Ok so say you have a 120" wheel base with front A arms and rear being leaf springs... So wouldn't it be changing while driving/loaded/bottom of travel? Looking at front A arm setups they are usaly tilted back by like 5*-20*. When you compress it you just moved back like 1/4"-1"..? The rear leads have a shackle at the rear of the spring because they get longer when you compress them? I know their fixed at one end but even that would cause it to move forward/back do to the curve of travel from the fixed point... Thus really your 120" could actually be 119"-121"depending..?? Am I wrong? SIH Sent from my SM-G920V using Grasscity Forum mobile app
Wheel base is measured with the steering wheels straight forward is center of the front hub to center of rear hub .
A little bit. The rear will move a bit, that's the reason for a slip yoke on the drive shaft. (that's a propeller shaft to the rest of the world) The A arm is leaning back for caster, like a shopping cart wheel. It trails the axis. The farther it trails (positive caster), the more straight line steering stability. The less it trails (less positive caster), the more responsive steering becomes. Turn the front wheel around on your bicycle and ride with the handlebars backwards and notice the exaggerated difference between positive and negative caster. Suspension must travel to keep you from biting your tongue going down the road. But it is set at "ride height". After you go over the bump it will return to it's setting. The road has a crown manufactured into it for water run off. Always driving on one side of the road makes the car want to veer to that side. Left and right side caster adjustment will be a few degrees different to compensate for the crown in the road to make the car go straight. It all changes with suspension movement, but is designed to return to it's adjustment settings at rest. When you put an overload of bricks in the back, or even a heavy trailer tongue, the rear suspension will be lowered/compressed and the front suspension will become raised/uncompressed, and now the geometry is all fucked up and result in squirrely steering. I know this is more than you asked, but I had some time to entertain myself, so.....pffft.
If the rear axle doesnt have a independent rear suspension aka one piece housing the axle only travels straight up and down , that is the reason for the slip yoke on the drive train . As far as I know the only axle that the wheel base changes on a would be a motor cycles front forks because the dampen at a angle .