Do You Need New Rims for Bigger Bike Tires?

Do You Need New Rims for Bigger Bike Tires?

If you are interested in changing the way your ride feels, you might consider putting bigger tires on your bicycle. Before you make any changes however, you should take into consideration whether you will need new rims for your bigger bike tires.

Do you need new rims for bigger bike tires? If you want tires that are bigger in diameter, you will need to get new, compatible rims. If you want tires that are bigger in width only, then your existing rims may work fine.

Buying bigger tires for your bike shouldn’t be that complicated. But there a few differences from one bike tire to another that don’t always make the right choice that easy. The bike you have and the type of riding you do will influence your decision. The rims your bike have will also factor into your choice. Ultimately, though, it’s whether you are looking at getting tires that are bigger in diameter or tires that are bigger in width.

Can You Put Bigger Tires on the Same Rim?

Bike tires and rim sizes are designed for compatibility. There is a distinct difference, however in bigger diameter size and bigger width size. You should first understand how tire sizing works.

Tire Diameter Sizing

Bike tire diameters may be measured in either nominal (traditional) or actual (ISO) size. Nominal sizing is vaguer, giving you a sense of relative size, but not telling you if a tire will be compatible with your rims. The International Standards Organization adopted a system to make diameter sizing more clear.

Called the true tire size, the ISO diameter description is represented by two numbers – the diameter of the inside, or more critically, the bead of the tire in millimeters, and the width of the tire in millimeters when fully inflated. The bead of the tire is the part that connects with the rim, so the true tire size is decided by what’s called the Bead Set Diameter (BSD).

Nominal Sizing

Bicycle tires come in an overwhelming variety of sizes. If you have an older bike, the sizing is even more confusing. To make things more confounding, before ISO standards, every country and most bike manufacturers had their own way of sizing tires. This created a situation in which same-size tires would be known by different numbers in different countries. To make matters worse, different-size tires that were not interchangeable were often marked with the same number.

The traditional system of sizing tires was based on the measurement of the outside diameter of a tire. This would typically be measured in inches (26, 27, etc.) or millimeters (650, 700, etc.).

As bike riding styles and tire manufacturing evolved, the measurements of the tires and rims became even more confusing. A bike tire, for example, that measured 26 inches at one point may have been tweaked to fit customers’ demands for something lighter and faster or bigger and more rugged. So, even though it is still considered a 26-inch tire, the outside diameter may be anywhere between 24-7/8 inches and 27 inches.

ISO Sizing

The European Tire and Rim Technical Organization (ETRTO) developed a system in the late 1970s to make tire sizing more consistent and clear. Their diameter sizing indicated the size of the rim, not the outer diameter of the tire. This makes the ETRTO system the most reliable guide to which tire will fit which rim.

The ISO adopted this system for use around the world. The ISO tire size is described by two numbers – the first number defines the width of the tire in millimeters, and the second number defines the diameter of the tire around the inside edge (the BSD), also in millimeters. As an example, an ISO size 25-622 describes a tire that is 25 millimeters wide with a bead diameter of 622 millimeters. The ISO size will either be printed on the tire sidewall or molded into the rubber.

The key ISO dimension is the three-digit number or the BSD. The BSD is the most important measurement that determines whether a given tire and rim will be compatible.

Typical Tire Diameters

There are six common tire diameter sizes that are used on today’s standard adult bicycles:

  • ISO 559 – This is the size used on most mountain bikes and some hybrids. Generally, any 26-inch tire with a width expressed as a decimal will be an ISO 559. For example, 26 x 1.0 or 26 x 1.75.
  • ISO 571 – This tire diameter is used for smaller road bikes and triathlon bicycles. It is mainly intended for competition. It is also called 650C or 26 x 1. A specific Schwinn bicycle, proprietarily labeled as “Schwinn 26 x 1-3/4” on the tire sidewall, also has the same BSD as ISO 571.
  • ISO 584 – Also called 650B, 26 x 1-1/2 or 27.5, this is used on most mountain bikes and was the standard size for most French utility bikes, heavy-duty touring bikes and tandems. The 27.5-inch version is a wider, knobbier tire that is also offered in an ISO 584 bead set diameter.
  • ISO 590 – This size tire was common on most English three-speed bikes, and used on some inexpensive 10-speed bikes. It is equivalent to the 650A and 26 x 1-3/8. It’s a popular tire size in Japan.
  • ISO 622 – Also considered a 700C or 29. This is most commonly used for modern road bikes.
  • ISO 630 – This is an older size, also called 27, but so many bikes were built with it, making it still readily available today.

Tire Width Sizing

Unlike with the tire diameter, bicycle wheels can handle a range of different widths. So, it is not absolutely necessary to replace your tires with one with the exact same width. As long as your bike has adequate clearance to handle a larger size, there are some advantages to getting a tire that is a little wider.

A wider tire will have a larger contact patch. It will provide better traction, less rolling resistance, slightly improved resistance to flats, and a much more comfortable ride. For most popular tires, there are a wide variety of widths available.

Typical Tire Widths

In the past, most rims designed for road bikes were relatively narrow, with an interior width of .5 inches or around 14 millimeters. In recent years, rim and wheel manufacturers have increased the width of the rims to improve aerodynamics, so it’s not uncommon to see rims of 17 millimeters or almost .75 inches. Even the narrower rims can accommodate tires as wide as 32 millimeters or 1.25 inches, but a typical road bicycle does not have adequate clearance to handle tires this wide, particularly if it uses rim brakes.

Typical widths for the city and touring bikes are 32 to 38 millimeters (1.5 inches). Most mountain bike tire widths are specified in inches, which typically range from 2 inches (about 50 millimeters) to 2.4 inches (about 70 millimeters) for cross-country and trail bikes, while enduro and downhill bikes will have even wider tires.

The most common width for road riding has historically been 23 millimeters although more bikes in recent years have come with 25 millimeters (around 1 inch) tires. These widths are the most recommended tires for recreational road cyclists. The 25 millimeter width is nice for long distance riding since it will provide a more comfortable ride.

For self-supported touring, a wider tire is desirable since the added load can be distributed over a larger contact patch. This will improve handling and reduce flats from occurring. If your bike can accommodate it, use a tire that is at least 28 millimeters (slightly over 1 inch).

Many touring and hybrid bikes will be fitted with even wider tires – up to 47 millimeters (almost 2 inches) wide. These wider tires will definitely provide a cushier ride, so if comfort is your main priority, sticking with these wider tire widths is a good idea.

For mountain biking, an even wider tire (2 to 2.5 inches) will provide more air volume which is beneficial for riding on loose surfaces. It will also prevent pinch flats on very rough terrain. If your riding is primarily on hard-pack dirt roads, a slightly narrower tire (1.5 to 2.2 inches) will reduce weight and provide better performance.

The Trouble with Tire Width

Keep in mind that not all rims and bike frames accept all possible tire widths. Usually going up one or two widths will work, as long as your frame can accommodate the larger sizing.

If a tire that is too wide for a rim is mounted, the tire shape becomes too tall and round – like a lollipop or a light bulb. It then becomes too floppy at the top because the casing is restricted. You will get more tire roll which creates more leverage on the tire, allowing the casing to collapse and roll over the rim, especially during hard cornering. Too wide of a tire will decrease traction and corner stability.

Reasons to Replace Your Bike Tires

There are really two primary reasons you would need to replace your bike tires:

  • Your tires have worn out.
  • You are not happy with how your bike handles or rides.

How to Identify Worn-Out Tires

Bicycle tires wear out in a number of different ways, but a common sign that they need to be replaced is that they continue to get flats. This can happen because the tread is so thin it can no longer protect the tube from sharp objects you ride over.

Inspect your tires when they are new, so you can recognize what good treads look like. Continuously check the depth of the grooves, and keep an eye on your treads. This way, when the grooves begin to disappear you know it’s time to replace your tires.

For most road bikes, tread wear-out happens around 1,500 to 3,000 miles for rear tires, and around 2,000 to 4,000 miles for front tires. Rear tires wear out much quicker because 60% of your weight rests on them.

Squaring-off is another sign of wear. This happens mainly to rear tires as the top of the tread flattens after many miles. Tires aren’t as fast after they have squared-off. If you continue to ride on the tires, you will eventually wear through the treads and expose the casing threads beneath it.

Tires simply wear with age, as well. If you store your bike for a long time, make sure to check your tires before taking a ride. The tread won’t be worn, but it might have hardened and cracked. Also, the casing (or sidewall) may have rotted, cracked or delaminated. All of this could cause a serious tire blowout.

Replacing Your Tires to Improve Ride Quality

Sometimes, you will want to replace perfectly fine tires because they don’t feel right or ride the way you like. This is common for off-road riders who require a particular type of ride for a certain course. But it can also be true for someone wanting a more comfortable ride for everyday purposes.

Increasing your tire width will not only provide a more comfortable ride, but you will also feel safer as there will be better traction and less chances for flat tires.

As long as you pay attention to the correct diameter size for your rim, and make sure that your frame has enough clearance, you should be able to put bigger, wider tires on your bike with no problems.