from Rookie’s keyboard

Hello, friends

You probably don’t know this, but I’ve been spending a few hours each week working as a bike mechanic at the local bike shop (my main job is in a warehouse).

And I routinely get into somewhat weird situations. I’m surprised how many people have very unexpected issues and requests.

The other day, a teenager came with two different wheels on his bike. He had a 27.5″ at the front and a 26″ at the back. And he wanted me to put a 26″ at the front to balance the bike and normalize its geometry.

He wasn’t sure whether this was possible because the fork was designed for 27.5″ wheels.

Well, it’s definitely possible in his case since the fork was designed for disc brakes. And when a fork operates with disc brakes, you can technically install any size wheel that would fit.

If the fork uses rim brakes, however, the brake bosses would be a bit higher, and the calipers won’t catch the rim.

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Below is a total list with all the requirements for swapping a 26″ wheel on a 27.5″ fork:

1. Tire Clearance

27.5 forks offer plenty of clearance for 26-inch wheels.

Still, it’s advisable to measure the distance between the fork’s blades near the crown if you’re running a road/urban fork and plan to use larger 26-inch tires.

Conversely, if you have an MTB fork as in my case, you can fit even wider tires thanks to the smaller rim diameter.

2. Correct Hub Width

The hubs and axles should match the dropouts of the fork. If the wheels are too narrow or wide for the dropouts, you can’t install them securely.

3. Disc Brakes

Disc brakes make for the easiest wheel swapping because the rotors are always in the center of the wheel regardless of its size.

Consequently, you don’t need new mounts when installing a smaller or larger wheel than what the fork is designed for.

Conversely, V-brakes, cantilever brakes, and Mini V-brakes create problems because the position of the brake bosses is dependent on the wheel’s size.

Smaller wheels require the braze-ons to be lower on the fork.

There are three main ways to lower the bosses, but none of them can be classified as convenient. Personally, I am not a fan. Nonetheless, here are the options:

• Cut the braze-ons and re-braze them

Theoretically, one can cut the brake mounts and re-weld or re-braze them lower on the fork’s legs.

If the fork is made of aluminum, thе procedure requires expensive welding equipment and heat treatment. In most cases, the hassle isn’t worth it monetarily and time wise.

If the fork is made of steel, the process is a bit easier, but it’s still necessary to find an experienced frame welder who can get the job done.

I wouldn’t bother. Just abort the procedure or get a new fork. Sorry for being so blunt.

• Remove the braze-ons and install V-brake clamp adapters

Another option is to cut the existing braze-ons and install V-brake clamp adapters lower on the fork. The downside of this approach is that V-brake clamp adapters are expensive.

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In my opinion, this conversion makes sense only if you have disc brakes.

Changes To The Geometry

If you put a 26-inch wheel on a larger fork, you can expect the following changes to the geometry of the bike:

• Lower bottom bracket

26-inch wheels will lower the bottom bracket unless they’re equipped with significantly fatter tires than the originals.

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It’s logical to think that the drop of the bottom bracket will equal half of the size difference between the wheels (1.5/2=0.75 inches), but in practice, the numbers don’t work quite like that.

The real diameters of the rims are:

26″=22in/559mm

27.5″=23in/584mm

The difference in rim diameter between 26″ and 27.5″ wheels is closer to 1in/25mm than 1.5in/37.5mm.

This is the value to use when calculating the lowering of the bottom bracket because it indicates the difference in diameter when both (26″ and 27″) wheels are equipped with the same tires.

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Therefore, the bottom bracket is expected to drop by roughly 1in/2=0.5in or 12.7mm.

The difference would be even smaller if the 26-inch wheel had fatter tires than the 27-inch model.

Is a 0.5-inch bottom bracket lowering a big deal?

It sounds like a small change, but it could be noticeable when riding on terrain with lots of obstacles. I recommended installing a bash guard to protect the chainring(s) and the bike.

In some cases, the lower bottom bracket may get the frame, and consequently the cranks a bit closer to the ground to the point where the pedals hit the ground when leaning to turn.

The Importance Of Having Matching Wheels

If you have a 27.5-inch bike and install a 26-inch wheel only at the front, the head tube angle of the bike will get steeper, and the rider’s weight will shift forward.

In the world of modern mountain biking, this geometrical change is undesirable.

To keep the bike’s new geometry as close as possible to the original one, it’s recommended to ride with matching wheels and tires.

The requirements for a 27.5-inch frame to accept a 26-inch wheel are the same as for the fork – if the frame uses disc brakes, you can proceed right away; if the frame relies on rim brakes, it would be wiser to abort the mission since the pads won’t align with the rim.

The Pros Of Running 26″

26-inch wheels offer the following benefits:

• Greater mud clearance

A smaller wheel would greatly increase the mud clearance of the bike.

• Faster acceleration

Smaller wheels accelerate faster than bigger ones because it takes less torque to get them rolling.

• Nimble handling

The smaller diameter of 26-inch wheels makes it easier to make tight technical turns.

• Fatter Tires

26-inch rims allow you to fit fatter tires than the original 27.5-inch ones.

• Stronger Wheels

All things being equal (rim, spoke quality…etc.), a smaller wheel is a stronger wheel thanks to the reduced diameter and shorter spokes.

• Lower center Gravity

26-inch wheels bring the bottom bracket closer to the ground and lower the center of gravity. The result is a bit more stability during tight turns.

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I hope this post was helpful.

Until next time, friends.

– Rookie