What's the deal with the incomplete brake pad overlap and the new brake discs?

Note that we have seen that the larger brake discs aren't compatible in c.2% of supposedly compatible frames. If that's the case, simply remount the old disc (we have a tutorial for that). The incomplete brake pad overlap won't be an issue for those bikes.

If we replace the brake disc, we also need to replace the brake pads. Otherwise, the old pads will only be making contact with the 165 mm brake disc on a 2-3 mm wide surface, making the rear brake very weak. We don't want that.

All compatible rear wheels (Cowboy 2 + Cowboy 3 Ideal) will now be shipped with the 165 mm brake disc.
⚠️ Don't forget to also replace brake pads every time we install a rear wheel with 165 mm discs installed. ⚠️

See drawing above for a more visual representation of the issue and solution, and Compatibility table below if you aren't sure which discs are now fitted on which wheel type.

Solution for new bikes

This problem was fixed by a redesign during the switch to our new frame manufacturer: the position of the calliper was adapted to ensure complete brake pad overlap with a 160 mm disc. This fix prevents the installation of 165 mm discs on recent (Ming) frames.

We can easily identify the frame type of a Cowboy 3 bike. Easiest is to check the orientation of the frame opening to remove the rear wheel:

• • Ideal: Pointing towards the back of the bike

  • Ming: pointing towards the bottom of the bike

Compatibility table:

This whole situation isn't an issue on Cowboy 4, since we reviewed the entire frame and brake design.

What can we expect for Cowboy 4 brakes?

During set-up

• Could be that brake lever can't be tightened, due to handlebar grinding not being done properly. As a workaround, we can try to slightly increase the diameter of the handlebar, with a bit of tape. If nothing helps: we will request a bike exchange.

• Brake lever may crack when adjusting it (we are testing at the factory to prevent this). This is either due to the brake lever itself or due the handlebar not grinded properly. When we have spare brake levers, we can try to replace the lever only (bleeding required, since we need to unplug the brake hose). In the meantime, we'll probably have to exchange bikes if this happen.

Wear & Tear

• At the factory, we are bleeding all brakes + adjusting piston position to get brake performance good. For the brakes to perform OK, we need the pads to be very close to the disc brake (1 mm), leading to risk of rubbing. In case of rubbing, out of the box: we'll have to carefully calibrate the brakes (same process as on Cowboy 3)

• Brake pads can move a bit less than before, and oil reservoir is a bit smaller, so bleeding likely to be needed more often.

• System is more sensitive to brake wear. Brake pad replacement will require to get the piston distance just right.
  In other words: usually when you replace brake pads, you push the pistons back in the caliper all the way. Instead, on C4, we will have to get the pistons partially out of the caliper+ a bleeding may be required. (if you feel that we hit the end of the brake lever, with new pads, with the pistons in the correct position).

Other considerations

• Syringe head for bleeding: SRAM standard (should be part of any universal brake bleeding kit)

• Brake pad retainer screw is different, there is a clip in the back to prevent the screw from coming out.

Brake discs

• C4 bikes produced since mid January use coated brake discs for corrosion protection (instead of passivated brake discs like on C3). As a consequence, brakes may feel a bit soft when the brake pads are brand new (the new coating changes the friction coefficient between the pads and the disc, making the brakes perform less well when brand new). 

• To prevent this, we need to bed in the brake pads by:

  • accelerating to c.15 km/h then braking until nearly coming to a complete stop

  • repeat this process 70 to 80 times (it takes longer until we reach good performance with coated discs than with passivated discs)

• We are adapting the user manual to reflect this change in the bedding process.

• Note that you should still feel like the bike is safe to use even if the pads aren't bedded in yet. This shouldn't prevent the bike from braking completely, just making it feel like the brakes aren't as good as you'd like them to be. If the brakes are really performing poorly, it's probably another issue.

• Less common: 

  • A bent brake disc can vibrate differently and make noise.

  • The material of the brake pad and the brake disc has an effect, since the frequency of the vibration (which determines the sound it can make) depends on the friction coefficent between the two materials. Generally speaking, softer brake pads (e.g. resin pads, a.k.a. "green" pads) are quieter but wear out quicker, while harder brake pads tend to be louder but last longer.

  • To be confirmed (and not be shared to customers): The incomplete brake pad overlap on Cowboy 2 and 3 (see specific explanation below) also changes the friction coefficient, which can lead to more noises. 

We saw this happening more regularly on Cowboy 3, even on new/very recent bikes. It's likely that the mounting surface of the brake discs isn't always perfectly flat, or that the pads' position moves slightly during assembly and/or transport. We implemented some improvements on recent bikes to improve this situation. 

Countermeasure: first realign brake calipers ("calibrate" them). While doing so, advise to check if the problem comes from a bent disc, that can be straightened as well Should they need help, a bike shop can definitely help. If they can't get rid of the noise, advise the customer to purchase resin brake pads and replace them (we have a video explaining how to do this + we sell resin pads if needed). Note that Cowboy 4 bikes and recent Cowboy 3 bikes should have resin pads preinstalled on the front & back wheels. 

We saw this happening more regularly on Cowboy 3, even on new/very recent bikes. It's likely that the mounting surface of the brake discs isn't always perfectly flat, or that the pads' position moves slightly during assembly and/or transport. We implemented some improvements on recent bikes to improve this situation. 

Countermeasure: realign brake calipers ("calibrate" them). While doing so, check if the problem comes from a bent disc, that can be straightened as well if the bend is limited.

Cowboy 4 update:

This issue is slightly more likely to happen on Cowboy 4, since we have to adjust the position of the pads to be very close to the brake discs for the brakes to perform well (1 mm on each side), which increases the risk of rubbing by decreasing the left/right movement tolerance. Adjustment process remains the same: brake calibration and/or brake disc straightening required.

• In case there is a leak, make sure the brake pads weren't contaminated with oil, and replace them if needed. Contaminated brake pads will look shinier than normal. In case of contaminated brake pads, clean them or use a fine sandpaper (120) to remove the surface layer. In the most extreme cases, replacement of the pads may be required.

• As explained in the C4 bleeding procedure, make sure you slowly pull the brake lever a few times during the bleeding procedure. This will help to get rid of any remaining air bubbles, and will also help to set the pistons in the right position.

• Be particularly careful about the gap between the pistons in the caliper. After bleeding, use the CHECK side on your C4 bleeding block: You should be able to slide it in with a bit of resistance, but it should not move around once inserted. If you can still move it, that would be a sign that the pistons are slightly too far apart (to move them closer, pull the brake lever while the syringes and are still connected.)

• If the brake performance remains poor after bleeding, check the system for any leaks (see explanation above). If needed, feel free to use the spare lever and/or caliper we supplied to the customer for this repair.