Are 650b Wheel Size Is The Best For Gravel Bikes?

Are 650b Wheel Size Is The Best For Gravel Bikes?

Changing Gravel bike with wheel size 700C and 650B

Wheel and tire sizes for racing bicycles, gravel bikes or touring bikes are 700C and 650B. What’s the difference, and why do so many people change the size of their bicycle wheels?

Bicycle wheel sizes vary and change from time to time. In the past, the most common wheel size choices were 700C for race bikes and 26″ for mountain bikes. Then on mountain bikes came the 29″ wheel size for maximum speed, then followed by the 27.5″ wheel size as a middle between 26″ excess tires and 29″ excess tires. On a racing bike the 650B tires have been around for a long time, were forgotten, but are shining again.

The 700C bicycle wheel has the same bead seat diameter as 29″, which is 622mm. Meanwhile, the 650B wheels have the same bead seat diameter as 27.5″, which is 584mm.

Bead seat means the rubber tire hook on the rim / wheel. Although the bead seat is the same, the two types of tires are not always interchangeable, due to the influence of the shape of the rim, frame and other supporting components. Just like the size of a bicycle wheel, not all wheel sizes can be exchanged.

The French unit is used for racing bicycle wheels, while the inch is used for mountain bicycle wheels.

For a complete description of all bicycle tire standards, sizes and codes, see: Bicycle tire sizes.

700C Wheel Size in mm

As we know, the 700C race bike wheel and tire size has proven to be the ideal bicycle tire for speed, due to its thinner, aerodynamic, and lower rolling resistance. 700C racing bicycle tires, because of their slim and thin shape, need to be pressurized high. This makes for a more stable spin due to reduced surface resistance, and a lower chance of a snake bite. But these thin tires provide poor resistance to vibration and shock, so driving the 700C wheels on uneven roads is a real shock.

Bigger rims mean more weight, but at the same time, the heavier and bulkier the bike carries with it more speed momentum.

Wheel and tire sizes for racing bicycles, gravel bikes or touring bikes are 700C and 650B. What’s the difference, and why do so many people change the size of their bicycle wheels?

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Bicycle wheel sizes vary and change from time to time. In the past, the most common wheel size choices were 700C for race bikes and 26″ for mountain bikes. Then on mountain bikes came the 29″ wheel size for maximum speed, then followed by the 27.5″ wheel size as a middle between 26″ excess tires and 29″ excess tires. On a racing bike the 650B tires have been around for a long time, were forgotten, but are shining again.

This makes the 700C wheel/tire ideal for high speeds on asphalt or smooth roads.

Dimensionally, the 700C (622mm) tire compared to the 650B (584mm) tire, the bead seat diameter is 38mm or 19mm larger if the radius is calculated. This should make the length of the tire circumference larger, so that one revolution of the wheel will cover a longer distance than the smaller diameter 650B wheel. However, this is not always the case, which will be explained later below.

650b Wheel Size

650B bike wheels are nothing new, have been around for a long time and mostly developed in Europe, not as popular as they used to be elsewhere. But the trend of fatter bicycle tires, and the development of gravel bikes, made the 650B’s rims and wheels popular.

Despite having a slim size, most of the 650B wheels and tires used have a bicycle rim/vleg shape that is wider than the 700C. This wider tire accommodates more air volume, and also a thicker tire. Making it have properties that are more like mountain bike tires, thick, wide, can be used at low air pressure. Where these things will make the bike more comfortable, because the tires are thicker and the air volume is large enough to absorb and withstand more shocks.

This is what makes 650B wheels and tires widely used on gravel bikes. The gravel bike is a racing bicycle derivative that can be used on dirt roads or light offroads. A wider tread and a more aggressive shape make this tire a stronger grip on uneven road surfaces.

700c to 650b Convertion Chart

The 700C bicycle wheel has the same bead seat diameter as 29″, which is 622mm. While the 650B wheels have the same bead seat diameter as 27.5″, which is 584mm.

Bead seat means the rubber tire hook on the rim / wheel. Although the bead seat is the same, the two types of tires are not always interchangeable, due to the influence of the shape of the rim, frame and other supporting components. Just like the size of a bicycle wheel, not all wheel sizes can be exchanged.

The French unit is used for racing bicycle wheels, while the inch is used for mountain bicycle wheels.

For a complete description of all bicycle tire standards, sizes and codes, see: Bicycle tire sizes.

As we know, the 700C race bike wheel and tire size has proven to be the ideal bicycle tire for speed, due to its thinner, aerodynamic, and lower rolling resistance. 700C racing bicycle tires, because of their slim and thin shape, need to be pressurized high. This makes for a more stable spin due to reduced surface resistance, and a lower chance of a snake bite. But these thin tires provide poor resistance to vibration and shock, so driving the 700C wheels on uneven roads is a real shock.

Bigger rims mean more weight, but at the same time, the heavier and bulkier the bike carries with it more speed momentum.

What does the letter behind the wheel/tire size mean?

Standard Metric/French, states that a tire size of 700 means it has an outer diameter (rim + tire) of about 700mm. The letters on the back indicate the thickness of the tire (not the width) of the rim. So there are actually 700A, 700B, and 700C tires, where A is the thinnest and C is the thickest. People and manufacturers prefer 700C tires, so this type of C tire continues to be used and developed today.

As for the 650 wheel/rim/tire size, although the 650B is the most popular, sometimes we still encounter 650A or 650C tires.
Currently there is no longer an official standard for bicycle tire thickness. The influence of air pressure, tread shape, lug/stud thickness can make different tire thicknesses.

Tires are wide and thick on the 650B, making the overall diameter (tyre + wheels) on the 650B can match the wheels of the 700C. Example: A 650B wheel 50mm wide has the same outer diameter as a 700Cx25c wheel.

So that in this condition, one rotation of the 650B wheel + tire has the same mileage as the 700C wheel / tire. So that at the same Cadence, a wheel measuring 650B has the same speed as 700C. So it’s not always true that bigger wheels will produce higher speeds.

A few more examples of tires with different bead seat diameters yielding the same total diameter:

700C x 23mm = 668mm = 650B x 42mm

700C x 28mm = 678mm = 650B x 47mm

700C x 32mm = 686mm = 650B x 50mm

700C x 35mm = 692mm = 27.5 x 2.1”

700C x 38mm = 698mm = 27.5 x 2.25”

Some other plus advantages of the 650B bicycle wheel size is that it has a shorter wheel radius, which is useful for making the wheel stronger, stiffer, and responsive to pedal rotation.

 

The disadvantages of the 650B’s wheels compared to the 700C’s are more rubber, low air pressure not only absorb shock, but also absorb some of the pedaling force and create higher rolling resistance. Aerodynamically also because it is wider, more or less affects the speed. And if used at low air pressure, more potential to make the inner tube pinched.

So, in character, the wheels and tires of the 650B are more suitable for use on relatively uneven roads, and cyclists who prioritize comfort over speed.

Conversions and compatibility

Maybe we are never satisfied with the performance of our bikes. Those who use 700C wheels want to convert to 650B, or those with 650B tires want to use 700C tires. If you look at the explanation above, indeed each of these types of wheels has its own advantages and disadvantages, no wheel is perfect for all conditions.

Convert 700C to 650B

This is what most people do, namely changing the bike wheel size 700C to 650B. Reasons for getting a more comfortable wheel, more on uneven roads, or changing a race bike to make it more optimum for a gravel bike.

Size wise this should be easy to do, as the 700C bike is bigger than the 650B bike. But there are some technical things to note, namely:

Bicycle brake

If the bicycle uses disc brakes, then there is no need to do anything else. But if you use rim brakes, then there are several things that need to be modified or taken into account whether they can still be used or not. Rim brakes (cetilever, u brake, v brake and the like) need to grip the rim to hold the wheel. By changing the 700C to 650B, which has a smaller rim diameter, the rim position will be lower. The 650B’s rim position will be 19mm lower than that of the 700C, so it’s necessary to rim brake with a longer caliper, or change the position of the caliper brake mount further down.

The rim brake specifications usually include the reach. For example, a 700C bicycle uses Shimano 105 BR-R7010-R brakes which have a reach of 51mm, so to adjust the new wheels you need brakes with a reach of 51+19=70mm so that you can grip the 650B wheels well.

Tire clearance

If the brakes can be tricked, then the next thing to look at is the tire clearance or the width of the fork (front tire) or chainstay (rear tire) in contact with the wheel. Don’t let the wider 650B tires rub against the bike frame. So you should make sure the bicycle frame has a shape that is wide enough to fit wider wheels.

The widest position of the 650B tires is at a distance of 325mm from the axle or wheel hub. The width needed also actually depends on the width of the new tires to be installed, and also the air pressure. For 38mm wide 650B tires at least 42mm of space is required in the fork and chainstay. For 47/48 wide 650B tires, at least 58mm width is required on the bicycle frame. So measure a distance of 325mm from the center of the wheel, and make sure the area has enough space for the wider wheel.

Some bicycle frames also list compatibility for the 700C and 650B. But you should check the width of the fork and chainstay according to the size of the tire to be installed.

Boost hubs on mountain bikes and some race bikes usually have a larger clearance, because these hubs are designed for fatter and sturdier bikes, so they can be fitted with tires that are wider than normal tires.

Bottom Bracket

Another thing to consider is the height of the bottom bracket. After the new wheels are installed, the bottom bracket height may be lower by 19mm or about 2cm. The distance depends on the thickness of the 650B bicycle tire to be installed, the air pressure, and the weight of the bicycle. If the total diameter (rim + tires) is the same as the 700C bicycle wheel size, then at rest, the bottom bracket position will not change. In a depressed position, because the 650B tires are softer (more air), the bottom bracket and bicycle pedals can be in a lower position.

This can be a problem for bicycles whose pedals are almost or often hit the road surface (pedal strike), especially when cornering. The lower the potential pedal strike will occur more often. To be on the safe side, expect about a 15% drop in the bottom bracket from its normal height (rest).
The same analogy applies to 29″ frames that want to use 27.5″ or 26″ wheels.

Convert 650B to 700C

Wheel size conversion from 650B to 700C is rare, but it is possible under certain conditions such as availability of wheels or wanting to get a faster bike. What is certain that needs to be considered is the position of the rim brake that must be changed, if using disc brakes it should be safe. There should be no problem with the clearance and bottom bracket, because the 650B’s frame should be wider than that.

This principle also applies to mountain bikes that have 26″ or 27.5″ wheels, want to upgrade or change the wheel size to 27.5″ or 29″, whether it can be done or not.

When changing to a wider tire, pay attention to the position of the bicycle chain against its width when compressed. This may not be critical on a race bike, but on MTBs where tires are very wide, plus the lugs are more aggressive, there’s a chance that the tires will get too close to the chain position. Do not measure based on the width of the tire specifications, because the shape of the tire will tend to widen in the middle, and under pressure (receiving the load from the road or the driver) the shape will be wider. So the tire’s safety distance from the chain is calculated based on pressure conditions, taking into account the air pressure of the tires we usually use.

Convertion Chart Calculator

press the button below for wheel size change from 700c to 650b