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Noticia: Camber car: Apliable to speeddown?




In 1960, AMercian engineer William Milliken - began building the MX-1 "Camber Car" to try to increase maximum lateral acceleration using round section motorbike tires with an extreme 22,5º camber angle.

The idea was to emulate the motorbike steering system wich generates the majority of lateral acceleration not by steering the handlebar but by leaning the bike, which generates camber thrust as the contact patch adopts a truncated cone like shape.

This thrust has the advantage of not generating friction as slip angle steering does.


This thrust has no load sensibility, so by doubling the load on a tire, its lateral thrust raises more than double. This forces to use a narrow trach vehicle with a center of gravity to track relationship betwwn 1/4 and 1/3 to generate lateral weight transfer. These measures are similar to those of a speeddown car.

He managed to increase maximum lateral acceleration around 25% ( 1,3 G with modern motorbike street tires ). All development - and many interesting stories about the origins of autmobile ngineering - are written on his book "Equations of motion".



The concept was recovered in 2013 by California Polytechnic State University team leaded by Maximiliam Slauter ( to whom we want to thank its gentle cooperation with our project ) which wanted to equal the lateral acceleration level of the other teams - that used wide rectangular section slicks - with small scooter tires using 40º of camber.

All details are in this very interesting DOCUMENT


At Zonagravedad we have tried to apply this concept to a C4 european class Sejkora speeddown car. Initial configuration is easy: just flipping the uprights upside down gives us 30º of camber. We slided the leaf springs to fix it in 25º - to avoid tire scratching on the body. We adjust the lenght of steering knucles and we're done.

After setting toe to 0º, we check out if rolling resistance increases too much. Theory says that the increment soulld be 1 - Cos ( camber ), which is 10% plus bearing friction increase. In our test track without any braking needed it became around 1 sec/Km, nothing exagerated.

As we had no safe test track to achieve more than 1,0-1,1 G that we get with 0º camber, we went racing to  Cabarceno Natural Park ( Cantabria - northern Spain ), with a difficult, twisty and bumpy track. This VÍDEO shows the onboard camera of the race and the test sessions.

Behaviour was nervous. It could be caused by camber thrust generated when we passed through one wheel bumps - which are not compensated by the opposite one. We felt a bit like "floating". It probably could be improved by adjusting toe settings, but we didn't wanted to increase rolling resistance and we didn't had time and resources for a fast and precise adjustment. Lateral traction is good, althoug because of the nervous behaviour we didn't notice any improvement. Drifting was easily controlled.

Camber thrust called to adjust driving technique, looking for lateral weight transfer and steering with less steering wheel imput, which reduces tire friction on bends. Braking performance didn't suffered noticeabily. 

Update:


Today I've been testing it with different toe settings and I've reached 1,15G with 1 degree toe out front and 0,5 degree toe out rear.  That's a 15-20% increase over 0 degrees camber.


The problem is that those toe settings increase too much wheel friction, so that a standard downhill run is slower...


After two months of testing, we haven't had any reliability problem in wheels, axles or bearing. Curiously, tire life doubles as you just use one side and you can flip it when it's over.

Another advantage is that it allows to deign a closed wheel body, with a smaller forntal area than zero cambered wheels, which should reduce aero drag. This idea has been applied - with 8º camber angle - by world record holding  Shell Eco-Marathon ETH Team with its Pac-Car II.


Does this concept make sense in speeddown racing? There is a clear improving potential: raising 25% lateral traction woulld clearly overcome the small rolling resistance increase in tracks with various braking areas, although it's important to improve beahiviour. C6 class could also benefit from its heavier weight to gain stability and, proportionaly, more camber thrust.







 
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Autor: Calixto García Velasco



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