Thread: turning radius

  1. #1
    John Berryman Jr. Guest

    Question turning radius

    On the subject of turning radius of differant wheel bases & wheel cut angle.Is there a formula?? I have two units one with a 206 wb/50degree wheel cut tires 22'5 and one with a 215wb/45deg.wheel cut 22.5 tires.I need to know how much space they will take up in a turn.. Any help or advice would be great
    Thank you..jb

  2. #2
    mike021 Guest


    Did you try calling the manufacturer? Or check the specs they should have the radius and everything in the specs. I know Pierce does that.

  3. #3
    SBrooks Guest


    the Society of Automotive Engineers ( has a method to calculate the turning radius, however when I looked a year or two ago, the pamphlet was $50 or so. I keep meaning to check and see if the local college library has it.

  4. #4
    DN Greenfeld Guest


    There is one more variable to take into consideration. That would be wether tires are 10R or 11R.

    10R/22.5, 206WB, Turning radius would be approx. 28 feet with curb to curb of 56 feet

    10R/22.5, 215WB, Turning radius would be approx. 30 feet with curb to curb of 60 feet

    11R/22.5, 206WB, Turning radius would be approx. 27.5 feet with curb to curb of 55 feet

    11R/22.5, 215WB, Turning radius woudld be approx. 29 feet with curb to curb of 58 feet

    Hope this is helpful.

  5. #5
    N2DFire Guest


    O.K. - I'm not ashamed to admit when I'm licked.

    DN Greenfeld - what formula or equation(s) did you use to come up with those answers ??

    The ONLY formula I could come up with (after several days of searching) was one to find the steering angle based on a desired turning radius and a given wheel base which I then transposed into the following :

    Turning Radius = (wheel base / tan(steering angle)) - wheel track/2

            WB     t
    TR =  ------ - - 
          tan(SA)  2
    and I am still very much in doubt about this formula.

    Saddest part of all is that about 7 years ago I recived an AAS Degree in Mechanical Engineering Technology - I should have been able to figure this one out (Too many years of being a computer programmer instead of an engineer I guess).

    PLEASE put me out of my misery and give me the equation(s) you used.

    Take Care - Stay Safe

    [This message has been edited by N2DFire (edited 02-14-2001).]

  6. #6
    SBrooks Guest


    I imagine there are things to consider such as tire scrub, etc.

    I would think that tire size would have a greater effect on cramp angle than it would on tire scrub.

    also look into "ackerman steering"

  7. #7
    DN Greenfeld Guest



    I didn't use a formula, just the Freightliner refernce guide.

  8. #8
    DonRobbie Guest


    Great article on the subject at:
    (be sure to check out the illustrations)

  9. #9
    SBrooks Guest


    Here's a doozy:

    TR = SQRT[(wb/tan(sa)+t)^2+wb^2]

    where wb = wheelbase
    sa = steering angle of inside wheel
    t = wheel track
    TR = turn radius

    make sure all units are the same (all feet or all inches)

    formula doesn't account for different tracks, front & rear. It doesn't make much of a difference.

    By the formula:

    Custom Pumper: 180" wb & 45 deg sa, TR = 27'
    Commercial Pumper: 199" wb & 50 deg sa, TR = 27'
    Meritor's new 55 deg axle = 217" wb, 27'TR

    Note that the 45 degree wheel cut is more than we've gotten in many years...most of our older (more than 5 years) wagons probably have somewhere between 40-45 degrees. Unless you've got interference with a front intake.

  10. #10
    RJE Guest


    Yeah, tell me about it. Try your formula on my new Pete tractors. 260" wheelbase, 96" track, and 39 degree wheel cut.

    You guys have it easy. ('course, that's why I don't drive anymore, either)

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