Improve your Track Car: Reducing Unsprung Weight
When chasing time at the track, weight reduction is vital in helping you reduce your lap times. In this article, we'll talk about ways you can reduce your unsprung weight to yield a better handling car and enhance your suspension system, all while lowering the stresses placed upon it.
Unsprung, Sprung and Rotational Mass
A car's weight can be divided into 2 categories, Sprung or Unsprung mass. Sprung weight is everything that is held up by the suspension. This includes the frame, body, engine, driver, seats, even the windshield. Unsprung weight is the mass of everything not held in suspension by your dampers, so the axles, wheels, brakes, wishbones, control arms and even the damper rods, lower bushes and fixings.
Rotational mass is the weight of objects that are spinning, like the flywheel, brake rotors, and wheels. Due to the spinning motion, the weight of these components is effectively increased.
Lowering unsprung weight can have a noticeable effect on your suspension, improving the response from the shock absorbers and keeping tires in contact with the ground more efficiently.
Studies have shown that in optimal conditions, losing 1lb of unsprung mass is equivalent to up to 20lbs of overall sprung weight reduction. In real-world scenarios, this likely is nearer to 6-10lbs but unsprung, and rotational masses should be prioritized as part of your weight reduction activities.
Decreasing the weight of a car will also help your power to weight ratio. It's literally a win-win situation.
Driver's Comments on Unsprung Weight Reduction
Many drivers report a more positive handling response and a definite improvement when reducing unsprung mass. You want to keep unsprung weight to as little as possible. This minimizes the momentum and energies that your suspension has to counter. In effect, it can make your shocks more sensitive.
How to reduce unsprung mass
Simply, we want to lessen the weight of unsprung components as much as possible without sacrificing strength and practicality. Here are several areas to concentrate on:
Road tires are heavy. They are designed to last for thousands of miles of relatively benign paved surface driving. To allow drivers to carry different loads they are also built with heavy steel wire banding and thick rubber.
With track cars and racing vehicles, we operate in a much more specific set of situations and we don't expect as long a life out of consumables like the tire. It's well worth then selecting a tire that is as lightweight as possible if your championship rules allow. If you're using a control tire then there are other ways to shed weight.
Also, consider reducing the wheel/tire diameter. Dropping down even just 1 inch could save several pounds per corner, returning fantastic acceleration and steering response.
As with tires, road cars have rugged steel or alloy wheels that are capable of taking a beating on rough roads. Primarily, manufacturers also go down this avenue because they are cost effective.
Lightweight alloy or even magnesium wheels are available that are also stronger than standard road wheels. They may not be as cheap as fitting factory rims, but you'll be improving your unsprung/sprung weights and rotational mass.
If you use your track day car on the road, or as a daily, it might be wise to keep your standard wheel/tire combo and fit those for normal driving. It'll keep your track day wheels in better condition and give you the option of running non-road legal performance rubber.
Nuts and Bolts
Literally, every ounce of weight reduction will benefit your lap times, so where possible, consider replacing fixings for lighter alternatives. For example, aluminum bolts can be used instead of steel ones on spoilers and wings. You may even be able to replace the fixing altogether by using adhesives or rivets.
Where you've fitted aftermarket lighting, use as short a fixing as possible. You only need 1 or 2 exposed threads for it to be safe, so cut down those bolts. Swapping to Allen bolt heads or cap headed bolts over traditional hex headed fixings will further save weight.
Titanium drilled head bolts and nuts are also available and are extremely lightweight whilst offering excellent corrosion resistance. The only downside is these are more expensive than ordinary parts.
For safety, when replacing nuts and bolts for mild steel ones, ensure you use a matching tensile strength, especially for any crucial fixings that endure significant forces.
Altogether, utilizing titanium or alloy fixings can add up to several pounds of weight reduction.
Even the lug nuts attaching the wheels to the axle can be lightened. We stock Works' Light Weight lugnuts that are available for any car running 12mm x 1.50mm or 12mm x 1.25mm studs and a 60 deg tapered seat on the rim (such as Team Dynamics, Enkei, D-Force, AME, SSR, Volk and most other popular aftermarket wheel manufacturers).
Lighter lugnuts also reduce rotational mass and when you consider you have at least 16 of these fitted on cars, the weight saving is multiplied.
The lower part of the suspension system factors into the total unsprung weight of your track car. Choosing a coil-over such as those from Fortune Auto or Yellow Speed will reduce weight where possible thanks to the use of extensively tested, precision, lightweight alloys. This redoubles the suspension performance and will give excellent handling and damping. These are a must for any serious track day enthusiast or gear head.
Brake calipers and rotors can further lighten your unsprung weight. Billet calipers are available that reduce weight by up to 25%. They are 20% stronger and offer superior braking force. The alloy caliper dissipates heat well too!
Think about combining your lightweight brakes with drilled & slotted rotors. These further enhance the brakes, helping you stop quicker and more aggressively whilst lessening the effects of brake fade.
Put your car on a diet
Grab yourself a decent set of digital scales and start stripping out the weight. Using our above suggestions, you'll make life easier for your suspension components and shave time off your laps. Handling will be improved and you'll have more consistent feedback from your car.