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.

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6 thoughts on “From D7 to T10, part 4: Front drivetrain upgrade

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