Is there a reason why beam axles always seem to set-up with positive chamber rather than the conventional negative? Early Fords came with around 1 degree positve from the factory and then you get the extreme cases as seen on Bugattis and other vintage racers. In my mind beam axles would benefit from negative chamber the same as IFS?
I believe that the thinking was it offered better directional stability and loaded the bearings against the hub, rather than away from it. Keep in mind the tires weren't capable of anywhere near the grip levels we see today. And no one had figured any of this out yet! Our 20/20 hindsight obviously says different...
i aint no alignment guy but that thing desnt have a sway bar and that makes the body lean way out with centrifigual force. so as it tilting it angles the outer wheel to get maximum traction s it hooks. see how the left wheel is flat but the right wheel is up. with independant front suspension youd have negative and a sway bar it squats and tilts to vertical to get the most traction. but that doesnt work here since a solid axle cant squat. but that is all a straight guess. im prolly wrong.
It was done on wagons to get the centerline of the tire contact under the center of the wheel bearing. In the early days I know there was a lot of concern about scrub(scrub radius) causing tire wear. Just guessing, but maybe that was all or part of why they did it? If that's the reason they could have just used a different king pin angle or changed the offset of the wheel.
On a tangent, do any of the current axle makers offer negative camber axles? Would it be a good thing? Gary
Look at the pic and you can see why it is not done any more.... The rear tires, which have zero camber have way more contact patch touching the ground, compared to teh front tires which have a bunch of positive camber and very little contact patch touching the road. Somewhere along they way, engineers figured out that a whole bunch of positive camber was not a good thing, but why they thought it worked in the first place, I have no idea. It does look kinda bitchn' on all those old race cars though... -Abone.
There were a few reasons for it. One of the most quoted had to do with the high crown and heavy ruts of the roads back then. With a beam axle there is very little camber change during suspension travel, especially when both wheels bump up (camber change only happens when one wheel travels more than the other). In heavy ruts the positive camber helped keep the car in the ruts, as versus climbing out and getting all sideways on the road. It also helped to counteract bump steer issues (and the dreaded death wobble) as well as creating much lighter steering effort. With the narrow tires and round profile, camber was of little or no benefit to cornering forces. It has been said that Mercedes, during the early 1900’s would actually measure the crown in a road when doing endurance racing and set the positive camber to match as it made the cars more stable at speed. One other thing to consider is wheel bearing loads and the technology in the early days. Have you ever noticed how the inner bearing is larger than the outer? Well on these really early cars it is even more so. By putting positive camber in the wheel the load is directed more towards the inner bearing. The vertical load is more direct with the inner bearing and this kept them from snapping off spindles which was a problem early on.
The strength requirements of the spindle stem dictate wheel bearing size. Smaller wheel bearings would be adequate, but those wouldn't fit over the spindle stem.
Right, but the bearing had to be larger because they had to make the base of the spud larger to support the loads due to the metallurgy of the time. The same can be said for the quality of the bearings themselves - it went hand in hand
This is a Model T tierod, spindle and axle. Notice the tierod has no ability to pivot...just turn. It works like a kingpin. The kingpin must also be mounted vertical to allow the spindle to work without binding. As a result, to get the scrub radius to match the center of the tire, the camber must be set positive. Once the manufacturers started using ball type tierod ends it was possible to design an axle for better tire contact/footprint in harder cornering, without compromising the scrub radius. Oh yes...it is "odd" that some later Fords might have retained slight positive camber! Especially when you consider how quick Henry Ford Sr was to jump onto the trick of the month when designing cars!
Try here for part of the answer, http://en.wikipedia.org/wiki/Ackermann_steering_geometry The other part of the answer is to get the point on tire contact directly under the pivot point. This makes the car track straight, tire wear better, and steering effort easier. Some manufacturers used offset wheels to get the desired result, others bent the axle.
I do um any way you want A friend of mine gets 0 on one side and 3 degrees neg on the other for his vintage roundy round car
Ackermans steering angles are only to achieve toe out on turns. The positive camber works in with the KPI (king pin inclination). The centre line through the tire and the king pin meet in the centre of the tire at the point of contact with the road,hence giving it a easy to steer pivot point and the camber also transfers the load to the inner bearing and therefore the base of the stub axle where it is its strongest,the outer bearing is mearly a stabilizer.How many trailers have you seen that were built with zero degrees camber on the stubs loose a wheel/hub when over loaded? Its not rocket science just mechanical engineering. JW
Thank you 26 T Ford, it took a long time for someone to correctly note the kingpin axis matching the tyre centre to reduce steering scrub and effort. Sure, there is caster to consider and a whole bunch of other stuff when you get to independent suspension, but that's the reason for positive camber on beam axles. Cheers.
Cheers dad-bud , and to Enbloc if you look closely at the Bugatti you will see the king pin is vertical hence the amount of positive camber so the two centre lines meet in the middle of the tire with the principal i mentioned above. JW
If you look closely at the Bug in the first photo, you can see daylight under the left front wheel. He's getting all he can out of the old warrior!
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