MODIFIED CAR SAFETY
by "Bad Ass" Bre
A 5-point harness is much better than a stock seat belt. 
One of the most important aspects of car modification is ensuring that your car can be used safely on public roads. Unfortunately, this is often one of the most overlooked aspects of modifying your car. A modified street car must be safe not only for you as the drivers, and your passengers, but it must also be safe for other road users, including pedestrians. In fact, once you decide to modify your car you need to take responsibility for the safety of other road users that you may come into contact with whether you're in the right or not. Remember a motor car can easily be used as a murder weapon and by modifying your car; you're turning it into a more lethal weapon. Therefore you need to use your car responsibly and take responsibility for the consequences of your actions, which begins with improving your car's safety.
There are four important aspects of car safety that you need to take into consideration when modifying your car:
- Car handling, which we cover in suspension tuning.
- Car grip, which is dependent on the condition of your tires and suspension.
- Car brakes.
- Car restraints, such as seat belts and roll cages.
Another important aspect of car safety is driver awareness and developing a responsible driving style, which boils down to being alert on the road and driving responsibly. You can also improve your driving by taking advanced driving classes, more so if you're intent on modifying your car, though an advanced driving class is not a license to drive recklessly on public roads.
On the car itself, the two most critical elements of car safety are undoubtedly the brake system and the tires. The car brakes can only be as effective as the car's grip allows it to be, and the tires are responsible to the car's grip. Furthermore, a large proportion of the forces responsible for accelerating and decelerating the car, as well as the forces and torques that provide the control and stability of the car act on the tires, and are dependent on the grip provided by the tires. For this reason we thought it best to discuss upgrading the tires and shock absorbers in this section on car safety, although we do discuss tires and shock absorbers in our section on suspension tuning. In this section, we will thus discuss improving car safety through upgrading your brakes and upgrading your tires.
However, there are two other areas of car safety that we need to consider: roll cages and seat belts. Roll cages are essential on race cars, for obvious reasons but they are not legal on road cars in some states. If they are legal in your state, fitting a roll cage would be a highly recommended safety mechanism for drivers and passengers but they do not protect other road users and do not absolve you from driving responsibly. If you are going to fit a roll cage, you should have it built and installed by a qualified professional.
Improving your seat belts, on the other hand, can be done yourself. A four- or five-point harness is more effective than the standard two-point harness that is used on standard cars. However, fitting a four- or five-point harness often requires fitting an aftermarket seat that makes provision for two shoulder straps, and requires secure multi-point mounting. Fitting aftermarket bucket seats is covered in our section on car styling so we won't repeat that here. Instead we'll start with upgrading your tires and shock absorbers ...
TIRE UPGRADES
Tires and shock absorbers play an important part in road grip, and it is road grip that ultimately allows the car to be accelerated and decelerated while also providing predictable handling and stability. As such road grip in an important element in car safety. Upgrading your brakes, for example, is a useless endeavor if your car has little grip due to worn tires or worn shock absorbers. This is obvious as worn tires with low grip may lock up and skid when you apply brakes, and the wheels need to be able to rotate to slow the car down. Similarly when the tires are bouncing through the air when you brake over bumps, road grip is lost and braking becomes ineffective.
A simple safety precaution would be to check your tires' thread depth and tire wear, but on modified cars with extra horse power, the grip provided by standard tires may not be sufficient even if the tires are in good condition. On modified cars you may want to fit larger or wider tires that provide a larger contact area with the road, or low profile tires that have shorter, less flexible sidewalls and provide more precise handling. You may also want to fit a tire that has a higher maximum speed rating and higher load rating. If you do opt for larger or wider tires, you will need to upgrade your shock absorbers (or dampers as they are also called) and possibly your springs to handle the increased unsprung weight.
But first you need to know what tires your car has, what tires are suitable for your car, and the effect of changing your tires.
UNDERSTANDING TIRE CODES
All tires have a standardized alpha-numerical code that is molded on the sidewall. This tire code indicates the width of the thread area, the height of the sidewall relative to the width (also known as the aspect ratio), the construction type of tire, the size of the rim the tire will fit, the tire's load carrying capacity (or load index), and the tire's speed rating. A tire with the code 205/55 R 15 91V, for example, has a thread width of 205 mm and an aspect ratio of 55%. The aspect ratio indicated the height of the sidewall as a percentage of the thread width. In this case the sidewall height is 55% of 205 mm, or 112.75 mm. The 'R' in 205/55 R 15 91V indicates the construction type of tire, and can be 'R' for radial, 'B' for cross-ply with belted bias, and 'D' for cross-ply with diagonal bias, though B and D are becoming increasingly rare. Radial tires are better for traction and grip. The '15' in 205/55 R 15 91V indicates the size of the rim (in inches) that the tire is designed for, which is 15 in. in this case and the '91V' indicates the load carrying capacity and the speed rating as indicated below in Table 1 and Table 2.
TABLE 1: TIRE LOAD INDICES
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TABLE 2: TIRE SPEED RATING
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The load index is the maximum weight each tire can carry. So, if your car weighs 2,000 Kg with 55% weight bias on the front wheels and 45% on the rear, then the front wheels should have a minimum load index of 88 as each front wheel would need to carry 550 Kg each (2,000 × 55% ÷ 2), assuming an even spread on the two front tires. Add another 500 Kg in weight and each wheel would need to carry an additional 125 Kg on average, which will require a tire with a load index of 95!
The speed rating indicates the maximum speed that the tire can safely sustain for a ten minute period. Thus an H rated tire is good for up to 130 mph but not for more than 10 minutes at 130 mph! In other words, if your modified race car has a top speed of 130 mph, you'd be better off with a V rated tire capable of up to 150 mph than an H rated tire. Z rated tires are rated for over 150 mph but are being replaced by W rated tires (for up to 168 mph) and Y rated tires (for up to 186 mph).
WIDER OR LARGER TIRES?
One method of improving tire grip is to increase the contact area between the tire and the road. This can be accomplished by fitting a tire with a larger circumference (i.e. a larger or oversized tire) or fitting a tire with a wider thread area. A tire with a larger circumference has a larger longitudinal contact area, which will provide better straight line stability but will affect overall gearing and will increase the ride height and the car's center of gravity, and will also increase the rolling mass the bakes will have to overcome. There is nothing that can be done to rectify the increased ride height and center of gravity; but the drivetrain gearing can be rectified by fitting a differential with a higher diff ratio. The increased rolling mass that the brakes need to overcome can be rectified by upgrading the brakes. However, even though a larger tire may be able to fit under the wheel arches when the car is static, it may knock against the body or suspension components when suspension travel occurs and during cornering. Stiffer suspension springs with less travel and stiff shock absorbers may compensate for the tire knocking against the body during suspension travel but will result in a harder ride.
Wider tires, on the other hand, have a wider contact area but will need to have a smaller aspect ratio to retain the overall circumference of the wheel. Thus going from a 185/60 R 14 91H tire to a tire that is 215 mm wide will require a tire with an aspect ratio of 50% as a 185/60 R 14 91H tire has a sidewall height of 111 mm (60% of 185 mm) while a 215/50 R 14 91H will have a sidewall height of 107.5 mm. A tire with a similar overall circumference to the standard tire will not interfere with the body or suspension parts during suspension travel but will be slightly heavier, and will increase the rolling mass that the brakes need to overcome, but not to the same extent that larger tires do. However, wider tires are also prone to knocking against the body or suspension parts during cornering. This can be overcome by fitting a wider wheel arch and fitting a spacer on the wheel hubs to allow the wheels to be mounted further away from the suspension parts. This will, however, place greater stress on the front wheel bearings and on the steering mechanism.
LOW PROFILE TIRES
A tire with a low sidewall is referred to as a low profile tire. These tires provide more precise cornering as the lower sidewall has stiffer sidewalls with less inherent elasticity. This means that the tire will suffer less deflection during cornering and will provide better lateral stability. However, reduced flexibility is not ideal for handling in the snow where flexibility is desired. In addition, the stiffer sidewall will result in a harder ride, especially over bumps, and will transmit more road noise. There is thus a bit of compromise involved when deciding on low profile tires but, under normal road conditions, the lateral stability provided by low profile tires make them a safer option. A low profile tire can easily be achieved by fitting a larger diameter rim. Thus, by going from a 14 in. rim to a 17 in. rim you can fit a tire with a sidewall that is approximately 1 ½ in. (38.1 mm) lower. This means that if your standard tire is a 185/60 R 14 91H tire, which has a sidewall height of 111 mm, you can fit a 185/ R 17 91H tire with a 74 mm sidewall (37 mm lower). If you fit a wider tire, your aspect ratio would also need to be less but your sidewall will heed to have the same approximate height.
Regardless of what size tires you fit, you check your tire pressure regularly to ensure optimal grip. With underinflated tires, the cars weight is concentrated on the tread near the sidewalls rather than being spread out across the full width of the tread. This causes the sidewalls to flex when the tire rolls and results in heat buildup in the sidewall. Excessive heat buildup and the constant flexing of the sidewall may lead to tire bursts! Overinflated tires are also prone to tire bursts as the air in the tire does heat up under normal conditions. If the tire is overinflated the normal heating of the air in the tire will increase the tire pressure further and may result in a tire burst. Overinflated tires also do not have the optimum tread contact and will give a stiff ride. You should also ensure that your wheels and tires are balanced and aligned correctly.
UPGRADING THE BRAKES
Improving and upgrading the brake system on a car is often the last item in a car modification project, yet it is the most important element in terms of driver and passenger safety, as well as the safety of other road users. It is essential that you upgrade your car brakes when you increase the engine power of your car as the more powerful and faster your car is, the more efficient your brakes need to be to stop your car in an emergency. The same applies when you increase the weight of your car by installing a heavy ICE (in-car entertainment) system for example. In most cases a standard brake system is sufficient for stopping a standard car but when you improve the car's engine power the brakes may not be sufficient to handle the extra hp and brake fade may occur. Fortunately, there are a number of things you can do to improve your brakes. These range from fitting larger diameter ventilated brake disks (rotors), fitting multiple pot (piston) calipers, fitting cross drilled or slotted brake disks, converting rear brake drums to ventilated brake disks, fitting a larger master cylinder, fitting braided brake hoses, and using brake fluid with a higher D.O.T. rating (and boiling point).
In this section we'll discuss some options related to improving your car brakes but before we continue please be advised that brakes are critically important safety equipment. If you are uncomfortable with working on brake components, have a qualified professional do the work for you. Also note that your brakes are only as good as the grip of the tires on the road. If your tires have little grip because of worn shock absorbers of the tires are too narrow, upgrading your brakes will be wasted. So make sure your suspension and tires are in good condition before embarking in a brake upgrade.
BRAKE DISKS (ROTORS)
Brake disks are far less prone to brake fade than brake drums but they are not immune to brake fade. Thus converting the rear drum brakes to brake disks will greatly reduce brake fade but there is so much more that you can do to your brake rotors to optimize your brakes. If you have solid brake disks, replacing them with ventilated disks will improve the heat dissipation characteristics of the disks. You could also have the ventilated disks cross drilled or slotted. The holes in cross drilled brake discs help disperse heat and further reduces brake fade while slotted discs help to de-glaze the brake pads, ensuring better friction between the brake pad and the brake disc but they will wear the brake pads faster. Of the two, slotted brake disks tend to perform better than cross drilled brake disks but they transmit more vibration though the steering wheel and are noisier. You should also note that slotted brake discs are directional, in other words, the slots must turn in a particular direction. Brembo brake disks, for example should be installed so that the end of the slot nearest the outer edge of the disc comes into contact with the brake pad first but this may differ with other disk manufacturers. Make sure which way the slots should rotate and install them correctly.
Another option is to fit larger diameter brake rotors. A larger diameter brake rotor reduces the braking effort as it gives the caliper more leverage to stop the disc rotating and allows the car to slow down much quicker without causing too much build up of heat. However, there are two factors that limit the diameter of disc that you can use: the size of the wheels; and the relocation of the brake calipers. The wheel size will limit the size of the rotors but wheel may also limit the placement of the brake calipers, especially if you are using alloy wheels. This is important as when you fit a larger brake disk, the brake caliper must be mounted further away from the wheel hub. Thus, when fitting larger diameter brake disks you need to ensure that you can mount the brake caliper and that there is sufficient clearance better the caliper and the wheel.
There are two disadvantages of fitting larger diameter disks though. Firstly, when you retain the standard brake calipers, the area of the brake disk that comes into contact with the brake pads remains the same. This will result in rust towards the centre of the disc that will not be removed by the brake pad when you brake braking. If you fit a larger brake caliper then you remove this problem. Another disadvantage is that a larger diameter brake disc will result in an increase in the car's unsprung weight, which can adversely affect handling.
BRAKE CALIPERS
Increasing the size of the brake caliper will also increase braking efficiency as a larger brake caliper will have larger brake pads with a larger friction area that will be in contact with the brake disk. The larger the friction area, the quicker the car will stop and less heat will be generated by the brakes. And less heat means less change of brake fade.
A similar effect can be achieved by fitting a multi-pot brake caliper. Most standard brake disks have a single pot caliper. These calipers have only one piston that presses the brake bad against the rotor. By fitting multi-pot calipers with more than one piston, the additional pistons apply more force to the brake pads without requiring more effort on the brake pedal. They also spread the force out over the brake pad. However, multi-pot brake calipers, such as four-pot calipers are often manufactured without dust seals. These are fine for racing applications and are not appropriate for road use. If you are using a multi-pot brake caliper on a modified street car, make sure that it has dust seals.
THE MASTER CYLINDER
The brake master cylinder is often overlooked when it comes to improving the brake system; however, fitting a larger master cylinder reduces the effort required on the brake pedal and reduces the pedal travel required to pump enough brake fluid into the pistons on the brake caliper. This is more significant if you convert from brake drums to brake disks, as the pistons in the brake calipers used with brake disks have a larger volume than the pistons in brake drums. They thus require more brake fluid to be pumped to the brakes, which can be accomplished by fitting a master cylinder with a larger bore diameter. However, the master cylinder must match the flange on the brake booster.
SPONGY BRAKES?
Finally, if you want to eliminate a spongy feel on the brake pedal, you could replace the rubber brake hoses with braided hoses. Rubber brake hoses tend to flex under pressure while braided brake hoses are a lot less flexible, resulting in a firmer pedal action and better brake response. However, the spongy pedal may also be caused by water contamination in the brake fluid. Brake fluid is not compressible but water and air are compressible, resulting in that spongy feeling. Replacing the brake fluid and bleeding the brakes will eliminate the spongy feeling.
Now we have all our brake components fitted but we're not quite done; we need to change the brake fluid, bleed the brakes and bed the brake pads in. Changing the brake fluid and bleeding the brakes are two similar processes. You bleed the brakes through the caliper nipples to remove air from the system while ensuring that the master cylinder reservoir does not run dry. When you change the brake fluid you bleed out the old brake fluid through the caliper nipples while again ensuring that the master cylinder reservoir does not run dry. You can use a turkey baster to remove some brake fluid from the master cylinder reservoir. This will reduce the amount of brake fluid that needs to pass through the system before the system is filled with clean fluid.
Bedding in the brake pads is another important process. Essentially, you want to put the brake pads through a heat cycle by increasing the temperature of the brake pads gradually and then allowing it to cool down. This can be achieved by performing about 30 light to medium brake applications of three seconds duration. Leave at about ¾ mile between each brake application. This will gradually increase the temperature of the brake pads without inducing thermal shock, and will mate the brake pad and disc friction surfaces. At the end of the repeated braking you should notice a little brake fade. Allow the brake pads to cool down by driving for several miles with little or no braking. Once proper cooling has been achieved, the system should maintain optimum performance at all temperatures.
(Credit to Custom Car US)
Upgrading your brakes to handle the extra power!
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