High and Low frame front suspension difference

[JonE]

There are several threads on the old forum and it seems that there is a consistent one degree difference in the high and low frame relating to "camber", (which I find notoriously difficult to visualise).
Tyre diameter is mentioned as one variable, but I'm unclear about whether front springs are different? 
What the implications are for using parts i.e. putting semi girling stubs onto an earlier axle, or later stronger radius arms (some mentions of cutting and altering slightly), or using a complete later Ruby axle on a high frame chassis for instance. This might be useful to have updated generally for some pointers for the uninitiated, or can people link any more recent threads that draw attention to this area?

[Bob Culver]

Camber or castor? Some old posts accidentally interchanged the words! 

Apparently the girling radius rods fitted to high frame cars reduce the castor (backward lean of kps). This would suggest 1933 and 1934/5 Ruby radius rods also differ but I dunno. To some extent castor with the pre Girling radius rods is adjustable by twisting. Tend to work themselves into a lesser castor state.
Many advocate at least original and preferably increased castor to reduce wander. 

Camber places the turning point on the road relative the kingpin axis extended. For the same angle the lateral location with a very large overall dia tyre is slightly different than with a very small one but hardly significant. I have noticed in photos a definite range of camber angle so possibly the angle incorporated in the stub axles did change at some time. But then when servicing kingpins how many diligently check for squareness?

(In current issue of VSCC LCES magazine two chummies with very different camber! Someone may be able to reproduce if that allowed)

With a vice, 1/2 inch rod. square and level not difficult to compare stub axles.

[JonE]

Bob - that just shows my starting point! I have found nothing yet that has properly lodged the information with clarity!
For instance, do high frames and low frames always sit parallel to the ground, or does the latter sit at a slightly different angle?
One comment was about tyres and wheels - so one varianbe presumably is the difference in rolling radiums of a 4.00/17 and a 350/19 tyre.

["Slack Alice" Simon]

Standing in front of the car, the front wheels are obviously angled, leaning together, nearer at the bottom than the top.

Isn't this "camber"?

Don't know why it is there.

[Mike Costigan]

... Don't know why it is there.

I don't know whether this is just an 'old wives' tale', but I have always understood that camber of the front wheels was to keep the tyre tread squarely on the road. That sounds daft today with our flat road surfaces, but when our cars were new even the main roads were quite narrow with pronounced camber of the surface to promote drainage, and with low traffic density it was normal to drive on the crown in the centre of the road; thus the wheels needed to be at an angle to maintain overall contact.

[Bob Culver]

Camber places the contact patch more or less in line with the kingpin. If it were say 3 inches outward when the wheel hit potholes or was braked more than the other side the hub would try to turn around the kingpin and and kick the steering.
 (With damped power steering and fwd in moderns all sorts of other arrangements are encountered.  Was also used on horse wagons  for other reasons; reducing the bending of the axle stubs and because the wooden wheels may have been dished)

With castor (for the same length and shape radius rods) it is the height difference between axle and radius rod ball joint which influences, not the tyre diameters assuming no absurd difference tilting car front to rear

["Slack Alice" Simon]

Thanks, now I know more than I did this morning.   Always a good feeling.

[AustinWood]

On most cars the tyre runs outside the centre line if the king pin. This makes the steering lighter at low speed because the wheel rotates as it turns instead of purely slipping.
This is what causes some front wheel drive cars such as Minis to pull so hard to the straight ahead when accelerating. The worst was Montego Turbo which would almost pull the wheel out of your hands in one front wheel lost traction when on full throttle.
The only exceptions I know of are Citroens and the Oldsomobile Toronado which are designed so that the line of the king pin passes through the centre of the tyre contact patch. There is a very big offset on the wheels and the brakes are inboard to allow room.
This means there are no interactions between steering, braking and drive. Also the car does not pull in the event of a front wheel blow out - Remember the Citroen GS adverts where the tyres were blown out at speed as the car passed between 2 HGVs?

[Tony Press]

The Austin Seven along with most pre war cars has a so-called 'cart axle' as the front axle and the suspension cannot be compared to later cars with independent suspension, let alone FWD.

I understand the Austin Seven always had vertical king pins with the 'camber' or wheel tilt built into the hub. This camber was as discussed usually arranged to have the king pin pointing at the centre of the tyre contact with the road to allow the wheel to rotate about this point on turning and not cause a 'turning' action when the front wheels were braked (remember front wheel brakes were a novelty when the Seven was built).    

The Morgan front end showed a completely different geometry with vertical 'king pins' (spring units) and no camber - must have a very strange feel under braking.  

The caster was set by the relationship between the radius arms and the front axle, cunningly adjustable on early cars. The original (was it around 2-3 degrees lean back ?) when new relied on the setting of the rear springs (which obviously changed when driver and passenger added) as the front ball joint position altered.

When the radius arms were fixed on later cars, caster adjustment needed a lot of work especially if the rear springs were too cambered.         

See elsewhere for a discussion on toe in.

Cheers, Tony.