High speed downforce

[Traian]

Has anyone done any aerodynamic modifications to their cars? On mine the steering becomes all light, the front end rises and the car becomes a little twitchier than I'd like at really high speeds. I saw some E34 with subtle little trunk spoilers that look very tasty, but I wouldn't like to put one on unless it actually gave me some more downforce (and I figure, I need it on the front, not the rear).

[Torque]

Unless the spoiler is above the roofline, it generally wont do anything ... besides you got it all wrong. You are looking at rear spoilers, when you need downforce on the front.

And how often do you go that fast to need it ?

[Alexlind123]

Mine stays pretty stable, even up a steep uneven grade at 95mph, havent taken it over 95 though. A mustang '86 5.0l lx takes the hill at 95 as well, so its not bad for a larger luxury car :).

[uscharalph]

Has anyone done any aerodynamic modifications to their cars? On mine the steering becomes all light, the front end rises and the car becomes a little twitchier than I'd like at really high speeds. I saw some E34 with subtle little trunk spoilers that look very tasty, but I wouldn't like to put one on unless it actually gave me some more downforce (and I figure, I need it on the front, not the rear).
I've never had that experience with mine.

[Alexlind123]

Also, keep in mind that the automatic 535i has a top speed of 144mph, a 540i is probably capable of even higher speeds. traian could be going faster than most of us to on a daily basis.

[uscharalph]

Also, keep in mind that the automatic 535i has a top speed of 144mph, a 540i is probably capable of even higher speeds. traian could be going faster than most of us to on a daily basis.
Could be!

[Paul in NZ]

subtle aero = mtech

[Interceptor]

Has anyone done any aerodynamic modifications to their cars? On mine the steering becomes all light, the front end rises and the car becomes a little twitchier than I'd like at really high speeds. I saw some E34 with subtle little trunk spoilers that look very tasty, but I wouldn't like to put one on unless it actually gave me some more downforce (and I figure, I need it on the front, not the rear).
540i brake ducts + subtle tailgate spoiler = might help a bit. Then put in a set of lowering springs and stiffer shocks. Low profile 17" tyres aren't a bad idea either.

[mattyb]

at what speed are we talking about. mine drifts a little bit at 200km/ph +.

[crashnburn80]

I've had my 535i to 130mph at which speed it feels firmly planted. I do not have any areodynamic mods but I do have Bilstein sports and Eibach springs running on 235s up front and 255s in the rear. I also have had my tie rods replaced and my steering tightened. I'm betting you need better suspension, not areodynamic mods. ;)

[632 Regal]

mine was a bit wondery before i lowered it, now it seems well grounded at 130+

[TheDuke]

150+ on the stock springs, and it was pretty steady, comparing to Subaru WRX or the new civic SI(which wont go over 140). Haven’t taken it yet to the other side of the clock with the new struts(stuck springs). Since, I've bent my rotor while replacing the hock. Anyways haven't we went over “to fast to stupid with big spoilers” issue already? Isn't the spoiler supposed to be welded to the frame to have any actual effect on the down force?

[Traian]

Thanks for the replies y'all. Hmm, never occurred to me that the suspension would have an effect on this. My car does sit rather high up, and I was planning to do a complete overhaul sometime down the road to lower it a tad and maybe put some 16s on it, but financially that doesn't look like something I should be thinking about for a while. Too bad, I was looking for a good excuse to stick a decklid spoiler on there ;)

[Arxon]

Never had problems at high speeds, not only that but the car becames more stable, I use Bilstein, but the car wears the originals tyres, 205/15/60, I think you dont need a spoiler for an e34, it's not a gti...

[RobPatt]

That's awesome.
I've rolled mine once at 125mph but could only stand it for about 2 minutes before concerns of just a simple nail in the road had me bring 'er down outta warp and into double digets.... There wasn't much, if any, left after 125 but it was pretty solid and smooth ( sachs kit, 17" style 5s w/michelin pilots ).... I've felt much more uncomfortable in other cars/SUVs at 80 than I did at 125 in the 525....

150+ ? WOW!!!

cheers,
Rob sends....


150+ on the stock springs, and it was pretty steady, comparing to Subaru WRX or the new civic SI(which wont go over 140). Haven’t taken it yet to the other side of the clock with the new struts(stuck springs). Since, I've bent my rotor while replacing the hock. Anyways haven't we went over “to fast to stupid with big spoilers” issue already? Isn't the spoiler supposed to be welded to the frame to have any actual effect on the down force?

[RobPatt]

.
.
That's awesome.
I've rolled mine once at 125mph but could only stand it for about 2 minutes before concerns of just a simple nail in the road had me bring 'er down outta warp and into double digets.... There wasn't much, if any, left after 125 but it was pretty solid and smooth ( sachs kit, 17" style 5s w/michelin pilots ).... I've felt much more uncomfortable in other cars/SUVs at 80 than I did at 125 in the 525....

150+ ? WOW!!!

cheers,
Rob sends....

[Interceptor]

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Yes, 150 mph is about where my 525i M50 + EAT tops out too. Just to mention - in my country, speed limit for the freeway is 80 mph. Then there's the matter of fuel consumption at that speed which is about 25 l/100 km or 9.5 mpg.

[kyleN20]

150 doesnt seem to crazy, my 535i is good for 140, and had room to go, i just ran out of safe road

[Interceptor]

150 doesnt seem to crazy, my 535i is good for 140, and had room to go, i just ran out of safe road
Don't expect it to go over 155, maybe 160 with an EAT chip and in excellent condition. These cars are not very aerodynamic, and resistance of air rises exponentially with speed.

[infinity5]

Not being rude, but you guys with stock cars that feel steady at 100+ are crazy people :) "solid" and "steady" must be extremely subjective. Theres aboslutely no way I could make myself beleive my car is anywhere near as stable at 90+ as it is at say, 65. I think the laws of physics forbid it. The steering is most definitly lighter. If I changed lanes quick enough I could easily see the car flipping over, or at least skidding off the street.

Maybe I've just never driven a crappy car to know what "light" REALLY feels like :)

[SharkmanBMW]

I have had my 540 over 215klm/h, easily of course, and it feels great at that speed.
But I have 17" with sticky rubber.
If i had a lowered suspension i would be more confident, but even then, at those speeds, even with downforce you will be a victim if you need to swerve!

I would NOT go past 100mph on the stock 15" without a change of underwear!

Drive a car that has been set up for high speeds and you'll see right away the difference... tight.

[angrypancake]

I've had both my 525 and 535 up past 130mph on the same stretch of highway near my house, and they felt pretty stable on the road, even with having to change lanes to avoid the regular speeders around 80mph. I wouldn't do it again without some modifications. Well, that and I don't drive like I used to. The only other time I've been over 130 was in an '87 prelude, and I thought it was gonna fly away, so that's my only basis for comparison

[Traian]

These cars are not very aerodynamic, and resistance of air rises exponentially with speed.

Actually it rises with the square of speed :) (I know I'm a jerk... ;) ) Why btw, would wheel size and tire choice affect high speed stability? I'm just talking about straight line / very wide curve highway driving, not track work.

[632 Regal]

Only thing I can see is a wider tire causes more rolling and wind resistance.


Actually it rises with the square of speed :) (I know I'm a jerk... ;) ) Why btw, would wheel size and tire choice affect high speed stability? I'm just talking about straight line / very wide curve highway driving, not track work.

[Jeff N.]

At 135+ on a less than perfect road, my car felt pretty floaty. When coming off a little lift, the car really didn't settle down that quickly. I really didn't like that feeling and got out of the throttle at that point.

Car has aftermarket springs (Dinan) and has been lowered a bit.

I've had the car up to 125 on the track. No problems.

[Torque]

I would NOT go past 100mph on the stock 15" without a change of underwear!+30, and I felt fine.

[632 Regal]

You dont think your struts could be a bit weak do you? My car is smooth and positive at all speeds within reason. I mean I wouldnt want to whip through traffic 4 lanes at 130 or anything but it seems real tight. Airpressure in the tires? When I have a low tire it can get a bit un nerving.


At 135+ on a less than perfect road, my car felt pretty floaty. When coming off a little lift, the car really didn't settle down that quickly. I really didn't like that feeling and got out of the throttle at that point.

Car has aftermarket springs (Dinan) and has been lowered a bit.

I've had the car up to 125 on the track. No problems.

[rnrn]

Suspension definitely has a huge effect at that speed. Prior to the Sachs kit, the OEM Boge's (which were worn) made me nervous over 100. Bigger rims and better tires will certainly help as well. No one's mentioned sways or bushings either which would only improve. You'd be surprised at the rake a Sachs kit can put on a rig. My front is w/o question much lower than the rear while still sitting pretty tight to Mother Earth.

[Jeff N.]

...not that this was that bright. An older 2 line highway and it had a fair number of small dips and lofts. Not a graded megaroad.

What I noted was that the car really didn't settle back down at speed when you got a bunch of air underneath it. I suspect I was getting a lot more air under the car than typical with this road.

Struts are 3 y/o bilsteins. Should be OK.

[jbraswell]

I had mine to 135 on US 65 in Alabama and it was extremely stable, no wandering or anything at all. My car has a sachs kit, poly bushings and new everything in the front. There were 3 people in my car who were asleep the whole time, so it was pretty smooth

[Jon K]

I think I may need a roof high spoiler soon :P

[Airborne001]

Theres aboslutely no way I could make myself beleive my car is anywhere near as stable at 90+ as it is at say, 65. I think the laws of physics forbid it.

Actually it is the laws of physics that allows it. Depending on the design of the aerodynamics of the car, it is entirely possible that the profile, drag, downforce, and suspension would all come together at higher speeds. (You don't need the car to be generating a lot of downforce at 55mph).

Think this is impossible? Try turning an aircraft at low speed vs. high speeds. At low speeds a plane can turn so sharply it can stall one or both wings, but at the higghest speeds, it can be dificult to turn the plane at all. WWII dive bombers had to have special brakes built in just so they could pull out of dives during attacks.

Enough history, just from personal experience, it seems like my car seems to squat down at about 85 and really grab a piece of the road. Had her to 125-130, and very little problems. Just make sure you have the right tires, and that everything is tight before you try it.

Remember, these cars are built for everyday cruising speeds in the triple digits in Germany.

[Qube]

Lowered Vogtland on Bilstein HDs... solid 240 kph. Any more and I start to unravel... not sure how the car would do :)

[VentoGT]

I have a bone stock M5 and have never had any high speed instability...my car feels like it handles better the faster it goes. If you have instability problems over 100, I would imagine you have issues with suspension alignment or components in your suspension are out of whack. As earlier stated, these cars were designed with long periods of high speed travel in mind, and if the car didn't come from the factory bespoilered, it doesn't need one to be stable at much higher speeds than you'll probably ever take the car.

[fkong777]

suspension definitely will help on high speed feel. Lowering with spring will give a better center of gravity and also let less air go under the car..

Damper rate helps also.
Just for reference.. On my S430 I have 3 damper setting. Soft , med , firm. when I drive on long stretch of Fwy.. at about 80mph+ the big S class will start to feel a little floaty.. I change the damper to Med and it get some of the float feel out.. Firm would be best but I wanted to let passengers sleep in peace.

[rob101]

Actually it is the laws of physics that allows it. Depending on the design of the aerodynamics of the car, it is entirely possible that the profile, drag, downforce, and suspension would all come together at higher speeds. (You don't need the car to be generating a lot of downforce at 55mph).

Think this is impossible? Try turning an aircraft at low speed vs. high speeds. At low speeds a plane can turn so sharply it can stall one or both wings, but at the higghest speeds, it can be dificult to turn the plane at all. WWII dive bombers had to have special brakes built in just so they could pull out of dives during attacks.

Enough history, just from personal experience, it seems like my car seems to squat down at about 85 and really grab a piece of the road. Had her to 125-130, and very little problems. Just make sure you have the right tires, and that everything is tight before you try it.

Remember, these cars are built for everyday cruising speeds in the triple digits in Germany.
downforce?
and just what on the car will produce downforce? there is no wing, no spoiler no ground effect venturis.
you will always get more rear lift especially when you travel faster (you will get front lift as well). might i point out the difference between a plane and a normal bmw e34 is that planes have wings. this is also the difference between an e34 and a champ car, is that they have ground effect venturi's and large wings. cars like the e34 never produce downforce from aerodynamics, they only produce drag and lift, because for the simple fact that the air going underneath is at a higher pressure than the air moving over the top surfaces of the car.

[Ausmpower]

downforce?
and just what on the car will produce downforce? there is no wing, no spoiler no ground effect venturis.
you will always get more rear lift especially when you travel faster (you will get front lift as well). might i point out the difference between a plane and a normal bmw e34 is that planes have wings. this is also the difference between an e34 and a champ car, is that they have ground effect venturi's and large wings. cars like the e34 never produce downforce from aerodynamics, they only produce drag and lift, because for the simple fact that the air going underneath is at a higher pressure than the air moving over the top surfaces of the car.

What gives the E34 downforce? The windscreen for one.

Air hitting the bonnet area of the car is forced up and over the cars turret are resulting in some extra down force at speed.......

The lower front bumper lip is there to reduce front end lift too. It also functions to turbulate the airflow under the car to reduce underbody lift.

Lift off the back end is reduced by airflow from under the car flowing up from the lower rear valance and meeting the high speed flow off the rear lip of the boot (shear layer rules in aerodynamics) that is why the boot lid lip in so sharp and the lower bumper valance so rounded.

BTW my 535 is rock solid at 200 + kph, no float, no feather light steering........ light steering at speed could be a toe angle issue.