Cervelo Aspero: Sunrace RX1 11-36T Cassette

On the Cervelo Aspero, the gravel setup has a 11-34T Ultegra-grade cassette on the wheelset. The sprocket sizes on the 11-34T 11 speed cassette are 11-13-15-17-19-21-23-25-27-30-34. When I'm riding gravel, I usually use the smaller 34T inner chainring for lower gearing. Due to cross chain issues, I cannot use the top gear (11T) on the rear cassette. Of course, I can shift to the larger chain ring for higher gearing, but this is usually not necessary.

This means that my gravel gearing is from 27 to 70.6 gear inches (shown below), which is not quite high enough. When I need to go faster, I will need to use the large chain ring. The low gear is good, although I will sometimes wish for an even lower gear when climbing on off-road terrain.

There are effectively 16 non-overlapping gears on this setup, biased towards the small chain ring for gravel riding.

I was thinking of getting a cassette with an even larger sprocket, for even lower gearing. For Shimano cassettes, the next step up would be an 11-40T cassette, which is too big a jump. The rear derailleur also will not be able to reach both the 40T sprocket and 30T sprocket on the gravel and road setup respectively, as I tested earlier.

Then, I came across this Sunrace CSRX1 cassette which is marketed as a gravel cassette, with a 11-36T gear ratio. I had previously used a Sunrace cassette on the MTB, and it worked pretty well. Therefore I was willing to give it a try as I think the quality should be quite decent. There is also another important advantage over the 11-34T cassette which I will reveal later.

Disassembled view of the Sunrace CSRX1 11-36T cassette!

Largest two sprockets are 32T and 36T, mounted on an aluminium spider.

Next three sprockets are 21T, 24T and 28T, also mounted on an aluminium spider.

Remaining gears are all individual sprockets from 11T to 19T.

Large spider with 32T-36T sprockets weighs 127 grams

Small spider with 21T-24T-28T sprockets weighs 119 grams

There are two bright red aluminium spacers which weigh 5 grams in total.

Aluminium lock ring weighs 5 grams

Entire cassette weighs 351 grams, which is 14 grams more than the 11-34T cassette, and a huge 145 grams more than the Dura-Ace 11-30T cassette.

One interesting detail is the small stamped circle just above the larger spline, to help identify and orientate the sprocket during assembly to the freehub body.

I was not sure if I needed to use a 1.85 mm spacer behind the cassette, as I could not find any documentation online. If the CSRX1 cassette is designed for road hubs only, a 1.85 mm spacer is not required.

However, if the CSRX1 cassette is designed for older 8/9/10 speed hubs, then a 1.85 mm spacer will be necessary. Only way to find out is to try it out!

Without the 1.85 mm spacer, the 11T sprocket barely protrudes above the freehub body. When I tightened the lock ring, it will bottom out on the freehub body, leaving the sprockets still loose.

After adding the 1.85 mm spacer, there is more clearance for the lock ring to tighten properly.

In conclusion, this Sunrace CSRX1 11-36T cassette is designed based on 8/9/10 speed freehub body length. It can be fitted on older hubs without any spacer. However, since I am installing it on the new 11 speed road ready Hunt 650B Adventure Carbon Disc wheelset, an additional 1.85 mm spacer is necessary. 

11T to 36T sprockets all visible! The quality of the nickel plating looks good.

The bright red anodised aluminium spider can be considered an iconic feature of Sunrace cassettes.

Overall view of the gravel wheelset with the new cassette and Venture 47 650B tires!

Distance between the guide pulley and the largest 36T sprocket is set to the minimum possible.

When the gravel wheelset is changed to the road wheelset, with 11-30T cassette, the distance will become larger. Shown here is still the 36T sprocket.

How it looks when the chain is on the largest 36T sprocket

Gravel drivetrain!

Backpedaling in the 36T sprocket may cause chain drop, so avoid this.

The GRX RD-RX815 Di2 rear derailleur has been adjusted to accommodate both 11-36T cassette and 11-30T cassette, which is a pretty big difference. It is able to shift properly across all gears, in both inward and outward directions, for both cassettes. This is very impressive, to have such a robust rear derailleur that can cater to a large difference in cassette sizes, without adjustment between cassette swaps.

Sometimes the shifting is slightly delayed on the 11-30T cassette, but shifting is always successful, so it is acceptable. Considering that the rear derailleur was adjusted for the 11-36T cassette, I can accept this slight issue on the 11-30T cassette. Otherwise, the shifting performance of this Sunrace CSRX1 cassette is no problem at all.

The first advantage of this CSRX1 cassette is to have a slightly lower gear with the 36T sprocket, compared to the previous 34T low sprocket. As shown below, the lowest gear is now 25.5 gear inches instead of 27 gear inches. Not much, but good to have anyway.

With the 11-36T cassette, there are 15 distinct gears. Note and compare the lowest and highest gear when using the smaller chainring, against the previous table which shows the 11-34T cassette.

The second and more beneficial difference is the higher gear ratio that I get when using this new 11-36T cassette. Previously, the HG800 11-34T cassette has gear steps of 11-13-15-17-19..., while this CSRX1 cassette has gear steps of 11-12-13-15-17...

Note the presence of the 12T sprocket on the Sunrace cassette, which avoids the big gear ratio change compared to shifting from 13T to 11T directly.

As mentioned earlier, when I am in the smaller chain ring, I can use all the gears except the top gear (11T). Previously, on the 11-34T cassette, the second-top gear is the 13T sprocket. Now, on the 11-36T cassette, the second-top gear is the 12T sprocket.

Gravel range on HG800 11-34T cassette: 27 - 70.6 gear inches

Gravel range on RX1 11-36T cassette: 25.5 - 76.5 gear inches

The gearing effect of this new cassette is a slightly lower low gear, and a higher high gear, which means a wider gear range, spread over 10 speeds. This is for pure gravel riding, when I only use the small 34T inner chain ring. The new top gear ratio of 76.5 gear inches is enough even for fast gravel riding, which means that I can stay in the small inner chain ring almost 100% of the time.

Updated bike specifications, with the Sunrace CSRX1 11-36T cassette.

Overall bike weight is still about the same. In road bike mode, 7.4 kg without pedals. In gravel bike mode, add 700 grams, to be 8.1 kg without pedals.

I am happy with this change, as I have expanded the usable gear range, with no discernable downsides, except for a very slight weight increase and a slightly slower shifting performance.