Tyre and Wheel Upgrades |
While your looking at upgrading your wheel options, then careful selection of tyres/tires needs to be considered. There are a number of different manufactures and performance application, the following needs to be considered in the equation:
- Tyre/ Tire Grip levels, especially in different weather conditions.
- Handling characteristics, are they easy to drive at the limit or will they suddenly lose traction the harder you push.
- Durability, will you get 10,000 miles out of them or will there last longer.
- Road noise, how will they perform on long journeys for normal driving.
- Availability and cost.
- Economy, are they good for your mpg figures and offer less rolling resistance.
Most car manufacturers have strict profit margins to reach and unless your driving a flagship or high performance model, then it is unlikely you will have the best rubber available. Also with continued tyre advances, new brands rise to the top for performance levels.
When looking at different tyre/tire constructions it is import to to take into consideration the environments these are designed for. Summer tyres designed for dry and wet roads will not have the same abilities as a snow tyre/tire in winter for example, as the rubber compound is designed to work at different operating temperatures. Most tyre tests follow a set criteria to gauge the classification: Grip, Handling, Durability, Road noise, Wear rates and the designed weather conditions they perform well in.
Racing Tyres/Tires or "slicks" as they are known have one ultimate goal, they are designed to have maximum available contact patch and ultimate grip. Due to the increased contact patch compared to road tyre/tires, it is possible to have softer rubber compounds which further increase performance capabilities. This could be a problem with Road tyres with grooves and slits on the tread pattern, as it will make the tyre/tire prone to blistering. Slicks will not deform as much as road tyres/tires under the heavy loads they are exposed to.
Due to the softer compound in the construction, wear rates dramatically increase and it is possible for well funded Race teams to go through many sets of tyres/tires at a Race meeting. Some sets will only last a few laps and are designed to give maximum traction in that time window, other designs incorporate harder compounds with a more endurance focused pursuit.
During varying weather conditions the introduction of wet weather slicks were designed to help combat aquaplaning and cut through standing water. These wet weather slicks normally have special chemicals and rubber composition to operate in the lower temperatures involved when the surface is wet. But caution must but be taken when the surface is drying as the rubber compound will quickly blister and deteriorate. Many driver will purposely drive through standing water and take the wet line to help save the tyres/tire in varying conditions.
Fitting larger wheels may seem like top of the agenda when first tuning your car, but careful consideration needs to be taken into account to get the right wheels for your car, let alone the optimum size.
Make sure that if you are going to increase the diameter of the wheels, that you also decrease the Tyre/Tire aspect ration, to keep the same gearing on the driven wheels. Smaller wheels will increase acceleration but hinder top speed, while larger wheels will decrease acceleration but give better top speed. Normally if this is the desired effect it is best done via the Gear Ration selection, especially for race applications.
When you want to increase the wheel size, you have to decrease the Aspect Ratio ( Tyre/Tire ride width divided height), as discussed the gearing on your car and also speedometer will change unless you follow these steps. Lowering Tyres/Tires aspect ratio will have the advantage of increasing the driving experience with a more performance responsive set up, because the sidewalls will be stiffer and less affected by flex under cornering loads.
Ultimately clearance is going to be the underlining issue when increasing wheel size, even if the aspect ratio is correct, wider wheels could be effected on full steering lock touching the bodywork.
For example a stock production car which left the factory with 15" Diameter wheels, will struggle to house 21" upgraded wheels. This is used as a extreme example, but wheel arch clearance will be compromised, with major body work including wheel arches having to be being rolled to take the larger wheels in some examples.
Another consideration will be the suspension geometry and mechanical set up, Ride hide, camber, toe, bump ect, will all have to be reviewed. From the extreme example above, the car will mostly likely bottom out (wheels hitting the top of the wheel arches) and probably lack the space for the wheels to turn fully. So a whole suspension redesign will mostly likely be needed, to even keep existing handling characteristics, let alone improve them.
Bear in mind that larger wheels will also likely increase unsprung weight if a light alloy,carbon or magnesium materials are not selected, this should be avoided as it will decrease the increased performance potential. Increased wheel size will let you fit larger braking systems though and some designs will also further cooling efficiency.
A term of "wheel stepping up" is a philosophy following minimal suspension revision, see the diagram below for a indication of the possibilities, with out major handling disadvantages.
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While standard alloys wheel options will always be lighter then steel constructions wheels, some designs may of been engineered for a budget to retain manufacturer's profits. Fitting specifically designed lightweight performance wheels will reduce the unsprung mass of the car as well as increasing the strength of the wheel, they have many benefits:
- More responsive steering.
- Improved vehicle dynamics and balance.
- Stronger construction, especially for performance driving.
- Improved economy due to less mass.
- Better brake cooling, depending on design.
We have learned that there are advantages of fitting different tyre applications to your car and they are one of the most important upgrades available. So apart from fitting wider tyres with lower aspect rations. What other reasons are there to invest in new wheels?
One of the greatest advantages of fitting a new wheels (apart from the upgraded rubber), is selecting a lighter wheel. A lighter wheel will decrease the unsprung weight of the vehicle. Unsprung weight can include wheels, tyres, brakes and some suspension components, if you jacked the car up it would be any weight not suspended by the chassis.This will directly increase the cars ability to turn in and increase steering precision.
Unsprung weight will affect your car's ability to corner, accelerate/brake and also it's ability to deal with different road conditions. When a car suspension is subjected to changes in the road, the suspension, wheels and tyres have to accelerate rapidly up and down to make sure the wheels stays in contact with the road. If the wheel can not do it's job, not only will handling be affected, but vibrations will be transmitted into the car's cabin, resulting in a more harsh ride.
If you have a heavy wheel, this will decrease your car's ability to respond to these varying road conditions quickly enough. You could imagine entering a sharp bend, heavily on the brakes. If you hit a bump or uneven patch of road, this could unsettle the car and cause you to miss the apex or worse still not make the corner. Also if the wheels can not keep in contact with the road, handling performance will be sacrificed.
With lighter wheels the cars ability to accelerate will increase as it will have less mass to be turned by the engine. Also braking efficiency will increase as alloys and other materials used in their construction are better conductors of heat and will increase the heat dissipation of the braking system. This will result in reducing brake fade and as the wheel design is focused on performance, normally also a more airflow friendly design is used to help cool the brakes.
Careful consideration will need to be taken before embarking on a new set of wheels, especially checking that your desired design is allowed in your chosen Motorsport Category. As there is a number of different materials in constructions including Alloy metals, magnesium and even Carbon Fiber. But with most higher quality material, the price will rise and it all comes down to the goals and objectives of the Upgrade.
