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What is a Turning Radius?

A car's turning radius is the radius of the sharpest turn it can make.
The steering rack in an older rack and pinion system moves from side to side to control wheel movement.
In a rack and pinion system, when a driver turns the wheel he rotates the pin, which moves the rack, which in turn rotates the wheels.
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A good turning radius may be important to you when considering a new car or truck. Generally speaking, it refers to the tightest turn a vehicle can make and is dependent on several factors. One obvious one is the width of the wheel base — that is, how far apart the front tires are. All other things being equal, a smaller wheel base can offer a tighter radius, while a large wheel base, such as those on large trucks, will have a larger radius, regardless of other factors.

Another factor in a car’s turning radius is the steering gear box, which translates the turning of the steering wheel into the pivoting of the front wheels of the car. Not all gear boxes are created equal; moving the steering wheel clockwise a quarter turn will have a different result in a big pickup truck than it does in a tiny sports car. Typically, the steering gear box is designed in accordance to the purpose of the vehicle: that big truck probably won’t ever need to turn on a dime, whereas the driver of a sports car will want solid cornering abilities.

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There are several different types of steering setups, each with different advantages. The oldest and most basic type of steering is called rack-and-pinion. The rack spans the width of the car between the front wheels; the pinion gear, which is on the end of the steering wheel shaft, attaches to the top of the rack. As the steering wheel is turned, the spinning motion of the pinion gear moves the rack from side to side via the gear teeth on the top of the rack. In the days before power steering, the driver moved this rack from side to side with only the force of the steering wheel, which explains why cars without power steering can be hard to steer, especially at slow speeds when the road offers more resistance.

To relieve the driver of some of the work of turning the wheels, power steering was invented. This type of system has become quite popular in modern times. One type is called recirculating-ball, which is a complex system that basically takes all of the work out of turning the steering wheel.

The gearbox is attached to the end of the steering wheel shaft. As the wheel is turned, the ball bearings in the gearbox circulate around the shaft in spiraled grooves, in a manner rather like the direction a stripe takes around a candy cane. This moves the gears, which in turn pivot an arm called the pitman arm. The pitman arm is attached to the gearbox on one end and the “track rod” on the other, so that when the pitman arm pivots, it moves the arms that control the direction of the wheels.

Another type of power steering is power-assisted rack-and-pinion. This means that the steering pump uses pressurized fluid to help the driver move the pinion with the steering wheel. Although this is a type of hybrid system, somewhere between manual and power steering, it is preferred by some drivers, as it is a more responsive type of steering.

The type of steering system a car has might have an effect on the vehicle’s turning radius. In a classic rack-and-pinion car, it is harder to turn the steering wheel far enough to achieve a tight turn, particularly because the car has to be moving slowly — or not at all — to make a U-turn. In a car with power steering, it is easy to turn the wheel all the way in one direction or the other, but the size of the gears used in the steering system will determine how tight the turning radius is.

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anon324305
Post 15

What is the turning radius of a exchem multiblend delivery truck? Also, what is the maximum gradient they can handle?

anon93387
Post 12

The pitman arm and the idler arm (which mirrors the movement of the pitman arm) have movement indicated in degrees and influenced by the connect, center to center length, laterally, disregarding drop. These values are missing in all reference material for these parts, depriving, one,the value of the "travel arc" from point zero. That arc value is basic to defining the turning circle. (deg)

anon78912
Post 11

lambda777: with respect to your replaced rack and pinion steering unit - based upon your description, the "rack" in the steering unit was not centered when the front wheels were aligned.

You should be able to determine if I am correct in my assumption with a brief inspection of the steering.

Look underneath the car where the rack and pinion connects to the front wheels. The outer ends of the tie-rods (the shafts that stick out of the rack and pinion) are threaded and onto these are threaded the tie-rod ends. The tie-rod ends provide a 90 degree connection to the steering arms at the wheels.

Measure the exposed length of threads on the tie-rod shaft at each wheel. If the steering arms are toward the front side of the tires, you will probably find more exposed thread at the right wheel than you find at the left wheel. If the rack is behind the wheels, the opposite will be true.

This can be corrected fairly easily, but will require another trip to the alignment shop.

Explain your problem, ask them to center your rack and realign the car, and they should have no problem correcting it.

If you feel up to it, add the two measurements together (measure closely and from the same reference points on both sides), divide the total measurement by two. Loosen the lock nut on one tie-rod end, loosen the clamp on the dust boot, fit a wrench onto the flats on the shaft, and adjust the length to your calculated length. Tighten the lock nut and then do the same thing on the other side. That will get you close to centered, but you may end up with a crooked steering wheel.

That can be removed and reinstalled in the correct position if you have the right tools. Good luck.

lamda777
Post 10

I just had the rack and pinion on my 1994 Mazda 626 ES replaced with a rebuilt rack and pinion and had the car aligned. It drives straight as an arrow with the steering wheel centered, there is no pulling to any side or noises of any kind. When I turn the steering wheel all the way to the left(approximately two full turns of the steering wheel) I get a nice tight turning radius. However, when I turn the steering wheel all the way to the right (approximately 1 1/4 turns of the steering wheel) i get a large turning radius. Is this normal? Could there be a problem with the rebuilt rack? Could it be the wrong rack for my car? Or does the problem lie with my mechanic?

anon35561
Post 7

what is the formula for the turning radius of a car?????????

anon33281
Post 6

Does the turning radius change with the direction of the vehicle? Can a forward turn have a smaller turning radius than a backward turn or vice versa?

karthik
Post 4

am having a problem with my car (baja vehicle), the wheel steers but the tire slips from the ground and i get a big turning radius, can anyone help me!

anon4918
Post 3

Your comments related to power steering, rack and pinion and circulating ball is factually inaccurate.

Most power steering system uses "rack and pinion" with hydraulic power assist. Circulating ball type steering in effect does not provide power assist. It just provides gear assist like the rack and pinion and the power assist need to be provided with additional hydraulic or by electric motor.

lamaestra
Post 2

Most car manufacturers base a car’s turning radius on the space needed to make a U-turn in a curbed-in street. So, basically, the turning radius equals half the distance (not the whole distance because that would be the diameter) of the car’s outer wheel just *before* it begins a U-turn and just *after* it completes the U-turn. So a car with a 16 foot (4.9 meter) turning radius could make a U-turn in a 32 foot (10 meter) wide curbed street. A car’s turning radius can also be based on the space needed to make a U-turn in a walled in street, like an alley. This would yield a higher figure as more space would be needed for the car’s fender and bumper to clear the turn. Additionally, the turning radius could be based on the car’s axis (center point, side-to-side) or inner wheel before and after it completes a u-turn. To be sure about your car’s turning radius figure, you may want to call your car’s manufacturer or dealer!

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