The short answer
For summer mountain biking, wear something that pulls sweat off your skin and dries fast. A proper MTB jersey is the best tool for long, hot or rough rides. A light polyester tech tee does most of the same job on shorter rides and looks normal afterwards. Cotton is the one to avoid: it soaks up sweat, gets heavy and stays wet.
That is the whole answer. The rest of this page is the detail, including where my own shirt falls short.
Cotton: comfortable until you sweat
Cotton absorbs water and holds on to it. On a hot climb that means a heavy, wet shirt stuck to your back, which rubs under a hydration pack and turns cold the moment you stop or start descending. For a flat half hour on a cool morning it is fine. For a real trail ride it is the worst option you own.
MTB jerseys: built for the job
A mountain bike jersey is cut for the riding position. The good ones have a few things a t-shirt does not:
- Wicking fabric, usually polyester, often with mesh panels for airflow.
- A longer back, so it does not ride up when you lean over the bars.
- Raglan sleeves or moved seams, so nothing sits under pack straps.
- Sometimes a UPF rating for sun protection, or a small pocket.
The downside is that most of them look like what they are. Bright panels and team-kit shine work on the trail and look odd at the pub or the taco stand afterwards, which is where a lot of rides end.
Tech tees: the middle ground
A light polyester t-shirt wicks and dries like a jersey but keeps a normal cut and a matte finish. You give up the longer back, the mesh and usually the UPF rating. You get a shirt you can ride in and then just keep wearing.
For most summer trail rides under two hours, that trade is worth it. For a full day in the heat, or a ride where you will be stretched long and low on the bike for hours, a jersey is better and I would tell you so.
Does it change on an e-MTB?
A little. On an e-MTB you usually climb faster, so there is more air moving over you on the way up, but you also fit more laps into a ride and spend more time out in the sun. Many e-MTB riders wear knee pads because they spend more of the ride descending, so shorts that fit over pads matter more. The shirt question stays the same: wick, dry fast, no cotton.
The rest of the summer kit
- Helmet. The only item on this list that is not optional. A trail helmet with a visor keeps sun out of your eyes.
- Gloves. Light full-finger gloves save your palms in a crash and keep sweaty hands on the grips.
- Shorts with a liner. Baggy shorts over a padded liner are the standard. Go for a breathable outer and a liner that fits.
- Knee pads. Light, ventilated pads are comfortable enough to wear all day now.
- Shoes. Flat-pedal shoes with sticky soles or clipless shoes; either way, not running shoes on rocky trails.
- Water and sunscreen. Neck, ears and the backs of your arms burn first.
Where my shirt fits, honestly
I make one shirt, the Watts tee, so here is where it sits in all of this. It is a light 4 oz polyester tee that wicks and dries fast and looks like an ordinary t-shirt. It has no mesh panels, no longer back and no UPF rating. The print on the back is a film, so that patch breathes less than the rest of the shirt.
That makes it a good shirt for shorter rides, after-work laps and everything after the ride, and the wrong shirt for an all-day epic in 35°C heat. It costs $55.95, ships free, and if the size is wrong within thirty days I send the right one and you keep the first.