At any car meet, you’re likely to see more than one model whose wheels arches are completely filled with a wheel much larger than the original spec of the car. Before you make these modifications yourself, there are a number of things to think about if you want to change the size of your wheels.
The cost of running your car could change, for example; bigger wheels are heavier, and will push up your fuel bills. The make of wheel you choose is also a factor, while they may be the same size, some brands are heavier than others and tyres are designed to perform differently in various areas. Because we know the need for speed is inside every petrol head, we’re answering the question, how does wheel size affect speed?
(Below we’ve assumed that every other aspect of the car has remained stock apart from the wheels.)
Larger wheels, better grip
In physics, the force of an object is equal to its mass multiplied by acceleration, so says Newton’s Second Law. Simply put, bigger wheels will result in a decrease in the driving force of the wheel, which translates to a decrease in acceleration.
The car’s engine will need to work harder to turn larger wheels, thus be under more strain which will also decrease the overall acceleration of the car. These larger wheels will also result in a lower fuel economy as the engine is working harder to compensate for the size.
Because cars speedometer and gears are delicately calibrated to the entire diameter of the wheel and tyre combined, the size of the tyre needs to decrease as the alloy size increases. To compensate for this, the tyre sidewall needs to be stronger leading to a decrease in comfort and a harder overall ride.
Smaller wheels, better ride quality
Decreasing the size of your wheels – while perhaps not the coolest look – can actually increase your car’s performance and handling. With lighter wheels the suspension doesn’t have to work as hard, meaning the ride quality will increase, along with the response to steering inputs. A lighter car can also mean a heavier wallet – fuel economy can increase with lighter tyres.
Most base models will usually be fitted with the smallest wheels and tyres.
Is it worth choosing between looks and performance?
Obviously, the wheel size on your car needs to match up to what you are asking of the car and, ultimately, this will dictate the wheel size that is right for you. If your only concern is curb-appeal, then you may favour bigger wheels at the expense of ride quality and cost. If you’re mainly a city driver, and you know you regularly use under-maintained roads full of potholes then smaller wheels are the wiser choice, with larger tyres – your suspension (and your back) will thank you for it!
If you’re considering changing the wheels on your car it’s vital you research the recommended size and load ratings. Check your handbook for these and don’t exceed them. The wrong size wheels can cause major problems to your car’s suspension, among other things, and lead to hefty repair bills.
Finally, don’t forget to check with your insurer. Most companies won’t mind modifications being made, but not checking with them can invalidate your policy.