I've done a bit of googling and some searches here and haven't come up with conclusive explanations of how one calculates the breakover (aka ramp over) angle of a vehicle. I found a common definition used by the US EPA, as well as Canadian and Australian MV departments, which states:

"Breakover angle" means the supplement of the largest angle, in the plan side view of an automobile, that can be formed by two lines tangent to the front and rear static loaded radii arcs and intersecting at a point on the underside of the automobile.

I also found one at offroaders.com that says:

Breakover angle (degrees): The angle formed by lines drawn from the front and rear tire’s contact patches and the point on the chassis which marks the mid-point of the measured wheelbase. The taller the vehicle’s chassis, the smaller the breakover angle.

Note that these differ in their specification of which point on the underside of the vehicle they measure from. The EPA definition says a point, while the offroaders def says the midpoint.

I've drawn up a few options (yeah, go ahead and laugh at the amateurish use of Visio) and would like those who know which is right (pick A, B, C or D) to tell me, or say it's none of these and suggest what it actually is.


Here, the angle is formed by lines that connect the centers of the tire patches to the lowest point, for instance the transmission skidplate.


Here, the lines are tangent to the tires and intersect at the low point. This seems closer to the EPA definition.


Here's another scenario. The lines are tangent to the tires and meet at a point under the vehicle (in this case, conveniently avoiding both the tranny and the cat). This is close to the loose EPA definition too.


Here's my final guess: the lines are tangent to the tires and intersect at the mathematical center between the centers of the wheels, per the offroaders definition. In this case, the cat, though it's higher than the tranny skidplate, is the centerpoint.

Any ideas? Thanks

 

there is no set brakeover angle... there are jsut too many variables involved to determine it

 

D and A make the most sense to me in that order.

I guess A woulkd be your "Real World" break over and D would be the ideal breakover angle.

Just my guess.

The real test is to drive OVER something and find out what BREAKS, this is your BREAK-OVER angle.

 

thanks guys for your replies. anyone else had occasion to measure this? it seems even among auto manufacturers there is no consistency. by some standards, i have a smaller breakover angle than, for instance, a stock outback, which i find crazy.

 

Anyone else? Links or URLs are just fine, though I've looked through pages of them on Google, too. Anyone work at an auto manufacturer and know their formula?

 

Your last one was closest, but you are measuring the wrong angle:














And the truck you drew needs bigger tires.

 

I've been an automotive chassis designer for nearly 30 years.

The answer is, emphatically, "D"!

No question about it. I don't know where these other concepts come from but they're WRONG!

Regards,
d

 

For a real world answer, I think you want to find the lowest angle obstacle that would just hit the under side of the chassis. Typically that would hit in the middle equal distance between the wheels (D), but if something hangs down lower in front or back of the center, that may hit first. So you can't just pick a single point ahead of time and work the angle off of that. One way would be to cut out a side view of the vehicle and some typical break over ridges and then see if indeed the center hits first or if some other point does as the front and rear wheels go up and over the ridge.

 

Seriously? Your first post and you bring back a 4 year-old thread and don't even provide explanation?

I don't even see how one could apply this "break over angle" concept on the trails. it's not like one would truly measure this angle before going over an obstical. Thats why we get skid plates.