CoiloverPro

InputFRONT

Length adjust0mm
+ raises / − lowers ride height
Preload0mm
Raises height & increases bump usage
Use 1.0 if unknown
= 78.5 N/mm
Simple-mode base value

SIDE VIEW (F & R)

FR00

STROKE SPLIT

60F6060R60
Height changeF
0mm
Bump travel leftF
60mm
Rebound travel leftF
60mm
Rake (F−R)
0mm

■ Controls

Mode (Simple / Precise)：
"Simple" calculates from your measured 1G compression — usable even without full data. "Precise" computes spring deflection from corner weight, spring rate and motion ratio (for pros).
Axis (Front / Rear)：
Switch to set each axle separately. Both values are kept, and the silhouette shows the front-to-rear difference (rake).
Body type：
Pick the shape closest to your car (sedan, coupe, SUV/wagon, kei/hatch). It only changes the visual, not the math. Front is on the left, rear on the right.

■ Inputs

Length adjust：
How far the coilover case (bracket) is extended/shortened from the baseline. + raises, − lowers. The main height control on full-length adjustable units.
Preload：
How much the lower seat compresses the spring. Increasing it raises height and increases bump-side stroke consumed.
Motion ratio (MR)：
Wheel travel ÷ shock travel. Strut ≈ 1.0. Multi-link and similar setups are usually below 1.0 — check your vehicle data. Leave at 1.0 for a relative comparison if unknown.
Spring rate：
Spring stiffness (load to compress 1mm). Enter in kgf/mm; the N/mm equivalent shows beside it.
Total stroke：
Full travel from fully compressed to fully extended.
1G compression：
How much the shock is compressed with the car on the ground. Measured value recommended. Base value for Simple mode.
Base height：
Current measured ride height (e.g. fender arch). Enter it to see the absolute height after adjustment. Optional.
Corner weight：
Weight on that one wheel. Used to compute spring deflection in Precise mode.

■ Reading the results

Height change：
Rise/drop from length adjustment and preload combined.
Bump travel left：
Remaining compression travel. Near 0 risks bottoming out. Shown in the upper part of the bar.
Rebound travel left：
Remaining extension travel. Lower part of the bar.
Rake (F−R)：
Difference between front and rear height change. + is nose-up, − is nose-down.

■ Regulations and practical notes

Minimum ground clearance：
In Japan the regulation requires at least 90 mm from the ground to the lowest point other than the contact patch (50 mm is enough for underbody covers built to take an impact). When lowering, check that the exhaust, oil pan, subframe and body kit stay above that. Measurement is taken unladen, at the specified tire pressure, with any ride-height adjuster at its standard setting.
Leaving enough stroke：
Lowering the car eats into bump stroke at static ride height. Keeping 30-50% of total stroke on the bump side is the usual guideline; with less than that the damper bottoms out at full bump, which hurts both ride quality and tire life. Watch the remaining bump figure in this tool while you split the change between case length and preload.
Preload cannot lower the car：
Preload is how far the spring is already compressed, so adding it can only raise ride height. To go lower, shorten the case length; keep preload at the minimum that stops the spring going slack. Using preload to gain height wastes bump stroke.
Re-adjustment afterwards：
Changing ride height changes alignment. Lowering adds negative camber and shifts toe, which wears tires unevenly. Headlight aim and side slip are also inspection items in Japan, so both need to be measured and reset after a ride-height change.
Front-to-rear balance (rake)：
The front-to-rear difference affects handling. Nose-down generally adds front load and sharpens turn-in; tail-down biases toward traction. A heavily nose-down stance exaggerates weight transfer under braking, so start with the same change front and rear and move in small steps.

FAQ

Q.How do I calculate ride height on coilovers?
On full-length adjustable coilovers, height change comes from how far you move the lower bracket (lock seat), plus the spring compression change from preload, multiplied by the motion ratio. Enter length adjustment, preload and motion ratio and this tool computes front and rear height change automatically.
Q.What is preload, and what happens with too much?
Preload is how much the spring seat pre-compresses the spring. Too much preload eats into bump travel, making bottoming out more likely and hurting ride quality. Start at zero, or just enough preload to keep the spring from going loose.
Q.What is motion ratio?
It is wheel travel divided by shock travel. Struts are roughly 1.0; double wishbone and multilink are usually below 1.0. It affects effective spring rate and height calculations, so check your vehicle data for accuracy.
Q.How much bump and rebound stroke should I keep?
Keep margin on both sides at 1G. As a rule of thumb, reserve roughly 30–50% of total stroke for bump travel; too little margin causes bottoming out or topping out. Use this tool to check remaining travel front and rear.
Q.Will lowering the car on coilovers fail the Japanese inspection?
Lowering is not prohibited in itself, but the car fails if the minimum ground clearance drops below 90 mm (50 mm is enough for underbody covers built to take an impact). Measurement is taken unladen, at the specified tire pressure, with any ride-height adjuster at its standard setting. Headlight aim and side slip are inspection items too, so both need measuring and resetting after a ride-height change.
Q.Can I lower the car with preload?
No. Preload is how far the spring is compressed in advance, so adding it raises ride height. To go lower, shorten the case length. Gaining height with preload wastes bump stroke and makes the damper bottom out more easily.

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