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So, since I've been investigating (actually for a number of years) tracking body roll and with the recent comments about accelerometer-based data acquisition systems being affected by hills, I thought that I'd post the actual effect. Effectively, the difference between the measured G load vertically and the actual G load is the cosine of the angle -- so up to 8 degrees of angle, the amount of error is still less than 1%. A 15 degree slope is only 3.4% off of the actual value. For those who don't know, an 8 degree angle is equivalent to a road slope of 13.9% (almost 14 feet of drop over 100 feet of travel). So, to calculate 5 degrees of body roll -- or for 5 degrees of slope -- the measured vertical G load would only be 0.996G instead of 1.000G (and the horizontal G load would roughly be 1 - vertical G, or 0.004G). That is roughly equivalent to a turn at 60MPH with a radius of over 11.4 miles! Even at 10 degrees (0.016G) at 60MPH, the radius of turn caused by slope is over 2.8 miles! Or, to put it another way, a sweeper taken at a measured 1.0 G at 60MPH with a car that has 5 degrees of body roll has an actual difference in radius (measured G - actual G) of approximately 0.9244 feet (242.9244 feet in reality versus 242 feet measured). I can detect and calculate the body roll, but the resulting value is so small that the effects are totally overwhelmed by the larger values of the cornering loads.

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Glenn L. Austin, Computer Wizard and Race Car Driver
2005 Ultra Yellow Nissan 350Z Track Model
2007 Packwood ProSolo "first loser" (0.081)
2007 SCCA Solo National Championships - 10th place

I should have added - 5 degrees of body roll on a car that is 78 inches wide is just over 6.824 inches of combined suspension movement (combination of compression on the outside and extension on the inside).

10 degrees is 13.7535 -- or just over 13 3/4 inches! To have that kind of body roll, the suspension would require almost 8 inches of compression travel and 6 inches of extension travel!

By the way, what you see in my avatar to the left is about 2.5 inches of travel across my car -- or only about 1.835775 degrees.

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Glenn L. Austin, Computer Wizard and Race Car Driver
2005 Ultra Yellow Nissan 350Z Track Model
2007 Packwood ProSolo "first loser" (0.081)
2007 SCCA Solo National Championships - 10th place

Glen, you have waaaay to much time on your hands.

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Jim Mueller
FSP 2003 Focus

Math is good.

My DL1, using the accelerometers, usually shows more G's than the MaxQ GPS stuff though.

Differences are sometimes almost .2 of a lateral G???? This is from the same place on course on the same run etc...

FM

I've seen spikes well above what is possible (0.5-0.8G) as GPS software recalculates acceleration to "catch up" with the actual car position.

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Glenn L. Austin, Computer Wizard and Race Car Driver
2005 Ultra Yellow Nissan 350Z Track Model
2007 Packwood ProSolo "first loser" (0.081)
2007 SCCA Solo National Championships - 10th place

But the MaxQ GPS only reads lower???

FM

Drifting through the corners can cause that.

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Glenn L. Austin, Computer Wizard and Race Car Driver
2005 Ultra Yellow Nissan 350Z Track Model
2007 Packwood ProSolo "first loser" (0.081)
2007 SCCA Solo National Championships - 10th place

as can an insufficient number of satellite signals, apparently...

Glenn I'll send you some really crappy data from NHMS, featuring that problem.  I'd bet the calculated accelerations spike at 4-5g or more! 

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Charlie Thompson
'04 JCW Cooper [STX]
NER Cannon Fodder

cmt52663:

as can an insufficient number of satellite signals, apparently...

Glenn I'll send you some really crappy data from NHMS, featuring that problem.  I'd bet the calculated accelerations spike at 4-5g or more! 

Well, it's not as bad as 4-5g, but looking at the data, it does look like there may be an "upper limit" that is likely within the range of the G loads of a well-prepared Solo vehicle on "sticky" tires. I'm even concerned about the limits of the accelerometers that are currently in use in devices (+/- 2G, with a "destruction" limit of 2.5G).

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Glenn L. Austin, Computer Wizard and Race Car Driver
2005 Ultra Yellow Nissan 350Z Track Model
2007 Packwood ProSolo "first loser" (0.081)
2007 SCCA Solo National Championships - 10th place