Sunday, January 31, 2016

Wheelsport Fantasy 2x10 Speed: Part 7 - Solving Chain Interference at FD + Extra Bottle Cage

Part 1: Original Bike Components
Part 2: Bike Disassembly and Component Weight
Part 3: Installation of New Components
Part 4: Final Assembly and Comparison

Part 5: Flat Bar to Drop Bar Conversion
Part 6: Geometry Comparison

While upgrading my friend's Wheelsport Fantasy 2x10 speed drop bar mini velo, I noticed that it had the same front derailleur mounting issue as seen on my own Wheelsport Fantasy bike. The angle of the FD mount on the frame is not suited for this small wheeled bike design. As such, there will be interference between the chain and the FD chain guide when the chain is in the small chainring. Let's take a look at the issue here, find out how it happened, and how it can be solved on this frame.

No issue with chain interference when the chain is in the large chainring

However, when the chain is in the small chainring, the chain will rub against the bottom of the FD chain guide in most gears

Close up view of the chain interference with the bottom of the FD chain guide

Chain barely clears the FD chain guide when in the front low and rear gear 3 setting. At gears 4 or higher, the chain will rub the FD chain guide.

After studying the differences between the mini velo and my Merida road bike, I have found the reason why there would be chain interference. The main difference in frame geometry that causes this issue is the position of the rear axle relative to the bottom bracket. More specifically, whether the rear axle is higher or lower than the bottom bracket.

On almost every adult bike, the bottom bracket is around the same distance from the ground, no matter a small wheeled bike or a full sized road bike. This is to maintain sufficient crank arm clearance from the ground, and yet allow the rider to climb on the bike easily.

However, the rear axle's distance from the ground will differ greatly, depending on the size of the wheel. A road bike with large 700C wheels will have the rear axle higher off the ground as compared to that of a 20" wheel folding bike. This affects the angle of the chain relative to the FD chain guide. If the FD mount is located on the mini velo seat tube with the same orientation as that on a road bike, it will cause FD compatibility issues for small wheeled bikes.


On the road bike, the rear axle is much higher than the bottom bracket. As such, the chain slopes more steeply upwards from the small chainring to the cassette. This ensures that the chain does not touch the FD chain guide even when in the front low/rear top gear combination as shown here.

On small wheeled bikes, the rear axle is lower than the BB. The chain is almost straight when in the front low/rear top gear combination. As such, the chain will touch the FD chain guide if the FD mount is not placed correctly on the frame. In the case of this Wheelsport Fantasy mini velo, the chain will touch the bottom of the FD chain guide in the top 7 gears of the cassette. Only when the cassette gear is set at gear 1, 2 or 3 will there be no interference.

Comparing the angle of the chain between road bike and mini velo. See how different the chain angle is, and the different height of the cassette.

For small wheeled bikes, the proper way to locate the FD mount on the frame is to place it behind the seat tube, and tilted to follow the curvature of the chain ring. However, on the Wheelsport Fantasy frame, the FD mount is parallel to the seat tube, and is located along the seat tube and not behind it. This means the FD will be fixed at the wrong position for proper operation.

On the Wheelsport Fantasy frame, the FD mount is placed parallel to the seat tube and right in the middle of it, which is not the correct position.

The correct way is to place it behind the seat tube, and to tilt it so that the FD chain guide can follow the curvature of the chain ring. Example shown here is from a Tyrell mini velo.

As can be seen from the Tyrell bike shown above, the FD mount is placed behind the seat tube and also tilted. This ensures that the FD is angled correctly relative to the chain and the rear axle position. To solve this issue on the Wheelsport Fantasy mini velo, I will need to move the FD to the correct position. As previously done on my own mini velo, I will use the same spacer and angled shims to move the FD position.

Using the spacer and the angled Ridea 4 degree shims

Together with a long bolt and some spherical washers, the new FD mount is created

New position of the FD with the custom mount. The FD has been moved rearwards and also tilted to follow the curvature of the chain ring.

Now, even when the chain is in the front low and rear top position, there is clearance between the chain and the bottom of the FD chain guide

Inner cable fixed up with the FD in the new position

FD support bolt is unable to push against the frame, but the FD is still rigid enough, and front shifting still works well

With the custom FD mount created, there is no more chain interference with the FD chain guide. In fact, the custom FD mount works much better than the stock bike condition. After giving feedback to the bike shop and the frame maker, I am glad to see that Wheelsport has improved their FD mounting on the mini velo for the model year 2016 frames. The FD mount has been moved rearwards on the seat tube, and it should now work without requiring the custom FD mount.

Another small issue with the Wheelsport Fantasy mini velo frame is that there is only one bottle cage mount. Having just one bottle cage mount is quite standard on most mini velo or folding bikes, so it is not really a problem with frame design. However, it is useful to have an extra water bottle when riding long distance, and so I found a way to add an extra bottle cage to the Wheelsport Fantasy mini velo frame, while keeping it neat and unobtrusive.

It is not possible to add an extra bottle cage mount for a standard water bottle within the frame triangle, as there is not enough space. Adding a small tool bottle is possible though, as already done previously on my own mini velo.

To have an extra bottle cage mount, I decided to use the Monkii Cage water bottle mount, which clamps on a round part of the frame and creates an extra bottle cage mounting point. The round clips are not used. Instead, a standard bottle cage is bolted to the Monkii Cage mount.

Monkii Cage mount. The two round clips are not required for this set up.

The Monkii Cage mount fits perfectly in this little triangle on the frame. Without this design element on the frame, it would not be possible to fit the bottle cage mount here.

A second water bottle fits nicely at this location. Although it is difficult to access the water bottle while riding, it is still acceptable as it is much better than having just one water bottle on the bike.

With that, the latest modification to this Wheelsport Fantasy mini velo is complete. The FD mounting issue has been solved, and a second bottle cage has also been fixed to the frame.

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