Tyre Sidewall Decoded: Read the Numbers That Matter

Most of us choose a tyre by brand and price, fit it, and never look again. Yet the tyre sidewall is covered in a code that tells you everything that matters — the exact size your car needs, how much weight and speed it can safely handle, and, crucially, whether the 'brand-new' tyre a dealer just sold you was actually baking in a warehouse for three years. Learning to read it takes five minutes and can save you from a blowout, a rejected warranty, or an overpriced wrong-size fitment.

Here is how to decode every important marking, in plain language, before your next purchase or your next long drive.

The size code: 195/55 R16 explained

The big alphanumeric string is the one to memorise. Take a common example, 195/55 R16 87V:

• 195 — the section width in millimetres, measured across the tread from sidewall to sidewall.
• 55 — the aspect ratio: the sidewall height is 55% of the width. A lower number means a shorter, sportier sidewall; a higher number means a taller, comfier one.
• R — radial construction, which is what virtually every modern car uses.
• 16 — the rim diameter in inches that the tyre is built to fit.

The golden rule: match this code exactly to what your car maker recommends, which you'll find on the driver's door-jamb sticker or in the owner's manual. Going wider or taller changes your speedometer reading, ground clearance and handling, and can foul the wheel arch. 'Upsizing' is possible but should be done knowingly with a matched rim, not by accident at a roadside shop.

Load index and speed rating: the small print that saves lives

The two characters after the size — 87V in our example — are the most ignored and most important. The number is the load index and the letter is the speed rating.

The load index is a coded figure for the maximum weight one tyre can carry. An index of 87, for instance, corresponds to roughly 545 kg per tyre; multiply across four and you have the car's rated capacity. Fit a lower index than specified and an overloaded family trip becomes a genuine blowout risk.

The speed rating letter marks the maximum sustained speed the tyre is engineered for — not a target, but a safety ceiling tied to heat build-up. Common ratings on Indian cars run roughly like this:

• T — up to 190 km/h
• H — up to 210 km/h
• V — up to 240 km/h
• W — up to 270 km/h

You can safely fit a higher rating than your car needs, but never a lower one. Downgrading to save a few hundred rupees compromises high-speed stability and can void claims if anything goes wrong.

The DOT date code: is your 'new' tyre actually old?

This is the trick every smart buyer should use. Rubber is perishable. A tyre that has sat in storage for years hardens and develops micro-cracks long before it is ever fitted, even though it looks pristine and the tread is full.

To check, find the DOT code — usually stamped inside an oval near the rim, sometimes only on the inner sidewall. The important part is the last four digits:

1. The first two digits are the week of manufacture (01 to 53).
2. The last two digits are the year.

So a code ending in 2524 means the tyre was made in the 25th week of 2024 — roughly mid-June. A code reading 0820 means February 2020, which is a tyre you should refuse to pay 'new' prices for.

At purchase, insist on tyres made within the last few months and certainly under a year old. There is no harm in asking the fitter to show you the date code on each tyre before they go on the rim — a reputable shop won't mind.

TWI: the wear bars that tell you to stop

You don't need a gauge to know when a tyre is finished. Look for the letters TWI (Tread Wear Indicator) or a small triangle moulded into the sidewall. Follow it inward and you'll see raised rubber bars sitting at the bottom of the tread grooves.

These bars sit at exactly 1.6 mm, the legal minimum tread depth. When your tread has worn flush with these bars, the tyre is done — it can no longer channel water away and aquaplaning risk on a wet road shoots up. A quick home test: insert a coin into the groove; if the tread is shallow enough that the bars are level with the surface, replace immediately, monsoon or not.

M+S, tubeless and other markings worth knowing

A few more symbols clear up common confusion:

• M+S (or M/S) means 'mud and snow' — an all-season tread pattern, not a true winter tyre. Most Indian passenger tyres carry it and it makes little practical difference here.
• TUBELESS / TUBE TYPE tells you the construction. Almost all modern cars run tubeless; never fit a tube inside a tubeless tyre as a 'fix'.
• Tread wear, traction and temperature grades (the UTQG line, e.g. 'TREADWEAR 320 TRACTION A') let you compare longevity and grip between models from the same market.
• A rotation arrow on directional tyres shows which way they must spin; fitting them backwards ruins wet grip.

The pressure number everyone reads wrong

Finally, the sidewall prints a maximum pressure figure — often something like 'Max Press 44 PSI'. This is the single most misread number on the tyre. It is the ceiling the tyre can hold, not the pressure you should run.

Your correct PSI is set by the car maker and printed on the door-jamb sticker or fuel-flap, typically in the low-to-mid 30s for most hatchbacks and sedans, often with a separate higher figure for a fully loaded car. Inflating to the sidewall maximum gives a harsh ride, uneven centre wear and less grip. Check pressure cold, at least once a month and before any highway run, and don't forget the spare.

Put it to use

Next time you're at a tyre shop, do three things: confirm the size code matches your door sticker, read the DOT date code on each tyre to make sure they're genuinely fresh, and verify the load index and speed rating aren't downgraded from your car's spec. Back home, glance at the TWI bars every few months and keep the PSI at the door-jamb value, not the sidewall max. None of it costs a rupee — and on Indian roads, in Indian heat, those numbers are the difference between a tyre that quietly does its job and one that lets go at the worst possible moment.