Downforce vs actual weight

[mjoekingz28]

Lets say I have a 3000lb car which has spoilers that put out 500lbs of downforce. Does this downforce contribute to weight or drag?

Meaning.....if at 100mph where the spoilers are creating alot of downforce, will this car handle, accelerate, decelerate like a 3500lb car OR a 3000lb car with aero drag? Or?

 

[d00df00d]

This is an oversimplification, but I'm assuming you don't want to get too far into the weeds on this (correct me if I'm wrong on that).

Two things to consider: ground pressure and momentum. Ground pressure increases grip. Momentum makes it harder to turn.

Downforce adds ground pressure. Mass adds ground pressure AND momentum.

A 3000 lb car with 500 lbs of downforce would have ground pressure like a 3500 lb car, but momentum like a 3000 lb car. So, more tire grip without the laziness of a heavier car.

As for drag: Yes, things that increase downforce often increase drag, but not always. Depends how it's done.

 

[Kuato]

Right...think of the downforce adding to the grip of the tires*. The car still weighs 3000 lbs, so will decelerate the same, except that with the downforce it will be able to brake harder. Changing direction when cornering is still only moving the mass of 3000#, but the additional grip provided by the downforce helps to keep the tires glued to the road. Acceleration is slightly slower because that downforce does create drag.

I read an article awhile back that F1 cars generate enough downforce at top speed to be able to drive upside down. A related article had an F1 car racing against a race motorcycle....cycle lost - badly - even though it had better acceleration and deceleration. The F1 car's downforce made it that much faster in the turns.







*(or tyres for our Aussie and English friends)

 

[lubricatosaurus]

If a spoiler is designed right, it can create some downforce while also reducing drag!

Originally Posted By: Kuato
Acceleration is slightly slower because that downforce does create drag.
Wings with heavy downforce usually do this. Even wings can act like spoilers if they are not asked to make a ton of downforce though.

Found a good explanation to carry this further: https://www.quora.com/How-much-downward-...on-acceleration

"To summarize:
Both wings and spoilers reduce up-lift at the tail of the vehicle, but use different mechanisms.
Wings are airfoils designed to directly deflect air upwards and thus push the rear of the vehicle down. They generally add quite a bit of drag.

Spoilers are barricades to undesirable flows, and thus are able to reshape airflow streams around the vehicle. This can help keep the rear of the vehicle down and decrease drag by changing the effective vehicle shape.

You need computational fluid dynamics and/or wind tunnel testing to quantify spoiler/wing performance.

Neither have any positive impact whatsoever on straight-line low-speed acceleration. Both are primarily intended to improve stability and cornering at high speeds."

 

[Garak]

To get an idea of how involved all this really is, it's notable that F1 teams tend to hire engineers in the field with PhDs.

 

[IndyIan]

Originally Posted By: Garak
To get an idea of how involved all this really is, it's notable that F1 teams tend to hire engineers in the field with PhDs.

And spend 10's of millions on windtunnels...
Essentially at speed, 500lbs downforce gives the 3000lb car the grip of a 3500lb car. So almost 16% more traction without adding any weight that would hurt acceleration, braking and turning.
Lots of road cars actually create lift at speed so you get less grip to turn and stop the same amount of weight.

 

[Alfred_B]

Originally Posted By: mjoekingz28
Lets say I have a 3000lb car which has spoilers that put out 500lbs of downforce. Does this downforce contribute to weight or drag?

Meaning.....if at 100mph where the spoilers are creating alot of downforce, will this car handle, accelerate, decelerate like a 3500lb car OR a 3000lb car with aero drag? Or?


.

 

[d00df00d]

Oh, please. Like you've never asked a newbie-level question.

 

[Alfred_B]

Good point.

 

[Jetronic]

Originally Posted By: Kuato

I read an article awhile back that F1 cars generate enough downforce at top speed to be able to drive upside down. A related article had an F1 car racing against a race motorcycle....cycle lost - badly - even though it had better acceleration and deceleration. The F1 car's downforce made it that much faster in the turns.


You don't need a F1 car for that, pretty much any half decent car is faster through the turns than a motorcycle. That's the issue with driving on the Nordschleife with motorcyclists. They overtake you after the turns, but you need to be careful not running over them in the next turn. I don't want to kill anyone so I don't drive there anymore: should one fall in front of me I couldn't avoid them.

 

[Garak]

Originally Posted By: IndyIan
And spend 10's of millions on windtunnels...

To the point that Sir Frank owns two of the things and is able to rent them out to others!