skidpad importance?
08-30-2004, 01:44 AM
#1
skidpad importance?
If you take two cars with equal braking and aceleration ability and just look at "equal" skidpad numbers, can you say that these two cars will potentially handle the same? In otherwords how important is the quantitative number of G's a car can grip at with a known tire compund.
08-30-2004, 01:54 AM
#2
Still plays with cars.
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I see the skid pad as more of a tire test myself....
08-30-2004, 02:41 AM
#3
Race Car
Lateral g's are one factor, but not everything. I was surprised when a rival of mine and I traded rides in each others cars. He has a Viper. I have an early 911 with a 3.6. We run very similar times at our local track.
I had always presumed that he was killing me on the straights, but that I was making up for it through the curves. But driving with him was eye opening. Predictably, his car was also a lot more powerful than mine in a straight line (he has double my power, after all), but he could also clearly sustain higher speeds (and lateral g's) than I could in the track's big, fast sweepers.
The area where I had an advantage was in transitions -- situations where a direction change was followed by an opposite turn, or where there were quick elevation changes combined with turns. In these instances, the lighter weight of my car (about 500 pounds less than him) made a difference in my favor.
Magazines test a few basic factors -- power, weight, lateral grip -- but putting together a meaningful picture of on-track performance is more complicated than one might initially think.
I had always presumed that he was killing me on the straights, but that I was making up for it through the curves. But driving with him was eye opening. Predictably, his car was also a lot more powerful than mine in a straight line (he has double my power, after all), but he could also clearly sustain higher speeds (and lateral g's) than I could in the track's big, fast sweepers.
The area where I had an advantage was in transitions -- situations where a direction change was followed by an opposite turn, or where there were quick elevation changes combined with turns. In these instances, the lighter weight of my car (about 500 pounds less than him) made a difference in my favor.
Magazines test a few basic factors -- power, weight, lateral grip -- but putting together a meaningful picture of on-track performance is more complicated than one might initially think.
08-30-2004, 08:32 AM
#4
Three Wheelin'
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The lat g's the car can pull is extremely important in how fast the car can go. It raises your minimum speeds at all turns on the track. When I get to the office I can post some data on the difference. Usually for our street cars, 1.2 -1.3 g's is pretty good (even on race rubber) and it's difficult to get above that.
08-30-2004, 11:38 AM
#6
Race Director
Yep,
Skid pad tells you steady state neutral throttle mid corner potential.
Like jack said and George eludeded to there is alot going at corner entry and exit that skid pad number only hint at. Out there in the real world depeing on the track transions can be just as to more imporant than steady state cornering.
Bottomline is that skid pad alone does not tell the entire story.
Just to pull from typical magzine test.
Skid pad = steady state cornering. Slalom ATTEMPTS to measure transitions, but really fails to do so well enough for proper race track potential comparisons.
Skid pad tells you steady state neutral throttle mid corner potential.
Like jack said and George eludeded to there is alot going at corner entry and exit that skid pad number only hint at. Out there in the real world depeing on the track transions can be just as to more imporant than steady state cornering.
Bottomline is that skid pad alone does not tell the entire story.
Just to pull from typical magzine test.
Skid pad = steady state cornering. Slalom ATTEMPTS to measure transitions, but really fails to do so well enough for proper race track potential comparisons.
08-30-2004, 01:19 PM
#7
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I'm not sure if your question is lat g capability regarding performance or usefulness of a skid pad. If it is capability, here are some numbers.
Turn 3 at Mid Ohio could/should be taken at about the following speeds as lat g capability increases:
53 mph @ 1.00g
59 mph @ 1.25g
65 mph @ 1.50 g
70 mph @ 1.75g
75 mph @ 2.00 g
As you can see, most street cars turn at 53 mph, a dedicated track car turns at 75 mph. Huge difference and g capability is a gigantic factor in car performance.
Turn 3 at Mid Ohio could/should be taken at about the following speeds as lat g capability increases:
53 mph @ 1.00g
59 mph @ 1.25g
65 mph @ 1.50 g
70 mph @ 1.75g
75 mph @ 2.00 g
As you can see, most street cars turn at 53 mph, a dedicated track car turns at 75 mph. Huge difference and g capability is a gigantic factor in car performance.
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08-30-2004, 01:34 PM
#8
Race Director
Originally Posted by M758
Yep,
Skid pad tells you steady state neutral throttle mid corner potential.
Like jack said and George eludeded to there is alot going at corner entry and exit that skid pad number only hint at. Out there in the real world depeing on the track transions can be just as to more imporant than steady state cornering.
Bottomline is that skid pad alone does not tell the entire story.
Just to pull from typical magzine test.
Skid pad = steady state cornering. Slalom ATTEMPTS to measure transitions, but really fails to do so well enough for proper race track potential comparisons.
Skid pad tells you steady state neutral throttle mid corner potential.
Like jack said and George eludeded to there is alot going at corner entry and exit that skid pad number only hint at. Out there in the real world depeing on the track transions can be just as to more imporant than steady state cornering.
Bottomline is that skid pad alone does not tell the entire story.
Just to pull from typical magzine test.
Skid pad = steady state cornering. Slalom ATTEMPTS to measure transitions, but really fails to do so well enough for proper race track potential comparisons.
Ideally you would tune your handling on the skid pad. Then you can work on the turn-in and exit, whether tuning the car or the driver.
The point about skidpad vs slalom is important. For and extreme example, I wouldn't consider autocrossing a car w/o a front sway bar, but I would consider racing a car without one (all depends upon the car of course - this is a real-world consideration for FWD cars). In autocross transition is much more impoartant than in racing.
08-30-2004, 02:00 PM
#9
Ditto above, transient response is everything in a road circuit. Say you are entering a medium speed turn going onto a straight. You experience three transients. Accelleration to brake. Brake to cornering, and cornering to accelleration. To use the full capability of the car, it must be in a steady state. During the time the car is transitioning from one steady state to another, the full capability cannot be used.... esentially it is "coasting" during this time.
Generally a light, stiffly spring, evenly weighted car tranitiions more quickly than a heavy, softly spring car with a front or rear weight bias. Because of this They can brake later, rotate up to max G quicker, and take full throttle sooner.... all the essentials for quick laptimes.
In the old days, ponycars such as Trans Ams with humumgous tires would turn eyepopping skidpad numbers... .92 or .95G. But on a roadcourse BMWs with relatively "modest" .78 or .83G numbers would stomp them by many seconds. The TAs were twitchy and nose heavy, and would push at entry, and it was really hard to get them to rotate... so they often couldn't get to that .95G cornering state in the real world turns.
Generally a light, stiffly spring, evenly weighted car tranitiions more quickly than a heavy, softly spring car with a front or rear weight bias. Because of this They can brake later, rotate up to max G quicker, and take full throttle sooner.... all the essentials for quick laptimes.
In the old days, ponycars such as Trans Ams with humumgous tires would turn eyepopping skidpad numbers... .92 or .95G. But on a roadcourse BMWs with relatively "modest" .78 or .83G numbers would stomp them by many seconds. The TAs were twitchy and nose heavy, and would push at entry, and it was really hard to get them to rotate... so they often couldn't get to that .95G cornering state in the real world turns.
08-30-2004, 02:40 PM
#10
Race Director
Originally Posted by JCP911S
Ditto above, transient response is everything in a road circuit. Say you are entering a medium speed turn going onto a straight. You experience three transients. Accelleration to brake. Brake to cornering, and cornering to accelleration. To use the full capability of the car, it must be in a steady state. During the time the car is transitioning from one steady state to another, the full capability cannot be used.... esentially it is "coasting" during this time.
Generally a light, stiffly spring, evenly weighted car tranitiions more quickly than a heavy, softly spring car with a front or rear weight bias. Because of this They can brake later, rotate up to max G quicker, and take full throttle sooner.... all the essentials for quick laptimes.
In the old days, ponycars such as Trans Ams with humumgous tires would turn eyepopping skidpad numbers... .92 or .95G. But on a roadcourse BMWs with relatively "modest" .78 or .83G numbers would stomp them by many seconds. The TAs were twitchy and nose heavy, and would push at entry, and it was really hard to get them to rotate... so they often couldn't get to that .95G cornering state in the real world turns.
Generally a light, stiffly spring, evenly weighted car tranitiions more quickly than a heavy, softly spring car with a front or rear weight bias. Because of this They can brake later, rotate up to max G quicker, and take full throttle sooner.... all the essentials for quick laptimes.
In the old days, ponycars such as Trans Ams with humumgous tires would turn eyepopping skidpad numbers... .92 or .95G. But on a roadcourse BMWs with relatively "modest" .78 or .83G numbers would stomp them by many seconds. The TAs were twitchy and nose heavy, and would push at entry, and it was really hard to get them to rotate... so they often couldn't get to that .95G cornering state in the real world turns.
08-30-2004, 11:24 PM
#13
Lifetime Rennlist Member
Originally Posted by fatbillybob
If you take two cars with equal braking and aceleration ability and just look at "equal" skidpad numbers, can you say that these two cars will potentially handle the same? In otherwords how important is the quantitative number of G's a car can grip at with a known tire compund.
I bet I can take my car, give it two differenst setups that produce the same steady state skidpad results, and have one setup at least 5 seconds slower than the other. So no, skidpad results can not necessarily be correlated with overall handling.
08-30-2004, 11:43 PM
#15
Still plays with cars.
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I'm with Sunday. As I posted way above, skidpads are useful for testing tires.