torque testing ELECTRIC POWER STEERING KIT FOR 240Z 260Z 280Z DATSUN 1970-1978 S30

Ok here we go with the first round of data collection.


These result are for Zero speed with the engines running.

Basically parking lot conditions.



If I’m telling what you already know I apologize, but I want to make sure we are on the same page and our understanding is the same


1). How do we measure how hard something is to turn?


- Torque (just like a torque wrench)


2) How is torque defined / measured?


- Torque is a force applied at a distance from

The axis of rotation


- like a torque wrench Foot x Pounds or

Inch x Pounds

 torque test 240z eps

3) So I have measured the Diameter of each steering

wheel and divided by 2 to give us the radius at

which we are applying the turning force


4)  distance the force will be applied from the center

of the steering column equals the radius of the

steering wheel.

 240z steering wheel

Datsun settling wheel  13 3/4”  diameter

6 7/8”  radius (inches)

0.573’  radius (feet)


Mini Cooper S wheel   14 1/2” diameter

7 1/4” radius (inches)

0.604’ radius (feet)


Porsche 911 (no power assist) 14 1/4” diameter

7 1/8” radius (inches)

0.594’ radius (feet)

 torque test 240z eps

5) Here is picture of how I am applying the force

to the steering wheel.  (Note that since Torque is

linear and all the mathematical functions are distributive

any errors cancel out as long as they are repeated

in each or the measurements)




6) I pull the scale to turn the wheel in a circular

manner to insure that I am always pulling at

A 90 degree angle to the axis of rotation

(center of the steering column)


7) After doing multiple pulls on each car, what I

noticed is is that there is one force needed to

start the wheel turning and another force needed

to keep it turning.  What I didn’t expect was that

the force need to start turning the wheel was

lower than the force needed to keep turning the

wheel. This is the opposite of that I expected!!


8) here are the measure forces to turn the steering

wheel.  The first number is the force needed to

start the wheel turning and the second is the

force needed to keep the wheel turning (usually

after about 1/4 of a rotation of the wheel)


Notice that in each case it is about 2.1 to 2.6 pounds

of additional force to keep the steering wheel turning

I suspect that this has something to do with the tire

contact patch but without some additional research

I can’t be sure


Datsun steering wheel turning force in pounds

2.30 pounds to start turning

4.31 pounds to continue after 1/4 turn


Mini Cooper S steering wheel turning force in pounds

2.45 pounds to start turning

4.75 pounds to continue after 1/4 turn  14 1/2” diameter


Porsche 911 (no power assist) steering wheel turning force in pounds

11.75 pounds to start turning

14.35 pounds to continue after 1/4 turn


9) Ok last step!  Calculating the Torque

- Force x Distance (radius)


Datsun turning Torque in Ft-lbs

1.32  Ft-Lbs to start turning

2.68 Ft-Lbs to continue turning after 1/4 turn


Mini Cooper S turning Torque in Ft-lbs

1.48  Ft-Lbs to start turning

2.87  Ft-Lbs to continue turning after 1/4 turn


Porsche 911 (no power assist) turning Torque in Ft-lbs

6.98 Ft-Lbs to start turning

8.52 Ft-Lbs to continue turning after 1/4 turn



- the Porsche with 205/50/15 tires & no power

assist is SIGNIFICANTLY higher at zero speed


-  the Mini Cooper S with 195/55/16 tires has a 12% higher

force to start turning and 10.2% higher force to keep the

wheel turning.



I wish I had these number for the Datsun before I

Installed your electric power steering system.  I know

They would have been much higher than the Porsche’s



I’ll collect the numbers for the car when it moving later in the week


Let me know what you think of these results


Hello Edan,


Happy New Year


Things were kind of slow today and there weren’t very many people out on the roads, so I did some testing.  I only did the testing on the Mini and the Datsun. (I’ll try to do the Test on the Porsche later this week)


1). I used the same arrangement with scale


2) I did a number of different test

- wheel turned 90 degrees and held in that position

- moderately aggressive land changes

- gradual lane changes


3) I did the tests at 5mph / 15 mph / 25 mph and 45 mph (lane change only)


4) what I observed is that both systems worked to keep the

turning effort at the same Torque level as the speed increases.

(The system turns down the boost to keep the force consistent.)

The system does not seem to increase the turning force (Torque)

to higher values of effort at higher speeds.  From a control point

of view, I guess this makes sense.   You don’t want to get people

to feel like their rack & pinion is binding up


5)  Since it is difficult to repeat turns exactly, I did

each test condition a number of times to get a range of



6)  The calculations are the same as the first test,

so I won’t repeat all the details again


7) Results:


Datsun turning torque range

0.92 to 1.15 Ft-Lbs


Mini Cooper S Torque range

1.17 to 1.53 Ft-Lbs



1)    Both vehicles measured lower turning

Torques when in motion than the Zero

Speed tests done earlier


2)   The percentage difference in the turning

Is in the range of 27-33% higher for the Mini

Cooper S


3)   Thinking about this further, differences in steering

caster adjustment could also result in different

steering torques.  Obviously the caster setting impacts

the force that causes the steering wheel to return to

center when you loosen your grip on the wheel after a turn.  

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