy the comments if you can see them.
If you missed last week’s article and all the great comments, click here to catch up: https://www.roadbikerider.com/thoughts-on-shimano-making-105-di2/.
Two More Thoughts on Electric Versus Mechanical Shifting
It occurred to me thinking about our e-drivetrain conversation that there’s a key difference with electric drivetrains that I should or could have explained more.
That difference is that while they have limit screws, pivots and pulleys just like mechanical derailleurs, they’re less mechanical. And as a result they’re not intuitive, easy to figure out or as fun to work on as mechanical derailleurs.
As just one example, the rear Di2 derailleurs have to have the high-gear limit screw adjusted so that the derailleur overshifts past the smallest cog, because the derailleur is controlled by a computer and it needs to overshift after which it moves the derailleur back directly under the cog.
No matter how skilled a mechanic you are, there’s no way you could figure this out on your own looking at the derailleur and fine tuning the limit screws. Because it seems to work just fine with the limit screw set the way you set all limit screws.
In order to figure it out, you either have to experience the potential gremlins this misadjustment can cause (premature battery failure is one), or find and read the manual. Yet, it’s a mistake even people who read the manual make because it is not how any mechanical derailleur is adjusted and counterintuitive (against mechanical principles), too.
I know from the comments that I’m preaching to the choir, but I thought the point needed to be made here so that people realize what they’re losing with electric shifting. In my view, while you might feel you’ve gained more precise, consistent and easier to use shifting, you have given up the ability to easily maintain your own drivetrain with your own mechanical ability and simple tools.
What was Shimano’s Best-shifting Mechanical Rear Derailleur?
That’s a rhetorical question and I’m interested in what you think, too. Please comment with your favorite rear derailleur even if it’s not a Shimano.
As I read all your comments and thought optimistically about what the future might hold for mechanical rear derailleurs, I thought of a recent bike I refurbished. It’s my get-around bike, not one for training or performance. But, I still love it and had fun getting it back on the road.
It’s a 1974 Lejeune, which the former owner told me was used as a backup bike in the Tour de France. It has eyelets on the dropouts so it’s possible that’s not true. But I know for sure the owner bought it in Paris from a bicycle store and was told that it had ridden on team cars in the Tour during the stages.
The main thing I did with this classic was upgrade the drivetrain. That’s where the best-shifting mechanical derailleur comes in. I built new wheels for the bike with 10-speed Shimano hubs so that I could install an 11-34 cassette. The bike has the same Campagnolo down tube shifters it’s always had.
Rapid Rise to the Rescue
I spent a lot of time thinking about what derailleur to install without coming to any conclusions. Then one day I received my friend Grant Petersen of Rivendell’s blog and he reminded me of Shimano’s Rapid Rise derailleurs.
I immediately remembered my two Specialized mountain bikes hanging in the garage, both with Rapid Rise derailleurs, an LX and an XTR – medium and top quality derailleurs respectively. One of the MTBs had already become a parts bike so I removed its LX derailleur to try it on the Lejeune retro-mod.
I’ve been riding it a lot now. I always liked how the Rapid Rise derailleurs shifted on my dirt bikes. On my Lejeune it seems even better, maybe because downtube shift levers are so much simpler to operate than mountain bike shifters. There’s also a completely different feeling to shifting into easier gears.
The standard design of rear derailleurs is that the spring inside pulls the derailleur back toward the smallest cog on the cassette as you push the shift lever away from you. Then to shift into easier gears (larger cogs), you pull the shift lever, which pulls the cable and moves the derailleur up the cassette.
Because the chain is climbing up onto increasingly larger cogs which can block the action, some force is required on the lever. And, you’re also overcoming the tension of the spring, which requires force.
With Rapid Rise derailleurs, the spring force works the opposite way. It pushes the derailleur towards the largest cog. This means that when shifting into lower gears it’s not possible to force the shift because the thing in control of the shift effort is the derailleur spring. And shifting into higher gears there’s no issues with forcing shifts because each shift is onto a smaller cog so the chain simply drops onto each cog.
The experience really got me thinking that if someone is to focus on making the new best mechanical rear derailleur that Rapid Rise or whatever clever new name they come up with – should be part of its design (Rivendell is working on one).
And While We’re at it, Let’s Talk About Disc Brakes
Our discussion about mechanical versus electric shifting attracted some comments and replies saying electric shifting is better than mechanical shifting the same way disc brakes are better than rim brakes. I understand how the two technologies can be seen as similar advancements.
So, I’d like to share a couple thoughts on the subject of disc brakes on road bikes. Just disc brakes on road bikes though, not discs on gravel or mountain bikes.
Firstly, I think it’s helpful in discussing the issue to appreciate that disc brakes came along in response to the use of carbon rims on road bikes. With carbon it’s possible to make lighter rims and more aero ones, too, so there was an instant demand since it affected performance so much.
The big problem with carbon rims was that rim brake pads didn’t and don’t work as well on carbon as they do on aluminum. There were carbon rims that had aluminum braking tracks to solve this problem, but the aluminum added weight and complexity in manufacturing. As a result, full carbon rims became more popular and in the greatest demand.
I have multiple sets of carbon wheels for my rim-brake racing Cervelos and have the carbon-specific pads made for these carbon-only rims. Right away I got used to the extra effort of braking with them and learned to start slowing sooner. When it’s dry it’s much less of an issue than when it’s wet. Carbon rims can make it pretty terrifying trying to slow and stop when it’s raining. How bad it is depends on the combination of wheels, brakes and pads you’re using.
But whatever carbon wheel rim-brake setup you have, if you try disc brakes you’ll notice a huge difference in braking power and control. With disc brakes you get all the benefits of full carbon wheels with top notch braking – or at least that’s the consensus of roadies who love their discs.
Too Much Brake?
Now that the professionals have mostly switched to disc brakes, I’ve been watching with interest to see how they’re working. At first I thought there might be pad dragging issues since this is something I’ve seen a lot – difficulty centering the calipers and keeping them centered. While I wouldn’t be able to see this watching racers on TV, if it was a big problem, it would probably be covered in the race reports. But I haven’t read many complaints so maybe the race mechanics keep it in check.
This season I have noticed something else, though – skidding. There’ve been some crashes during emergency stops and near crashes on descents and even on dry pavement. A few of these happened in recent Tour stages so maybe you saw them, too.
You can skid a bike with the best rim brakes but it’s not easy. And with carbon rims it’s very unlikely though it can happen if you heat some rims and carbon specific pads up enough on a descent, which happened to me descending during the Mt. Hamilton Road Race once – a classic climbers’ race in Northern California that passes the famous Lick Observatory at the top: https://www.lickobservatory.org/public-visitor-information/visitor-center/.
Thinking about the skidding this season I Googled a bit and stumbled upon a video by YouTuber DurianRider. I’m not sharing the video here because, let’s just say he has no issues with stating his opinion. You can easily find him by searching for his name on YouTube.
But, he made a fascinating point about disc brakes on road bikes and the skidding. It’s something completely obvious that I should have realized. He pointed out that road bike tires have tiny contact patches. And the size of the contact patch has a huge impact on braking.
Tires have gotten wider on road bikes but the contact patch is still miniscule on full-on race bikes compared to gravel bikes and especially MTBs. It makes sense that that’s what could be causing the best riders in the world to suddenly be skidding instead of stopping.
I don’t know if it’s enough of a problem that the brake makers are looking for solutions. But I have to think at least some of the riders realize skidding is dangerous. If it is deemed a problem, maybe the solution will be even smaller rotors, calipers and pads for road bike discs, which would reduce the braking force and save a few grams to boot.
Or, we could just ditch discs altogether and go back to aluminum rims and rim brakes 😊That setup sure worked well, near perfectly in my estimation.
I look forward to hearing your take on discs in the peloton, the best mechanical derailleurs and electric shifting in the comments.
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s cycling streak ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.