the weight is set at Mr . McKinley ' s weight , 158 pounds . The steer ing axle has a 21 . 5 - degree front tilt .

I would like to assure you that it is not my intention to get very technical about what we are talking about because that would take a long time and would not add a great deal to what you have to know . But I am going to limit what I say technically to those parts of this that I think are important .

In this picture what is important is where the centers of gravity are in relationship to what you are going to recognize in a short time as the dangerous axis of tilt .

So , we will go on . Now , this is looking down on the three wheels of the vehicle . And here , for the first time , perhaps , is where you have an opportunity to realize what the problem really is . On the right - hand side of the drawing you will see a line labeled tilt axis . That goes from the bottom of the front wheel to the bottom , in this case , of the right rear wheel .

The reason that is important is this : That is the axis about which this tricycle will tilt in most of its accidents . It is not generally rec ognized that the problem really is that the transition from a stable configuration to an unstable one is very sudden .

On the drawing is labeled the projection , which I will show you in the next postercard , of being tilted on a 20 - degree as compared to a 30 - degree surface . Those are the projections of the center of gravity , both of the machine and of the operator .

Now the gut point of this is that the minute you cross that axis this tricycle suddenly becomes unstable . There is no warning . On the inside of the axis it is stable . On the outside of the axis , it is not stable , and that happens in a flash .

If you will also associate this in your minds with the following : When you are traveling at 30 miles an hour , you are traversing 44 feet in a second ; 44 feet forward is the distance this vehicle moves when it ' s traveling at 30 miles an hour .

If you give the operator 1 second to react to a sudden change in the terrain , he has to make up his mind what to do about it within 1 second , which means that in the time he is making up his mind he has traveled 44 feet along the dangerous road . Would you please put the other one up ?

This is the origin of those projections . As you see , it tends to look as if you are looking straight down from the center of gravity onto the inclined plane , which is shown there at 20 degrees . But the dif ficulty is the points where they intersect the inclined plane have to be viewed with respect to that tilt axis I just showed you . You can ' t judge it here at all . You can ' t have any sense of what that means to the stability of the vehicle .

Mr . BARNARD . Are we looking at the vehicle from behind now ? Mr . MENKES . From behind .

Mr . BARNARD . OK . So we don ' t actually see the third wheel , but - -

Mr . MENKES . No ; I left it out because it would be confusing . Mr . BARNARD . OK . I ' m with you .

Mr . MENKES . And if you will put - if you don ' t mind , put that last slide back up again and maybe what I said will be a little clearer .