Tyre Upsizing

Tyres are the most amazing part of each car, as their small surface contact area with the ground, each the size of a postcard, belie their tremendous effect on the car's comfort and performance. In fact, to state that the tyres are the most important part of each vehicle would not be entirely false. Therefore, the changing of tyres is seen by some owners as the simplest method of upgrading the performance of their cars. Some sceptics might ask on the need to change the tyres that come factory equipped, as the car makers would presumably know best. The car makers do know best, but their decision may have been a compromise between performance, noise, abrasion resistance, and comfort. Factory tyres would thus be like jacks of all trades, and not the stellar performer enthusiasts are looking for.

The benefits of upsizing your tyres:

  1. Improved response to direction changes
  2. Greater contact area with the ground
  3. Increased traction
  4. Greater overall control and handling
  5. A sleeker and more modern appearance

Having understood how much the tyres affect the performance of the vehicle, we will now look into the various options of upgrades an owner has. The improvement in performance can take on one of two aspects.

Tyre Model upgrade

Pricier tyres usually feature the usage of improved materials; sporting better aesthetically designed tread lines, lesser road noise, and improved drivability on water and grip on roads.

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Tyre Specification upgrade

Another method of upgrading is the purchase of bigger wheels and tyres, within the safety limits set by the auto makers. The primary goal of most people who engage in this upgrade would be for the aesthetics of the car, with improved traction, safety and handling being complementary benefits. These are nonetheless tangible benefits so this method kills two birds with one stone!

From the above simple analysis, readers may be tempted to think, isn't the second upgrade a better option with all the improvements of the first option, as well as improving the profile of the car? While this may seem that way on the surface, the tradeoffs for bigger wheels would be an increased body weight, and greater traction due to their increased width, both having an adverse result on the vehicle's acceleration (another aspect of performance). The second option is also more expensive, as more and better materials are required in the production of bigger wheels and wider tyres.

Therefore, there are some considerations to be made before choosing which option is best for you:

  1. Are you really dissatisfied with the specifications of your current tyres?
  2. Are you looking to just improve one or two qualities? Noise, drivability in water, or traction?
  3. Is it more feasible to get a package deal upgrade, both wheels and tyres?
  4. Is your vehicle able to maximize the performance gains of the bigger wheels?

New vehicle owners should not rush to upgrade their factory wheels, as the new tyres that came with the car represent an irretrievable sunk cost. Instead, consideration should be made on whether you can accept the factory tyres' performance in the interim. Upgrading the tyres can be fully explored when the tyres need replacing.

One should consider the vehicle's horsepower (hp) before deciding on upgrading the tyres. If the hp is low, it will not improve performance by enlarging the wheel size. For example, a great majority of cars in Malaysia fall into the 1.3 to 1.6 litre passenger vehicle category. Most cars in this category weigh 1 to 1.2 tons and make between 115 to 135 hp, and use 185/60R14 tyres. In these cases, some performance gains may be actualized if the tyres were changed to 185/65R14, or if the width was reduced to 175mm. However, most owners choose instead to change to 195/50R15 or even 195/55R15, which only serves to increase weight and subsequently, fuel consumption.

Conversely, if your vehicle's hp is above 200, changing the tyre's size and width may serve to improve handling due to the increased traction.

After you have decided to upgrade your tyres, you should do some research. What the best tyres within your budget are, what the leading brands are, and which tread designs you prefer. Generally, the heavier the tyres, the more beautiful and deeper the tread designs, thereby increasing traction.

To a car owner, knowing he biggest wheel size that can fit into a vehicle is very important. There is a simple rule, which is the upgraded wheel's diameter should not be larger than 3% of the original. For example, if we take the 185/60R14 specification as an example, with the original diameter size as follows:

Wheel diameter: 14 inches, 14 inch × 2.54 cm = 35.56 cm
Sidewall: 60% of the tyre's surface, ?18.5 cm × 0.6 = 11.1 cm

But as each wheel has two sidewalls, the sidewalls have to be multiplied by 2,
Sidewall: 11.1 cm × 2 = 22.2 cm
Diameter: 35.56 cm + 22.2 cm = 57.76 cm

Is it possible to upgrade to a 195/50R15 tyre?
Wheel diameter: 15 inches, 15 inch × 2.54 cm = 38.1 cm
Sidewall: 50% of the tyre's surface, 19.5 cm × 0.5 = 9.75 cm

As before, as each wheel has two sidewalls, the sidewalls have to be multiplied by 2
Sidewall: 9.75 cm × 2 = 19.5 cm
Diameter: 38.1 cm + 19.5 cm = 57.6 cm

Compared with the 185/60R14 specification tyre's diameter of 57.76 cm, the difference is only 0.3%, which is well within the allocated range.

But what if we just increase the tyre surface without changing the thickness of the sidewall that is using a 195/60R14 tyre?
Wheel diameter: 14 inches, 14 inch × 2.54 cm = 35.56 cm
Sidewall: 60% of the tyre's surface, 18.5 cm × 0.6 = 11.7 cm again × 2 = 23.4 cm
Diameter: 35.56 cm + 23.4 cm = 58.96 cm

Compared with the 185/60R14 specification tyre's diameter of 57.76 cm, the difference is now 2%, which is basically still within the allocated range, but because the diameter has changed in a big way, the entire tyre circumference has also been changed, rendering the speedometer inaccurate. More importantly, the increased wheel size may cause the wheel to hit the inner wheel wall of the vehicle when the wheel is turned to its fullest. In serious circumstances, it will cause uneven wear and tear for the tyre.

What the "Plus 1" and "Plus 2" mean in the picture below.

"Plus 1" means, if the tyre's thickness is reduced from 70 to 60, the wheel size has to be larger by an inch, to ensure the wheel circumference is the same.

"Plus 2" means, if the tyre's thickness is reduced from 70 to 50, the wheel size has to be larger by 2 inches.

Tire Pic1
70" 65" 60" 55" 50" 45" 40" 35"
165/
70R13		 175/
65R13		 175/
60R14		 185/
55R14 		       
  175/
65R14		 185/
60R14		 195/
55R14		 195/
50R15		      
175/
70R13		 185/
65R13		 185/
60R14		 195/
55R14		 195/
50R15		      
  185/
65R14		 195/
60R14		 195/
55R15		 195/
50R16		 205/
45R16		    
185/
70R13		 185/
65R14		 195/
60R14		 195/
55R15		 205/
50R15		 205/
45R16		    
  195/
65R14		 195/
60R15		 205/
55R15		 205/
50R16		   215/
40R17		 215/
40R17
185/
70R14		 195/
65R14		 205/
60R14		 205/
55R15		 205/
50R16		 225/
45R16		    
  195/
65R15		 205/
60R15		 205/
55R16		 215/
50R16		 215/
45R17		 225/
40R17		 225/
40R17
195/
70R14		 205/
65R14		 215/
60R14		 215/
55R15		 225/
50R15		 215/
45R17		 225/
40R17		 225/
40R17
  205/
65R15		 215/
60R15		 215/
55R16		 225/
50R16		 225/
45R17		 235/
40R17		 235/
40R17
205/
70R14		 205/
65R15		 215/
60R15		 215/
55R16		 215/
50R17		 225/
45R17		 225/
40R18		 225/
40R18
  215/
65R15		 225/
60R15		 225/
55R16		 235/
50R16		 235/
45R17		 235/
40R18		 235/
40R18
205/
70R15		 215/
65R15		 225/
60R15		 225/
55R16		   235/
45R17		 235/
40R18		 235/
40R18
    225/
60R16		 225/
55R17		 235/
50R17		   255/
35R18		 255/
35R18
215/
70R15		 215/
65R16		 225/
60R16		   235/
50R17		   255/
35R18		 255/
35R18
    235/
60R16		 235/
55R17		   245/
45R18		 265/
35R18		 265/
35R18
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