Sometimes, the term 29er causes some confusion when you have to pick the right size of tires, so rule #1 to keep in mind is that this wheel format relies on the 700C rim (28 inch), which is the same for road bikes, trekking bikes and a number of city bikes. As for the extra inch the represents the difference between the rim size (28) and the tire (29), that’s simply because the mountain bike tires have an increased height that leads to the 29 inch diameter.
We constantly received question whether road or trekking tires work on 29er mountain bike wheels. Before giving the answer, we must properly set things apart: on one hand there are slick and semi-slick mountain bike tires and on the other one there are the road and trekking tires. The main difference between this two categories is the height of the tires, an their balloon, the slick/semi-slick surpassing the other two in this matters.
With trekking/road tires being narrower and shorter in height comes the problem of using these tires on mountain bike wheels, since the mountain bike’s rim is wider (actually the letter C in „700C” indicates a certain width, that’s why in the case of 27.5 inch mountain bike wheels the transcription in the French standard is 650B, B being a wider size than C, that accommodates properly the tires. Read more about this here). So, before mounting the road/trekking tire, you should find out if your mountain bike rim has the proper inner width, which should be between 19 and 24mm. It’s important to keep to this guideline, otherwise the tire may come off the wheel.
Coming back to the main theme, why would you mount such tires on a 29er mountain bike? Obviously, for increasing rolling speed. From this point of view, slick/semi-slick tires do a pretty good job and they spare you the entire measuring protocole that’s needed. Also, they have a bigger balloon that provides more comfort.
Steering will be influenced by using knob-less tires, since the geometry of the frame is designed to work best with normal mountain bike tires. The wheel, basically, becomes smaller in diameter and you’ll have to adjust the way you corner accordingly. This goes for all the tires we discussed about so far, and beyond the deciding if it’s good or bad, you simply should know about this alteration.
Of course, a pivotal role in your choice will be played by the budget. A dedicated 29er slick tire, with the special type of compound will take a greater toll on your wallet than a trekking one, and given that trekking tires are not exactly high-tech through their very nature, this price difference can prove huge.
The advantages of slick or semi-slick
When you first mount a slick tire on your off-road machinery, it’s hard to not be impressed by the rolling speed. Of course, you cannot compare to the edge a real road bike gives you, but speed grows significantly. Among others, you’ll feel a shift in maneuverability, and, if the balloon is big enough, you’ll get some extra comfort. Also hybrid versions of tires (some like the semi-slick) can be successfully used on mild off-road paths.