The Honda Brake-By-Wire System

Honda was the first motorcycle manufacturer who introduced a brake-by-wire system on a commercial available motorcycle, but are electronically controlled brakes really a step forwards?

Honda has first demonstrated its electronically controlled combined anti-lock brake system for motorcycles a few years back. The system, which is now available on a few Honda production machines, is a completely revised version of the 'old' Honda combined braking system (CBS), that links the front and rear brake systems, applying pressure to both circuits regardless of which lever the rider operates. But the main aim of the system is not to improve lap-times. Instead, it should increase stability under braking and reducing braking distances for less confident riders especially in an emergency situation.

Unlike the Combined Braking System (CBS) you find on some of Honda scooters, which work mechanically, the Electronic Combined Braking System with ABS system is completely electronic and has been referred to as brake-by-wire technology, meaning there's no need for caliper mounting mechanisms to mechanically operate the other pistons.

The calipers on the Honda CBR600RR are identical to the calipers of a CBR600RR without brake-by-wire system, but that's where the similarities end.
How does the Honda brake-by-wire system work? At speeds below 6km/h the brakes work normally – so fluid pumped by your hand or foot reaches only the caliper(s) you actuate. Above 6km/h a valve in the brake line operates and diverts brake fluid towards pressure sensors. Now when you pull the front brake lever you're not working the caliper. Instead the sensor sends a signal to the brake control unit (BCU) telling it what you're doing. The BCU then sends a signal to a pump, and it's the pump that generates the pressure at the front caliper, not you. At the same time the BCU also sends a signal to the rear brake pump, which is how the combined system works electronically. If you use the rear brake the system works in reverse.

In itself that's quite clever, but it's not the whole story, because there's also ABS to consider. Unlike conventional ABS systems that generate a pulsation feel when triggered, Honda's electronic system is completely smooth through the chassis and brake lever. Of course it works in the same way as other systems, monitoring the rate of deceleration and comparing this to threshold values, and reducing brake pressure as the threshold is approached and exceeded.. But because the pressure at the calipers is being generated by the pump, they're able to vary the brake pressure like a dimmer rather than a quick switching on/off switch.

In the short time I got to try the Honda electronic brake-by-wire system I was impressed. It's clear something out of the ordinary is happening, but it doesn't feel intrusive. For starters, the Honda brake-by-wire system was impossible to tell that pumps were operating the calipers and not me, and I wasn't aware of the ABS cutting in or out at any point.
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