Fnhon Gust: Frame

A new bike project offers the opportunity to learn new things. In this case, building a 16 inch bike up from scratch is new to me, as I have only assembled 20 inch 406 and 451 bikes previously.

As this 16 inch frameset is new to me, there will be inevitable mistakes made during the assembly, such as finding out that some parts don't match, or a wrong specification is used. Nevertheless, I am confident of solving these problems using the experience that I have from building up many different bikes previously. 

What we have here is a 16 inch Fnhon Gust frameset, which is an interesting frame. First of all, it has a unique geometry, with a large chainstay and no distinct seatstay. Instead, it has a couple of braces in place to reinforce the joint between the chainstay and the seat tube.

This is a steel frame, which means that it is likely to be heavier than an equivalent aluminium frameset, but of course also tougher. My one and only steel frame was the Dahon Boardwalk, which started me on the bike modification route. It is not ideal to make a lightweight bike using a steel frameset, as it is usually heavier than an aluminium frameset. However, for this project the priority is not to minimize the weight.

Let's take a closer look at the frame and see what makes it so special.

Black frame with gold accents! Reminds me of the Dahon Boardwalk with lots of gold bling.

Frameset comes with seatpost clamp and seatpost shim included.

Steel head tube. Looks pretty round to me, unlike the Crius AEV20 which I worked on previously.

Uses a standard Litepro headset. Black is the chosen colour here, although gold would work well too.

Headset bearing cups pressed in with a proper headset press. No difficulty here.

There are metallic flakes mixed into the paint, which looks amazing! Looks similar to the metallic look seen on the Cervelo Aspero frameset.

Fnhon logo embossed on the headtube in an attractive gold colour.

The model name is also painted onto the frame in a shiny gold font.

More details about the frame painted at the back of the seat tube. This gives the frame a really attractive classic look.

Gold plated folding lever? Not sure if it is real gold plating or not.

Gold bands painted on the chainstays as well.

Rear derailleur dropout is welded to the frame, instead of being a separate piece. As it is made of steel, it can be bent back to straight without cracking.

Lots of cable guides at the bottom of the frame, which is good for cable routing flexibility.

More cable guides!

Frame (inclusive of headset bearing races) is 2417 grams.

A pair of the headset bearing races that are pressed into the headtube weighs 16 grams.

The frame weight, excluding any headset parts, but inclusive of seat post clamp and seat post shim is 2401 grams, which is the same as the larger 20 inch Dahon MuEX aluminium frame. I think it is a good weight for a steel folding frame, since it is equivalent to that of an aluminium frame.

I was really impressed with the gold accents on this Fnhon Gust frame, as it really stands out from the black paint. This bike is not for my use, but I am helping to build it up for a friend. I think this is a really attractive 16 inch frameset!

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.

Cervelo Aspero: SLX 11-40T Cassette + Trial Setup

In the previous post, I modified the GRX RD-RX817 rear derailleur to have a longer cage, for more chain capacity. The intention is to test to see if it is possible to match a front double crankset to a wide ratio cassette.

My proposed setup would use the existing Dura-Ace FC-R9100 50/34T crankset, with a SLX CS-M7000 11-40T cassette. This is intended to be on the gravel wheelset, for a wider gear range than the current 11-34T cassette. Officially, there is no rear derailleur that can support such a wide range, as the chain capacity required for this setup is 16 + 29 = 45T, which requires a very long cage.

Based on the hybrid version of the GRX Di2 RD-RX817, with the RD-M8000 SGS cage, the chain capacity has theoretically been increased to 47T. Theoretically it should work...

However, I have another requirement, which is to use the same rear derailleur and chain, for both the road and gravel setup. The road wheelset has a much smaller 11-30T cassette, compared to the proposed 11-40T cassette for the gravel wheelset. Based on my requirement, there should be no adjustment of the rear derailleur during wheelset swap. There is a big 10T sprocket size difference between the low gear of these two cassettes, so I am not so confident that it would work. 

Before showing the results of the rear derailleur testing, let's take a closer look at this SLX CS-M7000 11-40T cassette.

Previous generation of SLX, with 11 speeds. This cassette has a gear combination of 11-40T. There are bigger ones such as 11-42T and 11-46T.

Pretty weighty compared to road cassettes, which are just 200+ grams. The HG800 11-34T cassette is 337 grams.

Many people think that going from a front double to a front single setup will save weight, but it is often not true, especially if your existing front double drivetrain is a lightweight one.

A basic equation, if you want to have weight reduction when converting from 2x to 1x on a road or gravel bike, is to make sure that the weight of removed front derailleur + second chain ring is more than the additional weight of the cassette. Many times, the larger cassette adds so much weight that the savings from removing the front derailleur and chain ring are totally cancelled off.

Exploded view of the CS-M7000 11-40T cassette. Only the last 3 sprockets are mounted on an aluminium spider.

The spider has a unique design, with 7 arms instead of the more common 6 or 8 arms.

Largest 40T sprocket is aluminium, while the next two 35T and 31T sprockets are just using normal steel.

There is a spider shaped spacer on this sprocket, to better support the sprocket during sideway bending loads.

11-40T cassette mounted on the Hunt 650B gravel wheelset. Looks good!

Objective:

Find a Di2 RD that can cater to both 11-30T and 11-40T cassettes, with front 50/34T double chain ring.

No adjustment of B-adjust bolt should be required when swapping between the two cassette sizes.

Using this modified GRX RD-RX817 with longer cage, I fixed it onto the Cervelo Aspero to test. Of course a longer chain is required due to the larger 40T sprocket.

Points to take note:

1) GRX RD-RX817 is originally designed for 1x11 speed drivetrains, with max sprocket size of 42T.

2) Original chain capacity is just 31T, but increased to 47T (theoretically) with the longer M8000 SGS cage.

3) There is an offset guide pulley, which means that the gear sprocket to guide pulley (GG) distance is the smallest at front low chain ring.

Special edition GRX Di2 RD-RX817 rear derailleur with longer SGS cage from RD-M8000.

Test Conditions:

1) At front low chain ring (34T) and rear low sprocket (40T), set the GG distance to be < 5 mm.

2) Use long chain length for 40T sprocket and 50T chain ring.

3) Test both inwards and outwards shifting performance.

4) Test with both 11-30T and 11-40T cassette, using GG distance setting at 40T sprocket.

5) Test with both clutch on and clutch off conditions.

Result table for hybrid GRX Di2 RD-RX817 with SGS long cage

Observations:

2 - As GG distance was set based on 40T sprocket, the distance becomes too big when used with 11-         30T cassette.

3 - Due to Di2 software limitation, when at front low, highest rear gear is 4th gear from top, which              is 17T in case of 11-40T cassette (11-13-15-17-19…).

4 - Synchronized shifting is not possible with RD-RX817, as the Di2 system recognises it as a front             single RD, and disables synchronized shifting.

Summary of testing with RD-RX817 long cage RD:

1) Inward shifting is OK with all conditions (different cassette, clutch on or off).

2) Outward shifting is the problem as the GG distance is too far for the smaller 11-30T cassette.

3) If you only need to use with the 11-40T cassette, it will generally work, but the gear range is electronically limited. If you use the small chain ring for gravel riding, then the top 3 gears on the cassette is inaccessible. You will need to shift to the large chain ring for higher gears.

In conclusion, this does not work for me as the RD cannot shift properly on both 11-30T and 11-40T cassette. However, I think that if you have a mechanical version of the RD, you can access all the 2x11 speed gears, since it is not electronically limited. 

In other words, making a long cage version of the mechanical GRX RD-RX812 may allow you to run a front double and rear 11-40/42T cassette, with no gear limitations.

Since I was doing the testing, I decided to try the same test conditions using the other GRX RD-RX815 rear derailleur. For a detailed comparison between these two GRX Di2 rear derailleurs, check out this post.

Points to take note:

1) GRX RD-RX815 is originally designed for 2x11 speed drivetrains, with max sprocket size of 34T.

2) Original chain capacity is 38T.

3) There is no offset guide pulley, which means that the gear sprocket to guide pulley (GG) distance is the same regardless of front chain ring position (low or top).

Standard GRX Di2 RD-RX815 rear derailleur, for 2x11 speed drivetrains.

Test Conditions:

1) B-tension bolt was tightened all the way in, and barely reaches the 40T sprocket.

2) Use long chain length for 40T sprocket and 50T chain ring.

3) Test both inwards and outwards shifting performance.

4) Test with both 11-30T and 11-40T cassette, using GG distance setting of 40T cassette.

5) Test with both clutch on and clutch off conditions.

Result table for standard GRX Di2 RD-RX815

Observations:

1 - Due to large GG distance when using 11-30T cassette, chain does not shift into next gear. This               causes the Di2 motor to stall. With the clutch on, the Di2 motor of this road-type RD is not strong          enough to shift the chain.

2 - As GG distance was set based on 40T sprocket, the distance becomes too big when used with 11-         30T cassette.

3 - Due to long chain, and insufficient chain capacity on this RD cage, chain will be slack at front low,          rear 14T.

4 - Synchronized shifting is possible with this RD.

Summary of testing with RD-RX815 RD:

1) Inward shifting is not good when the clutch is on, as the RD linkset is pretty stretched due to the B-tension bolt being screwed all the way in. As such, the Di2 motor is not strong enough. This Di2 motor is smaller and less powerful than the larger motor on the RD-RX817.

2) Outward shifting also does not work as the GG distance is too far for the smaller 11-30T cassette.

3) The only feasible one is with clutch off, using only the 11-40T cassette. This is meaningless as a clutch is needed for rough off road riding.

Comparison of GRX Di2 RD-RX815 and RD-RX817

There is an alternative idea, which is to use a Wolf Tooth Roadlink DM  to move down the rear derailleur. This would work well for a front single drivetrain. In this case, shifting should be OK, if only a 11-40T cassette is used. However, the chain capacity is still an issue, as the Roadlink does not increase chain capacity.

In summary, this combination also does not work. I realized that the main issue is that the same RD setting cannot be used for both 11-40T and 11-30T cassettes, as the GG distance has a huge difference.

Therefore, I had to reinstall the previous 11-34T cassette and RD-RX815 rear derailleur for now, and change back to the previous chain length. Also, I swapped the cageset of the RD-RX817 and RD-M8000 back to the original ones.

This was not a successful modification, but I did learn a lot on the shifting performance of the rear derailleurs, and also the setting up of the different cassettes and GG distance.