Tire Heating – The TMPH Rating ©Dr. B. C. Paul 2000 revised 2008 Note- These slides demonstrate the use of the FPC computer program developed by the Caterpillar Equipment Company and include screen shots from the program. Information and screenshots were also taken from the Cat Handbook

Haul Trucks are Very Large l Tires flex and can get hot as a result of working under load l To avoid tire blow-outs we use Ton Miles Per Hour – TMPH l Each tire has a rating l You get the average load * average speed and compare to the TMPH rating

Check for Tire Heating Problems l Cat 773 is normally equipped with 24R35 Tires with an E3 Rock Tread tmph rating is 300 l Ton Mile Per Hour is Defined as Average Load * Average Speed l Time Per Cycle is minutes l Get Number of Cycles Per Day

Calculating Average Speed l 8 hour shift with crews working 50 minutes out of l I’m assuming that when my driver takes a brake the truck does too l 8 *0.83 = 6.64 hours l 6.64 hours * 60 min/hour = l / = trips

Working on Average Speed l What are the chances of trips (you know people will take off when they can’t make another trip) 35 trips l ( ) = 9600 feet or 1.82 miles l 1.82 * 35 = 64 miles l 64 miles/ 8 hours = 8 mph av.

Get Average Tire Load l Gross Weight Loaded is 102 tons l Empty Weight is 43.5 tons l Distribution is 53% Rear Empty and 67% Loaded l Loaded on Rear Tires 102 * 0.67 = tons l Loaded on Front is tons

Working on Average Tire Load l Empty Rear is tons l Empty Front is tons l Average Rear Tire Load is ( )/2 = 45.7 tons Over 4 tires is tons l Average Front Tire Load ( )/2 = Over 2 tires is 13.53

Check Tmph l Note that front tire is more critical than rear l tons * 8 mph = tmph l Compare to 300 tmph rating at 100 degrees F l Tire heating will not change speed

Lets Do the FPC enhanced Check Go to the Fleet Input Tab and Note the place for TMPH entry When you see the little 3 dot Box it means there is a Subscreen for putting in or Calculating more I’ll click the box

The TMPH Screen Comes Up It starts out showing us how the Load is distributed on the tires And how many tires there are It needs manufacture Limits for the tires

To Get the Limits Check the standard Tire size for the Truck using the Cat Handbook My 785 uses R51

Check Out Manufactures Tables (These are from the Cat Handbook) If I pick a medium tread (S4) I will get 370

Plug it into FPC and Click Ok

Go to the Production and Cost Tab Select the tire Temp subtab

The Output Shows load Distribution (Note that front tires are usually more critical) Best possible time with no Waiting to load TMPH that would occur

More Output It also shows the results of a typical average cycle which includes Bunching and delays – clearly we are ok under these conditions

When Might We Get Into Trouble? l If the outside temp is 100 F And most of our trucks are down so that the remaining trucks have little wait and can go full speed ahead May need to simply direct drivers to take a tire heating break if they are averaging under 9 minute cycles