End of an era: Shimano 105 FC-R7000 crankset

The past couple of years, Hyro has enjoyed the substantial technological leap of going 11-speed with hydraulic braking. Majority of said leap came courtesy of parts from Shimano’s 105 R7000 groupset, with exceptions due to identical parts (the 105 FD-5801 front derailleur) or frame design decisions (Post Mount hardpoints require the BR-RS785 brakes and accompanying ST-RS685 STI levers).

I left one upgrade on the table for a very long time, though. I soldiered on with 11-speed everything except for my FC-5750 crank, from the Shimano 105 5700 10-speed groupset. The main reason I had stuck with it for so long was that I had just replaced its worn-out chainrings, and among all the parts of a groupset the crank is usually considered the one with the least compatibility headaches.

Or so I thought.

“Least compatibility headaches” might have been true at the beginning, when the chainrings were still fresh. However, with time and kilometers ridden, I suffered more frequent inside chain drop, especially if I wasn’t mindful enough to shove the chain onto the relevant end of the cassette before shifting at the front. Shimano also said the 105 R7000 crank was designed to better accommodate road bikes with disc brakes, as its stance and chainline are both slightly different from older 105 crank models.

It took the arrival of my 4iiii Precision power meter, itself based on a 105 R7000 left crank arm, to realize that maybe I had been holding back for too long. I was not doing Hyro and my riding any favors by continuing with a compromise, and besides – the crank is by far the visible heart of the entire groupset.

So here we are with Shimano’s 105 FC-R7000 crank, but still in the same spec: 50/34T chainrings, 170 mm arms, and the old reliable 24 mm hollow steel spindle. This is about as plug-and-play as a bike part install gets, especially considering my Shimano BB91-41B bottom bracket bearings from 2015 are still spinning smoothly and without any noise. Who says press-fit bottom brackets all creak? Mine don’t, at all. Kudos to Giant for making a fantastically reliable BB86 bottom bracket shell.

Spinning smoothly since 2015. If your press-fit bottom bracket creaks, blame your frame manufacturer.

That left crank arm is staying in storage, though. I have no reason to run that when I already have the 4iiii power meter crank arm.

724 g all in. 4iiii’s power meter pod adds 9 g.

The underside of the big chainring has its shift ramps scalloped out – a design feature carried over from the previous generation 105 FC-5800 crank, perhaps done in the interest of saving weight. This is about as weight-weenie as I’d get with cranks, and the reason I did not bother with Ultegra or Dura-Ace cranks with their two-piece hollow crank arm construction. While that technique of bonding two pieces into a hollow crank arm is impressive for weight savings, it’s also invited a spate of frankly dangerous crank arm failures.

Nice design, but I dread working on it. Better have some spare shift cable just in case you mess up.

Replacing the crank means re-tuning the front derailleur to suit. This is my least favorite part of working on a modern 11-speed bike, by far. While I appreciate Shimano baking in onboard cable tension adjustment into the cam-action pinch bolt, the instructions the Japanese firm publishes are best followed when you don’t have a chain running through the front derailleur cage. Dialing in cable tension with the 2 mm grub screw and lining up the tension marks can be frustrating with the chain in the way, and doing this enough times can kink and fray your shift cable into an unusable, wasted state (hint: better to put the chain manually on the big ring first if you don’t have a master link). If there is an argument for going the master link route with your 11-speed chains, this would be the biggest IMHO.

(L) 105 FC-R7000, (R) 105 FC-5750

That said, Shimano wasn’t lying about the 105 R7000 crank’s revised stance. At full throw, prior to readjustment and tuning, the front derailleur cage didn’t move outboard enough to shift the chain to the big ring. Limits had to be reset, cage orientation repeated, and even the little support bolt bracing front derailleur against seat tube needed adjustment. Once done, the now-completed 105 R7000 drivetrain is much more tolerant of front shifts at non-ideal rear cog placements. I have yet to suffer a dropped chain – fingers crossed this holds true even after much riding.

With the crank swap goes the final vestige of 105 5700 on Hyro, which was my favorite iteration of Shimano’s workhorse groupset from an aesthetic perspective. While I appreciate the functional and ergonomic improvements in newer groupsets, I haven’t yet warmed up to the brasher, chunkier, more angular cosmetics of 105 R7000, and by extension Dura-Ace R9100 and Ultegra R8000.

Replacing chainrings on a five-bolt crankset

Previously I wrote on how front shifting happens between chainrings, and I noted that mine were particularly worn. I got my Shimano 105 FC-5750 cranks second-hand to begin with, so adding thousands of kilometers on that starting point eventually meant Hyro’s front shifting was going to deterioriate sooner rather than later.

Unlike with a chain, measuring wear on chainrings isn’t straightforward. I found though that one giveaway is deteriorating quality and ability of upshifts to the big chainring. If you’ve ruled out the front shift cable and front derailleur adjustment, and you still have upshift failure in larger cogs, your chainrings may well be the culprit.

Unfortunately, many Pinoy cyclists would rather just replace an entirely fine cranket instead of just the worn rings, partly because they may not know any better, and partly because new chainrings aren’t easy to find locally in bike shops. Add to that the recent proliferation of proprietary asymmetrical BCDs (bolt circle diameters = the diameter of an imaginary circle that runs through all a crankset’s bolts) from Shimano, Campagnolo, and FSA, and you have one bike maintenance job that is losing popularity pretty quickly.

Today I’ll be walking you through chainring replacement on a crankset with a five-bolt spider of 110 mm BCD. This is pretty common on 50/34T and 46/36T chainring combinations. For reference, a 53/39T crank uses a 130 mm BCD, and many cranks for fixed gear use have an even bigger 144 mm BCD.

The process uses mostly standard tools, with the exception of a chainring nut wrench. This is best described as a fork with its tines shortened and thickened, then bent over at a 90-degree angle. Its purpose is to prevent chainring nuts from spinning as you loosen the chainring bolts on the other side.

On Shimano Hollowtech II two-piece cranks, I find it a little easier to remove the non-drive side crank arm first, then tap the crank spindle end with a rubber mallet just enough to free up room behind the chainrings. This way, the bottom bracket shell will act as a sort of “third hand.”

Insert the chainring nut wrench into the grooves of the chainring nuts on the back side of the chainring. On the front side, use the relevant tool to break the chainring bolt free. On my Shimano 105 FC-5750 crank, you will need a T30 Torx key and quite a bit of force, as Shimano recommends a torque spec of 12-15 Nm.

The inside of a pair of fresh chainrings. No shiny bits of worn-down anodization here, just a satin black finish.

Once all five pairs of chainring nuts and bolts are loosened, the chainrings should come apart from the crank spider. Pay attention to how they come apart, as most of the time chainrings are meant to mount in only one correct orientation. This is to ensure correct “clocking” of the various shifting ramps and pins and ultimately smoother front shifts.

Fresh teeth!

One feature to watch for on the big chainring is the chain drop prevention pin. On a Shimano crank, this is intended to live underneath the drive side crank arm. In the event of an overly eager upshift, or a sloppy high limit on a front derailleur, this pin is the last line of defense protecting your crank arms against the surprisingly savage cutting friction of a dropped chain.

Chain drop on the outside can literally eat your crank arms.

My outgoing big chainring lost this pin for some reason…hence the battle scars all over my crank.

Re-installation is the exact reverse of removal, although some prep needs to be done. As chainring nuts and bolts are a common cause of creaks, first you’ll want to clean them well with degreaser and a rag or paper towel, then smear some fresh grease on.

Align your new chainrings correctly onto the spider. On these Shimano chainrings, the chain drop prevention pin on the big chainring and an engraved little triangle on the small chainring have to line up with the drive side crank arm. You can see these on the inside.

Put the chainring nuts and bolts on the spider and turn until finger-tight. Then break out your torque wrench, attach its T30 driver bit, and tighten them to 12-15 Nm in a star pattern.

You’re done! Reinstall the crankset and you should be in good riding condition again.

A fascination with chainrings and front shifting

It’s been a while. It hasn’t been easy juggling work commitments and an ongoing course in Web browser test automation, while reserving mental capacity to write new posts. But here I am.

Look closely. Note the angled teeth and little notches on some of the cogs on this cassette.

Ever since I was first introduced to road bikes with my dad’s 1981 Peugeot P8, I’ve always been fascinated with the mechanics of how a chain literally jumps over to shift to another gear. On the rear of the bike, this is obvious for all the world to see. This funny-looking thing with the little pulleys on it, dangling on the underside of the frame, called a “rear derailleur,” somehow magically shoves the chain up and down the cogs. On newer cassettes, the cogs are shaped with little divots and other features which are meant to smoothen this process.

Up front, however, this is a lot less obvious, because chainrings are essentially huge cogs put in backward. All the little features and mechanisms that facilitate a front shift are hidden as they are sandwiched between the drive-side crank arm and the bottom bracket shell.

The front derailleur doesn’t help, either. Next to the rear derailleur, the front derailleur is a much more simple-looking mechanism, not doing as much to reveal the magic behind performing a front shift – arguably surrounding it with more mystique.

Curiosity taking over me, I decided to take a closer look.

Performing a downshift from the big chainring to the small chainring is a pretty straightforward affair, with the front derailleur cage doing the bulk of the work, along with any chain catchers or chain spotters. The chain is just pushed off, dropping onto the smaller chainring.

The real magic is how the chain gets to climb from the small ring to the big ring. How does it do that?

The front derailleur is just there to initiate the shift, again, by pushing the chain outboard sideways with brute force. That’s only half the job; the remainder of the shift is completed by the many features on the inside of the big chainring.

Looking on the inner edge reveals a few interesting things. There are little oval divots which seem to match the links of a chain, and they feed into raised shift pins. The divots and pins look like they follow a line tangential to the small chainring. This is effectively the other, hidden half of the front shift mechanism. On this Shimano 105 chainring, these ramps and pins are still rather simplistic compared to later iterations or more expensive chainrings, but for illustrative purposes they do the job.

Performing a front shift and breaking it down step by step reveals how the chain climbs a 16-tooth gap between chainrings. With the chain already traveling outboard from the initial push of the front derailleur, the shifting pin grabs it onto the big chainring, while the tangential divots serve as ramps to help up the rest of the chain off the small chainring.

As my chainrings have already been worn by many, many front shifts over many kilometers of riding, you can see on the inside of the front chainring just how the individual links have slid on and off.

That said, these are obviously worn chainrings, and the wear has made itself felt while riding. I used to be able to smoothly upshift in my third-largest 24T cog; now, the increasing failure rate of front upshifts is pretty bad when I’m in a cog larger than my sixth-largest 17T. Next time I’ll walk through chainring replacement.