turning radius

[John Berryman Jr.]

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

[mike021]

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.

[SBrooks]

the Society of Automotive Engineers (sae.org) 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.

[DN Greenfeld]

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.

[N2DFire]

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

or

 
        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
Stephen
FF/Paramedic

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

[SBrooks]

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"

[DN Greenfeld]

N2DFire,

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

[DonRobbie]

Great article on the subject at: http://www.firemagazine.com/fam_comm.htm
(be sure to check out the illustrations)

[SBrooks]

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.

[RJE]

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)