pre-war race car. lot of positive camber on front wheel why?
Discussion
r11co said:
Because the suspension of the time had the tendency to pull the tops of the wheels inboard under load. Still the case now but not to the same extent.
Eh?The pictured car has a beam axle and king pins, what force do you think will make the top of the wheels tend to go inboard?
It was to achieve centre point steering, where the axis of the kingpin strikes a line through the tread centre ie no scrub radius.
Quite why that was considered advantageous I don't know, may be to do with making a heavy steering system lighter to use ?
The tyre width being so small probably meant there was little to be gained by running negative camber anyway .. ?
Quite why that was considered advantageous I don't know, may be to do with making a heavy steering system lighter to use ?
The tyre width being so small probably meant there was little to be gained by running negative camber anyway .. ?
Camber has little or no effect on self centring in itself.
Self centering is governed by the caster (kingpin inclination in the longitudinal plane) and scrub radius.
Scrub radius is calculated by drawing a line through the centre point of the tread and a line though the steering axis of the front wheels. If the line through the tread contact the ground at a point outside the line through the steering axis it has positive scrub.
Positive scrub used to be prevalent on most cars up until the advent of ABS braking (Ford actually made a marketing feature of negative scrub for the Mk IV Cortina). When one wheel on an axle hits a bump positive scrub will tend to make the car dive towards the side hitting the bump. In conjunction with the bump itself this will create a significant force to pull the car in that direction.
Negative scrub will reduce the tendency of the car to steer towards the bump by steering towards the bump countering the effect of the wheel being momentarily put under a braking load from the bump itself. This makes the vehicle more stable.
In older cars there were problems with the suspension design in getting the scrub radius reduced to increase bump stability hence significant positive camber was used to move the tread centerline towards the centerline of the car, hence reducing the scrub radius and improving high speed stability.
As suspension design improved and wheel design became better the steering axis could be moved outwards so the requirement for positive camber was reduced and eventually done away with.
A car with ABS and positive scrub can be very hard to control under braking as the braking effort will tend to create a lot of kickback through the wheel, hence why most modern cars have negative scrub radius.
Self centering is governed by the caster (kingpin inclination in the longitudinal plane) and scrub radius.
Scrub radius is calculated by drawing a line through the centre point of the tread and a line though the steering axis of the front wheels. If the line through the tread contact the ground at a point outside the line through the steering axis it has positive scrub.
Positive scrub used to be prevalent on most cars up until the advent of ABS braking (Ford actually made a marketing feature of negative scrub for the Mk IV Cortina). When one wheel on an axle hits a bump positive scrub will tend to make the car dive towards the side hitting the bump. In conjunction with the bump itself this will create a significant force to pull the car in that direction.
Negative scrub will reduce the tendency of the car to steer towards the bump by steering towards the bump countering the effect of the wheel being momentarily put under a braking load from the bump itself. This makes the vehicle more stable.
In older cars there were problems with the suspension design in getting the scrub radius reduced to increase bump stability hence significant positive camber was used to move the tread centerline towards the centerline of the car, hence reducing the scrub radius and improving high speed stability.
As suspension design improved and wheel design became better the steering axis could be moved outwards so the requirement for positive camber was reduced and eventually done away with.
A car with ABS and positive scrub can be very hard to control under braking as the braking effort will tend to create a lot of kickback through the wheel, hence why most modern cars have negative scrub radius.
Was coming here to explain but it's been done better than I could!
Having the centre line of the king-pin acting through the centre of the contact patch does tend to reduce steering effort as well. For fairly 'extreme' examples look at 20s & 30s Bugattis from head on...
http://www.conceptcarz.com/images/Bugatti/30-Bugat...
Having the centre line of the king-pin acting through the centre of the contact patch does tend to reduce steering effort as well. For fairly 'extreme' examples look at 20s & 30s Bugattis from head on...
http://www.conceptcarz.com/images/Bugatti/30-Bugat...
stavers said:
Was coming here to explain but it's been done better than I could!
Cheers 
stavers said:
Having the centre line of the king-pin acting through the centre of the contact patch does tend to reduce steering effort as well.
That's the scrub radius.Modern cars have negative camber AND negative scrub due to improvements in suspension design.
One common 'tweak' on modern cars is to fit spacers. That used to give more feel in the days of positive scrub but on a modern car with negative scrub radius it can have exactly the opposite effect as it reduces the scrub radius.
lostkiwi said:
That's the scrub radius.
Modern cars have negative camber AND negative scrub due to improvements in suspension design.
One common 'tweak' on modern cars is to fit spacers. That used to give more feel in the days of positive scrub but on a modern car with negative scrub radius it can have exactly the opposite effect as it reduces the scrub radius.
Ah - that's interesting. Hadn't appreciated that's what was going on...Modern cars have negative camber AND negative scrub due to improvements in suspension design.
One common 'tweak' on modern cars is to fit spacers. That used to give more feel in the days of positive scrub but on a modern car with negative scrub radius it can have exactly the opposite effect as it reduces the scrub radius.
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