How to Read Your Tyre Size (The Easy Way)
A customer walked into our Sharjah branch last week, held up his phone and said: "I need 235s." Fair enough. But 235 what? Two of the four tyres on his car were 235/55 R18, the other two were 235/60 R18, and the sticker inside his door said something different again. Somebody, somewhere, had guessed.
That happens more than it should, and learning how to read tyre size is the whole fix. The size is moulded into the rubber in letters you can read from a metre away, and once someone shows you the pattern you never forget it. It takes about ninety seconds.
The size you should be buying is not always the size currently fitted, and that gap is what costs UAE drivers money every week.
Decoding 235/55 R18 99V
We will use that size all the way through, because it is one of the most common on the E11 — mid-size SUVs, big saloons, plenty of Nissans and Toyotas. Every character does a job.
- 235 — the section width in millimetres, measured from sidewall to sidewall when the tyre is mounted and inflated. Not the tread width. Bigger number, wider tyre.
- 55 — the aspect ratio, and this one confuses people because it is a percentage, not a measurement. The sidewall height is 55% of 235mm, so roughly 129mm. A 45 on the same width gives you a shorter, stiffer sidewall. A 65 gives you a taller, softer one.
- R — radial construction. Almost every passenger tyre sold today is radial. If you ever see a D there it is diagonal (bias-ply), which you will only meet on trailers and some old machinery.
- 18 — the wheel diameter in inches. Yes, millimetres and inches in the same code. Nobody has fixed it and nobody will. This number must match your rim exactly. An 18-inch tyre will not go on a 17-inch wheel, no matter how enthusiastic the fitter is.
- 99 — the load index. 99 means each tyre can carry 775kg at its rated pressure. Four of them gives you 3,100kg of capacity, comfortably more than the car weighs, which is the point.
- V — the speed rating. V is good for 240 km/h. H is 210, W is 270, Y is 300.
The last two are the ones people ignore, and they are the ones that matter most in summer. A tyre running below its rated load or speed builds heat faster, and heat is what kills tyres here. We wrote a longer piece on that: speed ratings and load index explained.
You will also see other things on the sidewall — the brand, the pattern name, "TUBELESS", "MAX PRESSURE", and a four-digit code inside an oval which is the manufacturing date. That one deserves its own read: how old is too old.
Where to find your size (and which source to trust)
There are three places to look, and they do not always agree.
1. The door jamb sticker — trust this one
Open the driver's door and look at the frame, near the latch. On most cars there is a small placard listing the original tyre size and the recommended cold pressures, sometimes with a separate line for a fully loaded car. On a few models it hides inside the fuel filler flap or the glovebox lid instead.
This is the size the manufacturer engineered the car around — the speedometer calibration, the ABS, the stability control, the load capacity. Start here.
2. The owner's manual
Same information, usually with the approved alternative sizes listed too. Useful if your car came with two wheel options and you want to know what else is legal.
3. The tyres currently on the car
Read them, absolutely — but treat them as evidence, not gospel. Cars change hands. Somebody before you may have fitted whatever was cheap that day. If the sidewall and the door sticker disagree, the door sticker wins unless you know exactly why the change was made.
The extra letters: XL, RF, M+S and run-flats
XL or Extra Load (sometimes written Reinforced) means a stronger casing with a higher load index, and it needs higher inflation pressure to deliver that extra capacity. If your car came with XL tyres, replace them with XL tyres. Fitting standard-load rubber to a heavy seven-seater because it saved AED 60 a corner is a bad trade.
M+S stands for mud and snow. You will see it on plenty of all-terrain 4x4 tyres sold here, and in the UAE it tells you almost nothing useful — it is a self-declared marking with no real test behind it. The three-peak snowflake symbol is the meaningful winter mark, and you do not need it in Sharjah.
Run-flats are marked differently by every manufacturer: RFT, ZP, SSR, ROF, DSST, HRS and others. They have a stiff sidewall that supports the car for a limited distance after a puncture. Two things worth knowing: they ride harder, and if your car came with them and has no spare wheel, switching to conventional tyres means carrying a repair kit and accepting that a blowout on the Dubai–Al Ain road leaves you waiting for recovery.
The mistakes we see at the counter
- Two different sizes on the same axle. Never do this. The car pulls, the ABS gets confused, and on a 4WD the drivetrain fights itself because the wheels are turning at different rates. Same size, same axle, always.
- Front and rear different by accident. Some sports cars are staggered from the factory and that is fine. If yours is not, match all four.
- Ignoring the load index on a loaded car. Seven passengers, luggage, a roof box and 48°C tarmac is a real load, not a theoretical one.
- Plus-sizing without keeping the diameter. Going from an 18-inch wheel to a 20 looks good, but if the overall rolling diameter grows more than about 3%, your speedometer under-reads. The camera on Sheikh Zayed Road measures your actual speed, not what your dial says.
Honestly, on plus-sizing I will say something most shops will not: for the majority of drivers here it is a downgrade. You get a stiffer ride over speed bumps, a higher price per tyre, more kerb damage, and slightly worse tread life. If you love the look, do it with open eyes.
Putting the numbers into our size filter
Once you have the three main numbers, finding stock takes seconds. Our filter is built around exactly the format you just read off the sidewall: width, aspect ratio, rim. For 235/55 R18 you would land on this list. Change the numbers in the boxes on the all-tyres page and the results update.
Then narrow by brand if you have a preference — Bridgestone, Michelin, Laufenn and the rest are all filterable. Check that the load index and speed rating on the tyre you pick are equal to or higher than what the door sticker asks for. If you are unsure, send us the size on WhatsApp and we will confirm it before you pay.
Frequently asked questions
What does 235/55 R18 99V actually mean?
235mm section width, a sidewall height 55% of that width, radial construction, an 18-inch rim, a load index of 99 (775kg per tyre) and a V speed rating good for 240 km/h. The first three numbers decide whether the tyre fits your car. The last two decide whether it can safely carry it.
Can I fit a different tyre size than the door sticker says?
Sometimes, but only if the overall diameter stays within roughly 3% of the original and the load index and speed rating are equal or higher. Outside that, your speedometer reads wrong and the electronics work with bad data. If you want a change, ask us first — it takes one message.
Where is the tyre size on my car?
On the tyre sidewall itself, and on a placard inside the driver's door frame. Some cars put that placard inside the fuel filler flap or the glovebox instead. The owner's manual repeats it and usually lists the approved alternatives. The door placard also gives you the correct cold inflation pressures.
Do all four tyres have to be the same size?
The two tyres on the same axle must always match in size, load index and speed rating. Most cars want all four identical. A few performance models are staggered from the factory, with wider rears — check your door sticker. Mixing sizes on one axle is unsafe and, on four-wheel drive, expensive.
What does XL mean on a tyre?
Extra Load: a reinforced casing with a higher load rating, which needs more inflation pressure to work as designed. If your vehicle originally came with XL tyres, replace them with XL. It is common on SUVs, seven-seaters and heavier saloons, and dropping to standard load quietly reduces your safety margin.
Still not sure what you are looking at? Send a photo of the sidewall to our WhatsApp on +971 800 525, or call 800 525 — we read these all day and we will tell you the size and what we have in stock. You can also come to the main branch on Al Nahda Street, Industrial Area 8, Sharjah, open daily 9:00 AM to 10:00 PM, where balancing, nitrogen filling and an alignment check are free with every tyre you buy. Minimum order is two tyres, prices on the site include VAT, and we deliver anywhere in the UAE.