For every temperature, humidity, type of terrain and trail, there’s a perfectly dialled setup. One of the most important aspects of this has and will always be the tyres – with the pressure and type being the two main considerations to make. The attributes you should take into account when choosing a tyre include rubber compound, tread pattern, pressure optimisations, casing, weight, and whether it is front/rear specialized. Here we have compiled a guide that should serve as a reference when buying any mountain bike tyre.
Mountain bike tyre rubber compound
The rubber compound of the tyre is one of the most important components to consider, as it affects the weight, rolling resistance, grip in different conditions, rebound damping and how fast the tyre will wear. Durometer is the most common measures for rubber hardness, with higher numbers signifying a firmer compound (70a is harder than 50a for example). This can only broadly be used however, as the make-up of the rubber will also make a huge difference to grip, rebound damping and rolling speed. The most useful measure that the durometer gives us is how fast the tyre will wear, with tyres that have a lower durometer score wearing faster than those with a higher one.
Mountain bike tyre tread pattern
Open tread patterns with thicker, more aggressive knobs will bite into looser surfaces and pick up less mud, the drawback of which would be increased rolling resistance. Thicker knobs down the edge of the tyre away from the centre give better grip while turning. Riders on courses that do not require aggressive turning may prefer a more balanced, rounded tread than the on/off feel of aggressive outer knobs, in order to cut down on the rolling resistance.
Mountain Bike Tyre air pressure guide
The pressure you put in your tyres should vary according to the conditions. As a general rule for downhill riding you should try for the lowest pressures you can get away with. The thicker the casing and higher the tyre volume, the lower the air pressure you can risk without pinch flats or rim damage. This goal will be helped considerably by riding tubeless. For XC riding rolling resistance becomes more of a consideration, so the lowest pressure possible is not necessarily always what you would want.
Ideal Mountain Bike Tyre Casing
The casing of a tyre has a huge impact on the feel of the ride. As can be seen in the picture below (courtesy of maxxis – https://www.maxxis.com) the tread sits on top of the casing and is one of the biggest deciding factors in the quality of a tyre. A heavier (thicker) casing will result in a tyre that crumples / folds less while taking turns at low tyre pressure and will puncture less – at the expense of acceleration due to increased weight, though this may be made up by the better stability once momentum is gained (for example in downhill).
(Image from maxxis.com)
Casing can generally be divided into 2 types – single ply casing, which is less rigid and lighter (so works better for light duty trail riding to road) and dual ply casing, where 2 materials are used providing additional protection and stiffness for downhill and enduro.
A standard measure of the casing of a tyre that is often used is the TPI or threads per inch. A Lower TPI gives better puncture, cut and abrasion resistance but is heavier. A Higher TPI conforms better to the terrain, offering a smoother, more comfortable ride while reducing the weight of the tire. From this we can draw that in an ideal world you would want a tyre with the highest TPI that you can get away with in respect to cost and how often you puncture.
Optimal Mountain bike tyre weight
As has already been established, more aggressive tyres need to use more rubber to support the larger tread this adds weight which means less acceleration and more rolling resistance. Any rotating weight on the bike should be considered with extra care as weight on the wheel will have double the impact of weight anywhere else on the bike (when accelerating) – excluding the difference made by rolling resistance. What should also be considered however is the confidence inspired by bigger, more grippy tyres that allow you to brake less/later and pedal with confidence in areas you otherwise wouldn’t be able to. Furthermore higher volume tyres act as another more effective suspension system that is more sensitive, responsive and predictable than any fork or shock. As Specialized suggest with their tyres “smooth is fast” – a rider will become tired less quickly if he/she has had a smoother ride.
Front vs Rear specific mountain bike tyres
Using a wider, higher volume tyre for more grip on the front makes sense from almost every angle – allowing the rear wheel to slip is less likely to result in a crash, the front takes the biggest beating so any extra suspension will help giving extra cushioning where it is needed. Slightly narrower rear tyres can also help with tighter turns at the expense of air volume, reducing damping and control. Rear specific mtb tyres focus far more heavily on rolling resistance, usually with a characteristic low profile centre (as pictured below) and so are often more directional than their front tyre equivalent (knobs will be optimised for the tyre to roll in one direction).