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Archive for January, 2008
Tire Wear on Set Back vs Set Forward Steer Axles
Posted by dolan from cookeville, TN, US on January 29, 2008
Werun trucks with set back ster axles and set foward axles, the set back axle truck wears tire out faster that the forwards do. We run the same tire on both. Can you tell me why this happens?
I forwarded your question to Mike Beckett, President of MD Alignment. Mike knows more about tire wear than anyone I know.
"First you get a more effective transfer of loads to the steer axle with a set back vs a normal axle set. This does not mean more than about 500 lbs per tire in load but it is a more consistent transfer and this will have some minor effect. The larger effect is the turning angle on set back front axles. Most set forward axles turn 20 to 25 degrees as compared to 30 to 50 degrees on set back axles.
This increase in steering angle increases the "ackerman" effect on Toe when the vehicle in in a turn. A sharper steering angle and more toe on turns causes the vehicle to turn shorter circles and therefore it is more maneuverable but it does this at the expense of tire life. In my experience, on line haul trucks the net difference in tire life is about 10 to 15% between the two.
If you want to change this, adjust the steering stops on the axle to reduce turning angle and see how much you save. Just remember that the truck will require larger areas to turn around."
switching 22.5 to 24.5 & fuel economy
Posted by Harinder Singh from Brampton, ON, CA on January 20, 2008
My Fld120 came with michlin XDA-HT 22.5 tires, 3:90 ratio13 speed .73 ratio.It was ruuning 62 mph @ 1500 rpm, I had them changed to bf goodrich DR444 24.5 now it’s running 62 miles @ 1400 rpm.I was hoping for better mpg, but with the same load,route,speed,weather the new mpg got worse from 6.8 / 7 mpg to 6.35 / 6.5 mpg, Can you explain why.thanks.
Many people make tire changes expecting positive results but forget that new tires with full tread depth will have higher rolling resistance than older tires that are nearly worn out. This could be your issue. Also, it is very difficult to have conditions really be equal in a real world situation. It is difficult enough in a true test situation.