If I knew then what I know now, and bought a new folding bike today…

When I bought the Dahon Vitesse, like many folding bike riders, it was a “first bike,” and I went into it knowing considerably less about bicycles than what I know now. Since then, you’ve seen how much it’s changed over the three years I’ve had it at this writing.

It also has to be said that as far as platforms go, with the Vitesse D7, I started at the bottom of the pile. The process of making the bike keep up with my developing abilities as a cyclist was costlier and more involved than I’d like, but it did help me understand the mechanical nitty-gritty of bicycles more.

That got me thinking. Given my current knowledge, if I was in the market for a folding bike now, or if I was advising someone I knew who was eyeing one…what would I be looking at?

AT LEAST EIGHT COGS ON THE BACK WHEEL

A Shimano Tiagra 10-speed cassette sliding onto a splined freehub body on a rear wheel. The same freehub body should work with 8- and 9-speed cassettes too.

This is priority number one. Make sure whatever folding bike you consider possesses at least an eight-speed drivetrain. This means that its stock wheelset has a rear hub ready to accept 8, 9 or 10-speed cassettes on its splined freehub body, considerably reducing on your expense, since you won’t need to switch out hubs or wheelsets.

Bikes with 6- or 7-speed drivetrains are based around freewheels, screwing onto a threaded rear hub. They’re fine to start with, but as far as drivetrain development and upgrade options go, they’re dead ends.

The rear hub is the foundation of most bicycle drivetrains; if you want the bike to grow with you, it is imperative you buy a bike with the correct one. Fortunately that just means that, at the minimum, an eight-speed bike is your best bet.

A REAR DERAILLEUR HANGER

My Vitesse came with a non-replaceable rear derailleur hanger and a screw-on freewheel.

This is easily second priority. I was lucky with the Vitesse, as it came with a rear derailleur hanger, albeit one fixed to the frame and non-replaceable.

Many of Dahon and Tern’s bikes come with Neos rear derailleurs. This used to be Dahon-speak (or Tern-speak) for “no rear derailleur hanger,” because these mount directly to the chainstay. This greatly limits your upgrade options for rear derailleurs. Fortunately this seems to have changed, and Tern at least offers aftermarket dropouts that can mount rear derailleurs – and makes bikes that can use them.

A Neos rear derailleur. The dropout looks like it can be swapped with one containing a rear derailleur hanger.

Sure, you can upgrade the rear shifter alone, as the rear derailleur is just a slave to it anyway. The moment you introduce drastically different cassettes into the picture, however, you might end up regretting being stuck with a Neos unit.

A DOUBLE CHAINRING CRANKSET

It’s not up there in terms of priority items…if we were back in 2013. These days, it’s hard to ignore the breadth of inexpensive folding bike options that come with a road double crankset as stock equipment.

Many folding bikes have a large single chainwheel of around 52T attached to their cranks. The intention is to give the bike’s drivetrain the gearing to emulate a full-size bike, reducing the need to spin the pedals at a crazy high cadence. This works most of the time…on the flats. Introduce a mild uphill gradient, however, and it’s tough negotiating it with such a large chainring, even mashing away with a 30T cog at the back.

A Dahon Vitesse P18. Note the brazed-on tab for the front derailleur, absent on single-chainwheel versions. Also note the large 55/44T chainrings, specifically made for small-wheeled bikes.

It becomes very handy, then, to have a smaller second chainring as a bail-out gear. Yes, bikes that have double cranksets (and relevant shifting hardware) are usually a little more expensive, but I feel it’s money well spent. Otherwise, the bike’s frame usually doesn’t have any provision to mount a front derailleur, which means resorting to front derailleur adapters…that can be expensive and hit-or-miss in effectivity.

Luckily, LitePro specialized itself around Dahon’s and Tern’s bikes, and other bikes with a seat tube outer diameter of 40 mm. Some bike brands however aren’t so lucky, such as Doppelganger.

My Vitesse D7 needed a LitePro SP8 front derailleur adapter, which mimics the braze-on tab on the Vitesse P18.

DISC BRAKES…?

A Dahon Formula S18 from 2013, sporting a double crankset and Avid mechanical disc brakes. Perhaps the ultimate iteration of the KA-series frame in flat-handlebar form.

Riding my TCX for two years now, I am totally sold on disc brakes. Sorry, rim brake fans, but they’re simply inferior. In my amateur motorsport days, I spent four years beating more powerful cars lapping around a racetrack simply because I had better braking as my primary weapon.

That said, my only concern with disc brakes on folding bikes is bimodal commuting. In a crowded train or bus, a rotor can get bent out of shape, have undesired liquids spilled on it, have somebody else’s finger or leg cut on it…or some other mishap.

And by the way, disc brakes are a feature of the frame itself; the frame tubes are strengthened to cope with the forces generated by these brakes. Attempting to retrofit disc brakes on a rim brake frame is a very bad idea.

WHEEL SIZE: 406 MM VS 451 MM

A modified Tern Verge X10, fitted with a deep-section 451 mm wheelset.

Due to the influence of both road bikes and mini velos, the 451 mm wheel size (the “fractional” 20″ size, e.g. 20″ x 1-3/8″) has gained popularity. The larger wheel size boasts many benefits, such as improved speed and decreased rolling resistance. Aesthetically it certainly looks nicer, and bulks up the frame of a folding bike quite nicely.

The 406 mm size (the “decimal” 20″ size, e.g. 20″ x 1.5″) is a folding bike mainstay for one big reason, however: BMX. Unless BMX dies out or becomes out of fashion, the supply of 406 mm wheels, tires and inner tubes isn’t going away.

Bino rolls on a 406 mm wheelset. Next to 451s, these look slightly dinky, but they do the job.

Besides consumables availability, there are other downsides to a 451 mm wheelset. You can’t get a 451 mm tire wider than 35 mm, and fenders this size can be harder to find. Technically, you can make a folding bike frame equipped with 406 mm wheels work with a 451 mm wheelset, but it will require relocation of the V-brakes.

451 mm wheels are tempting, but I can’t recommend them. Not yet, at least.

FRAME MATERIAL

Aluminum alloys, such as 6061 and 7006, are the norm for many folding bikes.

The default choice for many is aluminum: affordable, relatively light, and can be made pretty strong. Not the best reputation for ride quality, though, which is why you rarely ever see forks made out of the stuff. Combine that with the inherent disadvantage in ride quality on smaller wheels, and you’ll see why comfort isn’t a strong suit for most folding bikes.

Too many people underestimate steel, thinking that it’s heavy and cheap, but 4130 chromoly steel largely addresses those negatives while providing the material’s legendary ride quality. Indeed, my Vitesse came with a chromoly steel fork.

The whole business of folding these bikes introduces the risk of water ingress and rust, however, so I’d give the nod slightly toward aluminum. Stainless steel or titanium would be great options but cost too much.

SUMMARY

Look, it’s perfectly fine to get a 6- or 7-speed folding bike with rim brakes. Given proper maintenance it should give you years of enjoyment as is.

Unfortunately, it’s also a lousy platform for upgrading to better componentry. Depending on what bike you buy, it’s completely possible to spend more than its purchase price in upgrade costs alone.

At the very least, budget permitting, I’d recommend a 2×8 folding bike with 406 mm wheels and disc brakes. It will be more expensive at the outset, but it’s better equipped to grow alongside you as a cyclist, and should offer better bang for your buck overall.

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I hope you found this interesting, informative or educational. Let me know what else you want to see featured on the blog by leaving a comment. Happy riding.

A guide to rear derailleur cage length: Short, medium or long?

Ahh, the good old rear derailleur. You already know that it shifts your chain up and down the cassette. But did you know it has a second job?

The funny looking thing dangling on its bottom with the two pulleys is called the rear derailleur cage. Apart from moving the chain to the next cog via the top guide pulley, it has to keep the chain in tension by taking up the slack – using the bottom tension pulley and the P-knuckle spring inside the derailleur itself.

Smallest cog + small chainring on the Dahon Vitesse T20.
The Tiagra rear derailleur’s medium-size cage is set all the way back.

This is most evident when you shift to your smallest rear cog and smallest front chainring. In this combination, your chain is the slackest it will get, with barely any tension in its links. The rear derailleur cage will be set as far back as it will go as the P-knuckle spring tries to keep the chain tensioned.

Conversely, if you shift to the largest cog and largest chainring, the cage will be set forward as the chain is under the most tension.

If you look at different bikes long enough, you’ll notice the cage varies in length from bike to bike. Ever wondered why this is so?

First let me tell you what it doesn’t mean.

  • The length of the rear derailleur cage doesn’t determine shift speed.
  • The length of the rear derailleur cage doesn’t determine how cool a cyclist you are.
  • The length of the rear derailleur cage doesn’t necessarily determine the largest cog it can accept.

Let me return to that last point – it does, sort of, determine the largest cog you can use. However, it’s not the whole story. The whole business about largest cogs is only part of a bigger, more important picture.

The service instructions bundled with your rear derailleur contain all sorts of instructions, specifications and numbers. One of the those that doesn’t seem immediately obvious or self-explanatory is called total capacity or chain capacity.

WHAT DOES “TOTAL CAPACITY” OR “CHAIN CAPACITY” MEAN?

It’s the amount of potential slack chain the rear derailleur cage can handle — the discrete measurement of how well it can keep a chain in sufficient tension. Seeing as it’s expressed as a number of teeth, it’s derived by the following equation:

Chain capacity = (biggest cog teeth – smallest cog teeth) + (biggest chainring teeth – smallest chainring teeth)

Because it’s based the number of teeth of the entire drivetrain, the effective chain capacity varies from bike to bike. Drivetrain manufacturers therefore have to cater for these variations.

CAGE LENGTH: SHORT, MEDIUM OR LONG

Shimano categorizes its rear derailleurs into three tiers depending on the cage length, and they’re denoted by the suffix on the model number.

  • “-SS” refers to the short-cage versions, with a maximum chain capacity of 33T or less. These are usually the domain of road bikes. On the mountain bike side, the few true short-cage rear derailleurs that exist are for downhill or gravity racing applications, such as the Saint RD-M820 unit, since this discipline usually does away with large cogs and multiple chainrings.
  • “-GS” refers to medium-cage rear derailleurs, built with a maximum chain capacity of 37T to 39T or less. This is usually the longest cage offered for road bike rear derailleurs, but also the default “short” option offered for their mountain bike counterparts.
  • “-SGS” marks the long-cage rear derailleurs and this is exclusively the domain of mountain bikes or any unit marketed for touring bikes. A typical unit sees chain capacity well into the 43-44T range.
Shimano Deore RD-M615-SGS, long-cage.
Rated max chain capacity is 43T.

Shimano Saint RD-M820-SS, short-cage for downhill MTB.
Rated max chain capacity is 25T.
 

In the real world, how does this all work? Let’s look at my bikes.

CASE 1. BINO AS A 1×10 BIKE

When Bino first received a drivetrain upgrade, his rear freehub body received a 12-30T cassette and a Tiagra RD-4600-GS medium-cage rear derailleur was bolted onto his frame. This has rated chain capacity of 39T or less.

Bino in Dahon Vitesse T10 form. 1×10 drivetrain on the largest 30T cog.

Computing chain capacity on a bike with a single chainring is pretty simple.

Chain capacity = (30 – 12) + (52 – 52)

Chain capacity = 18 + 0

Chain capacity = 18T

For a 1×10 bike, in terms of chain capacity, the medium-cage Tiagra rear derailleur is actually overkill. While there is technically nothing wrong with running a medium-cage rear derailleur, given Bino’s small wheel size and potential ground clearance issues, many people prefer a short-cage unit for their folding bikes.

CASE 2. HYRO’S STOCK DRIVETRAIN

Tiagra CS-4600 cassette, 12-30T + 105 RD-5701-SS short-cage rear derailleur
FSA Omega cyclocross crank, 46/36T

Hyro came stock with a RD-5701-SS rear derailleur from Shimano’s 105 5700 groupset, specified to accept a 28T largest cog and a total capacity of 33T or less. It was paired with a 12-30T cassette and a 46/36T cyclocross-specific crank. On paper, the rear derailleur isn’t supposed to work with a cassette with a 30T largest cog.

An excerpt from the service instructions for the 105 RD-5700 rear derailleur.

Or should it? It doesn’t seem to make sense for Giant to have built up the bike with these drivetrain parts. Let’s use the chain capacity equation and compute.

Chain capacity = (30 – 12) + (46 – 36)

Chain capacity = 18 + 10

Chain capacity = 28T

This combination of cassette and chainrings is actually quite comfortably below the 33T limit. On the stock gearing I never had any shifting problems, and could even cross-chain if necessary.

CASE 3. HYRO AND BINO WITH ROAD COMPACT CRANKS INSTALLED

I completed the 105 groupset drivetrain parts by installing the FC-5750, a 50/34T road compact crankset. I used the exact same chain as before, and for a while I thought everything was peachy. Shortly after, I started getting poor chain retention and dropped chains when I used the two largest 27T and 30T cogs with the 50T chainring, which my chain catcher has been working overtime to combat.

Largest cog + large chainring. The rear derailleur cage is just too short, and the gear combination requires a longer chain as it’s no longer wrapping around the pulleys.

So what happened here? Let’s revisit the chain capacity equation.

Chain capacity = (30 – 12) + (50 – 34)

Chain capacity = 18 + 16

Chain capacity = 34T

Uh-oh. With increased gap between the 105 crank’s chainrings, my rear derailleur and chain are overwhelmed by the added chain capacity of the entire system. The effects are dramatic.

Largest cog + large chainring with the Tiagra RD-4600-GS medium-cage rear derailleur. The chain still makes an S-bend around the cage and pulleys, which means the rear derailleur handles this combination just fine.

Bino’s recently completed 2×10 drivetrain provides the answer. The cassette and chainrings are identical, but because the Tiagra rear derailleur has so much more chain capacity, used with an accordingly longer chain, I haven’t had any chain retention problems at all.

I don’t have the cyclocross crank any more, so solving Hyro’s problem requires a longer chain.

Smallest cog + smallest chainring with a short-cage 105 rear derailleur.

As seen in the above photo, retaining the short-cage rear derailleur while fitting a longer chain isn’t going to be enough, because its cage can’t handle any more slack. The chain is already close to rubbing on the rear derailleur’s guide pulley and the TCX’s chainstays.

CASE 4. REMEDYING HYRO’S ISSUES

I got a good deal on a second-hand RD-5700-GS medium-cage rear derailleur with 37T rated max chain capacity. It’s pretty rare, as most RD-5700 and RD-5701 units found in the Philippines are of the short-cage flavor.

Shimano 105 RD-5700-GS rear derailleur
The back side of the RD-5700-GS

I would then need to break the current chain and replace it.

With the chain broken and removed, off comes the stock RD-5701-SS short-cage 105 rear derailleur, and on goes its bigger brother.

Short-cage SS model on top, medium-cage GS model at the bottom

I paired it with a basic Shimano CN-HG54 10-speed chain.

Driving the joining pin into the chain.

With the rear derailleur replaced, I installed the chain. It’s now at 112 links compared to the outgoing chain’s 108.

Rear derailleur and chain swap complete.

To check my handiwork, let’s shift to the smallest cog and small chainring combination.

Smallest cog + small chainring on the medium-cage 105 rear derailleur.
A closer look.

The longer derailleur cage is doing a good job of keeping tension on the lower run of the chain. Let’s move the chain all the way to the other direction.

Largest cog + large chainring combination on the medium-cage 105 rear derailleur.

Things look good here too. The cage angle is nowhere near as horizontal as the short-cage derailleur was. Turning the pedals with the bike on the stand, I’m getting much better chain retention on the big chainring. The chain used to drop into the small chainring when I got within a sniff of the two largest cogs. Perhaps I could have even used all 114 links the chain came with.

While it’s still no good for the drivetrain to stay in a cross-chained state, with no optical gear indicators on the STI levers, it’s easy to lose track of gears when hustling the pace. Chain drop on such occasions can be catastrophic as forward drive is lost. With the 105 medium-cage rear derailleur and a suitably longer chain, my TCX can at least retain drive while remedying the cross-chained state.

CONCLUSION

With that, a quick summary of lessons:

  • A correctly sized chain is critical for a derailleur drivetrain with multiple gears.
  • A chain with insufficient length means there is too much tension to use certain gear combinations.
  • A rear derailleur is responsible for shifting the chain up and down the cassette, and maintaining tension on the slack links of the chain.
  • Rear derailleurs have different cage lengths in order to better handle the chain capacity of a drivetrain’s combination of chainrings and cassette.

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.