Decoding the markings on the tyre sidewall

It seems writing on walls has always been a thing.  Fast forward to the 80’s and it was nearly impossible to take a train without seeing some sort of graffiti on the side.  Walk through any City Centre and chances are there’s a few tags on walls somewhere.  Yup - markings on walls are natural.  

Which leads us to the markings on your tyre sidewall.  These aren’t there for the fun of it.  No shopping lists and no funny cartoons.  Just proper information that we should know.  It does, however, look a bit like some kind of code at first look.  But...it’s not that complicated once explained.  Which is what we’ll do here.

• Why You Need to ‘Speak Tyre’
• Manufacturer Differences
• The Basics
• The Extras
  
  

Why You Need to ‘Speak Tyre’

No-one likes not knowing.  Say you go tyre shopping and get hit up with some questions, starting with “what size are you looking for?”.... not knowing is going to be a hotbed for uncertainty.  It means you’re uncertain about all things tyre, which just might cause you to be suspicious of what someone tells you.  You know you know no different.  You know what we mean?  Uncertainty is a leading cause of anxiety.  Which is not nice.  Then before you know it (and because you don’t know it) the trip to the local tyre shop becomes a big worry and you start to dislike it.  Which is a little unfair as tyre shops can be great places and are usually filled with very friendly and honest staff.

Apart from the anxiety, if you’re a bloke then you might instantly feel you've let the side down as any sense of machismo is drained from you.  Before you know it the invites to watch rugby at a mate’s house will dry up, the chaps down the pub start to whisper about you and someone buys you some knitting needles for your birthday.

If you’re female, you might feel you’re being stereotyped and being looked at condescendingly.  Which is not pleasant.

Emotions aside, there’s the safety thing.  It’s worthwhile understanding your tyre sidewall so you maintain maximum safety and performance when getting some new rubber.

Manufacturer Differences

Let’s start by confusing things.  Not all markings are the same.  That is, whilst there are similarities between most all tyres there are also some differences.  For example, markings denoting the tyre as being run flat may vary from manufacturer to manufacturer.  Firestone uses ‘RFT’, Michellin ‘ZP’ and Continental ‘SSR’.  The good news is differences are relatively minimal considering how many tyre manufacturers there are.  And once you know the basics you can normally work out the rest with applied logic (a fancy way of saying you’ll be able to guess).  

We’re going to use Continental as the basis for the example to follow.

The Basics

We’ve called this section the basics although the 'fundamentals’ may be more appropriate.  These are the markings which tell you about the tyre size and about its limitations (or ratings).

Let’s begin with the following sequence: 225/45 R 18 95 H

At first glances this could easily be mistaken as coordinates for a bad guys secret underground lair.  But it’s not.  

225

This is the width of the tyre.  It’s measured in millimetres, from one sidewall to the other at the widest part of the tyre.  For NZ’s favourite vehicle (Ford Ranger), the tyres it comes with when new will most likely be 265 wide.

45

This is the aspect ratio.  It’s calculated by dividing the tyres section height by the section width, expressing the answer as a percentage.  But without the % symbol.  Sound confusing?  Think of it this way…in our example it simply means the tyres height is 45% of its width.  

This can still be a little confusing without complete clarification.  After all, you might be thinking the height is greater than the width - so how can it be only 45% of it?  Remember we are talking about the tyre only.  Not the complete wheel (tyre and rim).

Returning to the Ford Ranger, it’ll likely be 65.

R

The first letter in the sequence refers to the construction of the tyre.  An ‘R’ stands for radial.  It’s by far the most common type of construction and means the tyres internal ply cords run in a radial direction at right angles to the direction of the tyre’s rotation. 

If you’re looking at very old trailer tyres you might find a ‘B’ for Bias-ply or “D’ for diagonal construction in the tyre.  Or it might just be a dash with no letter at all.  Don’t worry about this too much as chances are your choices will be limited to radial tyres only. 

18

This is the rim diameter.  Measured in inches, it’s telling you how large the diameter of the rim is.  A typical Ford Ranger will be 17.

95

This is the load index.  You’ll be able to find the load index table in your instruction manual (or look online).  When you look up the index number (in this case 95) the table will show you the maximum load the tyre can carry when fully inflated.  A load index of 95 means the tyre can carry a maximum load of 690kgs.  

It’s important to note the load index defines the maximum load a tyre can carry travelling at the maximum speed as defined by the speed index (that’s coming next).  

When looking at replacing tyres, never do so with tyres that have a lower load index than specified by the manufacturer.  It’s dangerous and a big no-no. 

H

This is the speed rating.  Yeah - we know, it would make sense if this just showed the maximum speed the tyre can legally travel at - right?  Alas, you need to look up another table.  In this case, ‘H’ means you’re all good up to 210kmh.  By the way - that’s not a target.  It doesn’t mean you need to test it out.  Which may be why the code and not a number on the tyre sidewall.  

The Ford Ranger?  ‘T’ for 190kmh.  Again, that is not a target.

The Extras

The good news is, for the average motorist, you now know enough already to go tyre shopping with confidence.  But...you might want something a little different.  And whilst we’re on a roll…

The full set of markings on our example tyre are: 

225/45 R 18 95 H SSR MOE M&S DOT 3616

So we have a few more bits of code to explain then.

SSR

This denotes the tyre as being a self supporting runflat.  You’ll recall from the beginning the codes for runflat tyres can vary from manufacturer to manufacturer.  Uncle Google can always come to the rescue here.  

MOE

No, this tyre is not named after a bartender.  MOE stands for Mercedes Original Equipment.  The variations here come not with the tyre manufacturer but the vehicle manufacturer.  In some cases, the vehicle manufacturer will require their tyre suppliers to mark the tyres with a unique code.  Here’s a handy reference table which may help.    

M&S

British people of a certain age are now thinking of an upmarket supermarket-come-clothing store.  You’re wrong.  This does not mean you can get these tyres from Marks & Spencer.  For the M&S here stands for ‘Mud & Snow’.  It means the tyre is suitable for mud and snow conditions. It has no relevance to the New Zealand market.  

The symbol here might also be seen as ‘M+S’ or ‘M+S’.  Note though, it is different from the snowflake symbol.  M&S means the tyre is suitable for mud and snow but it is not a true winter tyre inasmuch as it does not meet the legal snow traction limit required for a tyre to be able to show the snowflake symbol.  

DOT 3616

This provides information about the date of manufacture.  DOT stands for Department of Transportation.  36 means the 36th week of the year.  16 means 2016.

Is this important?  Kind of, yes.  If you’re buying a tyre and can identify it as being 7 years old then you need to know it has a limited remaining life, even if it’s unworn.  Sunlight, moisture and storage temperature can all cause tyre deterioration. Continental says all tyres 10 or more years old should be replaced.

That’s it.  Lesson over.  You are now qualified in ‘Tyre Speak’.  It’s time to use this newly acquired knowledge.  You can walk up to strangers in supermarket car parks as they load up their vehicles and stare at their car tyres while rubbing your chin and nodding sagely.  Well, maybe don’t do that.