Just Some Aero Questions

[Dave_W]

Oversteer in a high speed kink sounds like a whole lot more excitement and a whole lot less fun than tailhappiness in a tight hairpin

Further on Norm's idea, with aero you can (wavy hands of generalization) tune different handling balances for low- vs high-speed corners. Low-speed corners will be influenced moslty by mechanical grip / balance, and high-speed corners should have more influence on handling coming from the aero balance. So, you can set the car up "mechanically" loose to rotate in the slow tight hairpin, but have the aero balance biased rearward so the overall balance becomes a confidence-inspiring slight understeer in the high speed kink.

If you don't want to spend money on a wing, you can get a reasonable amount of rear downforce from a cheap spoiler. Pick up some plexiglas and hinges at the hardware store while you're getting the plywood for your splitter, and use a junk trunk lid to mount it. The one below is for autocross speeds; for track work you may want smaller. Then again, it's easier to trim off excess than add more height.

 

[BKBoss302]

@Fabman
And others may be able to answer this aero question. What would be the effect of lowering my splitter about 1.5"? The splitter is about 5 inches off the road surface now. Any gains? Any losses?

 

[blacksheep-1]

S197s like lots of ride height and soft springs

 

[Fabman]

@Fabman
And others may be able to answer this aero question. What would be the effect of lowering my splitter about 1.5"? The splitter is about 5 inches off the road surface now. Any gains? Any losses?

A splitter 5" from the ground will have minimal affect. The closer, the better.

 

[BKBoss302]

@Fabman and @blacksheep-1
Thanks for the quick info. So if I can make a proper spacer for the splitter I think I can easily get 1.5" to 2" lower.

 

[That11GtGuy]

So I guess a quick follow up to the lowering splitter question is what would make a good spacer? @Grant 302 mentioned that the contour on the boss street splitter (sorry if that's not the formal name) is contoured enough that it might not be the best spacer, which makes sense. @blacksheep-1 also mentioned that its best to keep with the same wind tunnel design, so PWC splitter/wing or street splitter/wing. Would spacers not affect that balance they made in the wind tunnel? Obviously not questioning the validity of these statements, just curious what spacer is best and if spacers impact the aero balance?

 

[blacksheep-1]

Here's a pic of the 2015 PWC car/ splitter, notice the ride height.

 

[blacksheep-1]

If you lower the car too much, this happens, S197s like soft springs

 

[BKBoss302]

@That11GtGuy
Here is what I am working with. The stock 2013 Boss splitter and a flat ABS lower section. The foam is an idea that is extremely dense and easy to work with for the prototypes. I may keep it for the real thing if it proves to be strong enough. I put some aluminum tubes where the bolts pass through so it doesn't compress from the thru-bolts.

 

[That11GtGuy]

Here's a pic of the 2015 PWC car/ splitter, notice the ride height.

View attachment 63589

So thats probably, what, 1.25 inches lower in the front or so from stock? And I may be seeing really wrong, but is that a normal boss splitter with a ABS splitter under it?

 

[Grant 302]

@Fabman
And others may be able to answer this aero question. What would be the effect of lowering my splitter about 1.5"? The splitter is about 5 inches off the road surface now. Any gains? Any losses?

Lower will make more downforce. Go as low as your suspension can handle clearance wise. Or also consider that dynamic changes in pitch also affect how sensitive or ‘twitchy’ your downforce will be.

 

[blacksheep-1]

As I recall, the PWC stuff was basically the same as the above yellow Boss

 

[Mad Hatter]

S197s like lots of ride height and soft springs

That would be the in the range of 500# fronts and 300# rears?

 

[Mad Hatter]

Thats me...


Any lower and I cant drive to the track.

 

[blacksheep-1]

That was Grand Am, I think the PWC cars were a bit more because of all the aero, but it depends on the track. You really want to do 2 things on that splitter, 1. try to keep the exterior supports to a minimum because stuff like that affects the air in a bad way, and 2. (kind of in opposition to that statement), you want the splitter to be extremely rugged and sealed off from the body, because if not, that dude will definitely try and separate from the body work at high speed, especially in the center.
If you go to the build "junkyard dog" you will find a decent splitter design that does not use exterior supports.

 

[Mad Hatter]

What!! you don't like my rigging??? I know they are a bit on the large size.... will take a look at your junkyard dog design

 

[That11GtGuy]

Thats me...
View attachment 63601

Any lower and I cant drive to the track.

It looks like you're on 18s, right? I'm going to be on 19s, at least for now, so that would put the splitter a bit higher for me, and make ride height a bit less of an issue when it comes to scraping, but thank you for the height reference.

That was Grand Am, I think the PWC cars were a bit more because of all the aero, but it depends on the track. You really want to do 2 things on that splitter, 1. try to keep the exterior supports to a minimum because stuff like that affects the air in a bad way, and 2. (kind of in opposition to that statement), you want the splitter to be extremely rugged and sealed off from the body, because if not, that dude will definitely try and separate from the body work at high speed, especially in the center.
If you go to the build "junkyard dog" you will find a decent splitter design that does not use exterior supports.

So when you say sealed off, do you mean like minimal gaps between, in the image quoted above, the fascia and the splitter? Because to me, it seems like some darn JB weld between those suckers would fix that problem lol. But I'm sure there are better ways to solve that problem.

 

[Grant 302]

That was Grand Am, I think the PWC cars were a bit more because of all the aero, but it depends on the track.

Didn’t you say something like 650/400ish? In that other thread?

People need to consider how much their front suspension compresses in braking and cornering.

 

[Fabman]

The more effective the aero is the more spring you need to support it.

 

[Fabman]

@AJ Hartman has a ton of great videos: