DSE Suspension Testing

[Van B]

Originally Posted by Steve1968LS2

There is NO such thing as a 125 foot skidpad.. it's 200 feet...

Am I wrong, or is a skidpad not much more than a circle drawn on a flat piece of paved surface? Therefore it could be any size you wanted it to be. While 200 ft may be the standard, does it mean a smaller or larger one cannot exist?

[XcYZ]

Jeff, you're right. Lateral-g can be calculated.

Lateral g = 1.22 * radius of track / (lap time * lap time)

EDIT: I don't know where the 1.22 factor comes from, maybe someone could explain that to me. Dennis?

[Steve1968LS2]

Originally Posted by Van B

Am I wrong, or is a skidpad not much more than a circle drawn on a flat piece of paved surface? Therefore it could be any size you wanted it to be. While 200 ft may be the standard, does it mean a smaller or larger one cannot exist?

Sure.. you could have a 900ft skidpad if you want. Just plug into the formula. But I have never seen or heard of someone doing a 125 ft one.. heck, the 200ft one us and others use is pretty darn tight. At some point it just becomes a donut.. lol

That doesn't change the fact that the numbers through the cones is all wacked..

The skidpad results seem on track with a car running those types of tires, I had just never heard of a 125ft skidpad.. anyways, that's not really the point of contention.

[Steve1968LS2]

Originally Posted by XcYZ

Jeff, you're right. Lateral-g can be calculated.

Lateral g = 1.22 * radius of track / (lap time * lap time)

EDIT: I don't know where the 1.22 factor comes from, maybe someone could explain that to me. Dennis?

There becomes a point where it doesn't work though.. for example you couldn't have a 50 ft skidpad.. or one that is 3000 ft.. Maybe it was a 125ft skidpad. When I first made my mention that there is no such thing I thought the testing was done by Super Chevy and in that case there is no such thing. If some outside group or person did the testing then who knows what they used.

Still, the car did not go through 420 ft of cones spaced 70 feet apart at 58mph modified and 55mph with leaf springs.. no way.. no how.. :shrug:

[sinned]

Let me start by answering Scotts question about why use 1.22 as the constant in calculating lateral g forces. 1.22 is the simplified version of the real equation which should read: lateral acceleration = (2.0 x pi) squared X radius/time squared, and to find the force measured in “g” the value of 1G is plugged in using 32.174 (1.0G in feet per second per second is 32.174). When those numbers are plugged in the result is 1.2270286, rounded down to 1.227 (I am not sure who decided it should round to 1.22 rather than 1.23).

That said, using max lateral g as a measure of a vehicle performance capability is a marketing ploy used primarily by manufactures to show their vehicles performance. In reality very little about the 200 ft skid pad test relates to real world handling. The skid pad is a very controlled environment in which the vehicle is driven at its maximum speed while still maintaining its line within the circle. There is no braking, dive, acceleration, elevation change, direction change, or any other variable involved. A true test of a vehicle performance as it relates to handling can only be done on a technical road course where all of these variables are negotiated. Obviously if the driver is not a constant than the results as to how much of the ability is the vehicle and how much is the driver now come into play.

The 480ft slalom is more of a handling test than skid pad ever will be but still is plagued with the same lack of variables. I would like to see the SAE change its venue for performance testing to use a closed track that all manufactures must use when placing claim about vehicle performance as it related to handling capability.

[Steve1968LS2]

Originally Posted by dennis68

The 480ft slalom is more of a handling test than skid pad ever will be but still is plagued with the same lack of variables. I would like to see the SAE change its venue for performance testing to use a closed track that all manufactures must use when placing claim about vehicle performance as it related to handling capability.

Where would this track be located that all mfgs would have to truck their cars to?

Then of couse you would have to use the same drivers and make sure you have the same weather conditions.. lots of variables and it's another one of those "sounds good on paper" deals that really isn't practicle in real life.

Lets say the track is in Texas.. you truck the car there for the before.. truck it back to the shop in xyz.. do the mods then truck the car to Texas for the after and truck it home.. opps.. its raining so you do it again next week.. lol

These tests when done right are good for comparison and show a range of improvements (or not).. The track test would be the best, but it's just not practical unless you have hugely deep pockets.

[sinned]

Originally Posted by Steve1968LS2

These tests when done right are good for comparison and show a range of improvements (or not).. The track test would be the best, but it's just not practical unless you have hugely deep pockets.

I'm pretty sure most auto manufactures have deep enough pockets to handle this; they already spend millions on each platform during development. I agree that the driver variable will always be in issue, isn’t an issue with the skid pad and slalom as well? As for atmospheric variables, maybe on a drag strip or during 60-0 testing but on a 3 mile road course I really don’t think the difference between 60* and over cast vs. 80* clear skies are going to have a dramatic impact on the overall lap speed.

Although skid pad and slalom tests can be used to show improvement its not a realistic measure, you are only at testing solid state cruise speeds and there no significant direction changes in either tests (I left out the obvious variables that had already been discussed from the "lack of" list).

[Mean 69]

No big disagreement, Denny, but the last I looked, there were maybe a handful of cars that any of the manufacturers (and the list of cars gets REALLY thin with the big three alone) really care to think about road course/overall performance handling. There's a couple in Italy, a few in Germany, one really kick butt one in Sweden (of all places!!!), bla, bla.

And of course, just think of the liability!!!! One of the big three's lawyers actually endorsing performance/high speed driving! E-ghads! Good thought tough.

One note on the skid pad diameters. Theoretically, you'd expect slightly different numbers for lateral acceleration on different sized skid pads, but in practical terms, you'd probably never measure it. One biggie is steering input, and resultant slip angles of the tires. Ackerman, slip angles, boring book-crap like that. At some point, you have to come up with something practical, and I agree that the method that PHR and Primedia (out here anyway) do this stuff is a good overall compromise between a level playing field, good primary indicator, and safety for the cars and test drivers. Nothing's perfect. Unfortunately.

M

[Steve1968LS2]

Originally Posted by dennis68

I'm pretty sure most auto manufactures have deep enough pockets to handle this; they already spend millions on each platform during development. I agree that the driver variable will always be in issue, isn’t an issue with the skid pad and slalom as well? As for atmospheric variables, maybe on a drag strip or during 60-0 testing but on a 3 mile road course I really don’t think the difference between 60* and over cast vs. 80* clear skies are going to have a dramatic impact on the overall lap speed.

Although skid pad and slalom tests can be used to show improvement its not a realistic measure, you are only at testing solid state cruise speeds and there no significant direction changes in either tests (I left out the obvious variables that had already been discussed from the "lack of" list).

Well we use the same wheelman for our tests.. but yea. It's just that with a longer course the variables stack up more..

And while auto manufacturers have super deep pockets we are not discussing that here. We are talking aftermarket parts mfgs who in some cases are very small to medium sized companies. It would not make economic sense for these guys to ship test mules to a centralized location, so they do what they can.

We are sorta getting off topic here.. I think we could agree that while the 4 tests (slalom, skidpad, braking, 1/4 mile) are not the absolute best real world test of a car they are certainly a good guage if a part made improvements to a car and are valuable when done using correct scientific methods..

[Mean 69]

I bet they used a 480 slalom, I think that is the larger size that is frequently used? If so, ask Carl C how fast he did the cones several years ago in his leaf sprung car on a 480 slalom.

In everyone's defense on this though, my guess is that there is a whole lot left in DSE's test mule, it just needs sorting. I bet if you optimized the car overall for one performance benefit, it could do really well. Still, there doesn't appear to be "magic" in the setup even though the drama of comparitive numbers in the magazine would suggest it. Unless you know what other cars are capable of, it is hard to draw an absolute conclusion. Which, of course, is typical in competition for all of this stuff.

Mark