JackOlsen

I recently posted a thread where I was trying to get a context for my cornering speeds relative to faster cars that run at my home track, Willow Springs. When I was looking at the lowest speed in a given corner, I was surprised to discover that my 911 with its 1972 suspension and streetable R compound tires was actually not dropping down to as low a speed in some corners than much faster cars with slicks and pro drivers at the wheel.

There are two illustrations from that other thread. The first is a 997 GT3 Cup Car with a pro driver running a 1:25.53 lap.


He's faster than me. There's no surprise there. But he slows down more than me in several of the corners. I'm just about 10 mph faster than him through the turn 1 left-hander --- he drops down to 80 mph there and I go down to 90. Then I'm 4 or 5 mph faster than him through the long turn 2 sweeper (again, measuring by the speed at the slowest point in the arc). I drop down to 67 mph for turn 3, but he goes down to below 60 mph. He slows to about 52 mph for turn 4, while I'm never slower than 61 mph. For turn 5, he brakes down to 60 mph, while I only have to slow down to 70 mph. He's much faster through turn 8 and I'm about 4 mph faster at the apex of turn 9.

The second example is from James Sofronas punishing a whole pack of Porsches with the GMG Racing World Challenge Spec Audi R8 in a POC race. In the clip, jump to 2:54 to see his fast lap:


On the front straight, he gets up to 151 -- I only get to 132.
In turn 1, he drops to 91 -- I drop to 90.
In turn 2, he drops to 95 -- I drop to 96.
In turn 3, he drops to 62 -- I drop to 67.
In turn 4, he drops to 61 -- I drop to 61 too.
In turn 5, he drops to 67 -- I drop to 71.
On the back straight, he gets up to 152 -- I only get to 132.
In turn 9, he drops to 109 (which is amazing) -- I drop to 105.

Now, what is the point of all this? Well, it's not to say I'm faster than either of these cars. I'm not -- not by a long shot. And I never will be. But I'm trying to see if there's a way for me to get down to a 1:25.99 lap at Willow Springs -- that's 1.05 seconds faster than my best lap so far.

The problem is that I can't really do much about top speed -- my engine is what it is, and I'm just about out of gearing with the 132 top speed I'm currently hitting. My rev limiter in 5th gear will kick in at 134 or 135 mph. So I need to improve my cornering speeds -- and as the comparisons I've drawn show, my cornering speeds are already pretty good.

Here is my best lap to date (a 1:27.04), with the start/stop set at the cone at turn 9 of Willow:


A set of slicks would probably do it -- but I'd rather earn it the old fashioned (and less expensive) way. My primary new weapon is the change from Bilstein Sports in back to adjustable Öhlins shocks, customized for me by Wevo. So far, they haven't gotten me back into the :27's, but ambient temperature is very important for my car at Willow -- I need all the power I can get -- and it was something like 34° when I ran the 1:27.04.

So, I'd love to hear input from people who might be able to offer useful advice. It could be that I should be slowing down a little bit more at the slow part of some of these corners (like the faster guys), although it might also be that I'd need their horsepower to make that worthwhile.

I continue to play aorund with ride height, ARB settings and shock settings. I've gotten the car so it doesn't push as much as it used to. I've gotten better parity between front and rear tire temps. I've added some front and side skirts to improve my aero.

But I think for that last second, I'm going to need all of that and more. So I'm throwing the question out to anyone who's interested.

Where's my 1.05 seconds?

Veloce Raptor

How much wing are you running? What is the car's behavior at corner entry?

IcemanG17

slicks will find the 1 second EASY..... If I remember right you run Nitto NT01.....slicks are at least 3 seconds faster than NT01 at that track..... I dropped 2.5-3 seconds at Thunderhill using scrub Pirelli Slicks vs Hoosier R6-BFG R1.....

winders

Look at Sofranos' lines through 3 and 4. I think you are giving up time by trying to late apex the entries into 3 and then into 4. You are covering more ground through there......late apexing there as much as you are is probably costing you time as there is no advantage to it. The late apex advantage is at turn 5.

JackOlsen

Veloce, I'm running a lot of wing -- which I know is costing me some, in terms of drag. For the last day of testing, I made some bigger endcaps, which should make the wing more effective and let me back off a step and maybe get less drag overall. But the end cap mount got messed up early in the day and I had to take the caps off. So I'm hoping to have that fixed next time.

There's a little bit of push at entry on most corners, with the exception of turn 9, which is the decreasing-radius right where you have to do your braking early, then let up, and then turn in. My rear end tends to want to come around during the decel part. I know some guys left foot brake through there, and I think that would help me in terms of keeping the car planted. And I know I could carry a little more speed through there. But 9 is a scary corner to blow.

Iceman, I agree about the slicks. But they're expensive -- and a hard habit to break. I'd be much happier (and much less poor) if I could do this on my everyday tires.

Winders, I think you're right. 3 is a strange corner because of the way it get loose as the camber changes just past the apex. I tend to use a conservative entry because the common wisdom is that there isn't much time to be made on the uphill. Maybe I need to rethink that.

I drive an unconventional line through 4, but I've tried the more-common way and it's not faster in my car. But then, if I can get through 3 quicker, it might change some of the math for 4.

Thanks, guys.

jdistefa

Jack, have you tried less wing angle with a gurney flap? May cut your drag a bit. Gurney of 1-4% chord - you can pick up some 90 deg angle aluminum cut to different heights to test. Foot in mouth if you've already done this, haven't seen any close-ups of your wing.

JackOlsen

Thanks. I've got a plan for that. The wing has a permanent Gurney flap. And the more downforce I can get in turn 2 (the 95-100mph sweeper), the better. But as I understand it, taller end caps make the wing behave as though the overall span is longer, without much of a drag penalty. So I've made bigger ones.

Little:



Bigger:

jdistefa

Jack,

Gotcha on end plates. Are you disrupting low pressure flow under the wing with your ducktail? I wonder if your wing efficiency would increase, allowing you to run less angle with less drag, if you swapped to a flat decklid for track days. Thoughts?

Veloce Raptor

I was thinking the same thing.

Dang video, Jack, still makes it seem as if you're not rev matching. Ugh.

winders

End plates improve the lift to drag ratio, so they are almost always good to use.

The larger end plates help the lower wing surface so the wing plates need to be deeper on the bottom. The top does not matter so the original top profile you had would be better.

Matt Romanowski

What speeds does the car push at? Are you dealing with a mechanical grip problem or an aero problem?

winders

Also, the low pressure area under the wing extends forward of the wing slightly, so you don't want the profile you are using in the second photo. You want the leading edge of the end plate to drop straight down from just in front of the wing.

See an example here:

J richard

Winder's post illustrates an issue with the combination tails, the duck is putting high pressure on the low pressure surface of the upper element. You're short circuiting it's efficiency. By comparison on the two element 3.8 tail the lower element is flat on top, on the cup tail the lower element is very slighted uses a whicker and far below the upper element...That area of the car is very speed dependent, it could be that it is creating a transient situation causing erratic handling at certain speeds...or not.

^^^
Never mind Matt already said it....move along nothing to see, these aren't the droids you're looking for...

Juha G

Nice driving!

If there is a way to get actual data from any of the pro driven cups etc. I think you will be surprised.
You cannot determine much with corner speeds alone, you'd also need to know the exact line. There can be BIG differences in the length of lines on the same track. i.e. you can be faster than someone else through a corner but with a lot longer line resulting in longer time though that corner.
There is no way you can be faster through turns on semi-slicks vs. a properly driven CUP with racing slicks. (unless your car is sub 1000lbs, which of course would be impossible).

I think the best way would be to put a pro behind your wheel for a couple of sessions (so he gets familiar with the car) and have him throw some fast laps for your data acquisition system. Then just compare the data you vs. pro to find out where you are slower and why.

And then there is of course the racing slicks...

Veloce Raptor

THIS