Anatomy of a square-taper bottom bracket

Remember that Bino, my folding bike, had a three-piece crank as stock. I’ve since swapped it out for a Shimano FC-R565 two-piece unit and an SM-BBR60 Hollowtech II bottom bracket. Ever wonder what happened to the stock square-taper bottom bracket?

Here it is in all its greasy glory.

Mushrooming out of each side are the crank bolts, which I screwed into the ends of the spindles just so they won’t get lost. Otherwise, that’s how the bottom bracket would look like had it still remained inside the Dahon Vitesse frame’s bottom bracket shell, with the two bearing cups screwed in. One of the cups is fixed, on the drive side, while the other non-drive side cup is adjustable.

I’m holding the bottom bracket here by the cups. You’ll notice it’s actually pretty slender in the middle.

Moving the adjustable bearing cup outward reveals the actual ball bearings themselves, contained in a cage. They work with the spindle by suspending it by its raised flange in the middle, acting as a bearing race, with the rest of the support handled by the bearing cups. As you can see, this is pretty much the guts of any bottom bracket – the ball bearings that let the spindle rotate freely.

Over on the drive side, it’s a similar affair, except that the fixed bearing cup itself also acts as the cage for the ball bearings. The whole point of having an adjustable cup is to be able to tighten the entire bottom bracket and add pre-tension to the bearings so that they can still spin freely, but with zero play or looseness at the spindle.

As far as square-taper bottom brackets go, this CH unit is about as simple as it gets. It’s much simpler than, say, a Shimano BB-UN55 sealed cartridge unit.

Even with the relatively unsophisticated construction, however, this bottom bracket still does its job and spins smoothly. It’s easy to knock square-taper bottom brackets, but their design is sound, and thousands of bikes around the world still pedal on with this humble bottom bracket providing kilometer upon kilometer of reliable service.

I hope you found this interesting.

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From D7 to T10, part 4: Front drivetrain upgrade

In a previous installment of the T10 diaries, I mentioned that expanding the rear gearing from the stock 14-28T to 12-30T was not quite as large an improvement as I had hoped. I also said I still had a perfectly functional Tiagra flat-handlebar front (left) trigger shifter.

Well, after slowly collecting the requisite parts, now’s the time. I’m actually turning Bino into a Dahon Vitesse T20.

PARTS BREAKDOWN AND ANALYSIS

Crank swaps aren’t new to me; I’ve had Hyro’s front gearing widened from the stock 46/36 to a 50/34 road compact double. With Bino, I thought of going slightly in the other direction. I will be changing out the stock 52T single chainwheel with Shimano’s non-series FC-R565 road compact crank.

Bino’s stock 52T single chainwheel and 170 mm crank arms, driving a square taper bottom bracket.

Shimano compact cranks: FC-R565 on the left, 105 FC-5750 on the right. Note just how similar they look.

The incoming crank will cut out some of the bike’s top end. The little Dahon is my around-town beater bike, so I decided to emphasize utility this time. On the occasions that I decide to put Bino into long rides with ascents, the 34T small chainring should help me climb them via high-cadence spinning without taxing the frame too much.

The FC-R565 cranks do have a slightly longer 172.5 mm arm length, which should help with torque.

Shimano SM-BBR60 Hollowtech II bottom brackets, listed as Ultegra-class parts. Price in Singapore dollars.

A crank is useless without a bottom bracket enabling it to rotate. I bought these BSA-threaded SM-BBR60 bottom brackets by mistake while I was looking for a press-fit SM-BB91-41B unit in Singapore. They’re perfect for this upgrade, and I’ll have a spare on hand when the installed one goes kaput.

I got this Tiagra FD-4600-F braze-on double front derailleur for cheap second-hand. It had come off a built bike and was barely used.

Three years after purchase, it’s time to take this thing out of storage.

My left shifter is actually a Tiagra SL-4603 unit, meant for a triple-chainring crank. They are rare where I live, and they won’t fit on the little Dahon. For this setup, the third shift position will be disabled via the limit screws on the front derailleur.

LitePro SP8 front derailleur adapter. This is designed to work with Dahon’s KA-series frames (Speed, Vitesse, Mariner, Boardwalk) and Tern’s equivalent models (Link).

Outside of a few exceptions, such as the Vitesse P18 and Formula S18, the Vitesse frame wasn’t made to mount a front derailleur. If it was, it would have a brazed-on mount tab on the seat tube. This is where a front derailleur adapter comes in as a substitute. LitePro makes them for the 33.9 mm seat tube diameter of Dahon and Tern’s various folding bike frames, and I got the SP8 model for my frame.

As I don’t have the tools to fit the crank and bottom bracket, I went to Tryon for the installation, where I bought the front derailleur adapter as well.

Tiagra front derailleur mounted. Many people look down on non-series parts, but for me the polished chainrings on the FC-R565 crank are a handsome detail.

Non-drive side crank arm and a peek at the SM-BBR60 bottom bracket.

A better look at the LitePro SP8 front derailleur adapter as it wraps around the seat tube. Tryon had run out of other color options, which is fine since Bino’s LitePro hubs are also anodized red.

With better braking and wider gear range, the finished product is not too shabby for something built with so many second-hand parts. My Dahon Vitesse T20 is finally complete.

RIDING IMPRESSIONS

Riding at speed on flat sections, I definitely feel the shortened top-end, as I find myself shifting into the 50×12 top gear quite easily. The slightly longer crank arms also mean I get there a little sooner than I anticipated, as I cruise flats at 34 km/h. This reinforces the “easygoing utilitarian” remit I’ve assigned.

When hustling the Vitesse, I find myself riding in this top gear combo sooner than expected.

Spinning the pedals in the 34T small ring can feel a little comical because I’m turning the pedals at a high cadence but my road speed isn’t exactly increasing. I managed to crawl along at 4 km/h in the 34×30 lowest gear on a flat road once, just for fun. Climbing is a different story, though. Popping the left shifter on inclines, even in the middle of the cassette, aids ascents quite noticeably.

For most riding, I’ll leave it in the big ring, with the small ring as a bailout gear for tough climbs.

The middle setting on the optical gear display means the 50T big ring is active. After this, the front derailleur limit screws stop the shift paddle going any farther.

Mounting the left shifter does mean its larger paddle smacks the left fork blade when I fold the handlepost down. I had to figure out a way of folding Bino into his compact form while minimizing or eliminating parts hitting or interfering with each other. It can still be done, but the Magnetix parts no longer meet to hold the folded form together.

Range of the stock 1×7 drivetrain in gear inches.

After the 1×10 upgrade, overall range expands, but more toward top end. Still in gear inches.

After the 2×10 upgrade and crank swap, the bike’s range in gear inches increases towards the low end. Top-end range — and theoretical top speed — is decreased slightly.

Here’s a side-by-side comparison of speeds per gear at a given cadence. Left table is for the 2×10 50/34T crank; right table is for the 1×10 52T crank.

Time will tell if the current gearing is sufficient. If I do end up swapping cranks — perhaps for a Tiagra FC-4600 52/39 unit, if I wanted to get a full groupset — at least I wouldn’t have to change out any other parts, except a resized chain.

FUTURE PLANS

As far as the drivetrain goes, there’s really nothing left to upgrade. Once the current cassette gets worn, the Tiagra 4700 10-speed groupset ensures that I can swap in an even more climbing-friendly unit with 32 and 34T cogs without replacing anything else.

From what I’ve seen, the 11-speed route isn’t straightforward. There are a lot of parts required to make it work, most fundamental of which is the rear hub. Shimano’s 11-speed road groupsets also introduce a long-arm front derailleur, and the shorter cages on those may introduce their own issues. Finally, compatible flat handlebar trigger shifters, such as the Shimano SL-RS700, are not available locally and will have to be imported. For now, the hardware outlay makes me miss the point of 11-speed.

From D7 to T10, part 3: Bettering Bino’s brakes

Brakes are a pretty big deal to me. They’re the primary reason why I was able to post respectable lap times in an underpowered grocery getter back when I was still a privateer time attack race driver. Personally, I’m quite finicky with their feel and action, and that carried over to my two bikes.

Hyro has excellent TRP Spyre mechanical disc brakes as stock equipment. Coupled with 160 mm brake rotors, metallic brake pads, compressionless brake cable housing, and Shimano’s 105 (ST-5700) STI levers, there’s very little to complain about their braking power, modulation, and feel.

This was what the Promax front V-brakes looked like when Bino was new. Note how much free space there is on the top where the cable anchor bolt is.

Bino, on the other hand, came with Promax V-brake arms and brake levers. There’s a reason why the very first mechanical work I did on a bicycle was on the brakes: I wasn’t satisfied with them. Out of the box, squeezing the levers resulted in a spongy feeling, with not much tangible braking power in the first 50% of the lever travel. My personal preference is to have the brake pads biting well at that point.

Bino’s Promax front V-brakes tuned to my liking. They’ve been cinched up so much, the rubber cable boot isn’t even doing anything and is torn at the bottom.

This would be tolerable by itself, since V-brakes can be tuned and adjusted to provide the kind of feel and power you prefer – and I did cinch up the V-brake arms to my liking. However, the brake levers themselves are also disappointing. There’s tangible side-to-side slop you can feel when you tip the brake lever up or down with your fingers curled around it. Coming from the satisfaction of a solid-feeling brake pedal in my car and STI levers on my cross bike, that’s not very reassuring.

The rear V-brake arms tuned to my liking. The right arm is the one with the bad return spring. Notice the rubber cable boot torn up at the bottom as well.

I carried on with the stock brake setup for three years, until the return spring on the rear V-brake arms decided it was time to give up. With a bad return spring, the V-brake arms don’t readily return to their starting positions when you let go of the brake lever. This causes the brake pad to drag along the braking track of your wheel, making acceleration and maintaining momentum harder than it should. In some cases it can even interfere with the wheel’s rotation badly enough to prevent you from riding. It got to the point where I had to go against the textbook method of maintaining a rim brake, and skewed the brake pads downward just so I could avoid them terminally dragging on the rim.

At that point, I decided to just upgrade the braking system with Shimano parts. Despite mountain bikes having largely migrated to disc brakes, the Osaka bicycle component juggernaut still makes V-brake hardware.

After some shopping around, I got a good deal on some second-hand Shimano Alivio Trekking BL-T4000 V-brake levers. Nothing fancy or notable about these, except that they have barely noticeable slop at their pivots and have levers with slightly more girth. They’re little things, but they add up.

These levers got paired to Shimano Alivio Trekking BR-T4000 V-brake arms. Without “cheating” or looking at model or part numbers, they don’t give away that they’re actually part of a groupset. I like the simple, workmanlike aesthetic of all the brake hardware.

You can barely see the model number. It’s hiding behind the brake shoe bolt.

I had the brake hardware installed at Tryon. Hooked up, the mechanics did a great job tuning the brakes for solid initial bite; I doubt I’d be fettling with them soon. Riding around Makati, the levers have a great feel and good action with a minimum of unwanted movement, while the brake arms themselves give nice speed retardation. There’s definitely something to be said about V-brake arms that nicely spring back to their initial position once you let go of the lever.

Taking a closer look at the Promax and Shimano V-brake arms, I can see the main difference. As you go up from the V-brake mounting posts of the frame, the Promax arms are simpler and straighter, while the Shimano arms bow outward midway.  This shaping effectively lengthens the amount of cable that the system of brake lever and V-brake arms can pull, thus increasing leverage and braking power.

Rear pair of Alivio Trekking V-brake arms. See the curves in them and on the return springs?

Granted, there are still many reasons why V-brakes are inferior to any disc brake. Their rubbery brake pads won’t offer as good a modulation as the solid material of their disc brake counterparts, and the fact that they’re still rim brakes means they’ll wear away at wheelsets and they’re always going to be at some sort of disadvantage in the wet. Next to Hyro’s TRP Spyres, V-brakes are also nowhere near as simple to tune. Even with these quirks, though, a well-tuned V-brake is just about the most powerful rim brake you can get.