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· Subscribing Member
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Gil, this is the basic of basic formulas but you still need a drag sled to get an accurate reading. If you don't have a drag sled you can use standard (f) for dry road, or grass, etc..
The formula is

speed=square root of 30 X Distance X f
f=coefficient of drag

F=force in pounds to move drag sled (need drag sled and weight scale)
W=Weight in pounds of drag sled

Most crashes you have to use average skid distances. Measure skidmarks and divide by number of skids. This would be Distance. This is if you have 100% brake efficiency. If not then you have to adjust

speed=square root of 30XdistanceXfXn
n=braking percentage
So if you have a front wheel drive that had all four wheels lockup you have 100% so n=1
If you had the front right wheel not working you would have lost 35% of your total effectiveness, therefore n=.65

I hope i didn't confuse you too much!
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