A basic simple guide to tire care and replacement (upsizing)

Usually, when something pertains to my car or bike, it gives me immense pleasure and joy to go into the finer and deeper details and learn the skills. One such skill is playing with the tyre profile. A car maker usually gives the tyre size which they deem fit for the overall general public. So, while this works in most scenarios, one needs to find the the right tyres that can cater to their more specific needs.

My recent experiments with tyre upsizing has taught me a lot on how theory doesn't always transform into physical changes. Here, I have tried to make a simple layman's guide on how to select the right tire for your car.

1. Date of Manufacture: It is very crucial to look at the date of manufacture before getting a set of tyres for your car even if they are the same set you have received with your car. The date numbering on tyres is same from all brands.

 As shown in the image above it is usually a four digit number. The first two digits denote the week while the last two digits denote the year. So in the image above, the tyre has been made in the 9 week of 2007. Now why is it important to look at the year of manufacture? Simply because the compounds used in manufacturing a tyre harden over time. The case holds true whether the tires are used or stored in a warehouse. A tyre in use should not be run for more than five-six years at best. Also, when installing a new tyre, one should make sure it has not been stored for more than two years as idle tyres harden faster. (Do not listen to anybody who says otherwise.).

2. Tire wear: Based on the usage and tyre compounds used the normal life is around 40000-60000 kilometers ( 25000-40000 miles). Tyre wear is generally noticeable when uneven which is mostly due to negligence on the alignment and balancing part. Otherwise the best way to notice tire wear is to look for marks on the tread.

Another effective way it to take the penny test (we can use a 25 paise coin or a 50 paise coin in India).

3. Alignment and Balancing: A normal tyre consists of reinforced rubber with steel belts. While flexible such a structure is bound to lost its normal form due to effects of road conditions and irregular inflation pressures. Hence a tyre needs to be aligned and balanced after a specific mileage. While many car makers and tire makers recommend such practices every 5000 kms (3000 miles), one can go for a 10000 kms (6000 miles) if the vehicle is used under standard conditions at stable speeds.

4. Tyre upsizing : Most car owners make a big mistake while upsizing a tire. A normal tire should not be upsized, downsized with a more than 2% difference. For e.g. a Vw polo comes with 185/60 R15 wheels in India. The 185 denotes the width of the tyre which contacts the road, 60 stands for the tire wall height and 15 denoted the radius of the steel/aluminum wheel. An enthusiast will generally go for a 195/60 or 205/55 profile on his next tire change or shift to a lower profile 195/50 r16 tyres. While all the three sizes are can be installed on the VW polo, they all have severe impact on the driving experience. So lets see how each change on the tire size affects our driving experience.

a. going wide: Usually most car enthusiasts go for a wide tire. IMHO, 185/60 is already a wider size for a VW polo. The reason being, it is running a small 1200cc engine making a tiny 75ps of power with 110nm of torque. A wider profile will only increase friction thus reducing weighing on the already low torque. Not to mention how this reduces the Fuel efficiency and makes steering wheel heavier for city use. Also, wider tyres are usually more expensive. Another downside is having to reduce the sidewall height when one needs to go extra wide.  A wider tyre makes sense when the cars has ample torque at its disposal or the engine has been modified to put extra power. Such a situation is amplified when we are dealing with heavier cars.  While 185/60r15 on a VW polo is a good example of oversized tyres from the manufacturer, 175/65r15 on Honda City cars are a good e.g. of undersized tyres from Manufacturers. Compared to the VW polo, Honda City has more power of 115 horses and more torque (145nm). So under situations of spirited driving, the skinny wheels are bound to lose grip. So, in this situtation while 185/60r15 is would be a more ideal match  for the Honda City, A 175/65r15 size is a more ideal match for the VW Polo. But VW gives 185/60r15 size on the Polo because it is a much better size for its VW Vento( sedan based on Polo) with more power. While Honda city uses the same profile for its Honda Jazz and Honda Civic cars (the tyre size is perfect for the Jazz but not suitable for Civic or City).

b. going low: a low riding car looks sporty. But for a country like India it also means underbody damage on bad roads. It also means lower ground clearance on already low cars and a bad ride quality where the driver and occupants feel each and every bump. Again a higher ride means lower center of gravity and little compromise with handling with a rubbery feel at corners. For a car like VW Skoda Octavia, I would definitely recommend a taller rubber which will help absorb bumps and make ride comfortable while providing a little higher ground clearance. On the other hand, a car like Fiat Linea can run on lower rubber since it has  195mm of ground clearance to play with.

c. Tire Pressure change: When change a tire size, the tire pressure also change due to the change in the volume needed. For every 5mm increase in width, reduce 1psi tyre pressure and for every 5mm decrease in height increase 1psi tyre pressure. For a 1 inch radius change reduce tyre pressure by 2-3 psi based on your comfort. While there is no set rule of what tyre pressure should be maintained post upsize, playing a bit with 1-2 psi up or down should get your the right balance of handling and comfort.

Best of luck and happy motoring.