Quantifying the aerodynamic impact of lowering a car? (drag coefficient Cd)

[320touring]

I'm aware that lowering a car can improve the fineness (Length to height) ration, and also drops the cD of the car..

Its also not normally an economically viable thing to do..

However...

The golf's suspension is shot- very little damping up front, and the bottom arms are clanking. It will need replaced sooner rather than later.

there are two options (both roughly similar in cost..)

1. Replace with standard parts (dampers/springs/arms)

2. Replace with a coilover kit to allow for a 40mm drop


Would the impact of lowering provide any tangible savings that I could use to justify the work?

or am I better just going with original/pattern parts?

[Varn]

My Jetta was lowered with a similar setup. It rides terrible but gives good mileage. I can not quantify the change as it was like this when I got the car.

[justme1969]

In the post "fast n furious movie" world of automotive resale direct advantage to you and raises value. You will get better economy but it probbably wont be so amazing that you will be reimbursed the project cost ever.
It may make ride harsher as mentioned above andhas penalties with ground clearance and perhaps tire clearance.
But it looks cool and I say why not if its near same cost!
Especially if you are sure the parts are required no matter what.

[PaleMelanesian]

Ironic that you used the word impact when talking about lowering a car.

[320touring]

Originally Posted by Varn

My Jetta was lowered with a similar setup. It rides terrible but gives good mileage. I can not quantify the change as it was like this when I got the car.

Thanks-at least this suggest there wont be a disadvantage

Originally Posted by justme1969

In the post "fast n furious movie" world of automotive resale direct advantage to you and raises value. You will get better economy but it probbably wont be so amazing that you will be reimbursed the project cost ever.
It may make ride harsher as mentioned above andhas penalties with ground clearance and perhaps tire clearance.
But it looks cool and I say why not if its near same cost!
Especially if you are sure the parts are required no matter what.

Believe you me, if waterbeds had wheels and engines they'd handle and ride better!

as you say, its not really an "improvement", more a maintenance issue

Originally Posted by PaleMelanesian

Ironic that you used the word impact when talking about lowering a car.

good spot

Bumpstops add unnecessary weight

[Slow_s10]

Originally Posted by PaleMelanesian

Ironic that you used the word impact when talking about lowering a car.

I chuckled at that too.

[COcyclist]

Does the 96 Golf TD have the magnesium oil pan like the TDI? I put an aluminum skid plate on my Golf and resisted the urge to lower. I continued with a coroplast belly pan to the rear bumper instead. There are some downsides to lowering but IMO it can make a car look good. I think it is safe to assume that if you raise your suspension to mount giant tires you will lose mpg but I am not sure the reverse will gain you anything measurable.

[Frosty944]

Reduced height springs are used primarily to lower the vertical center of gravity in race cars to improve handling in circuit racers Not reduce undercarriage airflow.

Undercarriage air flow is reduced somewhat but that is better achieved by air dams and chin spoilers in the frontal area.
Drag reduction is better achieved by the use of undercarriage slipstream modifications by using bolt on flat panels of a suitable materials.These can be attached in such a way as to reduce he under carriage air mass ( road clearance ) by the use of stand offs. this requires no modification the suspension or ride.

The cleaner aerodynamics also contribute to lower overall drag for better performance and gas millage. If the panels contact the ground they are a cheaper sacrificial donor than your exhaust system or other expensive components.

Frosty 944

[Vman455]

Since the cost is a wash (you'll spend the money either way, for a new stock suspension or lowered), I am strongly in favor of lowering. I've seen widely-varying estimates on Cd change when a vehicle is lowered, from -.01 per inch to -.08 claimed by Ford on the Fusion 999 hydrogen Bonneville car, which was lowered several inches (but not 8!)--but all sources agree, lowering a car has a beneficial effect on drag. The primary benefit, I think, is not in the (tiny) reduction in frontal area or airflow under the car, but the improvement in fineness ratio, as you mention. I put coilovers on my car a year and a half ago, dropped it just until there's no gap between the top of the tire and fender, and haven't looked back.

[320touring]

Originally Posted by COcyclist

Does the 96 Golf TD have the magnesium oil pan like the TDI? I put an aluminum skid plate on my Golf and resisted the urge to lower. I continued with a coroplast belly pan to the rear bumper instead. There are some downsides to lowering but IMO it can make a car look good. I think it is safe to assume that if you raise your suspension to mount giant tires you will lose mpg but I am not sure the reverse will gain you anything measurable.

I honestly do not know re the sump- Think it may be steel.

The roads I use can be easily passed using the 328, and thats MUCH lower than I'd be going with the golf..the cheaper coilover kits prefer to have a bit of height to retain damping- 40-50mm drop max

Originally Posted by Frosty944

Reduced height springs are used primarily to lower the vertical center of gravity in race cars to improve handling in circuit racers Not reduce undercarriage airflow.
Undercarriage air flow is reduced somewhat but that is better achieved by air dams and chin spoilers in the frontal area.
Drag reduction is better achieved by the use of undercarriage slipstream modifications by using bolt on flat panels of a suitable materials.These can be attached in such a way as to reduce he under carriage air mass ( road clearance ) by the use of stand offs. this requires no modification the suspension or ride.
The cleaner aerodynamics also contribute to lower overall drag for better performance and gas millage. If the panels contact the ground they are a cheaper sacrificial donor than your exhaust system or other expensive components.
Frosty 944

i'm intending to fit a front airdam in addition to lowering the car- to get the majority of benefits of a bellypan, without the additional work, but you make valid points, especially if I was going to replace stock suspension that was in good order..

Originally Posted by Vman455

Since the cost is a wash (you'll spend the money either way, for a new stock suspension or lowered), I am strongly in favor of lowering. I've seen widely-varying estimates on Cd change when a vehicle is lowered, from -.01 per inch to -.08 claimed by Ford on the Fusion 999 hydrogen Bonneville car, which was lowered several inches (but not 8!)--but all sources agree, lowering a car has a beneficial effect on drag. The primary benefit, I think, is not in the (tiny) reduction in frontal area or airflow under the car, but the improvement in fineness ratio, as you mention. I put coilovers on my car a year and a half ago, dropped it just until there's no gap between the top of the tire and fender, and haven't looked back.

Thanks for the report oun your experience- I dont imagine I'll go as low as you suggest, more likely leave 1-2cm above the tyre for clearance reasons.

The addition of a front air dam should make up the "lost" drop!