How to work up to taking a corner flat

[Jamez]

I have a Swift DB4 that I am learning to drive and before I go crash it into a wall from having more ambition than talent I figured this would be the best place to ask:

Question: When working up to taking a corner flat in a ground effects car (such as a Swift DB4) is it a case of taking it faster and faster until the car starts missing it's line, or do you have to skip the working up part and try it flat with maximum down force because there is no middle ground?

Long story made as short as possible, I am taking a particular corner at a minimum speed of 100mph but it feels like instead of braking I could just take it flat at 145mph, the only reason I haven't is because it gets a bit twitchy in the rear just after turn if over a certain speed. No one has taken it flat before so I am pioneering but for comparison sake I am taking the corner at a similar speed to what a current day Formula 3 car does it at.

As I side note I am also fixing a lot of problems with the car before I take it out again in May, these range from:
-Shocks that weren't working so I am getting them rebuilt, this is important as there is an elevation decrease on corner entry.
-Corner weights varying by 30lbs per corner
-I have been using the "spare set" of rims that came with the car but didn't realise the track is 2inch less in the rear than the main set I hadn't used yet.
-The tyres were 18 heat cycles old R35 Hoosier's, I am going to swap to a new set of Avon A11's as they seem to suit the conditions better.

I know there are a lot of variables that will change the answer but any advice on how to approach it would be appreciated.

[S Lathrop]

There is an enormous difference between entering a corner without slowing the car either by a lift or brakes or some combination of both.

When you do anything that slows the car, you change the pitch of the car. With a grounds effect car, that change is more dramatic. Pitching the car up at the rear reduces down force and shifts the center of balance forward. As the front comes down, the front wings pickup down force because they are closer to the ground and the pitch angle is increased. Even a lift that results in any engine drag on the rear tires will reduce cornering potential of the rear tires.

Even in a car like a FF, the pitch change shifts the balance to more over steer as you enter the corner. And engine drag is reducing rear cornering potential.

Left foot braking is the least upsetting thing you can do to slow the car a bit but most drivers do not have the finesse to do that successfully.

That is the reason why going from slowing on corner entry to flat out is so difficult. . The best way to work up to doing a corner flat is to check, reduce, speed well before you get to the corner and apply full power even before you start the corner. Then increase the entry speed until you are not slowing the car.

With a FF, you can setup a bit of a yaw (pitch the car into the corner) and that will check the speed a bit and is less disruptive to cornering than lifting. But with ground effects, you will loose down force, but you might not change balance as much as with a lift.

It is the balance change that you are causing the car to go through when you slow the car for any corner is what makes sneaking up on a flat out corner so difficult.

One trick you might try is to increase the rear spring rate by 5% to 10% and lower the rear. The lowering will increase rear down force and the stiffer rear springs will stabilize the rear.

This opinion is mine and it is probably worth what you are paying for it.

[stephen wilson]

Left foot braking is the least upsetting thing you can do to slow the car a bit but most drivers do not have the finesse to do that successfully.

Steve, do you mean Left foot braking without lifting off the throttle, or with a slight lift ?

[S Lathrop]

Steve, do you mean Left foot braking without lifting off the throttle, or with a slight lift ?

No throttle lift. What you are doing is braking with the front. The engine will nearly cancel the rear brake effect.

Any throttle lift will upset the car just enough to make the corner difficult or impossible.

[stephen wilson]

That's what I though you were saying, thanks.

[Buc01]

Jamez:

I see you have the right life preservation skills. No way would I think of taking a challenging fast corner flat with:

18 heat cycles old R35 Hoosier's!!!!!!!!!!!!!!!

Your post makes it appear that you have many things (besides the tires) to correct before it is time to experiment with flat out!

I like Mr. Lathrop's approach and work up to it, but at some point you just have to have the cojones to do it flat....

I never drove a DB-4 but did race Ralt RT5 for several years that was ground effects car. FYI

Aaron

[BorkRacing]

No throttle lift. What you are doing is braking with the front. The engine will nearly cancel the rear brake effect.

Any throttle lift will upset the car just enough to make the corner difficult or impossible.

Exactly. Turn 1 at Nelson Ledges in a SRF could be done flat out if you left foot braked, if you lifted you spun.

[RobLav]

That's how I got to do the Uphill at Lime Rock Park (almost) flat out in an FB. A quick up / down on the throttle just before turn-in. No braking. It also helped not having Steve's RARB!... and to use the added G's to turn when hitting the hill, and turn enough to prevent a 360 before going over the dip.

If you have some data, you could probably use it to ballpark the speed you can attain through a corner. Figure the minimum turn radius of the corner, do a nonlinear regression equation of how many G's you can pull on a flat circle per MPH, then apply the equation to the minimum radius. Ballpark...

[Jamez]

Cool, I'll fix the problems and try working up to it by left foot braking and holding 5th instead of changing down to 4th, then gradually increase the speed before turn in until I am at the point I am confident enough to take it flat.

For anyone interested, it's the first corner in this video (my best lap last time out), it's worth noting that I took 1 second off my PB in this race and afterwards decided I was at the point of spending some money to fix the problems so I can push it a bit harder - https://www.youtube.com/watch?v=uYu2wqk80rk

Lastly, for any keen eye's that notice my mid sector is slower relative to the other corners, I was loosing about 0.8 seconds per lap because I geared the car to use 1st gear with a taller second, only to find my legs were to fat to get first so I had to use second at just over 4300rpm, this in turn (pun intended) meant I couldn't use the rears to steer out of the corner and scrub'd off a lot of speed on corner exit. I will also be changing it back to an effective 4 speed for next time.

[Daryl DeArman]

woo-hoo....57 seconds in I am thinking "I hope he knows how that guy races"...59 seconds in and you had me puckering....

[SEComposites]

From an armchair racer perspective T1 doesn't look like it would ever be flat. Cool track though!

[Dee]

Brake in a straight line, then put the gas to the floor before the turn, this is the fastest way thru a turn creep up on it slowly !!!!!!!!!! good spring rates help greatly.,

DEE Penske rt5
Rt 41

[alangbaker]

There is a free program called "SketchUp" that lets you grab a geographic location and use it in a 3D model.

I grabbed corner 1 at Hampton Downs and counting the width of the car, got something like a 292 feet radius for the turn after the start/finish.

For my Formula Ford, capable of cornering at (perhaps) 1.3g, that implies a speed of about 75mph. That would be a third gear corner... ...maybe (depending on gearing).

You should be able to determine what downforce you get at different speeds, and from there, determine your maximum cornering speed.

[Jamez]

There is a free program called "SketchUp" that lets you grab a geographic location and use it in a 3D model.

I grabbed corner 1 at Hampton Downs and counting the width of the car, got something like a 292 feet radius for the turn after the start/finish.

For my Formula Ford, capable of cornering at (perhaps) 1.3g, that implies a speed of about 75mph. That would be a third gear corner... ...maybe (depending on gearing).

You should be able to determine what downforce you get at different speeds, and from there, determine your maximum cornering speed.

Thanks so much, I downloaded SketchUp and a lot of things are starting to make sense, looks like I cannot expect much more than 110mph for the duration of the corner before I start to defy the laws of physics. So after all that its a 4th gear corner if I want to stay in the power band.

If I did take the corner flat the car would have tried to pull 4.4G

[JGB]

There is a free program called "SketchUp" that lets you grab a geographic location and use it in a 3D model.

I grabbed corner 1 at Hampton Downs ...

Hi Alan,
Interesting stuff. Have you done this for Mission and would you show the results?
Thanks,
Jim

[alangbaker]

Hi Alan,
Interesting stuff. Have you done this for Mission and would you show the results?
Thanks,
Jim

I have, Jim...

...but I'll only show you if you come on out and race with us!

[mark elder]

I was wondering if one of you smart young people might be able to give a little more info on how to use sketch up to model a corner etc. I was looking for a guide for dummies or a boys own guide. Some of us can barely post a reply on the internet. I think I was married before Apple computers ever existed.


I guess the next question is what lateral G's various cars can actually do. I have measured steady state of 1.9G in a kart but never done it in a single seater (yet). Yes, I know it depends on the tires etc.


Mark

[Jamez]

I was wondering if one of you smart young people might be able to give a little more info on how to use sketch up to model a corner etc. I was looking for a guide for dummies or a boys own guide. Some of us can barely post a reply on the internet. I think I was married before Apple computers ever existed.


I guess the next question is what lateral G's various cars can actually do. I have measured steady state of 1.9G in a kart but never done it in a single seater (yet). Yes, I know it depends on the tires etc.


Mark

How I did it,

1. Started SketchUp
2. Selected units, doesn't really matter if its metric or imperial, end up with a man standing in the middle of the screen.
3. Go "File" -> "Geo-Location" -> "Add Location" -> Follow your nose and then select area
4. Again in the top menu go "Camera" -> "Standard Views" -> "Top"
5. Select the "Arcs" tool ( I used 2 point arc)
6. Learn to draw an ark that looks sort of like the ideal arc around the corner. Use the eraser tool for mistakes
7. Select the arrow tool in the top left and click on the arc, then look under "Entity Info" in the top right to get the radius.

With the radius use a calculator like found at http://www.calctool.org/CALC/phys/newtonian/centrifugal to calculate the radius and speed, then see how many G's it would be pulling.

From my telemetry over the years I have seen the following max G's for Turn 1 Hampton Downs, all towards the exit of the corner.

1.3G - Honda Integra DC2 Road car with Dunlop ZII - 1:22.1
1.7G - BMW E36 M3 with Michelin Slicks - 1:13.0
1.9G - McLaren M10A with Avon Slicks - 1:05.9
3.1G - Swift DB4 with Hoosier Slicks - 1:02.7


Hope this info helps.

[jchracer]

For the "OLD" people. You can shoot a screen shot of the track with Google Maps and trace an arc using a circle template. Using the scale provided by Google you can then use some simple math to calculate the radius of each corner. Not as accurate as the above method but it will get you pretty close.

[BeerBudgetRacing]

Every track should publish a map like this:

http://www.chuckwallavalleyraceway.c...rack-Map-3.pdf

[captaineddie1975]

Watkins Glen does: http://www.theglen.com/Track-Info/Ne...aspx:thumbsup:

[alangbaker]

The formula to convert radius (in feet), maximum acceleration (in g) to speed in (mph) is:

speed = square root of (radius times acceleration divided by 0.067)

So if that corner at Hampton Downs can be taken with a radius of 296 feet at 3.1 g lateral acceleration, that would be about 117 mph.

Hope this helps.

[Wolf Pack Racing]

Not sure T1 will be flat. You already had a pretty big stab of oversteer, mid corner on that second lap. Im sure the tire life would not help, set up etc, but setting yourself the task of taking a corner flat is not productive. It will only cause you to focus too much on one corner, steer set up towards that corner only, and not put a complete lap together.

The most important thing to concentrate on for fast corners, in a ground effect car, is to not over pitch the car. Suddenly shifting all the weight forward will cause the floor of the car to not work as efficiently, on top of the standard handling characteristics that aggressively pitching a car forwards will induce. You will be better off lifting earlier but more progressively rather than trying to run 50ft deeper with a sudden, larger lift. This will keep the attitude of the car much flatter. You will have more grip, will be able to carry more speed, and most importantly be able to get back to power earlier.

Other than that keep lowering the car and checking the skid, run as low as you feel comfortable without burning through a plank every weekend. Cool Car. Best of Luck

Cool, I'll fix the problems and try working up to it by left foot braking and holding 5th instead of changing down to 4th, then gradually increase the speed before turn in until I am at the point I am confident enough to take it flat.

For anyone interested, it's the first corner in this video (my best lap last time out), it's worth noting that I took 1 second off my PB in this race and afterwards decided I was at the point of spending some money to fix the problems so I can push it a bit harder - https://www.youtube.com/watch?v=uYu2wqk80rk

Lastly, for any keen eye's that notice my mid sector is slower relative to the other corners, I was loosing about 0.8 seconds per lap because I geared the car to use 1st gear with a taller second, only to find my legs were to fat to get first so I had to use second at just over 4300rpm, this in turn (pun intended) meant I couldn't use the rears to steer out of the corner and scrub'd off a lot of speed on corner exit. I will also be changing it back to an effective 4 speed for next time.