How To Measure Rim Width
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Cycling has come a long way in the past decade. I don’t think many riders saw gravel taking over and becoming a professional discipline or electronic gearing becoming standard on mid to high-end groupsets. We have seen a lot of new technology, and it’s exciting times.
One thing that has changed a lot when it comes to components is rim width. With the influx of many riders using much wider tires, bike companies have had to react with wider rims to suit. In this article, we’re going to be discussing:
- What Is Rim Width?
- Why Is Rim Width Important?
- How To Measure Rim Width
- What Size Tire For What Size Rim?
What is Rim Width?
Rim width is the distance between each side of the wheel where the tire sits. If measured from the outside, then it’s called external rim width, and if measured from the inside, it’s called internal rim width.
Rim width over the years has changed a lot, and we are seeing it get wider and wider to suit modern tires which people are using. A decade ago, it was around 15mm on a road bike, but in modern times, we see 19mm and sometimes even 21mm depending on manufacturers.
A common thing you will hear in cycling is 700c is the same size as 29”. Generally this is cyclists referring to the actual diameter of the rim. This is true as far as rim diameter goes, but what sets them apart from each other is the fact a 700c has a small internal rim width (Road Bikes) and 29” is a wide internal rim width (Mountain Bikes).
Internal Or External
Our readers often ask us if measuring a wheel internally or externally is better when it comes to a rim’s width. In our opinion, the better measurement to take is internal. We have always found it much easier to measure internally so you know exactly what you are getting. External rim width (Wheel width) is useful, but internal tells you much more.
Why Is Rim Width Important?
A lot of cyclists don’t understand the importance of rim width. It has to be right or fairly close for a bike’s tire to handle properly and safely. Manufacturers do design their tires to be used with certain sized wheel rim.
A very interesting fact about rim width is that it can change the tire’s size. A good example is if you put a 28c tire on a 17mm rim, you will see it to be around 28mm wide. If you put that tire on a 21mm wide rim, it can measure as wide as 30mm.
Using a tire that is too small for a rim can stretch it too much, giving an unforgiving ride and potentially damaging the rim. Using a tire that is too big is also just as bad because it causes the tires to roll and it becomes too round, making the cornering nasty.
Do Different Bikes Have Different Rim Widths?
Different bikes do have many various rim widths. They have to suit different types of tires that that bike will use. Generally, the wider the bike tire, the wider rim required to suit. Here’s an example of what you can expect.
Road Bikes
Road bikes require a smaller tire than most other types of bikes, so it requires a fairly small rim width. You will typically see a rim width of 15mm to 19mm on a road bike wheel.
Mountain Bike
A mountain bike requires much larger tires for off-road terrain, and because of this, you do need a wider rim. These will typically be 25mm to 35mm, giving the tire a nice wide flat surface.
Gravel Bike
A gravel bike is unique because it has to work with a wide range of tire widths. We expect a rim width between 20mm and 25mm on a gravel bike.
Also Read: Gravel Bike vs. Road Bike
Fat Bike
Then we have fat bikes, and these have very big rims. Because the tires are up to 100mm, you need wide rims between 40mm to 70mm, which is incredibly wide.
How To Measure Rim Width?
There are a few different ways to establish the rim width. Here’s what you need to know:
Manufacturer’s Details
The first and easiest way to establish rim width is to check with the manufacturer’s specifications. Not only do you not need to take your bike apart, but it also gives you the most accurate data possible.
For example, under the specification, Mavic’s Aksium Disc wheels say they are 17mm in internal rim width. Making them perfect narrow rims for tires roughly from 25c to 30c.
Self Measuring
Next, you can measure it yourself, which is easy to do. Here’s our step-by-step guide:
Step One: Measuring Device
The first thing you need to do is find a measuring device. Many people use a measuring tape, but we recommend using a vernier caliper instead, as this is a much better tool designed for much more accurate measurements.
Step Two : Remove The Tire
Next, you are going to need to remove the tire. This will require you to deflate the inner tube and use a tire lever to remove everything inside. Once done, remove everything from the rim itself.
Also Read: Bike Tire Valve Types
Step Three: Measure External
Now you are going to need to measure the external rim width. You can do this by taking your tape measure or vernier caliper and measuring the whole width from outside to outside on the straight edge of the wheel rim where the braking surface generally is.
Step Four: Measure Internal
Now it’s time to measure the internal rim width. You can do this by taking your tape measure or vernier caliper and measuring from inside of the rim where the tire bead sits and locks in. Using the internal part of the vernier calipers is the best way.
What Size Tire For What Rim?
So now you know what the rim width of your wheels is, what size tires should you use for the best performance possible? Well, we will start by saying there are a lot of differing opinions online from wheel and tire manufacturers. We have taken our data from a mix of as many as possible to give you this correct size chart.
| Internal Rim Width | Optimal Tire Size | Type of Tire |
|---|---|---|
|
17mm to 19mm |
23c to 28c |
Road |
|
19mm to 21mm |
25c to 30c |
Road/Hybrid |
|
21mm to 25mm |
30c to 45c |
Hybrid/Gravel |
|
25mm to 30mm |
40c to 2.2" |
Gravel/Mountain |
|
35mm to 40mm |
2.2" to 3" |
Mountain/Mountain Plus |
|
40mm + |
3" + |
Fat Bike |
What Can I Expect Using A Tire Too Big Or Small For My Rims?
We are often asked what we can expect from using a tire that is too big or too small for the rim that I have on my bike. Here’s what you need to know beforehand.
Safety Concerns
The wrong tires for the wheels shouldn’t be used. Although it might sound drastic, it can be very unsafe and we recommend not to go down this route.
Also Read: How To Adjust Bike Brakes
Tires That Are Too Small
Tires too small for a rim will stretch the tire out very far. So it makes the tires profile much bigger on the floor, and you will find the tires to measure much wider. With the tire this stretched, you will get less comfort, and you do need to be careful as it doesn’t give the rim much protection.
Tires That Are Too Big
If you were to put tires on that are too big, it doesn’t work very well. The first thing you will notice is the tires become incredibly rounded. So instead of having a fairly flat top, it’s curved. It offers a decent amount of comfort in a straight line, but the cornering feels very uncomfortable and almost like it wants to roll over.
Does Rim Width Matter?
Rim width is important, and it’s something many cyclists don’t know much about when it does make a big difference. It’s easy to get lost in diameter and tire width when there’s a reason we have 700c and 29”.
FAQs:
How do I measure wheel width?
Generally most cyclists do the same measurement for external rim width as they do for wheel width. The best way to do this is with a vernier caliper and the tire off. Measure at the rim and not the bolt pattern or bolt holes as this is wheel offset and we are not measuring for negative offset here.
Does the diameter wheel size affect rim width?
Smaller wheels often have wider tires making internal and external rim size bigger. We wouldn’t overthink it personally just use the right size tire for the wheel sizes you have.
Do I need to use the exact size tire for my rims?
Generally the overall dimensions of a rim will work for many sizes of tires. For example 17mm rim will fit tires from roughly 25c to 30c and all will fit properly. Try not to fall out of the manufacturer’s range.
Robbie Ferri
Robbie picked up a bike ten years ago at the age of 26. It started with a ride from London to Paris. Since then, he couldn’t get enough of big mile cycling and started bikepacking and eventually ended up racing ultra distance and even breaking world records.
Robbie has also worked in bike shops and closely with brands to design bikes and new products. Now he loves to share his knowledge and experience to add value to other people's cycling.
