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Thinking about Cadillac Skidpad performance


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Magazine figures for modern Cadillacs in 200 foot skidpad testing tend to vary from 0.81G to 0.87G, with a max of 0.90-.92G.

For example, a base CTS sedan might score 0.81G. The new 08 CTS w/sport suspension scores as well as 0.85G.

The STS-V and 04-07 CTS-V and XLR/XLR-V tend to score 0.87G.

The new CTS-V can do as well as 0.92G.

For some perspective, my previously owned 1983 Porsche 944, considered an amazing handling car in its day, would do 0.81G on the skidpad.

People sometimes don't realize that today's sports sedans out perform yesterday's sports cars in cornering as well as

straight-line acceleration.

Motor Trend's method of skidpad testing:

The skid pad we use measures 200-feet across (or a 100-ft radius). This test assumes you will drive around the circle with the skidpad line directly under the centerline of the car—which is rather difficult to judge. Instead, we drive around the circle with the inside tires on the line which makes the effective radius 103 feet (assuming most cars are about 6 feet wide). This way, your circular path will vary by inches instead of feet and an observer can more easily verify that you’ve done it right.

Use the same timing equipment to time best laps in both directions. To convert a lap time (if you drive it like we do with the the tires on the line) into average g, use this formula: 126.381 divided by the squared time. Note: tires heat up extremely quickly and you will find times increasing by the third lap as the tires degrade. We suggest running just two laps in the counter-clockwise direction (driver inboard), then two laps in the clockwise direction. We average the best laps in both directions for the average lateral g.

So what does it mean if a Cadillac improves from 0.81G to 0.87G?

Well, looking at the formula G = 126.381 / Time^2, if G=.81 then Laptime = SQRT (126.381/G) = 12.49 seconds

If the Cadillac does a better, 0.87G trip around the same skidpad, then Laptime = SQRT(126.381/.87) = 12.05 seconds

These strike me as surprisingly close together.

Also, improving a CTS' cornering from 0.87G to 0.9G would mean a laptime improvement from 12.05sec to 11.85sec or .2sec on the lap.

A new Corvette might hit 1G plus, and lap the same skidpad at Laptime = SQRT(126.381)/1)= 11.24 seconds

I think it would be interesting to mark off a 100 foot radius (200 foot diameter) skidpad in a parking lot and run a couple of rings in each direction to see just how subjective the timing is for 1 lap.

This is something it would be very handy to have a lap timer data collection gadget for, since it would automatically keep very exact time for the runs.

Also, to put the skidpad in different terms, if the radius is 103 feet (see Motortrend writeup), then the circumference is 2*PI*Radius or 647.2 feet.

So the speed while circling the skidpad would be speed = (647.2 feet/laptime in sec)*(3600 sec/hr / 5280 ft/mile ) = speed in mph

Then, the 12.05 sec laptime of a 0.87G V-series Cadillac would mean a 36.2 mph average lap speed.

The slower 12.49 sec laptime of a 0.81G Cadillac would mean a 35.3 mph average lap speed.

Hard to think one would CARE if the Cadillac could go in a circle 1 mph faster or slower really, but that's the edge of performance.

Bruce

2023 Cadillac CT4-V Blackwing

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Nice background piece here on skidpads and how they came to be used by GM, Porsche, Mercedes.

Suggests something is off in my speed calculation.

Strong but not excessive understeer was a feature of the short-wheelbase Ferrari 250 GT, which with the Jaguar E-Type and Shelby Cobra, reached 55 mph on our circle. Most sporty models could attain 50 mph, while 45 mph was the limit for the Austin 850, Pontiac Tempest, Lancia Flavia and Jaguar Mark X. Slowest around the circle were the power-limited VW Karmann Ghia and Renault Caravelle.

Bruce

2023 Cadillac CT4-V Blackwing

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BASELINE TEST Article for reference:

The best times with the car as originally tested (fresh, but in stock configuration) stacked up like this (look for the complete result elsewhere in the story). In the 420-foot slalom, the Camaro posted an elapsed time of 6.80 seconds at 42.1 mph; The 200-foot-diameter skidpad test produced a best of 12.98 seconds counter-clockwise and 12.50 seconds clockwise averaging out at 12.74 seconds and equaling 0.76 g's--a respectable showing. The braking portion of the test produced 60-0-mph measurements of 201.07 feet on the initial try, and 197.39 feet on the second--a distance that'd make me think twice about tailgating, that's for sure.

Some mechanics discussed in the article above:

200 ft skidpad: 12.74s average in 2 directions at calculated to be 0.76g seem to match our method above, except perhaps figured on a 100 ft radius and not 103 ft radius.

Another tech article here decodes the radius calculation: G = 1.225 x Radius / LapTime^2

and this article gives some comparative times on the skidpad:

0.78 g of lateral force and an average test speed of 36 mph.

0.88 g of lateral force and had an average test speed of 39 mph We repeated the test three times and received consistent results.

Bruce

2023 Cadillac CT4-V Blackwing

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Good article and good observations.

I know my DTS is not a sports car, but with the MAG RIDE, big grippy tires and Four Channel Stabilitrac, it is surprising what a BIG car can do now a days. :D

It is kinda irritating when you are talking to someone about the good handling and ride of the newer Cadillacs, and they say "Sure. sure...it handles good...if you say so."

The only Caddys they have ever rode in was 20 years ago, or more.. :D ...and they don't have a clue what the newer cars can do.

Back then the smooth, soft, floaty ride was the norm for all big cars, including ones the size of the current CTS.

The current CTS with the DI 3.6 will out handle and maybe even outrun, a stock Vette from several years ago, but NO ONE on the street KNOWS THAT.

There would be a lot less Infinitys and Lexus's sold if people would just check out the new CTS.

And as far as the CTS V...

There is nothing on the market anywhere close to it's price range that can even attemp to compare itself to the CTS V. You have to pay close to double it's price to try to find a worthy competitor. :D

LONG LIVE THE V.

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So, a skidpad = empty parking lot.

The magazines tend to use timing lights and measure lap time. I think I would be inclined to use a G-meter to measure G force around the circle instead of single point timers.

It strikes me that the skidpad is another measure (like all measurements I have played with so far) that is very process dependent and difficult to compare one to another. The type of pavement, the weather conditions, etc would make havoc with site to site comparisons. It would be useful to determine a process to get repeatable measurements, then make changes to the car, and determine how the measurements change.

For example tire testing would be easy with two sets of wheels/tires present. Run one set, record, swap to the other set, record.

I am thinking of updating my CTS to the CTS-V suspension. It would be interesting way to measure and document the difference in handling between the two setups, running a skidpad test for the base, then repeat for the base (to show consistency of the test). Then after swapping components run for the new setup. Car is a bit lighter, but different wheels/tires than the CTS-V so we'll see how that works.

My impression from reading the test results from a variety of skidpad efforts is there is a lot of subjectivity in the test results. The question is sometimes not absolute grip but rather how comfortable and confident a car felt at that point. A car with a lot of lean pulling .82g's would be judged worse for handling than a car that is perfectly flat at .82g's, even if neither one can go any faster around the circle. I suspect this is a disadvantage for Cadillacs in testing.

Bruce

2023 Cadillac CT4-V Blackwing

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