CruiseGTi-R
Member
You believe in physics but haven't done the math. You also need to look at what the front of the car is doing.
Consider a car 2.5m long, with an overhang of 0.5m to the rear spoiler. Say the spoiler can produce a downforce of 40kg (good going for a road spoiler). Taking moments about the rear wheel to determine the reactions at the front and rear wheels, you get a downforce of 48kg to the rear wheel (note, more than 40kg) and a rather small 8kg lift at the front wheels. Yes, a clockwise moment about the rear wheel (if spoiler is past axle) will give an associated negative reaction at the front wheel. Agreed, its simple statics.
So the lift at the front is very small compared to the rear downforce. This small lift (in this case (not entirely unrealistic) of 8kg is easily overcome by any person simply sitting in the car, even filling the thing with washer fluid), hence its never detrimental to front grip.
Further and more fundamentally the speeds at which the rear spoiler produces any useful downforce at all, the front of almost any car in the world would be producing more than enough downforce by the very shape of its bonnet as a roughly aerodynamic shape.
Hence any theorectical uplift from an clockwise moment about the rear wheel is more than negated by inherent frontend downforce (and weight of people).
Problems arise with cars such as the Lambo Migura as unfortunately the front end shape produced lift at high speed. Yes a rear spoiler in this case would make this worse. But even here the contribution to front end lift would still be tiny.
Clarkson's recent ramble about the pathetic little boot spoiler on the Jag producing front lift is utter nonsense and is nothing more than a good cocktail party anecdote about the car.
To produce around 80kg of lift at the front (say just to offset the drivers weight) requires a rear spoiler 5m long (based on my example above).
Have you tried to lift the front of your car, you'd be able to lift more than the 8kg, but you'd soon get a feel for how much work a spoiler would have to do to affect front end grip.
Oh, and my goose still sucks for top end power...
Consider a car 2.5m long, with an overhang of 0.5m to the rear spoiler. Say the spoiler can produce a downforce of 40kg (good going for a road spoiler). Taking moments about the rear wheel to determine the reactions at the front and rear wheels, you get a downforce of 48kg to the rear wheel (note, more than 40kg) and a rather small 8kg lift at the front wheels. Yes, a clockwise moment about the rear wheel (if spoiler is past axle) will give an associated negative reaction at the front wheel. Agreed, its simple statics.
So the lift at the front is very small compared to the rear downforce. This small lift (in this case (not entirely unrealistic) of 8kg is easily overcome by any person simply sitting in the car, even filling the thing with washer fluid), hence its never detrimental to front grip.
Further and more fundamentally the speeds at which the rear spoiler produces any useful downforce at all, the front of almost any car in the world would be producing more than enough downforce by the very shape of its bonnet as a roughly aerodynamic shape.
Hence any theorectical uplift from an clockwise moment about the rear wheel is more than negated by inherent frontend downforce (and weight of people).
Problems arise with cars such as the Lambo Migura as unfortunately the front end shape produced lift at high speed. Yes a rear spoiler in this case would make this worse. But even here the contribution to front end lift would still be tiny.
Clarkson's recent ramble about the pathetic little boot spoiler on the Jag producing front lift is utter nonsense and is nothing more than a good cocktail party anecdote about the car.
To produce around 80kg of lift at the front (say just to offset the drivers weight) requires a rear spoiler 5m long (based on my example above).
Have you tried to lift the front of your car, you'd be able to lift more than the 8kg, but you'd soon get a feel for how much work a spoiler would have to do to affect front end grip.
Oh, and my goose still sucks for top end power...
Last edited:
. I would say I'm reasonably qualified to comment on the subject because its exactly what I've done for a job all my life, not just a general degree in 'engineering'.
