Wednesday, June 23, 2021

Cervelo Aspero: Front Single Conversion - Part 2

With the front single drivetrain components prepared earlier, now I can replace the current front double drivetrain with a front single drivetrain on the Cervelo Aspero

Last time, when I went off-road riding on the Aspero, there were some damage to the chain stay. That was due to insufficient clearance between the chainring and the chain stay for mud. After that I pasted a layer of protective film to prevent future damage.

Unfortunately, some time after that, there was another incident which again caused damage to the chain stay. This time, the chain derailed during a downshift on the chainrings, during an uphill climb. I'm not too sure how it happened, as it was the first time the chain derailed on the Aspero, it being a rare event for me.

Fortunately, I felt a weird sensation when the chain came off, and I immediately stopped pedaling. This avoided further damage to the chain stay.

Protective film damaged by the derailed chain.

After the incident where the chain derailed, I did not take any action, as the damage had already been done. I left the half-peeled off protective film on the chain stay for quite a while, as I was lazy to remove the crankset and replace the protective film.

Now, since I will be replacing the crankset, I finally took the chance to check out the damage and replace the protective film.

Ouch! It doesn't look pretty, but I'm glad the protective film took the brunt of the damage from the dropped chain, as it could have been much worse.

Pasting a new layer of protective film, after removing the torn parts and cleaning the frame.

It's like magic! The scratches are mostly covered up by the transparent protective film.

The next step is to install the new crankset with the new chainring. Since it is a front single crankset, and with a relatively small 38T chainring, I expect the chain stay clearance to be more than the 2 mm found on the previous Dura-Ace 50/34T crankset.

Checked with an Allen key, the clearance is 3 mm. Not as big as I thought.

View from the top. OK clearance, but thought it would be more than 3 mm.

Next step is to replace the current Sunrace 11-36T cassette with the SLX 11-42T cassette onto the Hunt 650B gravel wheelset. Replacing the 11-36T cassette with a larger 11-42T cassette, and dropping from two to one chain ring will result in an overall decrease in gear range. That's because the new cassette does not have a gear range that is wide enough to replace the double chain rings. Gear ratios to be compared at the end of this post.

11-42T cassette next to the 11-36T cassette.

Front single drivetrain completed! Here it is shown at the lowest gear, with the rear derailleur cage fully stretched.

SLX CS-M7000 11-42T cassette with GRX Di2 RD-RX817 rear derailleur.

Adjusting the B-tension on the rear derailleur, such that the guide pulley is as close to the cassette as feasible. This will help to ensure good shifting performance at the top gears (Eg. shifting between 12T and 11T).

The chain is now at the 11T top sprocket, with the rear derailleur cage fully retracted.

Still enough chain capacity, as the chain is still some distance away from the guide pulley.

Maybe not as much margin as I first thought, as the stopper pin is already quite close to the stopper.

Here it is shown at the middle of the cassette.

The 105 R7000 left crankarm with 4iiii power meter was also transferred over, along with the Deore XT M8020 pedals. This does not match the Ultegra crankset on the right, but I don't mind.

Small clearance between the 4iiii power meter and the chain stay. Similar to that with Dura-Ace crankset.

Testing the new drivetrain out on some real gravel

Looking good with the new front single crankset!

Love the new front single drivetrain, as it is simpler to use. It's awesome to test the drivetrain and tires on freshly laid gravel.

Overall bike picture with the front single drivetrain, it suits this Aspero gravel bike well.

By making this drivetrain modification, there is a change in overall bike weight and also the gear range. Let's take a look at the differences.

Weight comparison of the front double vs front single drivetrain that I used.

By comparing the weight of the components that I have changed, I found that I saved a grand total of 1 gram! Perhaps it is a few grams more if I include the front derailleur Di2 wire that I removed, but in the end it is a very small difference. Most of the weight reduction up front has been added to the larger cassette at the back.

Other than the weight, the gear range has also been changed. Here is a comparison before and after.

Previous gear range with 50/34T crankset and 11-36T cassette: 
25.5 - 123 gear inches over 15 unique gears.

New gear range with 38T chainring and 11-42T cassette: 
24.4 - 93 gear inches over 11 unique gears.

By converting to front single, I lose the top 3 gears which I almost never use when gravel riding, as it is just too high for me. Since I no longer use this Aspero for fast road rides, this is acceptable. Also, there is a big gear step from the 13T to the 11T sprocket, which is unavoidable on all the larger cassettes.

On the other hand, with a small 38T chain ring and a low 42T sprocket, I do get an easier low gear which is always welcome, especially when climbing steep off-road slopes.

In summary, changing from a front double to a front single drivetrain has no weight savings, while it retains most of the gears that I use during gravel riding. I will be using the 650B wheelset and tires as my primary wheelset on the Aspero, since it is now a gravel bike. A gravel bike can basically go anywhere, as it transits from smooth road to park connectors to gravel tracks easily.

Great 1x11 speed drivetrain!

Front single chain ring for simplicity

Wide range 11 speed rear cassette

2 comments:

  1. What brand is the protective film you use for your frame? Thanks!

    ReplyDelete
    Replies
    1. No idea, as it was given to me as scrap pieces by a friend. You can find many brands online.

      Delete

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