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Ikeya formula's Adjustable suspension arm
By using arms of our product lineups, you will be able to adjust
the changes in the alignment and also correct the roll center
position when normal arms are raised and opened up outwards
which is often seen in the cars with lowered height. On this
page, we will talk about "Suspension geometry" such as " Roll
center correction", "Alignment".

"About Changes in Alignment"-----
Since normal arm comprises rubber bush, the alignment
changes when the arm receives "force"(stress) and are
"twisted". Additionally, the difference in the car height effects
the alignment.
For example,when the suspension bumps, there would be
changes in the Negative/Positive direction on "Camber", and
In/Out direction on the "Toe", although it differs by types of cars or the structure of
suspension system. This brings the issues in, such as the feeling of tire contacted to
ground, the responsiveness of steering on breaking, and traction shortage To solve this
issues, we have changed the Rubber bush to Piro ball. Additionally, by adding the
adjustable function to the Arm, we have developed product lineup which can
accommodate the changes in the alignment. 


----- Does it necessary to adjust the alignment when changing
        tires or
 inch-up the aluminum wheel ?
----- Why are there instabilities transmitted from steering wheel

        during driving ? 

The following is various examples of car behavior or changes in tires.
 - Inside wear of tire ⇒ Excessive Camber/ Excessive Toe-out.
 - Outside wear of tire ⇒ Positive camber/ Toe-in/ shifted camber.
 - Excessive wear of tire ⇒ Extreme Toe-in.
 - Instabilities transmitted from steering wheel during driving ⇒ Camber or Toe is out of alignment. 
 - Center of steering is not in the correct position ⇒ Toe is shifted to either left or right.
 - Difficulties in driving straight ⇒ aster angle is not in the correct position.
 - Not possible to drive straight(strays to one side) ⇒ Only one side has camber/
SPACEdifferent caster angle between right/left side.
 - Whole car body is shaking ⇒ Camber or Toe is not even/ Unbalanced wheel

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"About correction of Roll center"-----

foot04.pngDrivers tend to consider that center of gravity would be lowered
and have more stability if car height is lowered. However, if you
are using the normal arm, the arms would be raised and opened
up outwards and the center of gravity of car and roll center
would be apart . And the roll amount unnecessarily increases
while the suspension stroke decreases, and causes the condition
of " Grip limitation between tire and ground surface will be
By using Ikeya formula's "Front lower arm", "Rear lower arm"
and "Tie-rod end" which possess the roll center adjuster
function will correct the roll center and set back to the position
where has the shorter distance between center of gravity and
roll center and then decreases the roll amount Additionally, we
would like to recommend to install both Front and Rear at the
same time.

Because the roll center of Front and Rear would be "shifted", if
mounting only on Front side, and the roll axis will be shifted on Front and the roll amount
changes on Rear, and causes loss of the stability in the car behavior. From these points,
we would like to recommend to wear both on Front and Rear.

foot-03.pngThe cross-point on the extension of
mounting position of suspension arm
and tread centerline is instantaneous
rotation center of contact point to
ground of the tire. Car inclines (roll)
with this point as a center. Roll
center is lowered if car height is
lowered with normal arms mounted.
Even with the same roll angle, cornering performance would be decreased because of
large distance from the rotation center which causes bigger movement.

column02.png----- Why are there hardness in riding in after mounting down-sus
        or shock absorber (with height adjustment function)? 

Although it's often considered that there would be more stability if car height is lowered
by wearing the shock absorber(with height adjustment function)and down-sus, the roll
amount increases because roll center shifts away. Therefore, the spring rate of the
off-the-shelf shock absorber and down-sus are set higher than the normal spring to
prevent from rolling the car body. As just mentioned, the roll amount is controlled by
having the higher spring rate, and this makes the hardness in riding in the car.


Next, for the experienced or intermediate drivers, we would like to talk about one of
geometry basics, "Bump Steer" which can even effects the cornering characteristics.

"What is bump steer"-----

One of the reasons that suspension setting is often said difficult is Bump steer.
Bump Steer is a change in toe as a wheel moves up or down in its suspension geometry.
Bump steer occurs because of the circular motion of suspension arm or tie-rod having its
pivot of the body or upright side as a center. Therefore, it is not possible to disappear it
completely unless fundamental structure is changed.
Now, we would like to talk about the relations between bump steer and handling.
Toe-change in case of tie-rod is on Front/ Back of hub center (the center of hub that
supports the car axis):

1. Case that it's mounted on
the front side of hub center 
Front side is pulled by
tie-rod upon stroke
Bump toe-in 

* Toe is shifted to "in" upon bumping or re-bumping when tie-rod is on a level. Large
cornering force is generated and the direction is changed sharply even with smaller
steering amount and large slowdown, because the tire becomes the resistance on the
toe change upon breaking.

2. Case that it's mounted on
the back side of hub center
Rear side is pulled by
tie-rod upon stroke
Bump toe-out

* Amount of cornering force generated against steer is decreased because of the toe
change to "out" upon bumping and leads to the stabilized handling. This can often seen
on stock-cars and its rear toe control rod is based on rear side of axle for the stability.

Let’s examine it with your cars!
Toe-chage in case of tie-rod is on Front/Back of hub center.

foot05.png foot06.png

Talking about the alignment adjustment, under 1G condition that suspension does not
work, preferably it's set to have high stability on driving straight and less rolling
resistance considering the balance of toe and camber. However, if you are using the
suspension type which turns toe-out when the front side is sunk down by breaking, the
toe only turn its direction less than the actual amount of steering. Therefore, have a
little bigger "toe-in" beforehand upon 1Gto have better cornering. This is for the type of
the cars which emphasizes steering related to the steering performance, although rolling
resistance is relatively increased on driving straight. On the other hand, for the car
which turns "toe-in" upon bumping and if toe is set to decrease rolling resistance upon
driving straight, the car is tend to become oversteer. To have the stability for cornering,
it's necessary to turn "toe-out" slightly on 1G. It's not the story limited only on breaking,
but also on lowering car height. When lowering car height, arm angle became the same
angle as that upon bumping, which causes the changes not only in the toe but also other
parts such as cambers and required alignment adjustment of 1G status again.

To solve the big toe-change issue
caused by lowering car height, we
would like to recommend our
Tie-rod (patent), which makes the
tie-rod angle almost horizontal.
This also satisfies car inspection
requirement in Japan.
  Suspension stroke
Tierod end PAT

Our various adjustable Piro Arm products bring you various merits as mentioned above.
Here is an example with item lineups for Skyline GT-R (BNR34).

Camber angle can be freely adjusted by negative upperlink and caster angle can be
changed by Piro tension rod. (the area where could not be adjusted in genuine part.) 
Normally, lowering car height causes arm angle to be poor and also rapid changes in
geometry. However, this problem can be solved by installing Roll center adjuster on
Adjustable lower arm to have the arm position horizontal. At the same time, if you
install our Tie-rod end together, the stresses placed on tie-rod end would be removed
and toe-changes upon bump/re-bump, which helps smooth steering operation.

nfrontajuplink.jpg gtrfrontlow02.jpg
Front upper link Roll center adjusterlower
Tierod end PAT

Adjustable upper arm and Traction adjuster rod are effective for alignment adjustment
and enable you to adjust the camber. In addition, it constrains the movement of member
bush on rear side as well as the unnecessary behavior even if the burden increased by
High grip wheel, by fitting the roll center to the Front with Adjuster rear lower arm and
also wearing Multilink spacers.

Rear camber
adjuster upper arm
Traction adjuster rod
Adjuster rear lower arm

As just described, the feeing of tire contacted to ground are improved by installing
Adjustable arm and the information transmitted to steering becomes accurate. Further,
by the correct operation of arm parts would produce changes in suspension movement
and shock movement is transmitted to linear. This total cares for "suspension", "shock
absorber" and "arm" will make you feel more pleasure in the driving.

 -Following graphs show the alignment changes comparison between normal arm and
Ikeya's full arms measured at our company ( with our self-developed geometry
measuring equipment). As these graphs show, the amount of alignment change with
Ikeya's arms are observed less than normal arms. You might also see the various merits
of using our arms form our actual data. We strongly recommend you to use and feel our

34GTR Front IF arm geometry date acquisiton result table


34GTR Rear IF arm geometry data acqusition result table



Tread Comparison


Changed Amount upon adjusted with Ikeya's arm(BNR34)

  Negative Upper link Tierod Rool Center Adjuster
Lower Arm  
Toe Change  About 0° 08' About 1° About -0° 20'
Camber Change About 0° 20' About -0° 05' About 0° 10'
  Rear Camber Adjuster
Upper Arm
Traction Adjuster
Adjuster Rear lower
Toe Change About 0° 30' About -0° 30 About -0° 06'
Camber Change About -0° 40' About -0° 05' About 0° 30'

(This shall be the values when shortened by one turn. ) 

S15 Front IF arm geometry data acqusition result table


S15 Rear IF arm geometry data acquisition result table






Corresponding list for FOOT WORK categorized by car type