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This post compares the differences between 700x37c and cycling 700x40c tires.

Weight Comparison

In theory, narrower tires should weigh less than wider ones of the same circumference.

However, many 40mm tires are notably lighter than 37mm ones because the final weight of the unit depends on the design and the used material.

In the table below, the average weight of the selected 40mm models is lower than that of the 37mm “rivals”.

The next table contains the weight of 37mm and 40mm tires representatives of the same model:

Conclusion: 37mm tires are roughly 10% lighter than their 40mm equivalents.

The difference may be important to cyclists trying to keep their machines as light as possible, but in practice, 40-80 grams are unnoticeable.

Air Pressure Comparison

The next table compares the air pressure supported by various 37mm and 40mm models:

Mismatched Models

Matching Models

Conclusion:

• When the tires are representatives of the same model, the max PSI difference is very small.

• 37mm tires can reach higher PSI. This property makes them better for cycling on the road because the greater air pressure results in lower rolling resistance which in return reduces the effort needed to propel yourself forward.

• 40mm tires can operate at a very low air pressure making them slower on the road but better performing off-road thanks to the increased contact patch. For that reason, MTBs and gravel bikes are often equipped with tires as wide as the frame and fork can support.

Also, low air pressure tires act as “natural” suspension and smoothen the ride.

The Advantages of 37mm Tires

1. Potentially Lighter

As the weight comparison has revealed, 37mm tires have the potential to be lighter than 40mm units because they require less material. The final weight, however, depends on the particular model.

2. A Slimmer Profile

The narrower dimensions of 37mm tires have the following benefits:

• Compatibility with a greater variety of frames and forks
• Easier installation of full fenders
• Less drag (narrower wheels are more aerodynamic)

3. Lower Rolling Resistance On Paved Roads

When the air pressure is equal, wider tires have a lower rolling resistance on the road because they deform less under pressure. The smaller deformation keeps the wheel as close as possible to a round circle. As a result, the wheel has an easier time rolling on the street.

However, this happens only when the tires are of the same model and operate at identical air pressure.

In practice, slimmer tires can be pumped to higher PSI minimizing the deformation and subsequently lowering the rolling resistance of the wheel. As a consequence, narrow tires have an easier time rolling on paved roads.

Note: The tread of the tires is very important too. Slick tires have a much lower rolling resistance on the road than all-terrain tires with an aggressive tread even when the air pressure isn’t very high.

The Disadvantages of 37mm Tires

1. Less comfort

Narrower tires cannot hold as much air as wider models and run at higher air pressure to avoid pinch flats.

The higher PSI results in a firm ride because the tire is not absorbing all the irregularities of the road.

The extra vibrations stress the joints when riding on uneven terrain.

2. More Difficult To Install On a Rim

Narrower tires are often more difficult to install and remove from a rim.

3. Worse Off-road Performance

Narrower tires are suboptimal for off-road riding because:

a. High air pressure tires don’t absorb bumps as well and cause the bike to jump upon meeting an obstacle. The outcome is reduced traction and subsequently stability.

For that reason, MTBs have suspension and run wider tires operating at low PSI. The extra cushioning keeps the tire on the ground and preserves traction.

Tubeless tires allow you to run even lower air pressure because there isn’t an inner tube that can get pinched.

The Advantages of 40mm Tires

1. Superior off-road Performance

40mm tires perform better on off-road terrain for the following reasons:

a. Lower air pressure + Extra Width

40mm tires can operate at lower air pressure. In the case of a tubeless system, the PSI can drop to 20-25.

As a result, 40mm tires become an “off-road monster” thanks to the superior absorption and the larger patch in contact with the ground.

b. Larger tread

The wider the tire, the bigger its tread can be. Since 40mm tires tend to be designed for off-road use, you will have an easier time finding one with an aggressive tread.

2. More Stability When Cornering

Wider tires are more stable when cornering thanks to the larger contact patch resulting from the additional tire width and the lower air pressure.

3. Better For Carrying Loads

Wider tires are better for hauling cargo because they reduce the stress transmitted to the frame, the rider, and the load.

4. Reduced Joint Stress

If you’re experiencing wrist, elbow or shoulder pain, a wider tire can alleviate some of it by softening the ride.

5. Better for Cities With Bad Roads

If you have to commute in a city that has less than ideal roads, wider tires will make the ride safer and more pleasant because you won’t have to worry about potholes as much.

The Disadvantages of 40mm Tires

1. Slower on the Road

Low air pressure tires are slower on paved surfaces due to the greater rolling resistance.

Additionally, wheels equipped with wider tires have a larger circumference making it a bit harder to pedal in higher gears.

If two bikes have the same gearing, but different size tires, the bicycle with the larger wheels will have the potential to reach higher speeds but will be more difficult to pedal.

That said, the wheel circumference difference between 700x37c and 700x40c tires is minuscule.

An average 700x37c wheel has a 2186.55mm circumference whereas that of a 700x40c wheel is 2205.40mm. The difference expressed in percentage is 0.86%.

2. Less Aero

Strictly speaking, wider tires are less aerodynamic than narrower ones. That said, the aero gains that one gets from running 37mm instead of 40mm tires are non-perceivable.

3. Require More Clearance

40mm tires are only 3mm wider than 37mm models, but volume increases in 3D (cubic fashion) rather than linearly. Consequently, 40mm tires take a lot more space than 37mm.

If you have a frame and fork with tight clearance, it could be difficult or even impossible to install 40mm tires (especially if you want to run full fenders).

4. More Tubeless-ready Models

Since many 40mm tires are designed for off-road use, you will have an easier time finding a tubeless-ready model.

Summary: What You Need To Know

1. The strongest features of 37mm tires are the extra clearance and the high air pressure. As such, they’re better suited for riding on the road.

2. 40mm tires, on the other hand, have better performance off-road thanks to their low air pressure and greater contact patch.

40mm tubeless tires can run at a very low PSI thanks to the absence of an inner tube.

3. The tread of the tires is very important too. For example, slick 40mm tires would roll better on the road than 37mm tires with aggressive treads.

4. The tire model has to match your goals. For example, if you want to ride gravel, a 37mm tire with a nice off-road tread would be a better choice than a slick 40mm tire despite the narrowness.

5. As long as the tire fits your bike and matches your style of riding, the difference between 37mm and 40mm tires isn’t big enough to cause a dramatic change in the performance of a recreational cyclist.