Tab 8 CMV Braking Efficiency Adjustments

Braking Adjustments for CMV Air Brake Efficiency Weight per Axle Tire Compounds Drum Brake vs. Disc Brake Heat Build-up in Brakes Mechanical Limitations Center of Gravity Height Weight Transfer

“Center of Gravity” affects vehicle handling characteristics and braking efficiency !

Center of Mass of Trailer and Product Load

General rules of thumb: TT w/o front brakes:25 – 40% ( ) TT w/ front brakes:70 – 80% (0.70 – 0.80) TTST w/o front brakes:50 – 70% (0.50 – 0.70) TTST w/ front brakes:65 – 80% (0.65 – 0.80) TTSTST w/ front brakes:75 – 90% (0.75 – 0.90) Buses(Motor coach)70 – 85% (0.70 – 0.85) St. Truck 60 – 85% (0.60 – 0.85)

A 5-axle TTST slid to a stop in a distance of 200 feet on a dry, asphalt surface. What was its beginning speed? (There was no impact with anything else)

A straight truck (with a reefer) slid into another car after skidding for 150 feet on a dry, asphalt surface. The driver said he was only going 35 mph before he began to brake. Is he telling the truth?

Your driver told you he was going 20 mph and had to skid to a stop. He did so in 30 feet on dry pavement. Does this conform to CFR-49 requirements for braking? Does it meet or exceed the requirements?

Reconstruct and Analyze the Crash If you have documented an adequate amount of crash data that was available from the scene, the vehicles and the people involved, then this information can be evaluated at a later time to more fully determine “how” and “why” the traffic crash occurred.

Match up Contact Locations

Use Data to Obtain Impact Profile

Impact Speed Evaluation

“Black Box” Technology

Vehicle Speed (MPH) Engine Speed (RPM) Percent of Wide Open Throttle Brake Switch Status (On or Off) Pre-Crash Graph GM Air Bag Module

Black Box Technology on Trucks Cat 3406 Engine

DDEC Data Printout