CalDrive

About CALDRIVE

CALDRIVE is a free set of calculators for checking your car’s suspension and wheel setup with numbers and diagrams before installation. Shock stroke distribution and wheel fitment are often left to experience and gut feeling, but anything that can be physically derived from your inputs can be calculated in advance.

All results are theoretical estimates based on your inputs and do not guarantee real-world behavior, vehicle-inspection compliance or driving safety. Adjust at your own risk and consult a specialist shop if unsure.

Start from what you want to do

If you already know the job, you can work backwards to the right tool. Knowing what actually changes before you type numbers in saves a lot of guessing.

Lower or raise the car

On a full-length-adjustable coilover, how you split the change between case length and preload affects not just ride height but how much stroke is left. CoiloverPro shows ride-height change and remaining bump and rebound travel for both axles at once, so you can find the range that will not bottom out.

Change wheels or get a flush fitment

The outer face is set by inset and rim width, and moving those two also changes clearance on the inside. Use FitmentPro to get the movement on both faces, then find wheels that actually exist by PCD, bolt count and inset in WheelFinder.

Change tyre size or plus-size

The first hurdle is whether the extra rim diameter is cancelled out by a lower profile. TireDiff puts two sizes side by side with the difference in diameter, circumference and speedometer error. Popular combinations already have their own comparison pages, which is the quickest way in.

Torque the wheel nuts

The correct torque depends on the manufacturer and thread size, and the nut seat has to match or it will not clamp properly. TorqueSpec lists reference figures by manufacturer along with thread specs, seat shapes and conversion between N·m and kgf·m.

Work out running costs or consider changing car

In Japan the lump sum at inspection time is weight tax, compulsory insurance and stamp duty, on top of the annual vehicle tax. TaxCalc breaks it down from a few choices. The surcharges that kick in past 13 and 18 years are included, so it also works as input for a decision to change car.

What to check whenever you change the suspension or wheels

Four things the inspection looks at

In Japan the four things that catch people out are minimum ground clearance (90 mm to the lowest point other than the contact patch, 50 mm where an underbody cover is built to take an impact), the relationship between indicated and true speed, the tyre protruding beyond the fender, and the load index staying at or above the placard value. Failing any one of them is a fail.

The numbers are theoretical; real cars vary

Everything on this site is derived from size markings and the values you enter. Actual tyre dimensions vary with brand, inflation pressure, load and wear, and the car itself has unit-to-unit variation. A speedometer already carries a few per cent of error from the factory, and any error from the tyres is added on top. Use it to get a figure to work from, and confirm on the actual car.

Look at the inside and at full bump, not just the outside

Poke is visible so you notice it; interference on the inside only shows up once things move. Check the gap to the strut, arms, caliper and fender liner both at full lock in each direction and with the suspension fully compressed. On a lowered car, upward clearance is what runs out first.

Finish the job with re-alignment and a torque re-check

Changing ride height or wheels changes the alignment, and leaving it will wear the tyres unevenly. Headlight aim and side slip are inspection items in Japan too, so both need measuring and resetting afterwards. Torque the wheel nuts to the specified figure and check them again after driving a while.

Frequently asked questions

Do I need to register or pay?

No. Every tool is free with no sign-up, and the values you enter are calculated inside your browser. Only the display language you pick is stored in the browser for next time.

Do the results guarantee passing a vehicle inspection?

No. The figures are theoretical values from your inputs and from size markings; they do not account for unit-to-unit variation, suspension geometry, or differences in real dimensions between tyre brands. Confirm fitment with a retailer, workshop or the transport bureau.

Can I use this for cars outside Japan?

The dimensional calculations — ride-height change, stroke, diameter, offset — work anywhere. The inspection thresholds and tax figures follow Japanese rules, so treat those as reference only elsewhere. The vehicle tax and inspection cost calculator (TaxCalc) is for the Japanese market and is Japanese-only.

Where do the figures come from?

Dimensions are calculated from tyre and wheel size markings. Figures tied to regulation are checked against primary sources such as Japanese Ministry of Land, Infrastructure, Transport and Tourism notices, and the date we checked is stated on the page. Tax rates are reviewed at each revision and the verification date updated.

Contact & Feedback

Bug reports, feature requests, wheel-data additions — feel free to send us anything.

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Calculation results on this site are theoretical estimates based on your inputs; their accuracy, completeness and safety are not guaranteed. The operator accepts no liability for any damage arising from the use of this site.