Low speed downforce

[vis]

I was thinking about aero devices focused on low-speed (around 100 km/h) downforce generation, to improve fast use of everyday car.
I would like to stay in the bed some 5 minutes more in the morning...

Assume I put a full-size rear wing on my VW Passat SW, and I get some 30 kg of downforce @100 kph.
Does this rear-biased force improve my weight balance, reducing understeer at speed, or the contrary, like what happens in F1 (games), where you get consistent understeer loading the rear wing (while running "flat" front wing)?

As you can see, I didn't fully understood bias between weight inertia/downforce...

[Steven]

Well obviously when you put weight (or downforce) to the rear, the front will be less pressured to the ground, allowing it to slip away more.

I'm not sure how you could improve steering on a front powered car. My own VW Golf is also pushing and the only possible solution would be then to create some diffuser shape under the front of the car.

Racecars make use of it (for example the Le Mans prototypes) but these are of course a lot lower to the ground, and the height of normal road cars causes troubles to implement such a diffuser.

If you need better grip all around, the best you could do is add that wing on top of your roof, in between the front and rear wheels, probably a bit more to the front when the car is pushing in normal conditions.

[RH1300S]

Have a look at what saloon racers do when they have the chance.

Things like front splitters - which should give you more front end bite.

For low speed aero - perhaps take in what the rally guys are doing and have done. Maybe think back to the Audi S1 & Metro 6R4 - As far as I know, the aero forces don't build much below 80/100kph so they cram on as much as they can. Don't forget these things have power to spare and are traction limited at most speeds on gravel.

If you want a faster journey , best to think about better brakes, lighter wheels, better tyres, take some weight off your flywheel and get some good suspension. Get the car set up well with spot on alignment. Also, every time I have changed a steering wheel in a car to a light one, the feel has improved massively (don't know where you go if you have air-bags 'though?)

In fact don't waste your money on aero at all...........

BTW - If a rear spoiler/wing is behind the rear wheel axle and is giving downforce, the cantilever effect will actually REMOVE load from the front wheels, probably making the steering worse.

[pyry]

vis, what year is your car? cheapest way to imporve your performance is to slap on better tyres and chip the car if its a diesel or turbo

[Ciro Pabón]

All right, I repost. I won't be satirical this time.

Most cars have natural understeer, as Tomba points out his VW has, to make them more secure. This way, if you take a curve to the limit, as you seem to imply you would like, you won't loose the back of the car but the front and thus, the ability to take such a tight curve. You will instinctively back off the throttle and recovery will be easier. Taking away this "security feature", especially when you are a little sleepy and in a hurry, does not seem wise. I strongly suggest using modified cars to go fast only in a secure environment, not on your way to work. Maybe I am wrong, but I could be right.

I also can't see clearly how putting aerodynamic force on the back of your car would rob you of front weight, so I would be grateful if you guys enlighten me.

[Steven]

I also can't see clearly how putting aerodynamic force on the back of your car would rob you of front weight, so I would be grateful if you guys enlighten me.

Looks to me as if there is a wing in the very back of the car and his rear wheels are more in front, there will obviously be an offset in the front of the car.

Front powered road cars are indeed almost always understeering.

So to vis, if you want to go faster, you will have to look into mechanics pointed out by RH1300S. And if you really want to go fast, go drive your car on a racing circuit or start with karting, it's a lot safer

[RH1300S]

I also can't see clearly how putting aerodynamic force on the back of your car would rob you of front weight, so I would be grateful if you guys enlighten me.

I'm surprised at you Ciro....you should know this

BTW - If a rear spoiler/wing is behind the rear wheel axle and is giving downforce, the cantilever effect will actually REMOVE load from the front wheels, probably making the steering worse.

Front powered road cars are indeed almost always understeering.

Peugeot 205 GTi 1.9........... No understeer

A great car, but probably should never be put in the hands of average drivers - it really will bite the unwary. On the other hand, the reward for a good driver is brilliant corss country pace

[mep]

Ciro Pabón wrote:

I also can't see clearly how putting aerodynamic force on the back of your car would rob you of front weight, so I would be grateful if you guys enlighten me.

It's interresting how everybody here tries to be cool and clever.
They say it's quite natural and everybody should know why
a rear wing removes pessure from the front tire,
but nobody explains why this is true.

On first sight you thing it's wrong, but if you calculate the forces you see
it immediately.
Lets make an example.
You have a car with:
a wheel base of 3m.
the center of gravity in the middle (1.5m)
a weigt of 6000N
a rear wing 0.5m behind the rear wheel center line
downforce by the wing of 3000N

Moment = Force * arm

Moment counterclockwise = Moment clockwise

F rear *3m = 6000N*1,5 + 3000N *3,5

F rear = 6000N*1,5 + 3000N *3,5 /3m
F rear = 6500N

F front = 6000N +3000N - 6500N
F front = 2500N
Withoud the wing we had 50:50 weight distribution.
This means weight at front was 6000N/2 = 3000N.
We lost 500N weight at the front tires.

[vis]

vis, what year is your car? cheapest way to imporve your performance is to slap on better tyres and chip the car if its a diesel or turbo

old good 1991 2.0 GLi, no turbo nor diesel, just 85 kW of pure gasoline power, achieving the amazing specific output of 55 hp/liter! Not bad for an european car!

BTW, I'm not actually drifting my way to work, as Ciro suggest, I was just thinking to improve handling (reduce understeer) by mean of aerodynamics.

Putting aero to work on everyday car is my mission!

[mep]

vis wrote

I was just thinking to improve handling (reduce understeer) by mean of aerodynamics.

I just got one idear.
But read my privios post first.

So now, it's hard to place a wing at the front of a normal street car.
But you can place a wing at the rear of the car which generates
lift (like an airplane) it would move the weight from the rear
to the front at high speed, like I explained in the other post.
But at low speed is the wing not producing a force.
So you can put a lot of weight to the rear and have a very
good acceleration. If you drive faster the wing starts to work
and gives you force at the front so you can take bends.

[vis]

vis wrote

I was just thinking to improve handling (reduce understeer) by mean of aerodynamics.

I just got one idear.
But read my privios post first.

So now, it's hard to place a wing at the front of a normal street car.
But you can place a wing at the rear of the car which generates
lift (like an airplane) it would move the weight from the rear
to the front at high speed, like I explained in the other post.
But at low speed is the wing not producing a force.
So you can put a lot of weight to the rear and have a very
good acceleration. If you drive faster the wing starts to work
and gives you force at the front so you can take bends.

No way! Generating lift to the rear to get aero balance is out of question!
And putting extra weight (ballast) on my car is out of the world!

But why front wheel drive car, which have, in the best case, 60:40 weight distribution, suffer massive understeer? Haven't they much weight on the front to grip front tyres more? I think it's a matter of inertia that prevents fast response and tends to continue on its motus (straight).

[kilcoo316]

I was thinking about aero devices focused on low-speed (around 100 km/h) downforce generation, to improve fast use of everyday car.

Put a flat bottom on it, and a splitter at the front.

[vis]

I was thinking about aero devices focused on low-speed (around 100 km/h) downforce generation, to improve fast use of everyday car.

Put a flat bottom on it, and a splitter at the front.

How a splitter works? How it generates downforce?
Sealing the undertray with a flat bottom will also reduce drag?

[kilcoo316]

I was thinking about aero devices focused on low-speed (around 100 km/h) downforce generation, to improve fast use of everyday car.

Put a flat bottom on it, and a splitter at the front.

How a splitter works? How it generates downforce?
Sealing the undertray with a flat bottom will also reduce drag?

A splitter lowers the stagnation point on the car nose, forcing more air up and over the car =>downforce.

A flat bottom will allow the air to flow under the car cleaner, giving you something of a venturi effect =>downforce. It will also reduce drag.