Colin Chapman, founder of Lotus, was responsible for one of the most quoted pieces of automotive wisdom ever uttered. “Simplify,” he said, “and add lightness.” It sounds like the kind of thing that gets embroidered on cushions. It is also, when applied to a classic car, one of the most effective performance modifications available and one that requires no specialist equipment, no engine work, and in many cases costs nothing at all. Performance tuning on a classic car is not exclusively about what you add. Sometimes the most significant gains come from what you take away.
Why weight matters
The relationship between weight and performance is straightforward and unforgiving. Every kilogram of mass in a car requires energy to accelerate, energy to stop, and energy to change direction. Remove that mass and the same engine produces more acceleration, the same brakes produce more deceleration, and the same suspension produces more agile handling. The relationship is not linear either. A lighter car puts less load on its tyres in cornering, which means more grip is available for actually going around the corner rather than just keeping the car upright. That lighter car also puts less stress on its brakes, its tyres, its wheel bearings, and its drivetrain components, which benefits reliability as well as performance.
Chapman understood this before most of his contemporaries and built Lotus cars around the principle with a thoroughness that occasionally alarmed his customers. His cars were light, fast, and not always possessed of the structural margins that made other manufacturers more comfortable. The principle, however, was sound. A car that weighs less needs less power to achieve the same performance, less braking effort to achieve the same stopping distance, and less grip to achieve the same cornering speed. This is why the original Lotus Seven, with a 750cc engine producing perhaps 35bhp, could embarrass cars with three times the power on a twisting road.
Where the weight is on a classic car
Before removing anything it is worth understanding where the weight actually is and which of it matters most. Not all weight is equal from a performance perspective. Unsprung weight, the mass of components that move with the suspension rather than being sprung by it, has a disproportionate effect on handling compared to sprung weight. Lighter wheels, lighter brake components, and lighter suspension parts all improve the suspension’s ability to follow road surface changes accurately. A kilogram saved from the wheel is worth considerably more than a kilogram saved from the boot.
Rotational mass is similarly disproportionate. Components that spin, such as wheels, brake discs, and flywheels, require energy not just to move forward but to spin up. Reducing rotational mass improves acceleration responsiveness and reduces the energy required to change speed.
What to remove: the sensible approach
There is a spectrum between sensible lightening and reckless stripping. At one end is removing the spare wheel for a track day. At the other end is removing all the sound deadening, the heater, the door trims, the passenger seat and the rear seat for a dedicated competition car. The correct position on that spectrum depends entirely on what the car is for. This guide covers the sensible end of the spectrum, aimed at road cars being improved for more enjoyable everyday use rather than competition cars being stripped for ultimate performance.
The spare wheel and tools
The spare wheel on most British classics of the 1960s and 1970s is a full-size steel wheel with a tyre, typically weighing somewhere between 15 and 20 kilograms. Removing it for a track day is obvious. For road use, removing it entirely is a personal risk assessment. The alternative of carrying a can of tyre sealant and a portable compressor is lighter, takes up less space, and will deal with a simple puncture, though it will not help with a more serious tyre failure. If you regularly use the car on long journeys in remote areas, keep the spare. If you mostly use it locally and have roadside assistance cover, this is a worthwhile saving.
Unnecessary equipment
Classic cars accumulate equipment over their lifetimes that was either added by previous owners or was standard equipment that no longer serves any purpose. The previous owner’s collection of tools under the boot floor that has been there since 1987. The full-size hydraulic jack that came with the car and weighs eight kilograms. The collection of tapes, oils, spare parts and emergency equipment that has slowly colonised the boot. None of these items is making the car faster. Walk through the car methodically and weigh what you find. The results are frequently surprising.
Lightweight wheels
Replacing steel wheels with lightweight alloys reduces both overall weight and unsprung weight, which improves both performance and handling. The weight saving from a good set of alloy wheels over original steel items can be significant, sometimes 3 to 5 kilograms per corner on an older car with heavy original steel wheels. The improvement in steering response and ride quality is often noticeable immediately. On a car used both on road and track, this is one of the most cost-effective modifications available because it improves multiple aspects of the car’s behaviour simultaneously.
The caveat is originality. On a car being maintained in standard specification, alloy wheels are a modification that changes the appearance significantly. Replica steel wheels in period styles are available for some models and provide a period-correct appearance while sometimes being lighter than the originals. Check the offset and centre bore carefully for any wheel being fitted to a classic car, as incorrect offset changes the scrub radius and can create handling issues and accelerated wheel bearing wear.
The battery
The standard lead-acid battery on most classics is heavy, typically 15 to 20 kilograms, and sits at one end of the car contributing to the weight distribution. Modern AGM batteries offer equivalent or better performance at reduced weight. Lithium iron phosphate batteries, now widely available for classic car applications, can reduce battery weight to 3 or 4 kilograms from a standard 18 kilogram lead-acid unit. The cost is significantly higher than a standard battery but the weight saving is one of the largest single component savings available without structural modification. If a lithium battery is fitted, a compatible charging system must be used as standard chargers can damage lithium batteries. Our voltage regulator guide covers the charging system in detail.
Exhaust system
The standard exhaust system on most British classics is heavy cast iron or thick mild steel. A stainless steel replacement system is typically lighter, lasts considerably longer, and often improves gas flow marginally. The weight saving is modest, perhaps 3 to 5 kilograms depending on the car, but it is saving unsprung and low-mounted weight which is disproportionately beneficial. A stainless system also removes the weight of the rust that accumulates on a mild steel system over the years, which on an older car can be considerable in itself.
Lightweight flywheel
The flywheel on a classic car engine is a substantial cast iron component designed to smooth the power pulses from a relatively slow-revving engine at a time when the alternative was an uncomfortably lumpy idle. A lightened or uprated flywheel reduces rotational mass and improves the engine’s ability to rev freely, making it more responsive to throttle inputs and improving the character of the engine at higher revs. The trade-off is a slightly lumpier idle and reduced ability to pull from very low revs in high gears. For a car used for spirited driving rather than relaxed cruising, this is usually a worthwhile exchange. The job requires the gearbox to be removed, which makes it one for a full engine rebuild or gearbox-out service rather than a standalone modification.
What not to remove
There is a point at which lightening a road car becomes counterproductive or dangerous. Sound deadening makes a car bearable to drive for extended periods. Remove it entirely and the car becomes exhausting to use at motorway speeds. The heater is not a luxury in Britain. A car with no interior sound insulation and no heater is a car that will spend a lot of time in the garage between October and April, which defeats the purpose of making it faster. The windscreen and windows are structural on most classic monocoques and their removal for a road car is neither legal nor sensible.
Seats are tempting targets for weight reduction but a lightweight bucket seat on a road car is a more complex modification than it appears. The seat mounting must be correct for the seat to provide protection in an accident, which may require custom fabrication of the mounting points. The absence of a passenger seat is also, for most owners, a significant practical limitation. Remove the passenger seat for track days if you want, but consider carefully before making it a permanent modification on a road car.
The weight budget
A useful exercise before starting any weight reduction programme is to establish a weight budget. Weigh the car at a public weighbridge before and after modifications. Weigh individual components before removing them. This gives you an accurate picture of where the weight is, how much you are actually saving with each modification, and whether the modifications are having the effect you expected on the car’s behaviour.
Many owners who go through this process discover that the most significant weight savings come from the simplest places. The accumulated tools, equipment and junk in the boot. The heavy original wheels. The battery. These require no specialist skills and no irreversible modifications. They are also the modifications that can be reversed instantly if the car needs to go back to standard for a show or a sale.
Adding lightness versus adding power
The classic car enthusiast’s instinct when seeking more performance is usually to look at the engine. A bigger carburettor, a better exhaust, a hotter camshaft. These are all valid modifications — our SU carburettor guide and electronic ignition guide cover two of the most common and cost-effective engine modifications in detail. But it is worth understanding the relationship between power and weight before committing to expensive engine work. Adding 10bhp to a car that weighs 900kg improves the power to weight ratio by roughly the same amount as removing 90kg from the same car. Removing 90kg from most British classics is significantly cheaper than adding 10bhp, and it improves not just acceleration but braking, handling, tyre wear, fuel consumption, and the loads on every mechanical component in the car simultaneously.
Chapman was right. Simplify, and add lightness. It works on a racing car and it works on a classic MG or Triumph on a Sunday morning in the Welsh hills. The principle does not care about the context. Weight is weight, and less of it is always better.