Aerodynamics: at what speed?

[Penoske]

On a road car, driving at speeds under 100mph, do aerodynamics play a significant role in lift/downforce?
It seems a flippant question, but I am currently finding myself reading Simon McBeaths 'Competition car aerodynamics' book and wondering how relevant it is to me.
So, is it worth starting to look into the aerodynamics of my car in an attempt to reduce lift, if I am never likely to be driving at high speeds?
Is it still worthwhile in the context of fast road driving?
The car in question is a 60's design, low drag but with no effort to reduce or control lift and a reputation for being unpredictable in certain circumstances.

[Tim.Wright]

If the aero forces get upto at least a few percent of the static weight forces you will feel some small handling differences but probably no measureable grip improvement. That starts to happen when the aero forces get to 5-10% of the static weight forces.

To get aero forces up to a few percent on a road car at 100mph you need pretty big changes. You're more likely to feel the difference if you pile the modifications on one axle rather than sharing it front/rear.

[bigblue]

The car in question is a 60's design, low drag but with no effort to reduce or control lift and a reputation for being unpredictable in certain circumstances.

Oh god, it's a Miura

[humble sabot]

Or a Porsche. They were even more notorious for lift. Actually, we could keep going. Very few cars saw windtunnels in the '60s and even those that did had major correlation issues, even just talking about pounds of total drag, nevermind lift.