Fnhon Gust: Caliper Brakes Setup and Chain Interference

With all the components ready, assembly of the Fnhon Gust can begin!

To complete the groupset, a pair of Dura-Ace 9000 caliper brakes were also supplied, to match the rest of the components. Previously, I have used caliper brakes on a few folding bikes, but they were never ideal. For example, I had to use long arm Tektro caliper brakes on the Dahon Boardwalk and Dahon Vitesse, but they were not ideal as the bike was not designed with caliper brakes in mind. Using long arm caliper brakes means less braking power.

Later, the Dahon MuSP was built, and it was designed to use caliper brakes by default. This is much better as the brake caliper position matches the rim diameter perfectly, allowing the use of standard reach brake calipers which have better braking power.

For this Fnhon Gust frame, I have seen both caliper brakes and V brakes being used. However, I am not sure how well they fit, as I am not familiar with this frameset. This provides a good opportunity to learn about this frameset.

Dura-Ace 9000 caliper brakes. Powerful and relatively lightweight at about 300 grams per pair.

As the crown of the fork has a curved surface, a curved spacer needs to be added to stabilize the caliper brake.

Original fixing nut is too long and cannot be used on this fork.

Luckily, I have a whole bag of fixing nuts with various lengths, and I chose one that fits.

Also found a curved spacer, which goes between the fork crown and the brake caliper.

For the rear brake, a curved spacer is not necessary.

With this combination of fixing nut length, the pair of brakes weigh exactly 300 grams.

At first look, it seems that caliper brakes can be fitted onto the frame with no issue. However, that is not the whole story. The next step is to see if the brake pads are able to touch the rims properly, and whether there is sufficient tire clearance.

Normally, the claimed tire clearance is about 28 mm, when used on standard frames and rims. However, this clearance can be a bit bigger, if the caliper brake is further away from the axle.

Surprisingly, the caliper brakes can clear a 35 mm wide Kojak tire!

For this frame, the caliper brakes are able to clear the 35 mm wide Kojak tires, but that is because the caliper brakes are further away from the axle. This poses another problem, where the brake pads cannot reach the rim braking surface. Starting with the front fork, let's see the problem in detail.

By purposely adjusting the centering bolt to favour one side, it is possible to make one brake pad lower, so that it just manages to clear the tires...

...while the other side will not be able to reach the rim.

The alternative is that both sides will not be able to reach the rims. As there is strong preference to use caliper brakes, I will try my best to make it work. I have a trick up my sleeve, which is to use brake pad extenders to shift the brake pad position downwards.

Using brake pad extenders, the brake pad can be offset by about 10 mm. This effectively increases the reach but also decreases the brake ratio and thus braking power.

After adding a brake pad extender on one side, it is able to clear the tire and touch the rim properly.

Front caliper brake with brake pad extender on one side only. 

Not much clearance for the rear tire, as the brake bridge is quite close to the tire.

The brake pad is barely able to clear the rear tire, with no margin at all. Possible to use but not so safe.

Small but sufficient tire clearance inside the brake caliper.

Based on these testing, it is possible to install caliper brakes on this frame to match the 16 inch 349 wheelset. However, there are some compromises, which means that it is not a direct and easy fit.

It seems to be possible to use a 18 inch (ETRTO 355 mm) wheelset, which is slightly bigger than 16 inch (ETRTO 349 mm) wheels, to fit caliper brakes. This will allow the standard reach caliper brakes to reach the rims properly without brake pad extenders. This is the size that is used on most Birdy folding bikes.

However, due to the tight tire clearance at the rear, a narrower and thus smaller diameter 18 inch tires will need to be used. There is a slightly narrower 18 x 1.25 (32-355) Schwalbe Kojak tire, but I think the diameter might be too big to clear the rear brake bridge. Maybe can, maybe not.

Moving on, I used a Rear Derailleur Hanger Alignment Tool to check the alignment of the rear dropout. This is to ensure that shifting performance is optimal, as a bent hanger will cause strange shifting problems.

Using the expensive but important tool to check the alignment of the rear dropout. This should be done before installing and adjusting the rear derailleur.

However, I soon discovered a big problem. When shifting the chain to the lowest two gears (Gear 1 and 2), the chain will touch the brake pad fixing bolt on the rear caliper brake!

At low gear, the chain rubs on the bolt.

Another view from the top.

Bolt of the caliper brake interferes with the chain path at the lowest two gears on the cassette.

At gear 3, the chain will be able to avoid the bolt. But this is not a solution as 11 speeds will be restricted to just 9 speeds.

I can't see a solution to this problem, unless we change some of the parts of the drivetrain. Some ideas which I had:

1) Change to a larger cassette sprocket, so that at low gear, the chain is higher than the bolt on the caliper brake. However, this small wheelset is unable to support a larger cassette sprocket, as the rear derailleur cage is already very low.

2) Change to a larger chain ring, so that at low gear, the chain is higher than the bolt on the caliper brake. Later on, I was told that a front 58T chain ring (instead of the current 52T), with a rear low 28T sprocket is able to clear the bolt.

3) Use a 9 speed drivetrain, as the low sprocket position is not so inwards.

4) Change to V brakes (the frame has V brake mounts), to avoid the interference.

From this view, a larger sprocket and/or larger chain ring will lift the chain to be higher than the bolt, at the low gear position. Hard to tell how much bigger is enough though.

View of the Dura-Ace drivetrain. Chain interference problem still pending to be solved.

For now, the problem that we have is interference between the chain and the brake caliper. Something needs to be changed, in order to solve this. It is a new problem which I have not encountered before, even though I have modified many 20 inch folding bikes. Something new to be learnt from this Fnhon Gust frame.