Wow how did this thread get so technical?
To clear up a few issues
matt_mr2t wrote:But you cant ignore the fact that 2 wheels are causing substantially less friction on the road once moving which completely changes the line of thinking.
I think i have the gist of what you mean, and if i do its not true.
theres no difference in friction acting on the driven and non driven wheels themselves.
their only friction is that in the wheel bearing.
road friction, tyre resistance etc does not act to slow down the undriven wheels and driven wheels differently.
the only difference in losses between the driven and undriven wheels is that the driven wheels cant rotate freely, they have the intertia of the drivetrain to overcome.
if the drivetrain is powering itself, or transmitting torque, it would be the friction in the drivetrain the wheels see.
haha it would be so incredibly negligible you wouldnt give it a 2nd thought.
its called skin friction.
to put it in context, for a vehicle moving at high speed, it will make up about 10% of the drag, much less at low speeds.
a car has an awful lot of surface area.
a shaft doesnt have much surface area, and you are applying a tiny drag force to it.
BarronMR wrote:
As for torque steering, I think that it is due the unequal length but not the extra frictional losses of such.
It's more down the increased amount of flex that the longer shaft will allow before driving the wheel.
That causes a momentary delay and the steering effect, but I'll ask my lecturer to try confirm this.
torque steer is caused by axle wind up.
if a longer shaft is identical in every way to a shorter one, bar its length, and transmits the same torque, it has a lower torsional stiffness, and as such will create more angle of twist between its ends compared to the shorter one.
because of the twisting there will be a difference in delay from when the torque is applied to the short shaft compared with the long shaft.
the short shaft wheel will turn its wheel first.
its also possible that because the force required to twist the long shaft is less than that required to move the vehicle, it becomes a lower resistance path to the torque than the short shaft.
because of the way diffs work, it will get more of the torque temporarily whilst it twists to its equilibrium point, and when it gets there will throw the car sideways.
which effect is greater will be a function of shaft length difference and diff performance.
there is another cause.
because one shaft is longer than the other it is also easier to bend.
the torque will inherantly create a bending moment.
if the shaft is now bent, it will try to turn the wheel it is attached to.
again whether this happens is a result of suspension geometry, steering resistance etc.
