Differences Between 700C Road Wheels and 29er MTB Wheels

Differences in “Compatibility Standards” Between Road 700C Wheels and MTB 29er Wheels

When comparing the “standards” of road 700C wheels and MTB 29er wheels, both fall under the same category of the European standard ETRTO as “622C (for 700C tires)” wheels. However, there are three major differences: the “rim,” “hub standards,” and “usage standards.”

Let’s take a closer look at each of these points.

Rim Width

Road 700C wheels typically have an inner rim width of about 21mm and an outer rim width of about 24mm, which is narrower compared to MTB 29er wheel rims.

Though the rim width is narrow, to enhance high-speed cruising performance, aero effects are often targeted with rims that are 35mm or higher in height. Since road 700C wheels have narrow rims, they can maintain a lightweight even with high rim heights.

On the other hand, MTB wheels are designed for thicker tires rather than high-speed cruising. The inner rim width of MTB 29er wheels is typically 30mm or wider, with low-profile rims around 20mm high. High-profile rims would add significant weight, so low-profile rims are standard for MTB wheels.

These differences directly affect the types of tires that can be mounted.

Although both road 700C wheels and MTB 29er wheels fall under the 700C category (622mm diameter) in the ETRTO standard, the rim widths differ, meaning the tire widths that can be mounted are different.

Road 700C wheels often support tires up to 700x32C, whereas MTB 29er wheels are designed to mount tires of 29 x 2.1 inches or larger, which in ETRTO terms is equivalent to 700x50C.

In other words, road 700C wheels cannot mount MTB’s wider tires, and MTB 29er wheels cannot accommodate road tires like 700x25C.

Hub Standards

When considering the major way of purchasing wheels today, which is “pre-assembled wheels (wheels sold in a completed state),” the hub standards also differ significantly.

For road 700C wheels, the main hub standards for rim brakes are “Front 100mm, Rear 130mm 9mm Shaft/Quick Release,” and for disc wheels, they are “Front 100mm, Rear 142mm 12mm Shaft/Thru-axle.”

On the other hand, the mainstream MTB 29er wheels use a “Boost standard” with “Front 110 x 15mm, Rear 148 x 12mm Thru-axles,” whereas older standards used to be “Front 100 x 15mm, Rear 142 x 12mm Thru-axles.” For entry-level 29-inch MTB, due to price concerns, the “Front 100mm, Rear 135mm 9mm Shaft/Quick Release” type is common. Therefore, MTB wheels have three different hub standards, all of which differ from road standards.

For hand-built wheels, since you can freely combine hubs and rims, you can select a compatible hub for your bike to clear compatibility issues.

Differences in ASTM Standards

Although not very familiar, wheels may have ASTM standards that categorize their intended usage. For sport bicycles, it is common to use standards set by ASTM (American Society for Testing and Materials), the largest international standardization and certification organization in the world.

Road wheels are generally classified under ASTM Condition 1 (for paved roads). Some of the latest wheels also expect use on gravel road bikes, with products available under Condition 1 (for paved roads + smooth gravel roads). If you check the wheel manufacturer’s website, they will often specify usage restrictions for each ASTM classification, such as “jumps up to 10cm.”

On the other hand, for MTB 29er wheels, ASTM Condition 3 or higher is the standard. This is because MTB courses usually cannot handle the “jumps up to 10cm” that Condition 2 class wheels are rated for.

Not adhering to ASTM standards doesn’t necessarily mean the wheel is unusable, but for example, using an ASTM Condition 1 wheel on gravel could result in rim damage. Therefore, when riding on unpaved roads, the ASTM standard becomes an important criterion when choosing wheels.

Differences in Choosing Road 700C Wheels and MTB 29er Wheels

Road 700C Wheels: Choose Based on “Weight and Aero Effect”

When choosing 700C wheels for road bikes, the main focus is on “cruising performance on flat roads” and “lightness for climbing.” As a result, choosing wheels based on factors such as front and rear wheel importance and aero effects (rim height, aero spokes, etc.) is the mainstream approach.

Modern 700C disc wheels now feature ultra-lightweight options that weigh under 1,300g, and rim heights have shifted. In the past, a 35mm rim height was considered low, but now, wheels with rim heights above 40mm are common, offering better aerodynamic performance.

For road bikes that mainly focus on high-speed cruising on paved roads, the goal is to “ride faster and farther with less effort,” which is why weight becomes a crucial factor in the selection process.

MTB 29er Wheels: Choose Based on “Conditions and Compatible Tires”

On the other hand, while “lightness is important” for MTB 29er wheels as well, rideability over large obstacles and rough trails takes precedence. Therefore, when selecting wheels, it’s essential to check for ASTM standards that indicate wheel durability and whether they can accommodate thicker tires that offer better shock absorption.

While not all manufacturers specify the ASTM standards, the width of the rim and markings on the rim can provide a good indication of the compatible tire sizes.

For 29er wheels, tires with widths of 2.1 inches or 2.3 inches are the minimum, and even wider tires like 2.6 inches are common choices.

A 2.6-inch tire is equivalent to a 700x66C tire in ETRTO, which means that narrow-rimmed road wheels cannot accommodate such wide tires.

Can You Use Different Types of Wheels?

So, can you use road wheels on a MTB 29er bike or 29er wheels on a road bike?

The answer depends on the “hub standard” and the “tire clearance” of the frame.

First, if the hub standards don’t match, it will be impossible to mount the wheel to the bike. Specifically, the 29er MTB front wheels often use a 15mm shaft, making them incompatible with the 12mm axles on road bikes.

Tire clearance is also crucial. While it’s no problem if you’re using a narrower tire, if you’re using a wider tire, insufficient clearance will result in the tire rubbing against the frame or fork.

In other words, as long as the hub and frame/fork standards are compatible, it is possible to use different types of 700C and 29er wheels.

We’ve explored the differences between road 700C wheels and MTB 29er wheels. It’s important to remember that neither is inherently better; the distinction lies in the different uses and purposes. Choosing the right wheel for your needs is key.