The simple answer is this:
700 = 27.5 inches
45 = 1.77 inches
Unfortunately, this comes with a massive dose of “Be Careful!” because, when it comes to bicycle tires, nothing is ever quite so simple.
The better (and still simple) answer is this:
If you’re looking for 700x45c bike tires and inner tubes, then I’d recommend:
What can’t you just swap from millimeters to inches?
Before we get to that, let’s have a look in more detail about what 700x45c actually means.
Partly it’s a metric way of measuring bike tires and it’s also a throwback to the old French system of categorizing tire widths. Breaking it down, we have:
“700” = the nominal diameter of the tire
“x” = just means ‘multiplied by’
“45” = the nominal width of the tire (when you stand facing the front or rear of your bike and look at the tire)
“c” = this is a tire width code, using the historical French system. Today, this way of categorizing tires is generally obsolete. However, it was formerly used (in France) to distinguish between tires from the narrowest (known as ‘a’) all the way up to the widest (which were called ‘d’). So, a ‘c’ tire would have been getting up towards the widest tires available.
The old French system is just one of many ways of classifying tire sizes, and many countries had their own system. Tires are measured in millimetres, inches, and (more recently) and ISO system. Weirdly, you’ll find that some tires which are marked with inches in decimals (e.g. 1.75 inches) aren’t the same size as inches in fractions (e.g. 1 ¾ inches).
Confused? You should be.
All of which means that, with bike tires, converting from millimetres to inches isn’t a safe idea and can lead to problems with tires not fitting at all, or punctures.
Your safest bet is to swap tires and tubes for new ones that have the same reference numbers as your existing ones.
When you’re choosing new tires for your bicycle, make sure you pick ones that say “700x45c”. It’s as simple as that.
Maxxis have got some great tires and this one pictured here is a fantastic example. Perfect sizing for your wheels and they get great feedback from reviewers: good for paved surfaces and off-road trails, puncture-resistant, grippy, and fast. Everything you could want in a bicycle tire.
Look in detail at the tread pattern and you’ll see they’ve got tightly packed rubber lugs along the center and more open tread along either side. This is a great combination as it means the tires perform well on a wide range of surfaces. The solid center gives smoother travel on paved roads or hard-packed trails. The more-open tread up the edges gives good grip and confident cornering on trails with gravel or dirt surfaces.
700x45c inner tubes
Inner tube sizes are shown with the diameter (e.g. 700) and a range of widths (e.g. 32-47).
The width varies according to the amount that you inflate a tube and so it can be used with tires of different sizes. For this tube, it will work for tires of size 700x32c up to 700x47c. So, it’s great for our 700x45c tires.
How to fit tires and tubes
First up, you need some basic kit with you when you head out on the bike:
Spare tubes (I generally pack a couple)
Tire repair kit
Tire levers (plastic ones are best, I think)
Pump (including the Presta valve adaptor I mentioned earlier)
Replacing a tube should then take 45mins max to complete. There are five basic steps to fixing a flat tire:
Take off the bike wheel
Slip off the tube
Find out the cause of the flat (e.g. thorn or nail)
Either repair or replace the inner tube
Fit the bike wheel back on
For an easy how-to guide, have a quick watch of this video.