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Grassroots motorsports had a good article on aero recently. Significantly, the article says that most cars have net lift in the rear. Tonight I removed my splitter/undertray. No sense adding drag just to make my rear end lighter.
Based on that article it seems pretty obvious that if you can’t put a rear wing on, you shouldn’t do anything that will add to front downforce.
Ranger wrote:
unless you have front grip issues (especially mid-high speed), that you can’t fix with suspension/setup adjustments…i’d take a loose car over a pushy car any day 
in theory, if you have an aero balanced or otherwise neutral car, then you are correct that you don’t want to add downforce to one end of the car without adding it to the other…there are exceptions to this of course…
It’s always good to keep air out from under the car, so an airdam is not a bad idea. It will help with drag too. Of course, these things don’t go fast enough to worry about the aero balance.
In order to be a more balanced driver, type-in www.mikeskeen.com and spend money where it nets a good return on investment.
RP
The SpecMiata guys a few years ago wanted to be able to fit air-dams and splitters, to be honest the improvements over the stock shape is non-existent… The cars with a stock power plant cannot benefit much from the limited aerodynamic changes allowable in stock-based classes. It’s best to stick with the most efficient front end you can get and slip through the air with ease. Your goal would be to add MPH at he end of the straight rather than the beginning of a turn. It will net you better results.
However Miata’s and probably E30’s would benefit tremendously from another 50+ HP and a balanced splitter/wing combination - in fact 949Racing has proven this out unequivocally for the Miata.
I’d rather “shave” my race car with a stock powerplant to be honest.
Kieran-
The car you describe races in GTS. We don’t need a chip, header or wing to make these cars fun.
A splitter helped significantly in the high speed turns 1-4 at Miller.
Don’t disagree with you… just making a point. I can imagine that T9 at Willow springs (100mph +) would be great with a splitter - little extra turn in etc. But would it help in lap times? Well, I’ll try to find out…
BTW I used to run an 88 M3 for about 5 years… I have been running BMW CCA events for 16 years + and I agreed a stock E30 is just about the most fun you can have in a car… My issue is whether lap times improve with any aero above and beyond the stock parts…
Your illustration of Miller is interesting… But it is very situational - to my point about Willow Springs… Also situational…
Steve D wrote:
[quote]
A splitter helped significantly in the high speed turns 1-4 at Miller.[/quote]
I’m hesitant to disagree because it wasn’t me driving the car, and you’re better then I am anyways. That being said, I’d be interested in hearing ideas from folks on how increasing front downforce in a car that has net rear lift can be helpful anywhere.
I’d be up for ideas that smoothed flow under the car, but I don’t want to create more downforce in front. Smooth flow is speed. Downforce is drag.
You can balance the e30 quite nicely with aero. If you don’t have a push issue at high speed, just add a air dam and keep as much air out from under the car as possible. If the car exhibits moderate push in high speed corners, a 2-3" splitter in addition to the air dam will alleviate the problem. CB
Ranger wrote:
[quote]Steve D wrote:
[quote]
A splitter helped significantly in the high speed turns 1-4 at Miller.[/quote]
… I’d be interested in hearing ideas from folks on how increasing front downforce in a car that has net rear lift can be helpful anywhere.[/quote]
Your assumption (paraphrasing of the article says most cars) is that we have net rear lift. I don’t know if an E30 is ‘most cars’ but I do know how the car behaved at Miller.
My rudimentary understanding is this. We have an unadjustable front bar. Well, unadjustable in the sense that you can’t vary the length of the legs on the U. You can, however, alter the load on the legs of the U, effectively softening or stiffening the bar. The splitter accomplishes that by adding load to the front wheels.
Yes, it will slow you down in a straight line. That effect is minimized if you can carry speed through the corners and keep yourself in the draft of a fast guy like Cobetto or Ferrario. Hypothetically speaking.
I had push in the corners Dave and Chuck described. I ran the splitter to the full rules depth and it was too much off the rear, so I ended up with maybe 2" of splitter extending in front of the air dam.
I haven’t found a track in the Southeast where it would be an overall benefit.
Lets see, brakes, then oil systems, then cooling systems, then engines, and now aero. Scott seems to have found another new passion.
Just saying…
I am waiting for Ranger to show at the track with tufts tape attached to the car:laugh: :laugh: :laugh: BTW, you might want to look at them very carefully on the trunk and rear spoiler.
SE tracks where aero makes a difference…RR…turns 2,3, and 9. RA 1,3,5,6,12. If you push in any of these, you have problems. cB
Steve D wrote:
[quote]Ranger wrote:
[quote]Steve D wrote:
Re. downforce from splitter altering the load on the legs of the sway bar. I’m sorry, but I’d have to be sold harder on that one. A sway bar only plays when the load on the wheels is different. And then in order to prevent the camber from rolling positive the sway bar reduces body roll at a cost of a net loss of traction. Front downforce increases net front traction, the opposite of what the stiffer bar does.
Re. improvements at Miller. I hear ya. Again, it wasn’t me doing it so my opinion isn’t worth much(is it ever?). But if it’s correct that we have net aero lift in the rear, yet we find that additional front downforce is useful, then we’re using downforce to compensate for some other problem.
Said another way, if our car should be light in the rear at high speed, but instead it behaves like it’s light in front, then there’s something going on.
Re. Another obsession. Nah. I built 5 different splitter/undertrays months ago before I found one that seemed sound. And then I tore it all off last night. That’s done.
Mostly I’m just obsessed by the need to understand everything.
So my question is should I bother to fit my 1987 325is front splitter or just forget about it? I would think that it would help, but perhaps I am wrong.
King Tut wrote:
As you’ve seen there’s no consensus. Do a bunch of research and then come back and present a body of evidence so compelling that we’ve no choice but to agree with you.
Can’t I just go with the tried and true evidence of the smart BMW engineers designed it so it must be good.
King Tut wrote:
Imagine a table with 6 chairs. 2 lawyers, 2 accountants, an engineer and a union rep. The German design decision committee meets each Thur afternoon over Wurst und Bier. Some days Hermann the engineer wins, and some days he doesn’t.
Look at the OEM alignment spec and ask yourself if that’s optimized for performance.
If you want your car to handle like a street car, leave the splitter off.
Assumption: rear gets lite at speed. Questions: What speed, and what is the reference/proof? In addition, aero on the rear spoiler is extremely dependent on the rake of the chassis. I did the tufts of string about 10 yeas ago…damn I miss my memory…but I think I concluded that the spoiler in the rear actually works above 80 or so mph.
Note, the splitter on my car started about 4" long, and was trimmed at RR to adjust the balance on the car in the high speed corners.
Ranger, when are you going to the wind tunnel to research this? Chuck
Ranger wrote:
OK - one last try then I have to get some work done.
The sway bar is a spring. (See? Chuck and I do agree on some things. :laugh: )
A thinner diameter bar is ‘softer’ (in racer parlance). A bar with longer legs on the U is softer. A bar carrying more weight is softer. By softer, we mean it is less able to transfer weight from the inside wheel to the outside wheel because the bar is deflecting. Hence, that outside wheel is farther from reaching its limits of adhesion. Ergo, no pushy pushy.
Short of self-producing various sets of bars (I figure a 45-60 bar run with different ‘leg’ lengths would give you 3-4 bar choices and would meet the rules requirement), we are stuck with the commercially-available, non-adjustable, spec-diameter bar. The only way I know you can adjust the spring rate of that bar is with wheel spacers and weight (whether that weight be static or aero).
PS - That new track width measurement procedure should be good for another 1-1/2" of track width, I’d guess. I haven’t gotten my bag of flour out yet.:blink: :woohoo:
Ranger, before you read the GRM article, did your splitter/under tray help or hurt your car’s handling?