When building or modifing a car, the suspension rates used can have a dramatic effect on the response of the vehicle, whether you are looking for a compliant ride in a road car or ultimate road-holding for a race car.
This section of the AC Parts web site includes some calculator utilities that you can run from within your browser to determine the spring rate of specified components as purchased or fitted to your car.
Torsion bar suspension uses a length of steel that is fitted into the suspension in such a way that the linkage applies a twisting force at one end of the bar, with the other end being fixed. The thicker the torsion bar, the stronger the resistance to twisting, hence a higher - or stiffer - spring rate.
Choices for uprating torsion bars are limited due to the different vehicle applications for their use. Mostly, they appear as an integral component in the rear suspension of modern hatchbacks, with few alternatives for upgrades available. Particular cars are catered for by certain suppliers, such as Harvey Bailey suspension kits for the Alfa Romeo 75 range.
A coil spring appears as its name suggests, with spring steel wire being wound into coils. In operation, the suspension compresses the spring, which closes up the coils under pressure. The effect actually translates into a twisting force on the wire of the coil, which you can imagine if you think of the wire being stretchd out in a line again. The thicker the steel wire, the higher the spring rate. This is also affected by the diameter of the actual coils, with a larger coil diameter providing increased leverage over the springs in creating a twisting force, which results in a lower spring rate.
Coil springs are available from specialist manufacturers in a whole range of sizes and rates, with various diameters, lengths and wire thickneses for many different fitments. Variations in coil spring design may include features such as tapered wire diameters or differing windings when creating the coils. These can result in a variable rate suspension design, where that is suitable for a particular vehicle.
Also known as 'cart springs' from their early use on the Horse and Cart!
Leaf spring suspension consists of one or more flat steel leaves bound together, with one end being fixed to the chassis and the other generally
attachd to a moveable link or spring hangar. The axle load is directed to the centre of the leaf spring, causing it to bend. The amount of flex
will depend on the thickness, lengths and number of leaves in the spring pack.
Generally viewed as a low tech suspension design, leaf springs can be made to work extremely well in certain suspension configurations, such as the rear suspension of a Group 4 Rally Escort, with four-link bars, panhard rod and 'slipper' type springs.
Other than for certain models, there is little choice available for uprated or modified leaf spring components. Longer spring hangers may be seen on vehicles that want a raised ride height, and extra leaves or spring assisters may be added to some configurations.
Note that these calculators require the use of JavaScript, so may generate warnings in your browser. Please be assured that there is no security risk in using the spring rate calculators.
Spring rate calculators provided for information purposes only.