W.i.m Geomatry!

[Tony-Bones]

Mr WIM , I'm not super technically minded , could you please explain this to me in laymans terms? Very interesting reading on the WIM site... http://www.wheels-inmotion.co.uk/

In the two cases it can be seen that the bigger the castor angle (either negative or positive) the greater will be the longitudinal offset, and the greater will be the shift of the point of application of the resistance force during steering, therefore, the conclusion can be drawn that the couple “rolling resistance and the kingpin axis extension” is both straightening and self - centring, and directly proportional to the longitudinal offset,

In the most common case, with a positive castor angle, the couple, which creates the steering return, will contrast the steering movement when a steering action is performed by the driver, thus, it could be said that, the bigger the positive castor angle, the greater will be the force exerted on the steering wheel to turn the wheels but, at the same time, there will be an increased conservation of the direction of the vehicle under the effect of perturbation forces against straight line travel,

Just I'm curious as to what caster does for steering feel .

Castor has a relationship with camber and the King Pin Inclination (KPI) so it's best they are explained together.

Typical Castor values range from 0 to +10 degrees.

Camber Change - If a wheel has positive Castor, then the top of the wheel leans into the corner whichever way it is steered. The change in Camber is approximately:

Camber Change = Castor x steer-angle / 60 (measured in degrees)

Example: Camber Change = 6 degrees

Steer-angle = 10 degrees

Then:- Camber Change = 6 x 10/ 60 = 1.0 degree

The change in camber that results from positive Castor is beneficial to the grip of both front wheels during cornering, providing it isn't excessive. A negative Castor (top of the steer-axis leaning forwards) changes the wheel Camber angles in the 'wrong' direction during cornering, this is not desirable.

Self-Centering phenomenon

Castor has a self-centring effect that is similar to that of SJI/KPI. As the wheel is steered away from straight-ahead its Camber angle changes and more weight is carried by one edge of the wheel. This shifts the wheelprint centre sideways and the offset force then acts to return the wheel to straight-ahead. As with the SAI/KPI self-centring this effect is proportional to the Castor and to the radius of curvature of the tyre.

Self-centring exists even if the tyre is narrow, although it is almost non-existent at small steer-angles. It is very evident on wide, flat cross-section tyres with stiff sidewalls.

Castor Trail

The common argument for the trail is wrong and it aggravates me since the example has become a seed for most attempting to explain the trail.

wim : explanation:- Sometimes people refer to a stabilizing 'Castor effect' when the effect is actually due to the trail. This confusion is probably due to the naming of wheels under furniture (Castor's) Castor by itself has only a small stabilizing effect, whereas trail by itself has a large stabilizing effect. When we increase the Castor on a cars wheel we usually also increase it's trail, this may contribute to the confusion.

[RedLexus]

I doff my cap to you Sir..... :)

[mcwatson]

Mr Wim, do you cover anything to do with the front suspension? If so, I may need to book my car in with you along with having the geometry done. I ask as my Is200 Sport has had a very annoying clunking / grinding noise coming from the front when I'm doing low speeds (under 15mph) and coming to a stop whether going straight or having the wheel turned. Its almost that if I have the weight of the car more to the front (ie. going forwards), it makes a horrible clunking noise. Its very irritating and I have no knowledge under the bonnet to know whats causing it but I'd love to get rid of it and get a nice solid driving experience back! Its best demonstrated when I'm turning into a parking space and coming to a stop. Let me know, Mark.

[RedLexus]

From comments previously posted , it would appear WIM can check out EVERTHING on the suspension , front and rear! As well as checking brakes and so forth...