Can you mountain bike in a funny t-shirt?

Yes, if it is made of a wicking fabric such as polyester or merino. Most funny bike shirts are cotton, which holds sweat and is uncomfortable on longer or hotter rides.

What print lasts best on a sports t-shirt?

Screen printing and DTF are both durable. Sublimation does not crack or block airflow but only works on polyester and is mostly used for full-colour jerseys. Wash prints cold, inside out, and never iron them.

What makes a good mountain bike shirt joke?

One that only riders get, about real trail life: climbs, crashes, gear obsession or the e-bike argument.

Are polyester t-shirts good for mountain biking?

Yes. Polyester wicks sweat and dries quickly, which is why most cycling jerseys are made of it.

Funny mountain bike t-shirts that you can actually ride in

The short answer

Search for funny mountain bike shirts and you will find thousands, mostly the same heavy cotton tee with a different joke printed on it. They are fine for the sofa. They are not great on a bike, because cotton soaks up sweat and stays wet. If you want a funny shirt you can actually ride in, check four things: the fabric, the print, the fit and the joke.

Full disclosure: I make one of these, so I have opinions. I will tell you where mine falls short too.

1. The fabric

This is the one most shirts fail.

Cotton: soft and cheap, but it holds sweat, gets heavy and rubs under a pack. Fine for after the ride, poor during it.
Polyester or poly blends: wick sweat off your skin and dry fast. This is what jerseys are made of, and what a ride-able tee should be made of.
Merino: excellent and naturally odour-resistant, but expensive and rarely used for printed joke shirts.

Check the product page for the fibre content. If it does not say, assume cotton. More detail in cycling jersey vs t-shirt.

2. The print

A print has to survive sweat, stretching and a lot of washing. The common methods:

Screen printing: durable, used for large runs. Thick ink can feel heavy on light fabric.
DTF (direct to film): printed on a film and heat-pressed on. Good detail and good durability, but it sits on top of the fabric and that patch breathes less.
DTG (direct to garment): ink printed straight into the fabric. Soft, but generally works best on cotton.
Sublimation: dye goes into polyester fibres, so it does not crack or block airflow at all. Mostly used for full-colour jerseys.

Whatever the method, wash it cold, inside out, and never iron the print.

3. The fit

A riding tee should be loose enough to move in but not so baggy it catches on the saddle. A classic or athletic fit works. Very slim fashion cuts ride up when you lean over the bars. Check the size chart, and look for a retailer that handles wrong sizes without fuss.

4. The joke

The best bike jokes are the ones only riders get. Generic "I'd rather be riding" slogans are for people who bought a bike once. The jokes that last are about real trail life: the climb, the crash, the gear obsession, the argument about e-bikes. If you have to explain it at the trailhead, it is not working.

Where to look

Print-on-demand marketplaces: enormous choice, low prices, mostly cotton, and quality varies from seller to seller.
Bike brands' merch: often well made, often more logo than joke.
Small rider-run brands: more likely to have a joke from the trail and a fabric chosen for riding, at a higher price.

Mine, honestly

The Watts tee is my attempt at this. The joke is for e-MTB riders: a stock chart on the back making higher highs and higher lows, which turns into the word WATTS, above "ARE OVERRATED". The fabric is a light 4 oz polyester that wicks and dries fast and still looks like a normal t-shirt.

The honest limits: the print is DTF, so that patch on your back breathes less than the rest of the shirt. It has no mesh and no UPF rating. It is $55.95, more than a marketplace joke tee, because it is printed to order on a technical blank, ships free, and is never discounted. Wrong size within thirty days, I print the right one and you keep the first.