As a runner, I believed I understood apparel. Shorts are shorts. A medium is a medium. If a shirt fits too snugly, you nod sagely and say, “dryer shrinkage,” then carry on. Then I started cycling. The first time I ordered a “medium” jersey online, I unboxed what can only be described as a brightly colored blood-pressure cuff. I checked the tag three times, held it up to the light for a manufacturing error, and finally tried to put it on. My wife, standing in the corner, laughing. Somewhere around the elbows I realized cycling sizes are a different universe, governed by a council of very fast, very aerodynamic moths.

Here’s the discovery in plain terms. In running, a bit of “winter storage” around the middle doesn’t force a crisis. Shirts are forgiving, singlets drape, and no one expects you to look like a Greek statue sprinting for the 5K finish. In cycling, however, it is all about being aero. The kit is designed to hug every contour you’ve ever owned and a few you didn’t know came standard. Even if you’re not fat, hello, it’s me, with a modest reserve for cold fronts, your usual size can turn into a public service announcement. My standard medium? In some brands I’m an XL. In others I’m a polite “return to sender.”

Then there’s Racing Fit. This is not just tight; it’s aspirational. Racing Fit is for people who can say “marginal gains” without irony. Within the same brand, their “club” or “endurance” line might flatter your dignity, while the racing line will ask probing questions about your life choices. I’ve gone up two sizes in a race jersey from a brand whose casual top fits me normally, and I still needed assistance from a loved one to get out of it. Nothing says romance like “pull from the hem while I exhale for dear life.”

Bib shorts add a fun twist. As a runner, shorts are an on-off affair. In cycling, you climb into them, accept that you now live there, and only re-emerge using techniques learned from watching nature documentaries about caterpillars. The payoff is real, comfort on the bike is night-and-day better with a good chamois and proper fit, but the first try-on session will test your self-confidence.

Watt I learned

You think you know your body. You do not. Not to a cycling brand. A helpful translation chart would read: “Runner’s Medium = Cyclist’s Maybe L.” European brands often run leaner; American ones sometimes throw you a mercy inch. But even that rule folds the moment “Pro”, “Racing” or “Aero” appears in the product name. When in doubt, read customer reviews. If three people mention “spray-on feel,” they are seriously not kidding.

There is, despite the comedy, a happy ending. Once you dial the fit, cycling kit becomes performance gear in a way running clothes rarely need to be. A jersey that doesn’t flap is quieter and less distracting. Pockets carry snacks like a mini pantry. Bibs keep you comfortable on hour three when lesser shorts would not.

I’ve adopted a few survival truths. Try the brand’s “endurance/club” fit first, then audition the race line when you’re emotionally prepared. Accept that a little snug off the bike feels perfect on it.

Cycling sizes are a different language. My runner’s medium became a cyclist’s large (or two), especially in Racing Fit. Once you find the perfect fit, though, you too will be team Lycra.