CST Downhill Innertube PV
Occasionally, without notice, manufacturers change product design and/or specifications.
Tyre Size Guide
Whether you are replacing a worn out tyre or want a performance upgrade, it is essential that you choose a tyre that is compatible with your bicycle as well as your riding style.
To find out which size tyre you will need have a look at the sizing information on your existing tyre. You can find this information on the side wall of the tyres, either in coloured print or embossed in the rubber itself. Both rim diameter and tyre width are shown in the size info.
Road bike tyre sizing
700 x 23c
A standard 700c road bike rim with a 23mm tyre width.
MTB tyre sizing
27.5 x 2.3
A 27.5” mountain bike rim with a 2.3” tyre width.
You will notice that road bike tyres tend to me measured in metric units while mountain bike tyres use imperial units.
What Size Tyre Do I Need?
Ypu need to knnow your wheel size and tyre width when chosing a replacement tyre for your bike
Wheel Size
Tyres are made to fit specific wheel sizes, so you need to know what size the wheel on your bike is.
The easiest way to do this is by looking at the tyres on your bike. On the sidewall you'll see a combination of digits such as:
700 x 28c (road bike wheel) or 27.5 x 2.4 (mountain bike wheel)
It’s the first figure that shows the diameter of the wheel or the wheel size.
The next figure is tyre width which is the other measurement you need to know.
Tyre Width
Inner tubes are designed to fit a range of tyre widths, so the next thing you need to know is the width of your tyre.
This is shown in the second number that’s printed on the side of the tyre.
700 x 28c (road bike wheel) or 27.5 x 2.4 (mountain bike wheel)
When choosing an inner tube you need one with a width range that covers your tyre width as well as exactly matching the size of the wheel. See the tables below for examples.
Note: Sometimes metric sizes are shown as c instead of mm. This is just a different way of saying the same thing. A 25c tyre is the same width as a 25mm tyre.
Traditional and ETRTO sizing
Sometimes the sizing info is listed in two different ways; the traditional sizing method shown above and ETRTO sizing which lists the tyre width first and the rim diameter second. The rim diameter size is measured differently with ETRTO, for example:
23-622
This is a standard 700c road bike rim with a 23mm tyre width, which is the same size as 700 x 23c.
We recommend that you use the traditional sizing method wherever possible as most tyres that we stock use this system.
Traditional and ETRTO tyre size tables
If you are unsure which tyre size you need you can use our handy comparison table to find the correct size tyre
Road bike tyre sizes
| ETRTO Number | Dimension |
| 700c road bike wheels | |
| 18-622 | 700 x 18C |
| 23-622 | 700 x 23C |
| 25-622 | 700 x 25C |
| 28-622 | 700 x 28C |
| 32-622 | 700 x 32C |
| 37-622 | 700 x 35C |
| 47-622 | 700 x 47C |
MTB tyre sizes
| ETRTO Number | Dimension |
| 26" mountain bike wheels | |
| 50-559 | 26 x 1.9 |
| 54-559 | 26 x 2.1 |
| 55-559 | 26 x 2.2 |
| 58-559 | 26 x 2.35 |
| 27.5" (650b) mountain bike wheels | |
| 50-584 | 27.5 x 1.95 |
| 54-584 | 27.5 x 2.1 |
| 57-584 | 27.5 x 2.25 |
| 29" mountain bike wheels | |
| 50-622 | 29 x 2.0 |
| 54-622 | 29 x 2.1 |
| 55-622 | 29 x 2.2 |
What are the different types of bike tyres
While road, mountain and hybrid tyres have their own specific differences there are some features that are common to all tyres.
- Clincher tyres - most bike tyres have a bead which hooks onto the rim to keep the tyre in place. Traditionally this bead is made from wire which is tough but heavy. Premium tyres use a folding Kevlar bead which is equally as strong as wire but is much lighter weight.
- Tubeless tyres - while regular clincher tyres require an inner tube to keep them inflated tubeless or tubeless ready tyres form an airtight seal with a compatible rim so you don’t need an inner tube. These are most commonly found on mountain bikes as they can be run at lower pressures without risking punctures.
- Tubular tyres - These are specialist road bike tyres that have the tube built into the tyre and are then glued onto a compatible rim.
Frequently Asked Questions
What size tyre do I need for my bike?
Look at the side wall of your tyre for any printed numbers indicating the size and width.
How do I know my bike wheel size?
The easiest way is to look at the side of your tyre. The size and width are printed on the tyre.
How do I choose a bike tyre?
Once the compatible size is known, choose an appropriate tread for the conditions you ride in.
Can I fit wider Tyres on my bike?
Look at your fork and frame where the tyre passes through, measure any available clearance to gauge what width tyre will fit.
Is a 28 inch tire the same as 700c?
700c wheels have a diameter of 622mm. While most 28 inch tyres are for a 622mm wheel, some are not. Check the ETRO number on the sidewall to confirm.
Customer reviews and Q&A's are disabled because you declined functional cookies.
To enable reviews and Q&A's click the 'Cookie Settings' button below and enable functional cookies.
No longer available
Sorry you missed the CST Downhill Innertube PV.
This product is no longer available.