Spring has sprung, and so it is time for me to get my mountain bike ready for a long summer of trail rides and morning commutes. The only problem is that I need to put new tires on my bike before it will be ready for even a trip around the block. So, I was wondering if I could put wider tires on my mountain bike to be more like the fat tire mountain bike I have been riding all winter.

A big front tire on a fat tire bike measuring nearly 5 inches wide
A big front tire on a fat tire bike measuring nearly 5 inches wide

Putting Wider Tires on Your Mountain Bike

Although you may never be able to convert a regular mountain bike into a full-fledged fat tire mountain bike, you can increase the width of your tires to some extent. The two main constraints are the width of the rim and clearance at the fork, with these kept in mind the width can be increased.

How Mountain Bike Tire Sizing Works

To begin, the most basic bit of information you will need to know is that mountain bike tires
come in three standard diameters. These diameters are…

  • 26 Inches
  • 27.5 Inches
  • 29 Inches

No matter what width your tire is this is the first thing that is necessary to consider when finding new tires for your mountain bike. The inside diameter of the tire must match the rim of your mountain bike or you’ll be completely out of commission as it simply will not fit onto the bike.

Most American mountain bike tire manufacturers will use this kind of marking to denote size although it is important to know that although marking that are in decimal form which are equal to their fractional counterparts are mathematically equal, in actuality they will be different sizes. It is always better to compare measurements found in the same format.

Mountain Bike Tire Wheel and Tire Width
Mountain Bike Tire Wheel and Tire Width

The second way that mountain bike tires are measured are by width. When it comes to regular mountain bikes the width will vary from 1.6 inches to 2.5 inches thick. Although, certain models will even come in at up to 3 inches, however, this is not the standard. Often thinner rimmed mountain bikes will accommodate widths around the lower end and thicker rimmed mountain bikes will, of course, fit the thicker ones.

I’ve had a chance to do real life “testing” on lots of different tires over the years. In-turn to share what I’ve learned and describe the characteristics of great tires I’ve compiled this list.

One good way to find exactly which size tire your mountain bike is meant to have by the manufacturers standards is to look at the number on the side of the tires that the bike came with. Understanding these numbers can be pretty easy with just a small bit of explanation. An example of what such a size denotation may look like is this…

27.5 x 2

Or perhaps

27.5 x 1 5/8 x 2

In the first example the first number (27.5) represents the diameter of the tire while the second number denotes the width of the tire. In the second example the optional representation of the height of the tire off of the rim has been placed in between the diameter and width. This is less common but you might encounter it so it is still important to remember.

But, these imperial markings do not always compare equally to rim diameters and widths perfectly, although the tire may seemingly “fit” the rim and in most cases will in-fact be the correct size. It is for this reason that the International Organization for Standardization (ISO), which may be formerly referred to at the European Tire and Rim Technical Organization (ETRTO) on some older mountain bike tires, has created a standard system of measurement markings. These marking will come in the standard sizes of…

  • 559 mm
  • 584 mm
  • 622 mm

These numbers match up to the common imperial sizes although are more standard amongst foreign and domestic manufacturers and in actuality denote the exact internal dimeter rather than the outer diameter of the mountain bike tires. Furthermore, the width of the tires in the ISO sizing system will also actually be shown before the number which represents the diameter. This number will be between 13mm and 40mm, again matching up to the imperial 1.6 to 2.5-inch denotation. Although rather than representing the width of the tires, it represents the internal width of the rim itself.

An example of what an ISO marking on the side of your mountain bike tire would look like is this…

Numbers on Side of Mountain Bike Tire
Numbers on Side of Mountain Bike Tire


This meaning that the tire is meant to accommodate a mountain bike rim which has an internal diameter of 622 mm and a rim width of 56mm.

How to Choose the Right Tires For your Mountain Bike

Putting all of these things together will allow you to choose a tire that fits. If you want to keep the same size tire as the one your bike came with then this is simple enough. Just match the marking on the side of your bikes tire to the new ones you plan to buy (considering the style of tire you want to purchase which I will be explaining further in a little bit). However, if you want to change the width then the process becomes a little different.

The two measurements which must match up to the designated sizes that your manufacturer recommends is that of the first and second ISO denotations. This cannot change much as if it did the tire would not fit correctly on the rim of the bike. However, the number which can change is the imperial measurement of the tire width. A

Again, two things must be considered when deciding how to change the width. The first is simply whether or not the width of the tire is one which will fit in-between the forks in the front, and whether or not it will interfere with the chain stay in the back. Aside from measuring these distances yourself there is no way to know whether or not the tire will fit, these do not have a standard size.

The second is whether or not the ratio of internal width and outer width for the tire is safe to have and will not cause any strange handling problems. Here is a diagram to show what ratios are safe and which are not.

The x’s represent those configurations which are safe. Furthermore, the outer dimeter measurements can be approximated to their closest imperial equivalents when comparing to the imperial denotations.

How to Measure the Fork and Chain Assembly for Proper Clearance

When trying to fit wider tires onto the mountain bike properly measuring everything beforehand can prevent a nasty surprise when you go to put the new tires onto your mountain bike. In the front you have to measure the space in-between the fork stanchions to accommodate for width and the height off of the rim to the first portion of the suspension that the tire may come into contact with to accommodate for the height of the new tire.

In the back depending on what your bikes frame looks like you may need to measure for width in-between portions of the frame. In any case, you are going to have to measure to see if the width of your new tire is going to, in any way, come into contact with the chain or chain assembly of your mountain bike. For obvious reason this would not be good.

What are the Benefits and Disadvantages of Having Wider Tires

Many riders these days prefer wider tires. The simple reason for this is that a thicker tire allows you to ride at a lower psi then thinner smaller volume tire. Having a low psi and a thick tire come with three main advantages…

  • Comfort: Riding at a low psi with a high-volume tire act as a sort of suspension system where a lot of shock is actually being absorbed by the tire itself. This is very beneficial when riding on ground that is not completely solid or trails that are particularly rough.
  • Easy Riding: Having thicker tires result in an experience which, overall, is more balanced. This makes it easier to control the bike at high speeds and when tackling uneven terrain. Wider tires provide a wider pivot point so it makes it more difficult to tip the bike.
  • Versatile: Bikes with wider tires can be great for trails and rough terrain, but they can also do really well with flat roads or trails. With a thicker, wider, tire you are not limited to one terrain as you could be with thinner tires.

Although, there are some disadvantages to having thick tires; all of which boil down to problems with increased friction. Having thicker tires by definition means that you are going to have more rubber touching the ground, and if your riding on the road a lot then this could mean that it won’t be as easy to get around. Particularly if you use your mountain bike for commuting.

Different Tires on MTBs
Different Tires on MTBs

Types of Mountain Bike Tires

  • Slick Mountain Bike Tires: These are specifically designed for road use and have almost no tread whatsoever. They do have a single track running across the circumference of the tire which creates V shapes that help when cornering.
  • Semi Slick Mountain Bike Tires: These tires are design which a smooth center and knobby sides. These provide maximum acceleration and rolling speed but still provide excellent cornering.
  • Knobby Mountain Bike Tires: These come in a wide variety of levels of aggressiveness in the tread. This is what are most commonly used for mountain biking as they provide the best traction in all situations.
  • Inverted Mountain Bike Tires: These have indentations which look exactly as you would think they would look like based upon the name. Instead of knobs that stick out they have indentations which go into the tire. These are often used for bikes that are meant mostly for road use but have the possibility of occasionally going off-road.

MTB Tools I Love and Recommend

Bike Hand Repair Stand
Bike Hand Repair Stand
Bike Hand 37 pcs Tool Box
Bike Hand 37 pcs Tool Box
Topeak Smartgauge D2 Air Pressure
Topeak Smartgauge D2 Air Pressure

I own each of these tools and only recommend things I own and use.

  • Bike Hand Bike Repair Stand.  Nice mountain bikes don’t have a kick stand so keeping your MTB safe but conveniently stored is essential.  I keep my bike on my stand whenever I’m not riding it.  This makes it easy to lube the chain, inflate the tires and adjust the derailleur.  Highly recommended – Bike Hand Bike Repair Stand (👈 Link to Amazon to see what thousands of others have said)
  • A basic MTB toolbox for replacing a chain, adjusting brakes and dialing in the fit.  Bike Hand has a 37-piece box that has most of the specialty bike tools to keep your MTB properly maintained.  The Bike Hand brand is value packed for the avid rider.  Check out the competitive prices with this link to Amazon 👉 Bike Hand 37 pcs Bike Repair Tool Kit
  • Get a good air pressure gauge, if you get just a tiny bit serious about MTBing you’re going to start playing with tire pressure.  A couple psi can make your tires sticking or not.  Get a good gauge, I highly recommend the Topeak Smartgauge D2, it’s accurate, flexible and easy to use.  An Amazon best seller, here’s a link 👉 Topeak Smartgauge D2
  • Carry a multitool with you on every ride.  I’m serious, most of the time you can MacGyver something to get back to the trailhead if you have a multitool.  I’ve got the Crank Brothers M19, it’s worn, rubbed and abused – but it still works.   Thousands sold on Amazon – check it out with this link 👉 Crank Brothers M19

How to Install a Wider Mountain Bike Tire:

  1. Choose the correct size of whatever tire style you plan to replace your old tire with. Remember to buy tires specific to the imperial sizing and if you are changing the width the other two specifications I mentioned.
  2. Turn the bike upside down and remove the axle allowing the wheel to be freed from the frame of the Mountain bike.
  3. remove the old tire by locating the valve stem and on the opposite side of the rim using the beveled end of a tire iron to separate the wheel from the rim. Keep doing this every inch until the old tire is completely removed.
  4. If your tire has a tube then wash it with water. It is a good idea to have the tube inflated to try and find any holes or tears. (Only do this if you plan on reusing the tube)
  5. Otherwise, put the new tire onto the rim. This should be easy as it is not yet inflated.
  6. Place the wheel back onto the bike and re-insert the axle to the mountain bike to re-attach the wheel to the frame.
  7. Pump the tire back up to the manufacturers standard or if you are an experienced rider then whatever psi you like to run the tires at.

David Humphries is the creator of DIY Mountain Bike. For me a relaxing day involves riding my mountain bike to decompress after a long day. When not on my bike I can be found wrenching on it or making YouTube videos at 👉 DIY Mountain Bike Read more about David HERE.