Suspension & Handling Calculators

From Spring Rate to Wheel Rate

A spring’s rate isn’t what the wheel actually feels. The suspension’s motion ratio – how much the wheel moves versus how much the spring compresses – changes that, which is exactly what the Suspension Motion Ratio Calculator works out from arm lengths or measured travel.

Wheel rate equals spring rate times the motion ratio squared, so a motion ratio under 1, common on most double-wishbone and strut setups, always softens the spring’s effective rate at the wheel.

That wheel rate, combined with the car’s sprung weight at each corner, sets the ride frequency, which is the number most tuners actually target rather than a bare spring rate in lbs/in.

Sizing a Shock’s Damping Force and Its Physical Length

A shock doesn’t just resist motion, it resists motion at a specific rate that changes with shaft speed, which is what the Shock Force Calculator adds on top of spring preload to find total force at compression and rebound.

Compression damping controls how fast the wheel moves up into a bump, rebound controls how fast it comes back down, and the two are tuned separately because a wheel that rebounds too quickly loses contact with the road just as easily as one that compresses too harshly.

None of that damping curve matters if the shock physically doesn’t fit, which is the separate problem the Shock Length Calculator solves. A shock’s collapsed length has to clear full bump without the shaft bottoming internally, and its extended length has to stop the suspension at full droop before anything else in the geometry runs out of travel first – lift, offset, and mount type all shift both numbers.

Cross Weight and What Racers Call Wedge

Corner weight is what four individual scales read under each tire, and cross-weight percentage – the number the Corner Weight Calculator centers its output on – adds the right-front and left-rear corners together and divides by the car’s total weight.

A car above 50% cross weight is said to be carrying wedge, and below 50% it’s running reverse wedge, terminology that comes directly out of oval-track and autocross setup work.

Adding wedge tightens a car’s handling in one turn direction and loosens it in the other, which is exactly why it’s used deliberately on ovals that only turn one way, and treated as something to neutralize back toward 50% on a road course that turns both directions.

Static weight distribution and cross weight are different adjustments entirely – jacking a corner’s ride height changes cross weight without touching the car’s left-side or rear weight percentages, which is why the Axle Weight Distribution Calculator and the Corner Weight Calculator answer two genuinely separate questions about the same car.

Breakover Angle and the Belly of the Vehicle

Approach and departure angles cover what happens at the front and rear bumpers, but breakover angle covers the middle – whether the underside of the vehicle clears a ridge or crown between the axles, which is what the Breakover Angle Calculator is built to check. The standard formula, traceable to SAE J689, is breakover angle equals twice the arctangent of twice the ground clearance divided by the wheelbase.

Wheelbase works against breakover in a way that surprises a lot of buyers: stretching a chassis without raising the belly makes the number worse every time, which is why a longer, more “capable-looking” truck can actually have a worse breakover angle than a shorter one with identical ground clearance.

Deflating tires for traction reduces actual ground clearance in the moment, which is why a breakover angle that looked comfortable on paper can still end in a high-centered vehicle on the trail.

Unsprung Weight and Why It Costs More Than It Weighs

Unsprung weight is everything the springs don’t support – the wheel, tire, brake components, and the portion of the suspension arms and hub that move with the wheel rather than with the chassis – and the Unsprung Weight Calculator totals that mass per corner.

What makes it matter more than its raw number suggests is the ratio between sprung and unsprung weight at each corner: a heavier unsprung mass has to be accelerated up and down by the spring and damper on every bump, which both degrades ride quality and momentarily reduces the tire’s contact force on rough pavement.

That same mass, combined with the spring and tire rate at the corner, sets a wheel hop frequency – the rate at which an unsprung assembly wants to bounce on its own, largely independent of the car’s main ride frequency.

A corner where that hop frequency lands too close to a bump input the car actually encounters is where unsprung weight stops being an abstract spec and starts being a driveability complaint.

Frequently Asked Questions

Does a stiffer sway bar make the ride harsher?

Not directly. A sway bar only engages when the car rolls, meaning one wheel moves up while the other moves down, so it has no effect on straight-line bounce frequency over bumps hit by both wheels together. Ride harshness on a straight, even road comes from spring rate and damping, not bar stiffness, which is why a stiffer bar can sharpen cornering without noticeably changing how the car rides over an isolated pothole.

Why does more caster make the steering heavier?

Positive caster creates a steer-centering effect, where the greater the caster angle, the stronger the wheel’s tendency to return to center after a turn. That same self-centering force is felt at the wheel as steering effort, and it’s also what makes a car with more caster feel more planted and stable in a straight line at speed.

Does adding negative camber always improve grip?

Only in the corner. Negative camber increases the tire’s usable contact patch while the car is leaned over into a turn, which is why it’s added for cornering grip in the first place. That same negative camber reduces contact patch, and with it straight-line grip and braking performance, when the car is upright, so any camber setting is a trade-off between the two conditions rather than a one-directional gain.

What does cross weight or “wedge” actually do to a car?

Raising the ride height at one corner adds weight to that corner and to the corner diagonally opposite it, while the other two corners lose weight, without changing the car’s overall left-side or rear weight percentages. On an oval that only turns one direction, deliberately running wedge above 50% cross weight can tighten the car through that turn, while a road-racing setup usually targets something close to 50% so the car handles evenly in both directions.

Why does wheelbase hurt breakover angle instead of helping it?

Breakover angle depends on ground clearance relative to how far apart the axles are, so stretching the wheelbase without raising the vehicle’s belly spreads that same clearance over a longer span and makes the angle smaller. A longer truck with identical ground clearance to a shorter one will almost always have a worse breakover number, which is why wheelbase and ground clearance have to be considered together rather than ground clearance alone.

Is unsprung weight really worth worrying about on a street car?

It’s most noticeable on rough or broken pavement, where a heavier wheel-and-brake assembly has more trouble staying in contact with the road between bumps than a lighter one would at the identical spring and damper settings. It matters less on a smooth track surface, which is part of why unsprung weight reduction shows up so heavily in road-racing and autocross builds specifically, rather than being an across-the-board priority for every car.

What’s the difference between a shock’s compression and rebound force?

Compression force resists the wheel moving up into the chassis during a bump, and rebound force resists the suspension extending back out afterward, and the two are tuned to different targets on purpose. Too little rebound control lets the wheel spring back and momentarily lose contact with the road, while too much compression force transmits sharp impacts straight into the chassis instead of absorbing them.