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CMV Braking Efficiency Adjustments

Braking Adjustments for CMV

Air Brake EfficiencyWeight per AxleTire CompoundsDrum Brake vs. Disc BrakeHeat Build-up in BrakesMechanical LimitationsCenter of Gravity HeightWeight 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% (0.25 - 0.40)

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

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