Wheel Rate Calculator
Two cars can run the same springs and feel nothing alike. The difference is geometry: how far the spring moves for every inch the wheel moves. This tool turns spring rate and that leverage into wheel rate, corner frequency, and a suitability verdict for how you use the car.
Wheel Rate Calculator
Spring rate and suspension geometry, turned into stiffness at the wheel.
Wheel Rate:
Natural Frequency:
Corner Weight:
Total Wheel Rate (with anti-roll bar):
Ride Height Sensitivity:
Suspension Stiffness Rating:
Application Suitability:
Comparative Analysis:
Tuning Recommendations:
Wheel diameter and tire sidewall height are kept in the form for reference but do not change any result in this version. The frequency is an undamped estimate from corner weight and wheel rate only: it ignores tire stiffness, damping, and unsprung mass, so treat it as a tuning starting point, not a measured value.
Quick Answer
Enter a spring rate and a motion ratio, and the tool returns wheel rate, natural frequency, corner weight, and a stiffness and application verdict. In the worked example, a 400 lb/in spring with a 1.10 motion ratio gives a 330.6 lb/in wheel rate, a 1.92 Hz natural frequency on an 880 lb front corner, and an Excellent verdict for autocross.
- Quick Answer
- How to use this calculator
- The formula, and the definition trap that ruins most answers
- Worked example, checked against this exact tool
- The unit conversion fix in this version
- Reading frequency bands without fooling yourself
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use this calculator
Start with the spring rate from the spring manufacturer, in the unit it is sold in, then enter the motion ratio exactly as this tool defines it: wheel travel divided by spring travel. If your suspension book gives the ratio the other way round, enter its reciprocal, or the answer will be wrong by the square of the ratio, which is a large error. Add total vehicle weight and the front and rear shares if you want corner weight and frequency. Leave the anti-roll bar blank unless one is fitted. Press Calculate and read the wheel rate first, then the frequency, then the suitability sentence. The frequency, not the raw rate, is the number to tune against.
One honest limit sits in the form itself. Wheel diameter and tire sidewall height are shown as inputs, but this version of the tool never reads them, so changing them changes nothing. They are kept for a future ride-rate version. Do not use them as a way to test a tire change here.
The formula, and the definition trap that ruins most answers
Wheel rate in this tool is spring rate divided by motion ratio squared, where motion ratio means wheel travel divided by spring travel. The worked example checks out: 400 divided by 1.10 squared is 400 divided by 1.21, or 330.6 lb/in. In metric, that is 330.6 times 0.175127, or 57.9 N/mm. Corner weight is total weight times the axle share, divided by two: 3,200 times 55 percent, divided by two, is 880 lb. Natural frequency is 1 divided by 2 pi, times the square root of wheel rate divided by corner mass, which gives 1.92 Hz for this corner.
The trap is that the industry uses the name motion ratio for two opposite ratios. Some sources define it as spring travel divided by wheel travel and multiply by its square. Others, including this tool, define it as wheel travel divided by spring travel and divide by its square. The physics is identical and the numbers are reciprocals, but mixing the definition with the wrong formula inverts the answer. A 400 lb/in spring with a 0.91 spring-over-wheel ratio gives 400 times 0.91 squared, or 331 lb/in, the same answer as 400 divided by 1.10 squared. Check which definition your source used before you type anything in.
| Input as your source states it | What to enter here | Worked result for a 400 lb/in spring |
|---|---|---|
| Wheel travel divided by spring travel, 1.10 | 1.10 | 330.6 lb/in |
| Spring travel divided by wheel travel, 0.91 | 1 divided by 0.91, or 1.10 | 330.6 lb/in |
| Spring travel divided by wheel travel, 0.70 | 1 divided by 0.70, or 1.43 | 196.0 lb/in |
Worked example, checked against this exact tool
Use a passenger car on coilovers, set for autocross. Spring rate 400 lb/in, motion ratio 1.10, no installation ratio override, total weight 3,200 lb at 55 percent front and 45 percent rear, front left corner, 18 inch wheels, no anti-roll bar rate. The tool returns a wheel rate of 330.6 lb/in (57.9 N/mm), a natural frequency of 1.92 Hz, a corner weight of 880 lb (399 kg), total wheel rate not available with no anti-roll bar, ride height sensitivity of 330.6 lb/in per inch, a Firm, performance oriented rating, and an Excellent verdict for autocross, because 1.92 Hz sits inside the 1.5 to 2.2 Hz autocross band and within 10 percent of its 1.8 Hz optimum. The one recommendation is to consider adding anti-roll bars for better roll control in racing applications, which follows from leaving the bar rate blank.
Takeaway: judge the frequency, not the rate. The same 330.6 lb/in wheel rate on a heavier corner would give a lower frequency and a softer feel, while on a lighter corner it would feel stiffer. Rate without corner weight is only half a setup.
The unit conversion fix in this version
This rewrite corrects a real error in the previous tool, and the correction changes answers for anyone entering metric spring rates. The old tool treated a newton per millimetre as if it were a newton per metre, using 0.00571 instead of 5.71 lb/in, and it did the same for kilogram per millimetre and newton per metre inputs, understating every metric spring rate by a factor of 1,000. A 70 N/mm spring, which is about 400 lb/in, previously computed as if it were 0.4 lb/in. The display conversion had the opposite error, multiplying lb/in by 175.127 instead of 0.175127 to get N/mm, so a 330.6 lb/in result once displayed as 57,893 N/mm instead of 57.9 N/mm. Both conversions are corrected here, and the imperial path, which was already right, is unchanged. If you previously used this tool with metric units, rerun your setup: the old answers were not close, they were a thousand times out.
Reading frequency bands without fooling yourself
Frequency bands in the tool are broad guides, not pass marks. Street use sits near 1.0 to 1.5 Hz, autocross near 1.5 to 2.2 Hz, track days near 1.8 to 2.5 Hz, and formula cars near 2.5 to 4.0 Hz. A frequency inside the band does not mean the car handles well: damping, tire stiffness, geometry through travel, and front to rear balance all sit outside this calculation. Use the band to choose a spring shortlist, then test. If the car feels harsh on real roads at a frequency the tool calls Excellent, believe the road, not the band, and soften the setup or add damping control before chasing a higher number.
What competing calculators miss
Most wheel rate tools on the web ask for spring rate and motion ratio and stop there, returning one number with no corner weight, no frequency, and no warning about which motion ratio definition they used. That is how a user enters 0.7, meaning spring travel over wheel travel, into a tool that expects wheel over spring, and gets an answer wrong by a factor of more than four (816 lb/in instead of 196 lb/in). This page names its definition in the label, explains the reciprocal trap with a table, adds corner weight and natural frequency from real vehicle weight, rates the setup for a chosen application, and now converts metric units correctly, which the previous version of this very tool did not. What it still does not do is model tire stiffness, damping, or rising rate through travel, and the article says so rather than implying a single number settles a setup.
Related reading on the same site: the companion wheel offset calculator compares current and proposed wheels for fitment, the fork spring rate calculator covers spring rates for motorcycle forks, and the spring wire length calculator covers coil geometry from wire and coil dimensions.
Frequently asked questions
Spring rate is the stiffness of the spring itself. Wheel rate is the stiffness felt at the wheel after suspension geometry has its say. The same spring gives a different wheel rate on two cars because their leverage differs, which is why spring shopping by spring rate alone misleads.
Wheel travel divided by spring travel for the same bump. With that definition, wheel rate equals spring rate divided by motion ratio squared. Some sources define motion ratio the other way round, as spring travel divided by wheel travel, and multiply instead. Both give the same physics if you keep the definition straight. If your source gives spring travel divided by wheel travel, enter its reciprocal here.
Jack the car to ride height, mark a point on the wheel and a point on the spring, then move the wheel a known distance, say 2 inches, and measure how far the spring moved. Motion ratio for this tool is wheel movement divided by spring movement. Measure near ride height, because the ratio changes through travel on many suspensions.
There is no single good number, because frequency matters more than rate alone. A typical passenger car rides near 1.0 to 1.5 Hz. Enter your weight and corner, then judge the frequency result against the application band rather than chasing a round wheel rate number.
Corner weight is total weight times the axle share, divided by two. A 3,200 lb car at 55 percent front gives an 880 lb front corner. Without a corner weight there is no natural frequency, so the frequency and suitability results show as not available.
In this tool, half the anti-roll bar rate is added to the wheel rate for the total wheel rate result. That is a simplification: a bar resists roll, which is a two-wheel motion, differently from a single-wheel bump. Read the total as a roll-biased figure, not a pure bump rate.
They are collected in the form but the calculation never reads them. They are kept so a future version can add a true ride rate, which combines wheel rate and tire stiffness in series, without changing the form. Do not expect a different wheel size to change any number here.
No. Too stiff a setup loses grip on uneven surfaces, skips over bumps, and punishes tires. Too soft a setup rolls, pitches, and bottoms out. The right rate is the one that puts your corner frequency in the band for how you actually use the car.
It is the wheel rate restated as force change per inch of ride height change. Raise the car 1 inch at a corner and the spring force at that corner changes by roughly the wheel rate, before geometry and damping complicate the picture.
Treat it as a starting point. It uses total corner weight, not sprung corner weight, and it ignores tire stiffness and damping. Real tuning still needs a test drive, and ideally a shock dyno and track or road data, before you buy springs on the strength of one number.
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References
- Penske Racing Shocks. Spring Rate in Racing Suspension: Wheel Rate, Motion Ratio, and How to Calculate What Your Tire Actually Feels (motion ratio as spring displacement divided by wheel displacement, wheel rate equals spring rate times motion ratio squared under that definition, worked 400 lb/in example). Accessed October 24, 2026.
- Penske Racing Shocks. Natural Frequency, Ride Frequency, and CPM in Race Car Suspension (ride frequency from wheel rate and corner mass, corner mass as corner weight divided by 386 in/s squared, worked 600 lb and 300 lb/in example). Accessed October 24, 2026.
- Call to Grid. Spring Rate Calculator: What It Is and How It Is Calculated (motion ratio as wheel movement divided by spring movement, spring rate equals wheel rate times motion ratio squared, 1 N/mm equals 5.7 lbs/in). Accessed October 24, 2026.
- Units Converters. N/mm to lbf/in (1 N/mm equals 5.7101 lbf/in, 1 lb/in equals 0.175127 N/mm). Accessed October 24, 2026.
- Best Springs. Spring Constant of a Car Suspension: Definition, Formula, and Selection Guide (ride frequency as 1 divided by 2 pi times the square root of stiffness over mass, passenger car band near 1.0 to 1.5 Hz). Accessed October 24, 2026.
- Mark Ortiz, Chassis Newsletter (via Rejsa.nu). Combined spring rate of suspension and tire (system rate from suspension rate and tire rate in series, and why a compliant tire lowers the combined frequency). Accessed October 24, 2026.
- The Ranger Station. How To Calculate Motion Ratio and Wheel Rate For A TTB Suspension (wheel rate equals spring rate divided by motion ratio squared under a wheel-travel definition, worked 430 lb/in example). Accessed October 24, 2026.