Un­der­stand ABS and use it wisely

Elec­tronic safety net for panic sit­u­a­tions

Motorcycle News (UK) - - This Week -

Bob Gray For­mer road tester who’s spent the last 16 years work­ing as tech­ni­cal ad­vi­sor, en­gine-man­age­ment tech­ni­cian and crew-chief for BSB teams

There are two prob­lems with brak­ing while cor­ner­ing on a mo­tor­cy­cle. The first is the front loses grip and you crash. The sec­ond is the bike sits up and runs wide, and you crash. It’s not some­thing most peo­ple try more than twice. But cor­ner­ing ABS aims to change that – which is good news in panic sit­u­a­tions, and for those who didn’t get it after the first two oc­ca­sions.

Cor­ner­ing ABS works by cal­cu­lat­ing the bike’s at­ti­tude (roll and pitch) us­ing an in­er­tial mea­sure­ment unit (IMU). When the ECU thinks the bike is lean­ing, it lim­its how pres­sure is al­lowed to build in the brak­ing sys­tem – re­duc­ing the sit­ting-up ten­dency. It also mod­u­lates the pres­sure based on a per­cep­tion of grip (like nor­mal ABS) – pre­vent­ing the wash­ing-out prob­lem.

Bikes sit up if the brakes are ap­plied sud­denly while cor­ner­ing be­cause a sud­den torque is gen­er­ated in the steer­ing as a re­sult of the trail and the dis­place­ment of the tyre con­tact patch with the bike’s ver­ti­cal plane of sym­me­try. In other words, dab the brakes while lean­ing and the bars will at­tempt to turn more into the cor­ner. This has the ef­fect of turn­ing the bike out of the cor­ner just like counter-steer­ing to flick a bike through a chi­cane.

The lack of grip when cor­ner­ing is sim­ply down to force. As­sum­ing a con­stant road sur­face, the more ‘down­ward-force’ (weight) there is on any tyre, the more it grips. When lean­ing, only part of a bike’s weight presses ‘ver­ti­cally’ down through the tyre; the rest at­tempts to re­sist the lat­eral force push­ing the front around the cor­ner. Quite sim­ply, there is less grip be­cause the tyre isn’t be­ing pushed into the road as hard.

From an ABS point of view, the sys­tem mon­i­tors this in the same way as when the bike is up­right, but us­ing more sen­si­tive pa­ram­e­ters, and safe in the knowl­edge that the peak pres­sure will never be as great as when the bike is up­right.

‘Cor­ner­ing ABS is good news in panic sit­u­a­tions’

Brak­ing in a cor­ner doesn’t have to end badly

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