What's the set up needed to have a high level track SL-C that can still run down a public road? Splitters/ spoilers/ camber/ ride height/ etc...

#1
Hey guys, interested in picking up an SL-C in the somewhat near future. For me the right one has a ton of potential to participate in local track events (and possibly set some street car lap records), but also would be interested in the TX Mile , also the Big Bend Road-race event interests me as well. To top it off, I want to be able to drive it to the office a couple of days per week.

I've done some tracking both on motorcycles (and race winning) and cars and I go better than most. That said I don't get a lot of track time nor am I that knowledgeable about setting up a car (or rich!). To top it off, I've never driven a Mid-Engine car in anger and don't really know what to expect from them when pushed to the limit. But I'd like to have a starting car set up that's in the ballpark.

1) I see there is a street tail and a big wing? How much does this alter the handling? Is the car unbalanced at the limit with the street tail? How much difference does the race tail make in lap times and overall handling? Do you alter your set up or driving otherwise to adjust to the different wings?
2) What kind of alignment are the guys on race tires running? Do these cars respond well to Hoosiers or is there such a thing as too much traction?
3) What about ride height, splitters, fender vents, etc....? What mix of components results in a car with nice balanced handling characteristics?
4) Anything to be aware of regarding handling differences? I read where someone said you could not apply exit throttle as soon on an SL-C which seems counter intuitive to me.
5) How different is your set up for high speed events? I don't want to discover that I have a light front end as I pass 190 mph for instance.

I look forward to hearing from experienced members that have ran these cars hard.

Thanks!
 

Cam

Active Member
#2
I figured by now you'd get some responses but looks like it's crickets so I'll throw my 2 cents in.

The events you’ve mentioned are at an extreme level for their category of racing. You can show up in just about any car at the events you've listed and have fun. If you want to be competitive or win ... then that's a whole 'nother ball of wax.

Frank Clark has run BBORR twice with his SLC. Unfortunately he blew his motor both times; he's got a new powerplant for his next run at the event. He's the only SLC builder I know of who's spent a significant amount of time at what I would call "high speed".

https://www.gt40s.com/threads/big-bend-open-road-race-report.48310/#post-492417

For your general "race/track day" type questions I'd refer you to Howard Jones as he's fairly active and has a very meticulous record keeping of his setups and how changes have affected his car.
 

Will Campbell

Bronze Supporter
#3
Any street-capable car won't be very good on the track, and vice-versa. But having said that, assuming you are going with the standard suspension (as opposed to the race arms and uprights), here are what I would start with for a track-focused car that sees occasional street use:

Factory front fender vents, similar ones for the rear. Make them easily removable for max downforce at fast tracks like Daytona.
Track splitter
Race tail with carbon wing (this wing has the better Selig 1223 profile compared to the FG wing)
Gurney flap on rad outlet, and possibly on the rear wing.

Hoosier A7s (not the R7)
CCW C10 wheels, 11" & 13"

Factory ride height or just under
Very small static toe-in in front and rear
Bumpsteered by a competent shop
-1.5 camber in front, -1.0 in rear
Front springs starting at around 750-to 850, rears at 900-1000, depending on the drivetrain weight, etc.
Consider upgrading to the track suspension (replaces ball joints with heims, but reduces turning circle, esp with the CCWs)

Running this setup with the wing fairly flat will be a good start, adding more wing angle as needed to reduce oversteer at speed. The wing begins to stall at 14 degrees, so don't run more than that (you won't need to, as the problem will always be to get more front grip, not rear).

Finally, although you didn't ask, I'd consider power steering and traction control. Powerful mid-engine cars like the SLC can be a handful for even experienced drivers, so TC is a first-order risk-reduction strategy, IMO.

Probably the best improvement you can make to the car is a few weekends at a real racing school. Even the pros start out that way, and use coaches to improve their skills.
 

Will Campbell

Bronze Supporter
#4
And optimum setup is different for every track. But starting out with the above as a baseline gets you in the right universe. You can start tuning when you are comfortable with the car.
 

Howard Jones

Gold Supporter
#5
My track car is street legal in California and was licensed when I live there. I haven't got around to doing that again in Texas by I don't think it would be a lot of trouble.

It was built as a track only car BUT with the ability to convent it back to a street car if I wasn't to later. It has a full set of lights, two seats, and the street suspension.

I would encourage to review my build thread. I have covered the entire multiyear process in depth.

In the end it will come down to either or not so much both. The street suspension isn't really suited to be pushed hard on dot slicks and the race suspension isn't really intended to be used on a street car. If you want a both car, build it out as a street car and if you want to track it once in a while then run street tires and have fun. As far as open road events. I consider that a full on race car event if the car has the speed capabilities that a SLC does.
 
#6
Any street-capable car won't be very good on the track, and vice-versa. But having said that, assuming you are going with the standard suspension (as opposed to the race arms and uprights), here are what I would start with for a track-focused car that sees occasional street use:

Factory front fender vents, similar ones for the rear. Make them easily removable for max downforce at fast tracks like Daytona.
Track splitter
Race tail with carbon wing (this wing has the better Selig 1223 profile compared to the FG wing)
Gurney flap on rad outlet, and possibly on the rear wing.

Hoosier A7s (not the R7)
CCW C10 wheels, 11" & 13"

Factory ride height or just under
Very small static toe-in in front and rear
Bumpsteered by a competent shop
-1.5 camber in front, -1.0 in rear
Front springs starting at around 750-to 850, rears at 900-1000, depending on the drivetrain weight, etc.
Consider upgrading to the track suspension (replaces ball joints with heims, but reduces turning circle, esp with the CCWs)

Running this setup with the wing fairly flat will be a good start, adding more wing angle as needed to reduce oversteer at speed. The wing begins to stall at 14 degrees, so don't run more than that (you won't need to, as the problem will always be to get more front grip, not rear).

Finally, although you didn't ask, I'd consider power steering and traction control. Powerful mid-engine cars like the SLC can be a handful for even experienced drivers, so TC is a first-order risk-reduction strategy, IMO.

Probably the best improvement you can make to the car is a few weekends at a real racing school. Even the pros start out that way, and use coaches to improve their skills.
Thanks for the thorough response. I have questions/ comments. Please don't take any of this as disputing your knowledge, just looking for clarification.

1) The fender vents reduces trapped air under the fender wells I guess? That is meant more to increase down force than brake cooling I presume? Why would that same theme not carry over to front straight at COTA for instance? Or did you mean to indicate that it increases drag notably and so maybe the increase in down force isn't worth the trade off?

2) How much time around a medium track is that big wing good for? Personally, if the wing makes the car understeer notably, I'd probably rather lose a second a lap and have a better balanced car.

3) In my limited track experience, I have not found my C6 that has ride height/ aero/ alignment/ tires/ wheels/ suspension set up for the track to be any detriment at all on the street. The only place I don't go all out is on tires as I only run R888rs. It's a very fast track car ime, and cruises really nicely on the street too.

4) Why so little camber, is that how these cars work best or is that a result of very stiff springs on a light car? I run double that on other cars I've tracked. Even with good suspension and sway bars on my C6, I would lose 2-3 seconds a lap and destroy the outside edges of my tires if I only ran -1.5 up front! Educate me. The race suspension would be nice, but I'd have to think about that expense and the trade offs. I still want a street car. I want to bake my cake and eat it too, as they say.

5) CCW is a great wheel, and I run a 10" F and 12.25" R CCW on my C6 and they work great, but I don't think they are the only high quality option.

6) What does the power steering gain you, besides comfort? Is it needed on these cars?

7) Some cars might go faster with TC, I don't care. As long as the car is balanced and predictable, I want nothing to do with TC even in a pouring rain storm on a greasy public road on my race tires. If the car is poorly balanced naturally and really needs TC to be safe, it's probably not the car for me honestly when modern production cars do this so well. I'd like to hear input on this.

I get that Fran has tons of experience with chassis dynamics, but I also understand that he doesn't have a multi-million dollar budget to set up his cars with Pro race drivers at the 'Ring. He also can't predict how your particular aero, mods, and drivetrain choice are going to effect weight distribution. This is out of his hands entirely.

Thanks again for your input.
 

Will Campbell

Bronze Supporter
#7
Thanks for the thorough response. I have questions/ comments. Please don't take any of this as disputing your knowledge, just looking for clarification.

1) The fender vents reduces trapped air under the fender wells I guess? That is meant more to increase down force than brake cooling I presume? Why would that same theme not carry over to front straight at COTA for instance? Or did you mean to indicate that it increases drag notably and so maybe the increase in down force isn't worth the trade off?
The fender vents are for downforce- they allow high-pressure air in the wheelwells to be expelled, and at the top of the car.

I don't understand your reference to the straight at COTA- presumably you are asking about the drag/downforce compromise here? If so, a typical race car run by a good team will attempt to optimize the car for each track, including the instant conditions, that the car sees. Depending on the track, the weather, driver preference, car adjustability limits, etc, different compromises will be made. The downforce/drag compromise is one of them.

[QUOTE="SunH, post: 526666, member: 27848"2) How much time around a medium track is that big wing good for? Personally, if the wing makes the car understeer notably, I'd probably rather lose a second a lap and have a better balanced car.[/QUOTE]

The answer to that question is, of course, that it depends. There is no simple answer like "1.35 seconds a lap". Pro teams have groups of highly-paid enginnery people to determine the answers to those questions for their cars, at each track they visit. Because a wing is adjustable, it complicates things further.

[QUOTE="SunH, post: 526666, member: 27848"3) In my limited track experience, I have not found my C6 that has ride height/ aero/ alignment/ tires/ wheels/ suspension set up for the track to be any detriment at all on the street. The only place I don't go all out is on tires as I only run R888rs. It's a very fast track car ime, and cruises really nicely on the street too.[/QUOTE]

Any fully-developed track car will be unpleasant on the street. If your C6 is fine on the street, it's not fully optimized for the track, and there is likely lots more there in the car.

[QUOTE="SunH, post: 526666, member: 27848"4) Why so little camber, is that how these cars work best or is that a result of very stiff springs on a light car? I run double that on other cars I've tracked. Even with good suspension and sway bars on my C6, I would lose 2-3 seconds a lap and destroy the outside edges of my tires if I only ran -1.5 up front! Educate me. The race suspension would be nice, but I'd have to think about that expense and the trade offs. I still want a street car. I want to bake my cake and eat it too, as they say.[/QUOTE]

The nominal purpose of negative camber is to compensate for poor suspension design- that is, suspension that cannot keep the tires flat against the track surface under all conditions. It turns out that the SLC has a pretty good design, and so with proper spring rate, sway bars (in some cases), shock tuning and tire pressures, you don't need as much negative camber as with other cars. It should be obvious that excessive camber not only increases tire wear, but also reduces the effective tire patch in most cases, reducing the ability to put power down coming out of a turn. Like everything else in a race car, it's a compromise. That's one reason why I said the settings above were a beginning. You may find that your car, setup and driver preferences at any given track may require more or less camber. That doesn't mean the general recommendations were wrong, just that you are optimizing for your own, specific situation.

[QUOTE="SunH, post: 526666, member: 27848"5) CCW is a great wheel, and I run a 10" F and 12.25" R CCW on my C6 and they work great, but I don't think they are the only high quality option.[/QUOTE]

There are plenty of good wheels, as you point out. But that specific CCW wheel has been proven over time, and several race cars, to be a great compromise between cost and performance for the SLC. It's also easy to order, since CCW already knows the specs.

[QUOTE="SunH, post: 526666, member: 27848"6) What does the power steering gain you, besides comfort? Is it needed on these cars?[/QUOTE]ot

Some drivers want a faster steering ratio. To get that requires either power steering, or biceps like Popeye. Try your car out with the regular steering setup, and if it works for you, keep it. If not, consider an upgrade to PS.

[QUOTE="SunH, post: 526666, member: 27848"7) Some cars might go faster with TC, I don't care. As long as the car is balanced and predictable, I want nothing to do with TC even in a pouring rain storm on a greasy public road on my race tires. If the car is poorly balanced naturally and really needs TC to be safe, it's probably not the car for me honestly when modern production cars do this so well. I'd like to hear input on this.[/QUOTE]

It's up to you, of course. One data point is that during the National Championship race with the factory 01 car, the driver was adjusting the TC for every turn on a damp/raining track. He lapped everyone but the top 3 cars, IIRC. And he still spun the car anyway. This is with a pro driver, with lots of experience.

[QUOTE="SunH, post: 526666, member: 27848"8) I get that Fran has tons of experience with chassis dynamics, but I also understand that he doesn't have a multi-million dollar budget to set up his cars with Pro race drivers at the 'Ring. He also can't predict how your particular aero, mods, and drivetrain choice are going to effect weight distribution. This is out of his hands entirely.[/QUOTE]

One thing that has been done is a lot of CFD work to get more downforce on the track, largely at the front, since that is where these cars always need it most. But you are right- every car, driver and track is different, and that's why simple predictions are more like WAGs than anything else.

Sorry about the multi-quote issues. I don't seem to be able to do that right.. :)
 

Howard Jones

Gold Supporter
#8
Will and I have arrived at nearly the same camber/caster/toe results. This car just is so light and wide it just doesn't produce much roll, especially on stiff springs using anti roll bars and it doesn't need a lot of camber. My spring rates are a bit softer than his at F750 R850 but the next change I make is going to be to move the 850s to the F and put 950-1000s on the rear. I think I was getting close to a neutral areo balance at about 6-7 degrees of AOA on the fiberglass standard wing. At that setting I was getting noticeable suspension compression at the rear above 140MPH or so and near the point of understeer. This would indicate a few things. 1. The standard rear wing will produce enough downforce to overcome the standard front areo setup. This is something we all knew. 2. Putting the carbon wing on a standard front aero car is a waste of money. 3. the front of the standard car's aero package can be helped with fender vents, keeping radiator cooling air out from under the car, and adding diffusers ahead of the front tires to prevent "packing" of air in front of the tire. Some additional downforce also should be produced with these diffusers as they do seam to help with the lack of front downforce. 4. next on my to do list is a extension of the splitter forward a couple of inches.

As far as drag goes, there are no rules with open track cars so drag really isn't much of a factor. Build as much downforce as possible and over come with more power. My speed at COTA was near 150 on the front straight and 160+ on the back straight. Don't overlook the much shorter braking distances even at these higher than most other cars speeds. That's enough for me to get into my fun zone.

This means: if you are not using the big ass race front splitter/wing the standard rear aero has the capacity to completely overcome a neutral areo balance setup and induce high speed aero understeer. However...……….the standard car with 500HP and minor aero mods on Hoosiers will run laps several seconds a lap faster than a ZO-6. It is a 1000 pounds heavier, front engine, and has no real downforce car after all. You should expect a reduction in lap time of at least 10 sec at COTA with a standard track delete car like mine, decreasing to as much as 20 or more with the race car parts on slicks and driven with gusto.

If I was building a open track car I would order the race cage and interior/lights/AC etc. delete, race suspension and aero package, put 550HP in it, run slicks and go get em! On the other hand the street car is pretty fast on good summer only tires. I would order the street tail, same power, AC, nice interior, build it to license, add a pretty paint job and have fun

The full on cars like Frans green 01 (national championship/ pro driver by the way), and the blue 25 hr car( likely the most developed long distance SLC ) , run track times right at PRO run/driven GT3 Porsche times OR BETTER!!!!! How fas$$$$$$$$t do you want to go.

If you want to talk, PM me for contact info.
 
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#9
Lots of great info. I want a very nice street car, that can track at a high level, not vice versa.

I would be a street trail guy and would probably add any aero that I could access to the front of the car to try and maintain balance. I've never driven a ME hard so really don't know what to expect. There is a track (Harris Hill Raceway) that is not but 1 mile from my trucking yard that offers very affordable track time. This will allow me ample opportunity to work on the set up, at slower speeds anyways.

The racer that did so well with the car that spun, was interested in going 11/ 10s. I'm not. I can 'win' (LOL) the track days driving at 8/10s. Seriously, driving within my means is important to me as standard auto insurance does not cover my vehicles when on the track so I work hard not to screw up. But I drive well so can still go quite fast within my limits.

The fact is, any car I can afford that is notably faster than a well set up C7Z is fantastic to me, and frankly all I need or want as I'm not trying (nor can I afford in time or money) to run a race series.

Interesting about the camber, what a great feature, and usually not touted advantage of a car like this.

I am shopping for an extraordinary already built SL-C,, but am not quite ready to buy. But will be in the near future. Now to actually see and look at one.

Thanks again guys.

PS. Sounds like these cars really need the PS option to be enjoyable to drive.
 
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#10
Sun, I am in New Braunfels TX 30 mins from Harris Hill. I have had both my car there GT40 and SLC and it is too bumpy for both. But it seams we are close to each other. If you what to drop by PM me with your contact info and we can chat.
 
#11
Thanks Howard! I sent you a text!

Ps. HH had many connections done to the surface about 18 months ago. However it's always been a track that you have to be willing to abuse the car a bit. I am.
 
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