quickgrip st albans
TYRE SIZES & MARKINGS EXPLAINED

How to Read Tyre Size:
Tyre Width, Profile, Rim Size, Load Index & Speed Rating

Tyre width, profile, rim size, load index and speed rating - what every number and letter on your tyre sidewall actually means, in plain English.

6
Key pieces of information encoded in a standard tyre size marking
205
The tyre width figure in mm - the first number in the most common format
3+
Additional markings to know - XL, run-flat, M+S, C, and directional indicators

If you've ever looked at your tyre sidewall and seen something like 205/55 R16 91V, you're not alone in wondering what it all means. Knowing how to read tyre size helps you buy the correct replacement, avoid mismatched tyres that affect handling and safety, and give a fitter the right information quickly - especially for mobile call-outs.

This guide breaks down tyre markings in plain English, with UK-friendly examples and practical advice for when you need new tyres fitted in St Albans or surrounding areas.

01

Where to Find Your Tyre Size

Look on the tyre sidewall for a long string of numbers and letters. It's moulded into the rubber and usually easy to spot once you know what you're looking for.

Common formats you might see include:

  • 205/55 R16 91V - typical for most family cars
  • 225/45 R17 94Y - common on sportier or larger vehicles
  • 215/65 R16C 109/107T - often seen on vans and light commercial vehicles
If the sidewall markings are worn or hard to read, the manufacturer-recommended size can also be found on the door jamb sticker (driver's door area), the fuel flap, or in the vehicle handbook. The handbook is always the safest reference.
02

The Most Common Format Explained: 205/55 R16 91V

Let's break it down step by step using the most widely seen format.

EXAMPLE TYRE SIZE 205/55 R16 91V
205 Width (mm)
55 Profile (%)
R Construction
16 Rim (inches)
91 Load index
V Speed rating

What each part means

1205 - tyre width in millimetresThe width of the tyre from sidewall to sidewall, measured in mm. A wider number means a broader tyre.
255 - aspect ratio (sidewall height as a percentage of width)55 means the sidewall height is 55% of 205mm - not 55mm itself. A lower number means a lower-profile, sportier-looking tyre.
3R - radial constructionR stands for radial, meaning the tyre's internal layers run radially across the tread. Virtually all modern road tyres are radial.
416 - wheel (rim) diameter in inchesThe diameter of the wheel the tyre is designed to fit, measured in inches. This must match your wheel exactly.
591 - load indexA code that indicates the maximum weight the tyre can carry at its rated pressure. A higher number means a higher load capacity.
6V - speed ratingThe letter indicates the tyre's maximum approved speed capability. V = up to 149 mph. Always match or exceed the rating required by your vehicle manufacturer.
Important: always fit tyres that meet your vehicle manufacturer's specifications - found on the door sticker or in the handbook - not just whatever fits the wheel. A previous owner may have changed the size.
03

Quick Tyre Size Examples

Here are two further examples so you can recognise the format when you see it on your own tyres.

Example A: 225/45 R17 94Y

  • 225mm wide
  • 45% profile - lower sidewall, sportier appearance
  • Fits a 17-inch wheel
  • Load index 94, speed rating Y (up to 186 mph)

Example B (van): 215/65 R16C 109/107T

  • C indicates a commercial (van-rated) tyre
  • Two load indexes (109/107) for different loading conditions
  • Always match the commercial spec your van requires
  • Do not swap C-rated tyres for standard car tyres

Always match what your vehicle requires - not just what physically fits the wheel. Check the door jamb sticker or handbook to be certain.

04

Other Markings You Might See

These aren't always part of the main tyre size code, but they matter when choosing a replacement.

XL / Reinforced

Designed to carry higher loads at higher pressures. Some vehicles require XL tyres - fitting a standard tyre where XL is specified is not safe.

Run-flat (RF / RFT)

Designed to support the vehicle for a limited distance after a puncture. Exact limits vary by brand and vehicle. Conversion to standard tyres is possible but not always advisable.

M+S and 3PMSF

M+S (Mud and Snow) is a general marking. The three-peak mountain snowflake symbol indicates tested winter performance - seen on winter and many all-season tyres.

Directional arrows

An arrow on the sidewall shows the required rotation direction. Fitting a directional tyre the wrong way round affects grip and drainage.

C (Commercial)

Indicates a van or light commercial tyre with stronger construction for heavier loads. If your vehicle specifies C tyres, do not substitute with standard car tyres.

Outside / Inside markings

Asymmetric tyres have distinct inner and outer faces. These markings must be respected during fitting - an incorrectly fitted asymmetric tyre will not perform as designed.

05

Does the Size, Load Index and Speed Rating Have to Match Exactly?

In most cases, the size must match - width, profile, and rim diameter should all correspond to what your vehicle is specified for.

What must match

  • Tyre width
  • Aspect ratio (profile)
  • Rim diameter
  • Load index - meet or exceed the vehicle requirement
  • Speed rating - meet or exceed the vehicle requirement

Risks of mismatching

  • Affected handling and braking performance
  • Inaccurate speedometer reading
  • Clearance issues within the wheel arch
  • Potential insurance implications
  • Possible MOT failure

Load index and speed rating should meet or exceed the manufacturer's requirement. You can generally fit a higher load index or speed rating, but never lower. If you're unsure, follow the vehicle placard or handbook, or ask a fitter to confirm what's correct for your car.

If you're unsure - don't guess. Use your vehicle's door jamb placard or handbook, or call QuickGrip on 01727 221822 and we'll help you confirm the correct specification.
06

Common Mistakes - and How to Avoid Them

These are the mistakes that most often lead to people fitting the wrong tyre - or having a mobile fitter arrive without the right one.

Reading the sidewall but ignoring the car's spec

Previous owners sometimes fit a different size. Always double-check your door jamb placard or handbook - don't assume the current tyre is the correct one.

Mixing load or speed ratings across tyres

Even if sizes match across all four wheels, mismatched ratings can affect handling and may cause issues at MOT. Keep all four tyres consistent where possible.

Right size, wrong type

Run-flats, XL reinforced tyres, commercial C tyres, and seasonal tyres can all share the same size code but are not interchangeable. Always confirm the type as well as the size.

07

What to Tell a Mobile Tyre Fitter

If you're calling QuickGrip for mobile tyre fitting in St Albans or a surrounding area, having these details ready helps us get you the right tyre and a fast, accurate quote.

Information to have ready when you call

  • Tyre size - e.g. 205/55 R16 91V (a photo of the sidewall is perfect)
  • Vehicle registration - helps confirm the specification where possible
  • Your location - home, workplace, or roadside address or postcode
  • How many tyres - one, a pair, or a full set
  • Any special type - run-flat, XL reinforced, or van C tyre if applicable
  • Locking wheel nut key - let us know if you have it (or if you're unsure where it is)
  • Any visible damage - sidewall cut, bulge, nail, or impact mark

Key points from this guide

  • The tyre size code contains six pieces of information: width, profile, construction, rim diameter, load index, and speed rating.
  • The sidewall shows what's currently fitted - not necessarily what your vehicle should have. Always check the door sticker or handbook.
  • Load index and speed rating should meet or exceed the manufacturer's requirement - never go lower.
  • XL, run-flat, commercial C, and seasonal tyres are not interchangeable with standard tyres of the same size.
  • Directional and asymmetric tyres have markings that must be respected during fitting.
  • When calling for mobile fitting, a photo of the sidewall and your vehicle reg is the fastest way to get the right tyre quoted.
FAQ

Common questions about tyre sizes and markings

Look on the tyre sidewall for a code like 205/55 R16 91V. You can also find the manufacturer-recommended size on the door jamb sticker (driver's door area), the fuel flap, or in the vehicle handbook.
205 = width in mm, 55 = profile (sidewall height as a percentage of width), R = radial construction, 16 = rim diameter in inches. These four numbers and letters define the physical dimensions of the tyre.
That's the load index and speed rating. 91 = load index (the maximum weight the tyre can carry at its rated pressure). V = speed rating (the tyre's tested maximum speed capability - V indicates up to 149 mph).
In most cases, yes. Width, profile, and rim size should match your vehicle's specification. Fitting the wrong size can affect handling, braking, speedo accuracy, wheel arch clearance, and insurance suitability.
Often you can go higher (never lower than the vehicle requirement), but the tyre should still meet the manufacturer's specification. If you're unsure, follow the vehicle placard or handbook, or ask a fitter to confirm.
The sidewall shows what is currently fitted - but a previous owner may have fitted a non-standard size. The door sticker or handbook is the safest reference for what your car is meant to run.
Usually, but not always. Some cars have staggered fitment with different sizes front and rear. Check each tyre sidewall or the manufacturer placard to confirm what each axle requires.
XL (Extra Load) or Reinforced tyres are designed to carry higher loads at higher pressures. Some vehicles require XL tyres as standard. If your vehicle specifies XL, it is important to match that - do not substitute a standard tyre.
C typically means Commercial (van-rated) tyre. These have stronger construction designed for heavier loads. If your van specifies C tyres, do not swap to standard car tyres - even if the size appears similar.
Run-flats are designed to support the vehicle for a limited distance after a puncture. Exact limits vary by brand and vehicle. Some cars can be converted to standard tyres, but it is not always advisable as it may affect handling and systems designed around run-flat fitment. Best to confirm before switching.
M+S means Mud and Snow - a general marking that does not always indicate certified winter performance. The three-peak mountain snowflake symbol indicates tested snow performance and is seen on winter and many all-season tyres.
Use the door jamb sticker or vehicle handbook to get the recommended size. You can also share your registration with a fitter - and a clear photo of the tyre and wheel helps too.
Incorrect or mismatched tyres can create safety issues that affect MOT outcomes. As a rule, keep sizes and ratings in line with the vehicle specification and replace unsafe tyres promptly.
To get the right tyre and a fast quote, share: tyre size (a photo of the sidewall is ideal), vehicle registration, your location (home, work, or roadside), whether you need one tyre, a pair, or a full set, any special requirement such as run-flat, XL, or a C van tyre, and whether you have the locking wheel nut key.
The bottom line: tyre size markings look complicated at first, but they follow a consistent pattern. Once you know what each number and letter means, reading your tyre sidewall takes seconds - and it's the single most important piece of information you need before ordering a replacement or calling a mobile fitter.

Need Tyres Fitted in St Albans?

If you've found your tyre size - or even if you haven't - QuickGrip can help you get the right tyres supplied and fitted without a garage visit. Call us with your size (or reg) and your location.

No garage visit needed · Fully equipped mobile vans · St Albans and surrounding areas

Call 01727 221822 Book Online
Mobile service - we come to you Right tyre, right spec, every time Based in St Albans