Lateral G Test
May 13, 2012, 02:58 PM
#1
Lateral G Test
So my suspension is completely blown (all four struts are out, ya, I know that's bad) and I've been waiting for almost a month and have no clue when my bilstein's and swift spec R's are going to be in, I guess bilstein takes a while to ship. In the meantime though my friend had a little physics experiment he wanted to run to determine lateral G's, naturally I jumped on the opportunity, I thought it would be interesting.
We went down to the local highschool, that has a nice large parking lot with no obstructions (light poles curbs stops etc.) We set up a 80 foot circle (40 foot radius) and started to drive in circles. As a side not the parking lot was not perfectly flat, there was a double camber downhill, not to steep, but it definitely had an effect, right at the steepest part of the downhill is when the car would understeer the hardest. Oh also there was some weather. I wanted the parking lot to be perfectly dry, but obviously we couldn't do this on a school day, and I have to go out of town. Anyway the parking lot was a bit damp to which probably played a role.
Thirdly in no way do I consider myself a good driver (racing wise that is). In other words there are a plethora of people on this forum that would destroy me around the track.
We used the equation Lateral G forces = 1.22 X radius/laptime squared.
We also used the average lap time for a three lap period and we did this three times.
Averaged Times
8.4
7.5
7.8
which equates to
.69 lateral G's = pretty terrible
.86 lateral G's
.80 lateral G's
I'm actually pretty happy about this considering my skills as a driver, the location used, and the condition of the "track". I'm wondering what effect 4 blown struts would have on this test, considering my springs are presumably still good?
Like I said thought I'm pretty happy with this I think I read somewhere that this car averages .95 lateral G's on a skid pad.
I'm definitely going to re-run the test in the same location and hopefully the same location after my suspension finally comes in.
Sorry for the essay, I like to write.
We went down to the local highschool, that has a nice large parking lot with no obstructions (light poles curbs stops etc.) We set up a 80 foot circle (40 foot radius) and started to drive in circles. As a side not the parking lot was not perfectly flat, there was a double camber downhill, not to steep, but it definitely had an effect, right at the steepest part of the downhill is when the car would understeer the hardest. Oh also there was some weather. I wanted the parking lot to be perfectly dry, but obviously we couldn't do this on a school day, and I have to go out of town. Anyway the parking lot was a bit damp to which probably played a role.
Thirdly in no way do I consider myself a good driver (racing wise that is). In other words there are a plethora of people on this forum that would destroy me around the track.
We used the equation Lateral G forces = 1.22 X radius/laptime squared.
We also used the average lap time for a three lap period and we did this three times.
Averaged Times
8.4
7.5
7.8
which equates to
.69 lateral G's = pretty terrible
.86 lateral G's
.80 lateral G's
I'm actually pretty happy about this considering my skills as a driver, the location used, and the condition of the "track". I'm wondering what effect 4 blown struts would have on this test, considering my springs are presumably still good?
Like I said thought I'm pretty happy with this I think I read somewhere that this car averages .95 lateral G's on a skid pad.
I'm definitely going to re-run the test in the same location and hopefully the same location after my suspension finally comes in.
Sorry for the essay, I like to write.
May 15, 2012, 01:57 PM
#3
Props for doing some actual measurements on your situation and sharing the data. Always good to see more of that here.
A few comments on your test setup:
How accurate would you say your circle diameter was? Did you measure from the inside wheels, outside wheels, or centerline of the car? How accurate was your timing? Did you consider timing 5 complete circles and dividing by 5 to get some averaging?
Also, what tires were you using? And how is your alignment?
As you already mentioned, a true skid pad test would require a flat surface. The goal is to reach steady-state cornering at a constant speed on flat ground. At which point, the valving of your shocks/struts no longer matters as they aren't handling any dynamic movement. So in theory, the fact that your shocks and struts are all "blown" as you say shouldn't have much effect on the test.
What matters most, however, are the grip of the surface, the grip of your tires, your alignment, and how your suspension (springs + sways + geometry) keep the load distributed across the tires.
Don't discount the variability of surfaces. Old asphalt surfaces can be surprisingly slippery.
A few comments on your test setup:
How accurate would you say your circle diameter was? Did you measure from the inside wheels, outside wheels, or centerline of the car? How accurate was your timing? Did you consider timing 5 complete circles and dividing by 5 to get some averaging?
Also, what tires were you using? And how is your alignment?
As you already mentioned, a true skid pad test would require a flat surface. The goal is to reach steady-state cornering at a constant speed on flat ground. At which point, the valving of your shocks/struts no longer matters as they aren't handling any dynamic movement. So in theory, the fact that your shocks and struts are all "blown" as you say shouldn't have much effect on the test.
What matters most, however, are the grip of the surface, the grip of your tires, your alignment, and how your suspension (springs + sways + geometry) keep the load distributed across the tires.
Don't discount the variability of surfaces. Old asphalt surfaces can be surprisingly slippery.
May 16, 2012, 06:21 AM
#4
Props for doing some actual measurements on your situation and sharing the data. Always good to see more of that here.
A few comments on your test setup:
How accurate would you say your circle diameter was? Did you measure from the inside wheels, outside wheels, or centerline of the car? How accurate was your timing? Did you consider timing 5 complete circles and dividing by 5 to get some averaging?
Also, what tires were you using? And how is your alignment?
As you already mentioned, a true skid pad test would require a flat surface. The goal is to reach steady-state cornering at a constant speed on flat ground. At which point, the valving of your shocks/struts no longer matters as they aren't handling any dynamic movement. So in theory, the fact that your shocks and struts are all "blown" as you say shouldn't have much effect on the test.
What matters most, however, are the grip of the surface, the grip of your tires, your alignment, and how your suspension (springs + sways + geometry) keep the load distributed across the tires.
Don't discount the variability of surfaces. Old asphalt surfaces can be surprisingly slippery.
A few comments on your test setup:
How accurate would you say your circle diameter was? Did you measure from the inside wheels, outside wheels, or centerline of the car? How accurate was your timing? Did you consider timing 5 complete circles and dividing by 5 to get some averaging?
Also, what tires were you using? And how is your alignment?
As you already mentioned, a true skid pad test would require a flat surface. The goal is to reach steady-state cornering at a constant speed on flat ground. At which point, the valving of your shocks/struts no longer matters as they aren't handling any dynamic movement. So in theory, the fact that your shocks and struts are all "blown" as you say shouldn't have much effect on the test.
What matters most, however, are the grip of the surface, the grip of your tires, your alignment, and how your suspension (springs + sways + geometry) keep the load distributed across the tires.
Don't discount the variability of surfaces. Old asphalt surfaces can be surprisingly slippery.
Our timing wasn't pinpoint accurate with lasers or something. It was just my friend outside the car with a stop watch. We had a chalk line in front of one of the cones as a finish line.
For tires, I'm using some very old tires that are coming off the car next week, like seriously there worn. Also, my alignment is not that great (which obviously will be changed when I replace my suspension). Running no toe camber or anything.
May 16, 2012, 07:39 AM
#5
As for the test, I'm assuming the front end started to lose grip at the limit, right?
May 16, 2012, 09:35 AM
#6
Also you have basically 4 line crossings for 3 laps and only two timing events, start and stop. So the error over 3 laps can be reduced by a factor of two. If I were to add an error analysis to it, I would do 5ft error or about 0.15sec per timing event, so 0.3 per 3 laps. That gives 0.1sec per lap and 0.02g error.
May 18, 2012, 06:00 PM
#7
Double checked the math cause wasn't sure and was bored, but your numbers are solid. Though 0.3 sec on a 40ft (rad) loop is 10 feet at the speed of running 7.5sec laps. Id think you could be closer than that.
Also you have basically 4 line crossings for 3 laps and only two timing events, start and stop. So the error over 3 laps can be reduced by a factor of two. If I were to add an error analysis to it, I would do 5ft error or about 0.15sec per timing event, so 0.3 per 3 laps. That gives 0.1sec per lap and 0.02g error.
Also you have basically 4 line crossings for 3 laps and only two timing events, start and stop. So the error over 3 laps can be reduced by a factor of two. If I were to add an error analysis to it, I would do 5ft error or about 0.15sec per timing event, so 0.3 per 3 laps. That gives 0.1sec per lap and 0.02g error.
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May 19, 2012, 10:21 PM
#9
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The lateral acceleration force should be calculated based on the car's Center Of Gravity, not by the inside tire. If you are a super precise driver and were hugging the cones closely, use a radius of 43 ft (your average radius may vary!). This increases the calculated g levels by 7.5%, so they now range from .74 to .93.
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