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Guide to choosing your bicycle tyres by Eurocycles, Ireland's best cycling shop

A guide to bike tyre sizes.

When your tyres need replacing, it might become confusing to look at the options available, and the tyre sizing systems can leave you a little perplexed. 
In this guide, we will try to make this a little less daunting and help you find out what size tyre you need, whether you are looking to try something different (different tyre width or grip) or want a like-for-like tyre. 

How are bike tyres sized?

There are two main measures when it comes to tyre sizes: The tyre diameter and its width. 
Some tyres use the metric system (road bike tyres and gravel bike tyres, for example), while others use the imperial system (like mountain bike tyres, showing the US roots). 
Most road bike tyres are 700C, while mountain bike tyres are mainly 27.5" and 29". 

While the outer diameter of a tyre may vary due to the tread pattern and pressure, the inner diameter always stays the same. The inside diameter, also called the Bead Seat Diameter (BSD), is the measurement used by the ETRTO standard.
The most popular BSD are the following:

●     559mm = 26"
●     584mm = 27.5" or 650b
●     622mm = 700C or 29"

What is ETRTO tyre sizing?

ETRTO stands for European Tyre and Rim Technical Organisation. It is a system controlled by ISO standards and measured in millimeters. 
If you've ever looked at the sidewall of a tyre, you have seen an ETRTO sizing embossed onto it. The ETRTO looks like this: a number followed by a dash followed by another number. The first number refers to the tyre width, while the second refers to the tyre diameter (BSD). 
For example, 25-622 is a 25mm tyre for a 700C wheel.

Unfortunately, even with this standard in place, manufacturing tolerances mean the fit between the tyre and the rim can be slightly tighter or looser, depending on the tyre. 

What tyre width do I need?

While the tyre diameter depends on your bike wheel size, the tyre width can fluctuate a little depending on your needs. 
Mountain bike tyres and hybrid bikes will have wider tyres than road bikes (that are looking for the least rolling resistance). 
Tyre width can vary from something as narrow as 18mm to as broad as the high 50s. The only limiting factor of width is the frame clearance. For example, most road bikes' clearance will only allow for tyres up to 32mm maximum. 

Mountain Bike Tyres with knobbly thread

Slick and Thin Road Tyre

Hybrid Tyre in between MTB and Road

How do I find the size of my tyres?

You will find your tyre size printed on its sidewall. 
The ETRTO measuring has yet to become the point of reference for most riders and isn't understood by all. Therefore, manufacturers mark the sidewall with the ETRTO number and metric and imperial sizes. This results in markings that look like this: 622-25 (700x25 - 28x1.00)

Tyre Sidewall markings indicating tyre size - Eurocycles Ireland

Sidewall markings on a tyre.

To make things a little easier for you, we've created the tyre size chart which will  help you know what size tyre you need no matter what system is used on the tyre. 

What pressure should I use in my tyre?

The recommended pressure for your tyres is indicated on their sidewalls. It is sometimes a recommended pressure and sometimes an absolute maximum. Do not go over the absolute maximum pressure. 

How to know when your tyre needs replacing?

Most tyres come with wear indicators in the form of pimples or grooves. These wore out over time and are a good measure of when to change your tyres. However, some tyres do not come with these indicators, and they are only that; indicators. 
The things to look for when checking your tyres are:

●     cuts and slashes to the sidewall and tread
●     flat spots on the crown
●     unusual bulges and bumps.  

And, if you can see the tyre casing, it is time to retire your tyres no matter what.

Faulty tyres with marking showing that it is time to replace them - Eurocycles

Various stages of wear on tear on tyres. 

Road Bike Tyres Sizes

Some older road bikes will use 27" tyres, and small-sized women's specific road bikes will use a 650C tyre diameter. But 99% of road bikes have 700c tyres. 
Therefore, width is the key factor determining the best road bike tyres for you.
Wider tyres will offer better grip and comfort but a higher rolling resistance. 
Thinner tyres are lighter and therefore make it easier to get to speed. 
However, things have changed a little over time. The norm used to be of 23mm tyres in the past for road racers. Today, 25 and 28mm tyres are the most common sizes used on road bikes. 
Some more casual riders are even going as wide as 32mm for comfort if the frame clearance allows it.

Mountain bike tyres

Mountain bike tyres come mainly in 2 diameters: 27.5" and 29", and are wider than road bike tyres. The best mountain bike tyres depend on the discipline you practice. 
The typical range of their width varies between 2" and 2.6". The width you pick is dependent on your riding type. 

●     Cross-country bike tyres range between 1.9" and 2.25".
●     Trail and all-mountain bike tyres range between 2.25" and 2.4". 
●     Downhill bikes meant to take more abuse than the others will have tyres as wide as 2.5".
●     Fat bike tyres designed for all-season trail riding range between 3.7" and 5"+.

Gravel Bike Tyres

The best gravel bike tyres need to balance wheel size, tyre width, and tread to find the best option for the type of terrain and cycling you are going to do. 
Usually 700c (or sometimes 650b), gravel tyres can have tyres from 32mm to 50mm range, where the average is 40mm.
While similar to cross-country tyres, they are not the same. XC regulation requests that tyres are not narrower than 33mm. 

Hybrid Bike Tyres

Hybrid bike tyres are wider, heavier versions of road bike tyres with more pronounced treads of 30 to high 40s tyre width. These tyres are more comfortable to ride than road bikes and perfect for longer journeys where speed isn't essential. 

Tubeless Tyres

Tubeless tyres (as their name suggests) are tyres without an inner tube. Tyres suitable for tubeless rims are embossed on their sidewall with the indication "Tubeless ready" 
A tubeless tyre must have a close fit, especially for road bikes, where the pressure is higher. If not correct, there is a risk of blowing out. 

Other Tyres

BMX and folding bikes use 20" tyres. These tyres are also suitable for 20" kid's bikes. 
Tubular tyres are primarily designed for racing and fixed to the rim with glue, cement, or adhesive tape. 
Aside from cycling, we also have to mention our selection of Go-Kart tyres which are 12.5" tyres to replace your worn-out Berg Go-Kart ones. 

Can bicycle tyres be recycled?

Unlike inner tubes, tyres are built with more than one material, making them difficult to recycle. 
However, some companies like Continental and Vittoria are working on pilot projects to retread worn-out tyres.