Bottom Bracket, Pedals, Belt, Sprockets

Cowboy 3 - First 10.000 bikes (all bikes produced before July 2, 2021): Gates CDX Belt
Cowboy 3 - As from bike 10.0001 (bikes produced after July 2, 2021): Gates CDN Belt (resistance more in line with the requirements for our belt)

Cowboy 4: Gates CDN belt

Cowboy 1-4:
Crank: +-21cm long. Tighten 35Nm.

Cowboy 3 gear ratio: 63 in front, 22 in rear → Gear ratio of 63/22 = 2.86

Cowboy 4 gear ratio: 60 in front, 21 in back -> Gear ratio of 60/21 = 2.85

Cowboy 4ST gear ratio: 57 in front, 21 in back -> Gear ratio of 57/21 = 2.71. This means that at the same speed, the pedals on the C4 ST will be turning slightly quicker than on the normal C4, allowing for a more comfortable (yet slightly slower) ride.

What is a bottom bracket (BB)? How is the BB different on C1 and C2/3?

The bottom bracket is the part that make the junction between the 2 cranks through the frame. It needs to be able to turn inside the frame without friction and to connect the left and right crank well enough, as the force on the pedals is usually pretty strong.

The C1 and C2 bottom bracket are both square tapered, meaning the crank are attached on it via a square interface and a screw. They are both 84mm in length (inside the frame).

They different in their cups. C1 has external cups, C2/3 has internal ones.

Because C1 is a torque sensor, the spider is separate from the right crank, which is not the case on C2/3.

Both are custom-made so can not be replaced by off the shelf components from well-known bike part manufacturers (e.g. Shimano). Note that the C2/3 uses the BSA standard (a BB standard).

Cowboy 4 goes back to a torque sensor in the bottom bracket, making this part custom-built for us.

Why the move to a CDN belt on Cowboy 4 and recent Cowboy 3 bikes?

We are using the Gates CDN belt on Cowboy 4 (vs CDX belt on first Cowboy 3 bikes produced), since CDN is the belt designed by Gates for urban usage. You can expect a 10.000 km lifetime when correctly maintained (regularly cleaned and lubricated using silicone spray), which is 2x more than a typical bike chain. We will keep selling Cowboy 4 belts as a spare part.

We have partnered with Gates to develop a specific belts size (132t) and a specific front sprocket on C4 ST (57T) to match our requirements.

We made this change since the CDX belt was a bit of an overkill for an urban e-bike, the level of performance of a CDN belt is definitely good enough for us.

Known issues

Common Issues

Belt - Broken/Damaged Belt

Models impacted: mostly Cowboy 1 + Cowboy 2

Symptom: broken belt

Root cause:

Cowboy 1: Worn rear sprocket. The rear sprocket get worn because some dirt stays in the sprocket. This dirt grinds the sprocket over time as it is made out of soft aluminium material. It has an especially strong effect on the rear sprocket because he force there is much bigger than on the front sprocket (because there are 3 times less teeth but the same force being transmitted). Since C2, we have made the rear sprocket in Steel which should increase its lifetime by a factor of at least 3.
Cowboy 1-2: the belt we use is not as durable as we hoped - part of the reason for a move to a Gates belt, which is a well-known manufacturer.

Countermeasure:

C1: Replace belt (part shipment) + replace rear sprocket via dedicated repair if it's still aluminium, which should be organised by the Repair team.
C2: replace belt.
C3-4: replace belt + ship the broken belt back for Quality investigation

Belt - 'Clac' Noise Due To Low Tension

Models impacted: Cowboy 1/2. Could also happen on Cowboy 3, but much rarer with the belt design we use.

Symptom: Clac noise as the belt "skips" in the rear sprocket. Video example on the right

Saved Reply: BIKE_BELT_TENSION

Root cause(s):

When the force on the transmission is big and the tension in the belt is low, the belt can change shape under the big force exerted on the pedals. This shape change allows a teeth to "skip", meaning jumping a hole in the sprocket, which creates the loud clacking noise.

Countermeasure: tighten the belt to the correct tension.
We include a belt tensioner in the box as from Cowboy 3 to do this more easily.

Belt Noise Due to Dirt / Runin

Models impacted: Mostly C2. Can also happen on C3/C4 in rare cases

Symptom: Belt making noise when it turns. No noise when the belt doesn't move, i.e. when freewheeling.
Video example on the right.

Root cause: When a belt is new, or dirty, its teeth do not match the shape of the sprocket holes perfectly. Meaning that as they go into the hole, they slip a bit, which creates vibration and noise. As time goes by, the slipping eats through the metal and the 2 start matching perfectly. When the belt is dirty, it may experience the same slipping effect.

Countermeasure: clean + lubricate the belt. Gates, the manufacturer of the C3/C4 belt, recommends using silicone spray (available and cheap at your local DIY store) and avoiding using WD40 since it's quite aggressive and can do a chemical reaction with the carbon in the belt, further damaging it.
At some point we also recommended using a bit of soap as an alternative.

Crank - Crank Arm Loose (Crank <> Bike)

Models impacted: C2/C3

Symptom: crank arm coming loose, typically on the non-drive side. It will typically get wobbly, then fall off in extreme cases.

Not to be confused with: Pedal - Damaged Crank Thread Due to Incorrect Pedal Installation (Crank-Pedal). Crank Arm Loose is only for issues where the crank arm can't be attached to the bike properly (not when the pedal can't be mounted to the crank arm).

Root cause: over time, the crank arm may come loose. If the customer keeps on riding with a loose crank, this can damage the square hole in the crank which becomes "rounder". This would lead the crank to keep coming loose over time, requiring us to replace it.

Note: if you replace the crank, also replace the crank arm screw (which is a separate shipment item).

Countermeasure: if it's the first time, tighten the crank arm to 35-45Nm. If it's keep on happening, confirm damage to the crank arm hole, and replace the crank arm + crank arm screw (it's one set).

In case it's happening to the drive-side crank arm (much less likely): remember to also replace the front sprocket bolts + 5x front sprocket nuts.

Pedal - Damaged Crank Thread Due to Incorrect Pedal Installation (Crank <> Pedal)

Models impacted: all, especially brand new or very recent bikes

Symptom: Damaged crank thread where you mount the pedals.

Not to be confused with: Crank - Crank Arm Loose (Crank <> Bike). This tag is only for issues where the pedal can't be attached to the crank arm anymore (not when the crank arm comes loose or falls off the bike).
Video example on the right.

Root cause: Typically associated with a user mistake - Pedals must be installed properly, and this can sometimes be counterintuitive since all pedals use a different rotation direction on each side so they self-tighten during bike use.

Possible mistake 1: trying to install the left pedal on the right crank arm and/or vice-versa. The left and right pedal can be told apart by the 3 grooves on the left pedal only.
Possible mistake 2: cross-threading, ie. not installing the pedal straight on then forcing it in. The crank arm thread is made of aluminium while the pedal thread is made of steel, so the crank arm will be damaged first (aluminium being softer than steel).
Possible mistake 3 (not the customer's fault) - On Cowboy 4/4ST only: Mistake done during assembly where the right and left crank arms were inverted (or two of the same crank arms were installed). This cannot happen on C2/3, since the crank arm design is different.

Countermeasure:

Check both pedals, even the one which is still attached - Confirm that each pedal (L/R) is on the correct side through the 3 grooves on the left pedal only
Look closely at the thread on the pedal which fell off, to assess any damage on it
On Cowboy 4/4ST:Confirm that the each crank arm (L/R) is on the correct side of the bike. Each crank arm has a L or R on the inside, near the pedals.

Depending on the outcome: replace one/both crank arms + the pedals if needed.

R/L for Right/Left Crank Arm

Crank - Clicking Noise from Crank

Models impacted: C2/C3 + C4

Symptom: Clicking noise from the pedal crank. Typically happens at every crank rotation, at the same spot, when pushing hard on the pedals.

Countermeasure: First, make sure the clicking sound isn't coming from the pedal (tighten the pedal harder).
If not, we need to remove the crank arm (usually the non-drive side one), clean any junk that could have accumulated there, apply a bit of grease and reattach the crank arm.

Bottom Bracket - Noise from Bottom Bracket(C2, C3)

Models: Cowboy 2, Cowboy 3, Cowboy 4

Cowboy 2 and Cowboy 3

Symptom: Noise coming when crank arms spin, which persists when the belt is removed.

This is a very unlikely issue, so make sure to rule out other noises that can happen while turning the crank arms: mostly Belt noise (lubricate to get rid of it), clicking noise from crank (click at every pedal turn, in the same position, when load is applied), and Torque Sensor/Motor Cover noise (coming from the rear wheel, not the BB).

Note that the cause of such noises on C4 is likely to be different, to be checked.

Countermeasure: Replace bottom bracket and bottom bracket housing via CMS intervention

Cowboy 4 - As of end June 2023

Noise clearly comes from the BB area, and should be replicable by pushing the cranks back and forth without moving the bike (see videos on the side)

We suspect this issue to come from one/multiple screws of the BB that aren't correctly tightened and/or don't have Loctite on them, probably the drive-side screws (hidden behind the front sprocket).
Therefore, if we confirm a noise coming from the BB on C4:

- Remove the belt, both crank arms and the front sprocket
- Remove the drive side crank, then the front sprocket/chainring
- Remove the 2 x 5mm bolts on the drive side
- Clean and grease the cup
- Remove the drive side cup and clean it and the inside of the frame - an aluminium spacer should be on this side of the BB. Remove it with the BB cup. If the spacer was on the NDS, remove it from there and place it on the drive side (The spacer may have a notch or burr on the inside and outside. You can file this down.)
- Lightly grease the drive-side cup
- Tighten the 5mm bolts on the drive side (8Nm)
- Reinstall the front sprocket, lock ring (30Nm), belt and crank arm (45Nm)
- Check the torque of the rear sprocket lock ring if the noise remains (45 Nm)

Belt - Belt too Tight; leading to Resistance/Vibration

(Cowboy 2 and 3)

Symptom: Customer feels that resistance when riding the bike, particularly when freewheeling.

Note that you will always feel a little bit of vibration (transferred from the rear wheel to the pedals via the belt), so this is, to some extent, not a real issue.
There could be other reasons for vibrations during use, this issue is easy to 'spot' since it can easily be solved by loosening the belt (see below).

Root cause: The belt was overtightened (probably by the customer himself, since this is something that can be adjusted). This leads to more of the wheel's rotation (and vibrations while doing so) to be transferred to the pedals, where the customer feels it.

Countermeasure: Loosen the belt, using the belt tightening tutorial. The tension can be checked using the Gates app, sweet spot should be between 45 and 60 Hz (you basically use the belt as a guitar string and check at which frequency it vibrates, which indicates how tight it is). We can use the same measurement as a baseline for the Cowboy 2 belt as well.

Note that while on Cowboy 2, if a belt was too loose it could lead to a 'clac' noise as it could skip on the rear sprocket. This is far less likely on Cowboy 3 due to the new sprocket design, so it's OK to ride with a slightly looser belt.

Preferred interaction: Digital

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