The Ultimate Guide to Suspension and Handling – Bump Steer/Toe Steer


Some suspensions such as the semi trailing arm type found in mid 80’s BMWs, Mark 2 Toyota Supras Nissan Z cars and the Datsun 510 have severe toe steer by design. Their semi-trailing arm suspensions go into toe out under roll and squat giving these cars a severe case of trailing throttle oversteer and instability under acceleration.


Sorry hipsters, racing heritage or not, the BMW E30 and earlier models have semi trailing arm rear suspension that causes the car to toe out under roll.  Lifting the throttle or really heeling the car into a turn will causes instability and snap oversteer. 
Same goes for Datsun 510 and 280 and 300Z's.  Even though these cars have a winning racing history, they suffer from handling ills caused by their semi trailing arm suspension.
Yes sir, even the mighty 911, until the 964 model had semi trailing arm suspension.  All of its rich racing heritage doesn't change that fact.  The rear suspension and tail heavy rear engine layout is what gave 911's the reputation for being hard to drive fast.
Semi trailing arm suspensions like the one from a E30 shown here have control arms that tilt inward at an angle.  They were created to solve the problem of a super high roll center that the first independent rear suspension design, the swing axle suffered from.  Because of the diagonal pivoting of the arms, the semi trailing arm toes out under compression.  Toe out in the rear of the car causes oversteer in cornering and instability under the squat of acceleration.
The angle of pivoting that causes the toe out is shown clearly here.  Over lowering a semi trailing arm suspension car results in truly wicked handling.


  1. I lowered my 991.2 Carrera GTS (2017) by approximately 30 mm in the front using Öhlins shocks. The lower control arms are hence directed somewhat upwards, however, the rod is also directed upwards. Maybe, they are nearly parallel. I am not sure if I should compensate for bump steer or this modern car compensates it automatically. I do not know if it developes a significant amount of bum steer as it is now.

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