Product Colors and Sizes

Special product, Innovation Special product, New Release Special product, Special product, Sale

Mountain Bike Undershorts ST 500

Sale price: $19.99 Regular price:
Color: Select a color
Size: Select a size
Size Guide
Sale price: $19.99 Regular price:

Free returns

Free shipping over $30

Free pickup

San Francisco, 735 Market St. Options

Select an available color and size to see options.

Model: 8529624

Product Features

A photo of the Mountain Bike Undershorts ST 500 in use

Mountain Bike Undershorts ST 500 is designed for mountain bike touring. Have fun exploring new playgrounds.

Are you looking for a good balance between support and simplicity for your rides? With their thick pad and breathable fabric, these ST 500 mountain biking undershorts keep you comfortable and cool.

Seat comfort

Ride comfortably for up to 3 hours thanks to the ergonomic 12 mm foam pad.

Moisture wicking

Stay dry: the airy mesh fabric quickly wicks perspiration.


More support for more comfort thanks to the elastic band and gel bands.


You just need one: these undershorts are compatible with our men's MTB shorts.

Product Customer Reviews

Skip to reviews
214 Reviews
Write a Review 

Mountain Bike Undershorts ST 500,black
Filtered by reviews Loading reviews…
Good quality... although I think a little small

I wanted to give cycling shorts a go as my bot was getting a little tender when out on the gravel paths on my MTB. I've only just started getting some exercise again and didn't want to spend too much on something I may not continue with so I purchased these. Initially they're a little strange to wear to start with - not quite as if you're wearing a soggy nappy, but it does feel as if you've got a little more going on down there than you had before. Pulling the shorts up as high as you can makes them a little more comfortable and the padding feels as if it's in the right place around the back of your premises, but front of shop will require a bit of rearrangement to ensure an enjoyable ride out. I've used these for two weeks now (yes, I've washed them and I have two pairs) and I can't help thinking I should've gone a size up. I'm a 32R in jeans and have little to no bum (I'm all belly) so despite some reviews reporting the shorts come up a bit small I thought in my condition size M would be pretty spot on. I think L may have been more comfortable for me, but as I've worn them I can hardly return them to try the larger size. Quality wise they seem fine to me. I've oiked them up a fair few times and they havent torn so personally I recommend them as a fine introduction into the world padded pants.

icon-circle-checkmark verified purchase
Visited first time to Decathlon store

Visited store to purchase cycle pant. Product is great and comfortable. As per visit of store it was great experience .. staff was friendly and helpful. Available sports item was fab.. everything can be available related to any sport in decathlon store.

icon-circle-checkmark verified purchase


icon-circle-checkmark verified purchase
Bad Fit

Found these shorts to be large in the waist but very tight round the thigh. Not the best of fittings. Returned and went for a completely different make, all be it at double the price.

icon-circle-checkmark verified purchase
Dear Sir,
I'm sorry to read that these undershorts did not fit well enough.
The Rockrider clothing team will pick up your review and take it into consideration for any future tailoring updates.
Peter, Cycling Manager, DECATHLON

The product is made up of good quality materials. The inner soft pad make riders bum shockproof..........!!!!!

icon-circle-checkmark verified purchase

Its very helpful for riders

icon-circle-checkmark verified purchase
Good product for lengthy bikers

Cycling made very comfortable with this. You don't feel any comfort if you wear this while cycling.

icon-circle-checkmark verified purchase
Rockrider st500 bike undershorts review

Good quality product

icon-circle-checkmark verified purchase
All terrain riding short

An excellent product i have been using it daily ,eay to wasy and a sturdy product.Not even a single tbread had worn out .If the cushion of the product is enhanced than product will more worthwhile.

icon-circle-checkmark verified purchase
Good fit

Helped me for my long rides on my bicycle. It's comfortable very much required for any long distance rider.

icon-circle-checkmark verified purchase
Mountain Bike Under pads

Very comfortable and nice material.

icon-circle-checkmark verified purchase
Useful product

Good quality product for outdoor cycling.

icon-circle-checkmark verified purchase
Great product

Comfortable to wear. Good cushion and grt price

icon-circle-checkmark verified purchase
Nice product


Bike Undeshorts

Excellent quality with excellent comfort while riding.

icon-circle-checkmark verified purchase
Skip to reviews

Size Guide

Size Guide Visual

Additional Product Information


Main fabric

  • 100% Polyester cationic

Padding - Inner fabric

  • 100% Polyester cationic

Padding - Outer fabric

  • 80% Polyamide
  • 20% Spandex

Are these undershorts supportive? we explain all.

Bibless undershorts can be much more practical. But do you get enough support? To guarantee the support you need, even without straps, we have made a pair of undershorts that hugs your body just like boxers. The elasticated waistband adapts to fit you and stays in place with no adjustment needed. And to stop the shorts riding up as you cycle along, there are gel bands at the bottom to keep your undershorts just above your knee.

A second skin with comfort to boot.

Feeling comfortable in the saddle is a top priority when you're on the go for several hours! For maximum comfort, even when you're hurtling down mountain bike trails, your undershorts have an ergonomic 12 mm foam pad. Besides making the saddle more comfortable, the pad reduces rubbing so you won't get chafed.

Several layers for less heat?

In the middle of summer in particular, you need to get rid of heat quickly. That's why the ST 500 undershorts have a breathable foam pad and mesh fabric, to wick away perspiration quickly. The result is that you don't warm up, even though you're wearing 2 layers of shorts.

How our ideas and your feedback made these undershorts.

We entrusted our mountain biking team with the task of designing bibless undershorts that give you a good balance between simplicity and support. It took 5 people 18 months of studying, designing, prototyping and running lab tests... And we also had your feedback. We traveled to France and Italy to meet up with around 30 intermediate mountain bikers and run a series of functional tests in real situations. The result was a product that's suited to your sport and meets your needs!

Shorts, undershorts, pad? here are our tips!

Undershorts are to MTB what kilts are to Scotland: you wear them against your skin! To avoid chafing, we therefore recommend changing them and washing them as if they were underwear. And when you're riding, your shorts and undershorts should never be attached. Why? Because each has their own role to play: - The undershorts stay in place for comfort and support. - The shorts move with you for better freedom as you cycle along.



Product testing

Our engineers always have real riders test all our products in real conditions. These tests round out our lab tests and let us validate all our products before they hit store shelves.

Superior quality. Unbeatable prices.

For 40 years, Decathlon has delivered the best value in the retail sports industry by offering high-quality, sustainable and cost-effective products.

Decathlon makes the difference
  1. product-research

    Research and development

    delivers high-quality cost-effective products

  2. State-of-the-art production processes

    minimize manufacturing costs

  3. Optimized supply chain

    reduces retail prices

  4. laptop-checkout

    Minimal retail footprint

    lowers overhead and indirect costs


Size Guide Visual