Friday, February 14, 2020

Cervelo Aspero: Fork

After taking a close look at the Cervelo Aspero frame in the previous blog post, let us now take a look at the front fork.

The Teal colour does not show up well in photos when using indoor lighting. Looks almost like a black fork.

Here is how the Teal colour should look like, with some glitter and paint specks visible.

There is no need to install a crown race as it is already integrated into the carbon steerer tube. Bottom steerer tube diameter is 1 1/2 inch for extra stiffness.

Hose entrance for the front brake hose, located on the left side fork leg.

Hose exit on the left fork leg, near the brake caliper mount area.

One of the main feature and key highlight of the Cervelo Aspero is the ability to adjust the trail of the bike. For a super detailed explanation about the amount of fork trail on a bike, refer to this excellent article.

The way that the Aspero adjusts the trail is by moving the front axle forward or rearward, relative to the fork. This is done by using a reversible dropout called the Trail Mixer, which can be set in the forward or rearward position. The trail difference between the two positions is 5 mm.

The theory is that for wheels with larger circumference (such as large 700c x 40 tires), the trail naturally increases, making it too stable and not so easily steered. In that case, the Trail Mixer is set to the forward position to reduce the trail and make it steer more easily.

On the other hand, if you are using smaller wheels (such as 700c x 25 or 650b x 43), the trail will be too small if you set it in the forward position. In this case, you should set the Trail Mixer to the rearward position, to increase the trail to make it more stable. Or, if you prefer a more agile bike, you can still set it in the forward position to reduce the trail.

For me, I will be using the rearward position, as my wheel sizes are relatively small (700c x 28 and 650b x 43), so I want more trail for more stability.

Trail Mixer is at the forward position, which reduces the trail.

The Trail Mixer is held in place by a small screw that clamps the Trail Mixer to the fork.

The slot is symmetrical,which allows the Trail Mixer to be swapped between the forward and rearward position simply by flipping it around.

Trail Mixer is made of aluminium, which also has the threads to match with the front thru axle.

Theoretically, it should be possible to swap the Trail Mixer parts between the left and right side. The thru axle lever is by default on the right side on the front fork, but for the rear, it is located at the left side. It would be neater and more convenient if both thru axle levers are located at the left side of the frame.

However, there is another problem that complicates this matter. The problem is that when the front hub axle is seated into the front fork, the hub axle hole does not line up properly with the hole on the Trail Mixer. This makes it difficult to insert the thru axle fully for tightening.

The hub axle hole is not concentric to the hole on the Trail Mixer, as the hub axle is unable to sit in further on the step of the fork inner surface. As all the tolerances are tight, a little offset is sufficient to cause this problem. What makes it more difficult is that there is some looseness between the Trail Mixer and the fork, which means that when I tighten the little bolt on the Trail Mixer, it will shift slightly.

Area circled in red shows the offset in concentricity between the hub axle and the Trail Mixer.

It took a lot of adjustments and fine tuning before I could insert the front thru axle through the Trail Mixer and hub axle, and tighten it to the other side of the Trail Mixer.

Finally, after lots of trial and error, I managed to align the Trail Mixer within the fork, such that the thru axle is able to be fully inserted. I did not want to realign the Trail Mixer again, which I why I used the default thru axle setting, with the front thru axle lever located on the right side of the frame.


Flat Mount disc brake caliper mounting. Seems like the surface is prepared properly to ensure that the brake caliper will rest properly on the fork.

Weight of the front fork with uncut steerer tube is 416 grams, which is a bit heavier than the 361 grams of the Canyon Endurace.

The Trail Mixer concept is good but it feels that it is not being done properly, as there is some difficulty in aligning the Trail Mixer to the front hub axle. There are some other issues which I discovered, which I will share in a later post after assembly is completed.

3 comments:

  1. Hello. Do you happen to know what the crown to axle measurement(s) is? Also, do you think the flange around the base of the steer tube would be a problem for mounting this fork on other frames? Thanks

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    Replies
    1. The crown to axle distance is about 390 mm for a size 51 frameset.
      Not sure about the flange, but even if it fits other frames, it will not match well as the shape is designed specifically to match the Aspero head tube.

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  2. Hello Hands on bike,

    Over the past 25 years I have come across so many "little" issues like what you have shared in this post. After all the hours spent and frustration endured, it is so easy to just move on after finding a solution. Thank you so much for documenting everything and managing this site. I really enjoy the level of detail and appreciate the time you put into it. Your photography and explanations are excellent and I especially like your comparisons.

    Like you, I always have a new bike project in the shop. It all started because I am tall and it was difficult to find the perfect bike that fit me, was stiff enough, responsive enough, and provided me with the confidence and ultimately the satisfaction that I crave. About 5 years ago I found some frames that started to match my criteria. Despite having a few bikes that I am happy with, I want to know what different styles of bikes feel like. So I build up touring, city, gravel, road and mountain bikes just to learn and experience the different philosophies. The problem is that I have also extended this hobby (obsession) to the bikes of my wife. She too has many bikes of different styles but is more overwhelmed and does not appreciate the dramatic differences between them. And yet I still continue. Anyway… :)

    Just to share a couple more recent stories with you:

    On one of my new carbon bike builds. The rear disc brake pads were hanging over the rotor by more than 2 mm. Meaning the pads make a less than full contact with the rotor and will wear with a large lip remaining on the pad. I tried a few different callipers and the result is the same no matter if a Shimano 785 post mount calliper, a mechanical BB7, or a Sram Ultimate. I noticed that the threads of the post mount where sticking out of the carbon by about 2mm. I don’t know if this was intentional, or if it was meant to be flush with the top of the mount. To solve the issue I removed 2mm off a PM to PM brake calliper adapter. I don’t have a milling machine to remove this material perfectly square so I used sand paper, a file, Vernier calliper, and a square. It took hours to get the adapter square enough so that the calliper was sitting on the frame parallel to the rotor. I have about 500km on the bike and so far so good.

    On another recent build, a steel touring bike with IS disc brake mounts, the rear IS mount is welded in at quite an extreme incorrect angle. It was impossible for all but one type of disc brake calliper to achieve a parallel position. As far as I’ve found, only the Avid mechanical disc brakes such as the BB7 have the option of a cup and cone washer (like on V brake pads) above and below the calliper mounts. This means that the calliper can be tilted to achieve parallel surfaces. Luckily the BB7 works well enough to keep it on the bike, but I would prefer a hydraulic solution. I looked into modifying an IS to PM mount to accommodate for the cup and cone washers but was not willing to put in the hours to experiment.

    Although I am addicted to the challenge of finding a solution, as customers we should not have to endure these types of issues.

    From a fellow bicycle mechanics fanatic.

    All the best,

    Bob

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