Condensed answer: It’s possible to install 27.5-inch wheels on a 26-inch frame if there’s enough clearance, and the bike uses disc brakes.
The conversion limits the width of the tires and could also greatly impact the geometry of the bicycle to the point where the modification becomes questionable.
In most cases, the effort isn’t justified. It’s better to stick with 26-inch wheels or switch to a dedicated 27.5-inch bike.
Requirements To Install 27.5-inch Wheels On a 26-inch Frame
To install 27.5-inch tires on a 26-inch frame, the following requirements have to be met:
Most 26-inch frames have enough room to accept a 27.5-inch wheel as long as the tires aren’t very wide.
To know with certainty, it’s best to use a 27.5-inch wheel equipped with the tire that you want (or a model with a similar width) as a reference.
You can borrow a wheel from a friend or go to a bike repair shop. More than likely, they will have multiple 27.5-inch wheels available.
2. Disc Brakes
Rim brakes are no good for this conversion.
27.5-inch wheels have a larger rim diameter than 26-inch wheels. When you insert a 27.5-inch wheel into a 26-inch frame, the rim ends up too far above the brake bosses, and the brake pads can’t grab it.
Conversely, disc brakes do not create this issue because the rotor is always at the same place (the center of the wheel).
Having said that, there are ways to make the conversion work even with rim brakes. The solutions will be discussed further in the article.
Changes To The Geometry
27.5-inch wheels will affect the geometry of the bike as follows:
1. Bottom Bracket Elevation
The larger 27.5-inch wheels will raise the bottom bracket of the bicycle.
26-inch rims have a 22in/559mm diameter whereas that of 27.5-inch wheels is 23in/584mm.
If all other parameters are equal (tire width, air pressure…etc.), 27.5-inch wheels will raise the bottom bracket by 0.5 inches. This number is derived by calculating the difference in rim size (23in-22in) and dividing it in half.
The division is necessary because only one part of the wheel is in contact with the ground at every point. Hence why we use the radius rather than the diameter of the wheel to calculate the bottom bracket elevation.
How will a 0.5in higher bottom bracket affect the bicycle?
It’s hard to tell because every frame is different. Having said that, a higher bottom bracket is expected to decrease stability when cornering because the bike would have a higher center of gravity.
The positive side of a higher bottom bracket is the extra ground clearance which is helpful when covering terrain with lots of obstacles.
2. Longer Wheel Base (Potentially)
A bike’s wheelbase is the distance between the front and rear axle. If the frame has sliding rear dropouts, and you have to push them back to accommodate a 27.5-inch wheel, then the wheelbase of the bike will increase ever so slightly too.
A longer wheelbase is considered good for stability but hurts maneuverability.
Note: If the 27.5-inch wheels are equipped with substantially narrower tires than the 26-inch model, then the difference in wheel circumference will be very small. As a consequence, the changes to the geometry of the bike will be minimal.
26 To 27.5-inch Conversion and Rim Brakes
As already mentioned, rim brakes create a major problem when converting to 27.5-inch wheels because the brake mounts are placed lower than necessary.
To make the set-up work, one can try the following options:
- V-brake elevators
There are V-brake adapters that mount to the original brake mounts to provide elevated braze-ons.
- Clamp-on V-brake Bosses
Another option is to install a set of V-brake clamp-on bosses a bit higher than the original braze-ons. This way the brake shoes will end up at the right location.
The downside of this method is that V-brake clamp-on adapters could be expensive and don’t always make financial sense.
- Re-weld The Braze-ons
Another option is to cut the brake bosses and re-weld them to an appropriate place. This approach requires welding experience and special equipment. Most people will have to hire a skilled frame builder to get the job done.
The Advantages of Converting To 27.5-inch Wheels
1. Smoother Ride
Larger wheels have a greater “roll-over-ability”. Or in other words, they roll over small obstacles better than smaller wheels. The result is a smoother ride.
2. More Grip
Since the wheel is larger, the contact patch is greater too and provides extra grip.
The Disadvantages of Converting To 27.5-inch Wheels
1. Limited Tire Width
If you convert a 26-inch bike to 27.5-inch wheels, you won’t be able to run wide tires with large threads due to the lack of clearance. If you’re riding off-road, this limitation will be a major problem.
2. Poor Fender Clearance
Larger wheels will limit your options when it comes to fenders too. Chances are that there won’t be enough space for full fenders, especially if you run the widest possible tires.
If you plan to use the bicycle for touring or commuting, this issue could create a lot of annoyance because full fenders offer the greatest protection and no other model comes even close.
3. Poor Mud Clearance
The reduced distance between the frame and the fork’s arch will make mud accumulation a real problem.
4. Compromised Geometry
The new wheels will raise the bike and subsequently affect its geometry. As a consequence, the handling of the bike may suffer noticeably.
Unfortunately, it’s difficult to predict to what extent because every set-up is different. You won’t know how the bike will feel until you try it out. Be prepared for unpleasant surprises.
5. No Warranty
There’s a strong chance that the manufacturer of the frame and fork won’t respect the warranty if you install 27.5-inch wheels because the components haven’t been designed for such use.
6. Low Financial Incentive
Truth be told, the difference between 26 and 27.5-inch wheels isn’t groundbreaking enough to justify a “ghetto” transition. Many people would be better off keeping their existing 26-inch wheels or buying a “real” 27.5-inch bike.
7. Suspension Issues
The reduced clearance opens an avenue for problems for bikes with suspension.
The front tire can easily come in contact with the fork’s crown when the fork reaches its maximum travel (bottom out). This malfunction could cause an accident due to loss of control.
In addition, the rear tire can just as easily hit the seat tube if the bike is full suspension.
Summary: What You Need To Know
It’s possible to install 27.5-inch wheels on a 26-inch frame if:
- The bike uses disc brakes
- The tires aren’t very wide
- There’s enough clearance for unhindered operation of the suspension.
The pros of the conversion are:
- Smoother ride
- More grip
The cons of the conversion are:
- Unpredictable bike handling
- Low financial sense
- Poor mud clearance
- Limited tire choices
- Poor fender clearance
- Voided warranty
- Suspension issues due to lack of clearance