5 replies to this topic

[jpw1275]

Hi peeps ..... Was pottering around trying my badge in several places on the front and noticed my drivers wheel slightly turned but my passenger wheel is straight..... Is this normal.... Or has something happened whilst it's been stood there..... I've had the driveshafts out for a repaint but that's about it..... Could it be the tracking needing adjustment

Cheers James

Edited by jpw1275, 19 October 2013 - 06:30 PM.

[minimadles]

It can be tricky just looking but if you have a slight lock on say to the drivers side the inside wheel will look like its turned more because the outer wheel has further to travel than the inner wheel it's called aikamen angle

[Carlos W]

Get the tracking checked, it wont cost too much!

[jpw1275]

ah ok..... the cars not on the road so im in no rush ... i was just puzzled

cheers james

[Ethel]

Could be perfectly normal, the front wheels should tow (point) out slightly, so if one looks straight ahead the other will point out more. The effect will be exaggerated if the wheels are off the ground.

[tiger99]

No such thing as aikamen angle. Don't believe all that you hear down the pub......

 

Actually is is Ackermann angle, and has nothing to do with this, which is simply the static toe setting, if it is not just an optical illusion due to the shape of the body.

 

Ackerman angle relates to the change in toe as the steering is moved from centre, so that in a turn the inner wheel is steered to a larger angle than the outer. Ackermann achieved it on beam axle suspension, on a horse and cart, by angling the steering arms so that a line through the king pin and track rod end on each side met at the centre of the rear axle. With independent suspension it is far more complicated to get right, in fact it is not usually right, because in high speed turns you need less than ideal geometric Ackermann, as the less heavily loaded inside tyre will want to understeer more than the outer tyre, and you want them to understeer at the same rate so that cornering load is shared to best advantage. Actually, it is more complicated, but that is a good approximation to the simplified truth

 

In the Mini, Ackermann is controlled by the steering arms being angled inwards. Note that this is the same for saloon and van, despite the extra wheelbase, so one at least would be incorrect. But it is also influenced by the track rod angles, in the horizontal plane, which change as the rack moves. But they, and the rack length, have to be set in the vertical plain such that bumpsteer is low.

 

Now you see why Issigonis was a genius, because in addition to that, and the camber, rate of camber change on bump, and roll centre height, all necessary for good handling, he also had to get the king pin inclination and scrub radius correct, followed finally by castor, which fortunately has little effect on the other settings but does allow the amount of self-centering of the steering to be set. Then there was toe..... But in a very short development cycle, he created a car that handled brilliantly.

 

When people mess with any of that, except for a small amount of negative camber, they very rarely make a genuine improvement, although many are deluded into thinking that they have. There was a reason for the Mini having positive camber front and rear, and that was to make the power-on understeer and power-off oversteer come in more smoothly and progressively, to suit the average driver. The camber is worth tweaking, within moderate limits, and we now have radial tyres (early Minis were on crossplies) so some small amount of static negative camber is more tolerable.

 

But you should never need to change the Ackermann. If it is wrong, you have bent stering arms, or a rack that was not centred with the pin before setting the toe.