Today, we're going to be covering a topic
that you see a lot of on the internet,
and that is why you would put a rear wing
only on a front wheel drive car, cause
many people talk about the drive is going
to the front, so why would you want
downforce on the rear lifting the drive wheels
up. And basically it boils down
to the fact that, yes, a wing behind your
rear axle is going to cause a lack of
traction on the front as the speed increases,
but the overall benefit can be seen
in your overall laptime, particularly in cornering
and braking, and I'm going to
go in depth on why that is the case for a
rear biased aero that isn't particularly balanced.
Now let's just start off with a little disclaimer,
I stand by what I said in my
"do car spoilers actually work" video, for
road applications with slow speeds and
heavy cars wings don't do anything you will
notice, but, lets consider theoretical
performance improvements and how adding a
rear wing could help with laptimes in a
lightened car or even a ricer going around
a circuit, and how that could be an improvement.
Normally when we talk about aerodynamics,
we want aerodynamic balance, we want
to basically make it so the force at the front
and the rear to be balanced so we
have it matched to whereever our centre of
gravity is. So on a front wheel drive
car our engine is forward and our centre of
gravity is about here. So you would
think that you'd need a decent splitter size
there to get a bit of downforce back
if you want to run any sort of wing at the
rear. But, we can actually do something
a little bit trickier. If you watch my "how
does ackerman work" video you'll see
that basically in low speed corners you need
to overcome a yaw inertia as well as
just turn the car into the corner. Now this
means that at low speeds, tighter
corners your car will inherently understeer.
Now most people will know this if you've
ever driven a car around a hairpin you'll
know that even if it's balanced normally it
will understeer a little bit in the hairpin
unless you set it up really well beforehand.
So, we can see from that that we're understeery.
So, lets balance the car so that at
low speeds it's neutral, lets strip a little
bit of grip of the rear axle and give it to
the front, you can see my "How do anti-roll
bars work" video for how that works. Now,
we've now gor the front with more grip and
the rear with less grip. Now this means that
at high speed when we turn it into corner
we now have an inhernetly oversteery car,
there's less yaw moment that you need in the
higher speed corner, you're relying more
on ultimate grip. As such, your neutral car
in a low speed corner will now be oversteery
in a high speed corner. Now that's not great,
the car's going to feel sketchy, it's going
to feel very hard to control, so what can
we do? We want to make the rear end planted
more as the speed increases as the requirement
for yaw moment is dropping. So, we add aero
to the rear, we don't balance it out at the
front. So that means that as the speed
increases, grip will return to the rear axle,
therefore balancing our car out as we go.
Our centre of pressure may be behind our centre
of gravity, but as we've set our suspension
up to be naturally oversteery, the aero is
actually bringing it back to a neutral balance,
and that's why you can get a car that works
well, with just a rear wing.
Of course, lets now say we're not doing anything
tricky with our suspension, and we
haven't set it up to be oversteery in the
high speed so that it's neutral in the low
speed and lets just say we're dealing with
a normal car, we've taken a street car,
and taken the ricer approach of just throwing
some part on it. What you're going to
see around a laptime is a benefit in braking,
because of the increased drag, as well
as the downforce on the rear axle, which is
going to translate to an increase in overall
grip once you hit the brakes and the weight
goes forward, and in cornering if the wing
was on line or fore of the rear axle you would
actually see an improvement in cornering,
and if it was rear, depending on how understeery
the car is you would see a lack of
improvement. Of course this scenario changes
a little bit when we are under power, and
this is the thing most people talk about they
say "oh you don't want rear downforce on
a front wheel drive car". The thing you've
got to remember is that a circuit is so much
more than just powering out of corners, if
you can get super traction in braking zones,
that makes up for inferior acceleration out
of the corners. So, it's all a compromise
sort of thing. Obviously, yes we do want good
balance, but you may see a lap improvement
with just a rear wing, you don't nessecarily
need front and rear aero.
Also, having the understeer from the rear
aero balance and also the inherent stability
from having you centre of pressure rear, means
that a novice driver may find the car easier
to handle. The other thing I want you to take
away from this is you don't nessecarily need
to have a car to feel balanced to go fast,
you can have a car that the driver hates,
but
if it's a second a lap faster who cares what
they feel like, the car is faster. So just
keep that in mind for any setup changes, and
if you're racing you're actually going for
the
fastest time, not the most driver enjoyment,
so that's something to keep in mind.
Just as a final disclaimer, I don't condone
rice in any form, if you were adding something
to your car I really would think that you
would want for it to do something, so that's
half
the reason why I'm doing these videos. So
keep that in mind before you reply angrily
in the
comments section saying that I'm a ricer.
Thanks for watching, hopefully that settles
a few arguments out there, and see you next
time!
