Advantages and Disadvantages of 29-Inch Tires and Tubes Compared

Well into the 2000s, MTBs were standardly equipped with smaller 26-inch wheels and tires, which gave the bike high maneuverability and a low center of gravity for off-road use. In moderate terrain, however, this isn'tnecessarily required. A mountain bike wheel with a larger circumference promises better rolling performance. The table below compares the respective pros and cons of the 29-inch size:

Tire Logic: 29-Inch Tires Fit 28-Inch Rims

Something worth knowing when buying a 29-inch tire or tube: there are no rims that actually measure 29 inches. A tire or inner tube of this size fits a rim with a 28-inch diameter, or 622 millimeters outer diameter in the ETRTO system. You could also say that 29-inch tires and tubes are simply the extra-voluminous version of a 28-inch model. 

The most likely reasons for splitting these into two separate tire size categories were, beyond better marketing as something new, the associated tubes and how they are sorted on store shelves. Tires and tubes wider than 50 millimeters are used almost exclusively on mountain bikes. To avoid mixing their products with those for road bikes, the extra-wide tires and tubes were given their own category. The one-inch larger diameter referencesthe noticeably longer radius of the complete wheel including the wide tire — the "29 inches" does not come from a precise measurement. In the ETRTO system for tire size designations, 29-inch wheels continue to belabeled the same as 28-inch tires and tubes: 622 millimeters. 

The 29-Inch Bicycle Tube

Tire casings from size 50 x 622 millimeters and up differ primarily in their tread pattern, weight, and puncture protection. These factors significantly influence the bike's riding characteristics. The same is true for tubes in the 29-inch size. Because they must expand to fit the large tire cross-sections, they very rarely fit tires narrower than 1.8 or 2.0 inches. A 28-inch bicycle tube, conversely, would have to stretch so much that its wall thickness — especially in the case of butyl rubber tubes — would become so thin that adequate flat protection could no longer be guaranteed, leading to frequent flats. So despite sharing the same rim diameter, you do needa dedicated tube for 29-inch tires — but which one?

Valve Types on 29-Inch MTBs

In the mountain bike sector, almost exclusively Presta valves (SV) are used, with Schrader valves (AV) being extremely rare — which simplifies the choice. Important: other valve types will not fit through the narrow rimhole designed for Presta valves. Valve length depends on the rim design and depth; the valve must protrude far enough from the rim for the pump head to seal properly. MTBs are rarely built with very deep rim profiles, so the vast majority of MTB tubes are butyl models with a short 40 to 42 millimeter Presta valve — for now.

The Conventional MTB Tube is Dying Out

Two innovations are set to displace the common butyl inner tube on mountain bikes, and therefore in 29-inch sizes: tubeless technology and the TPU tube. Tubeless tires are familiar from the automotive world — the tireand rim seal against each other using internal air pressure, there is no inner tube, and the valve must be airtight when bolted to the rim. The weight savings from eliminating the tube makes the entire wheel more agile, though part of this advantage is offset by sealant fluid. This latex sealant can fill and seal small holes in the tire without a tube. However, setup and maintenance are more complex as a result. 

A considerably simpler path to better flat protection and lower weight on a 29-inch MTB is the TPU tube. TPU as a material group used in bicycle tubes is relatively new, while the butyl rubber tube has been around forwell over 100 years.

The TPU Tube on Mountain Bikes

Even among specialized MTB tubes, the wall thickness of a TPU model is extremely thin. And yet the tube is more resistant to punctures and other damage compared to a conventional butyl tube. The low weight — especially so far from the wheel's center of rotation — has a positive effect on the bike's agility; acceleration and tight, fast corners require noticeably less effort. The weight savings over butyl can be as much as 81 percent! Even the AERON/TPU models with the best puncture protection are still lighter than a conventional tube. 

AERON/TPU tubes are extremely easy to deform, which not only extends their lifespan but also reduces energy loss when the tire and tube have to flex considerably more at lower air pressures. In this regard, an AERON/TPU tube is on par with an expensive latex racing tube. 

Advantages of the 29-Inch TPU Tube

The modern material TPU — a heat-moldable polyurethane — offers particular advantages in high-volume tire sizes. Larger circumference means a lot more material with butyl, and therefore a lot more weight that needsto be set in motion. By switching to an AERON/TPU tube, you bring this rotating mass down to roughly the level of a tubeless setup with sealant — depending on how much sealant is added, the tubeless configuration canactually be slightly heavier than the average AERON/TPU tube. 

And unlike butyl rubber, TPU is flexible enough that the same model can be used for both 27.5 and 29-inch wheels. Thanks to their high pliability, AERON/TPU models cover tire sizes from 1.7 to 2.5 inches. A variant upto 3.0 inches — or 622 x 76.2 millimeters — is even planned, and despite this, the version with a 40 millimeter Presta valve and maximum puncture protection still weighs under 200 grams.