Plus size is a term used to describe large-volume mountain bike tires for 27.5″ rims. They’re smaller than fat bike tires and wider than regular “Wide Trail (WT)” MTB tires.

Anything from a 2.8″ to a 3.5″ tire width is considered a plus-sized mountain bike tire.

They combine the benefits of 29″ diameter wheels with the disadvantages of fat bike tires: Momentum, traction and comfort with sluggish handling.

Since most bike frames don’t fit tires this wide, they are quite uncommon.

They were most popular before 29″ MTB wheels caught on but never made it to the mainstream. Now, they’re mainly used for adventure bikes that focus on comfort instead of speed.

plus size tire width and tread pattern
Plus size vs regular 29″ tires compared. // Image Credit: EMBN

These widths sit between the ranges for Enduro and Fat Bike tires and are a prime example of how tire width impacts the handling of an MTB.

Pros

  • momentum over rough stuff
  • more grip through larger contact surface
  • harder, durable compounds
  • comfort and forgiving
  • reduced vibrations and small bump feedback

Cons

  • higher rolling resistance
  • thinner, more vulnerable sidewalls
  • less support in corners
  • not suitable for muddy conditions
  • slightly heavier

Plus sizes blur this line between a couple of regular MTB tire sizes because the additional volume of a plus tire comes from an increase in both tire height and width.

Before the “plus” name stuck, these wider tires were also called 28″ – as the diameter is larger than a regular 27.5″. Almost as big as a 29″.

For example, a 2.8″ wide 27.5″+ tire is similar in diameter to a 29″ at 2.3″ width. See image above.

So, is bigger better?

There has been a trend over the last decades towards wider and larger wheels, hubs, handlebars, and bottom brackets. But there is a limit to all of these size increases.

Generally, mountain bike tires benefit from a wider profile and more volume. The increased surface area allows them to provide more traction, control and comfort over rough terrain.

Going wide comes at the cost of poor traction in sloppy conditions, corner instability, rolling resistance and heavier weight.

plus sized MTB
Hardtails can benefit from more tire volume like this plus sized adventure MTB

Plus tires can run harder compounds while keeping the same level of grip due to increased surface on the ground.

Due to the larger footprint and usually lower tire pressures (between 20 and 25 psi), they tend to feel less precise.

On the flip side, plus sizes can significantly compensate for rider mistakes and provide comfort on unfamiliar trails.

Size comes with weight

Surely all the extra rubber leads to a huge weight increase.

This reasoning is why manufacturers started out their plus tire line-ups with thinner sidewalls to save excess weight (and probably also bad press). Fully aware that the compromise in durability would lead to more punctures.

A weaker MTB tire casing also has less support in corners, when the tire has to hold up to lateral g-forces.

For a Maxxis Minion tire, in 2.3″ and 2.8″ widths, in exactly the same compound and casing, the plus tire is heavier by about 175 g. That’s 804 g for 2.3″ and 980 g for 2.8″ tire width.

plus size MTB
Weight is of little concern for some MTB disciplines

An entire plus-sized wheel (including rum and hub) would be 75 g heavier than its 29″ counterpart. So, depending on your wheel and tire setup, the plus-sized wheel may just end up very similar in weight and rotating mass to the 29er.

But in handling, as we discussed earlier.

Putting plus-size tires on your MTB

So, what about if you’re thinking of switching to plus size?

The first thing to take into account is if your frame is able to accommodate a larger volume tire, both in height and width.

These things are huge rubber whoppers. They are so wide, that only bike frames designed for them can actually fit plus size tires. Normal margins are usually tight.

They require the fork stanchions to be wider apart as well as a wider rear end so that the tires don’t rub on the frame.

IMG 0589
Margins are tight. Clearance is usually not abundant even using regular tires.

Secondly, a swap to plus tires may result in a rather significant change in bike geometry.

The difference in wheel height shifts the bottom bracket and center of gravity and impacts the handling.

Some newer bikes come prepared for this kind of wheel swap by employing a flip-chip. This lets you switch the frame geometry slightly to make of for different wheel sizes.

In any case, you need to check the frame measurements or user manual first and foremost before starting such a project.

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