Steering kickback

[MikeB]

Folks

After about a quarter turn of the steering wheel I get kickback. I have measured an angle on my steering arms of circa 10 deg upwards to the ball joint on the upright, circa 25-30 mm.

So my question is on a RHD car how much can you raise the steering rack to counteract this?

The car is a 1981 MY Backdate as per below

[911hillclimber]

About 10mm.
The only way to remove bump steer is the pull the torsion bars out and travel the suspension the full extent of the damper travel and check the toe change.
The ideal is zero toe change, but quite impossible in reality.
Much depend on where the suspension is at rest, i.e. How low is it?

It will need a compromise in the end.

[jb]

What is kickback?

[MikeB]

What is kickback?

When cornering at faster speeds the steering wheel occasionally does sharp tugs, my understanding is that it can be brought about due to the steering rods being not running close to parallel to the road, I.e. They get tilted up if you are running the car below standard height. So it can be counteracted by either raising the steering rack or by lowering the point where the arm bolts onto your strut.

Bump steer is a different phenomena, where due to the suspension geometry as the wheel travels up and down it can change the amount of toe in or out of the road wheel.

[911hillclimber]

I get that kick on my car too, just assumed it was the 911 way.
Bob Watson set my car once, lower arms parallel to the road, sets a lower ride height and reduces pesky bumpsteer largely.
Had kick back on rough bends.

[jb]

I assume this is different to the self centring that Nick Faure used to use to straighten up out of hairpins and chicanes?

[MikeB]

I assume this is different to the self centring that Nick Faure used to use to straighten up out of hairpins and chicanes?

Yes, very different, Nick was using the self centring that comes from the castor setting on the car, which will make the wheels on the car return to pointing straight on.

Kickback us the steering wheel jolting when in a corner.

[jb]

Thanks. Good to know.

[DustyM]

More commonly known as bump steer.

You can raise the rack 10-12mm with spacers but if the car is really low you’ll need to raise the spindles on the struts. The amount you can do this depends on the diameter of the wheel you are using. 19mm is the max with 15” wheels. More with larger diameter wheels.

Raising the spindles also keeps the geometry of the A-arms correct on a lowered car as well as the steering arms.


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[hot66]

I’m running raised spindles at the max distance for 15” wheels and don’t have any bump steer ( which is what you appear to be referring too)

[fetuhoe]

I think that we need to differentiate between 'bump steer' and 'kickback' as they are normally associated with different fault conditions and have different remedies.

A car suffering from bump steer will suffer steering problems on any rough and uneven surfaces.

The change of toe that creates bump steer will occur even in a straight line and cars suffering from this problem will tend to dart around and be relatively difficult to drive in a straight line unless the surface is even.

It will suffer from the same problem in corners but the effects aren't really a 'kickback' of the wheel but an inability of the car to respond accurately to a steering input.

All 911s have a degree on Bump Steer designed into their basic geometry as they use a very limited amount of Ackermann and need some bump and camber change to be able to turn in effectively.

Removing all of the bump steer can increase the tendency to understeer which may not be the best idea.

Kickback is more commonly associated with wear on the rack, steering joints or poor damper control and if this is the cause of your problem than adding a 'bump steer' kit will have little impact on the car's behaviour.

A car suffering from kickback will have a different 'feel' compared to a car suffering from bump steer and it shouldn't be too difficult to diagnose.