Here’s the simple answer:
700 = 27.5 inches
40mm = 1.57 inches
Ok, here’s a more detailed explanation of what the correct kit is for your bike with a bonus history lesson
700x40c is the measurement of your bicycle tire and is sized according to what used to be known as the ‘French system’.
‘700’ is the nominal diameter of your tire, measured in millimeters.
‘x’ just means multiplied by.
‘40’ is the second number and is the nominal tire width, also measure in millimeters.
‘c’ is the identification code (from the old French system) for the tire width. This is the part of the tire that you’d see if you were sitting on the saddle looking down at the front tire. Today, this ‘c’ classification is usually obsolete, but it used to be part of a coding system in France that categorized tires from narrowest (‘a’) to the widest (‘d’). So, a ‘c’ tire would have been nearly as wide as they come.
Determining your tire size
Thankfully, for the majority of tires, this is a simple process.
First up, let’s find the tire sidewall. This is the part of the tire above the metal wheel rim. It’s often smooth (as opposed to the knobbly part that touches the pavement) and can be a different color, such as tan or white.
Take a close-up look at this sidewall and you’ll see words and numbers printed or embossed onto it. It might have the brand of tire (such as Continental) and you will also see the tire identification code “700x40c”.
To summarize, the diameter of your tire is nominally 700mm and width is nominally 40mm.
Choosing the correct tire size for your bike
Whenever you buy a new tire for your bike, make sure that it says “700x40c”. Search around for long enough and you’ll see a ton of tires that are nearly the same. Unfortunately, there’s so much variability between tire brands and sizing schemes, that “nearly” generally means “won’t fit”. Punctures and other issues are normally the result of tires that aren’t quite correct. It’s not worth the pain and cost.
So, just make two choices: (1) what brand you want and (2) how grippy the tires are. Smoother tires will be faster but may have less grip in slippery and icy conditions. Thankfully, I’ve got a tire for you that is great at both jobs.
Take a look at these tires which are fantastic value-for-money.
Made from a long-lasting compound, these have excellent puncture protection. Look closely at the tread pattern and you’ll something really interesting. What you get is a virtually unbroken strip of rubber down the center of the tread and knobbles leading up from there towards the wheel rims. What does this mean? Well, the knobbles give you good grip on loose stuff, particularly when you’re cornering. The smooth rubber in the center means that the tires will roll faster along paved trails and without the vibration that you get when using mountain bike tires on such surfaces.
A great choice and great value.
Tires? Sorted. Let’s move on to inner tubes
Thankfully, picking the correct size of inner tube for your bike is as easy as tires.
Here it is: pick a tube that matches the numbers embossed on your tire (i.e. “700x40c”).
The size of an inner tube varies with the amount of air that you fill them with. So, they’re sold by fixed diameter and range of widths e.g. “700×35-43” (which would work for tires ranging from 700x35c to 700x43c).
Want a recommendation? Well, this is an awesome tube from Co-op Cycles that has a Presta valve.
Quick bit of detail on Presta valves. If these look different from car tire valves, that’s because they are. Car tires have a type of valve called Schrader, which are shorter and fatter than Presta. If you have an air pump fitted for car tires, then you’ll have to pick up a little adaptor. They’re easy to fit and use and mean that your pump can be used for both Presta and Schrader valves from now on. Take a look at the pictures on Amazon for more info on how to use these.
You’ve got the tires. You’ve got the tubes. Now how do you fit them?
A little prep, a small amount of knowledge, and the right kit will mean that tires and tubes are easy to fit.
Make sure that, when you head out on the bike, you take:
- Spare inner tubes
- Tire repair kit
- Tire levers
- Pump (including the Presta valve adaptor)
Swapping out a tube and tire will then take around 45mins to carry out.
For an easy how-to guide, have a quick watch of this video.