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Rockrider ST500 Mountain Bike Undershorts Men's

Sale price: $20.00 Regular price: $24.99

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.

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Sale price: $20.00 Regular price: $24.99

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Final Sale: No returns or exchanges

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San Francisco, 735 Market St. Options

Select an available color and size to see options.

Model: 8529624

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Product Features

A photo of the Rockrider ST500 Mountain Bike Undershorts Men's in use

Rockrider ST500 Mountain Bike Undershorts Men's | These comfortable mountain biking undershorts are designed for rides lasting over 2 hours.

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.

Questions & Answers

Product Customer Reviews

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Rockrider ST500 Mountain Bike Undershorts Men's,black
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Good price

Great price

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Thank you for your review!

Doesn't sit right

Tient pas en place

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Nous sommes désolé de lire que vos nouveaux shorts de vélo ne tiennent pas en place. Si vous le souhaitez, vous pouvez passer en magasin et nous verrons avec vous se que nous pouvons faire!

Merci et bonne journée.

Fits well good quality

Fits well. Good quality .

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Hello Empress! 


Thank you for taking the time to write to us about your product experience.


We would really appreciate it if you could also drop us a google review, it will help others find out about our store easily: 


Wishing you a fantastic day :)


Decathlon Brampton Team

Nice and comfortable.

Great to wear under regular shorts for cycling. Comfortable to wear and they seem good quality for the price.

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Nice product


Good, but buy the next size up

Mine are size M, which is the same size as RC500(road) shorts. Whilst the size M road shorts are correct for me, these undershorts are a size too small. I've worn them twice but no longer as they're too uncomfortable. Size L would probably be OK.

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Great purchase

Ideal for everyday use.

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very comfy, size up bigger

Bought these to renew my old tired undershorts. Game changer for better comfort over those, the orange pad is much more moulded and considered for comfort, put up with discomfort post ride previously now non (4hrs + Scottish trail centre in summer sun conditions). Would definitely go bigger on size, I'm medium build 36" waist needed XL.

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Great for use under non cycling shorts

I use these under normal styles of shorts when cycling shorts are not convenient

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Hello Geoff,

Thank you for taking the time to post your review.

Have a good day,


Go 1 or 2 sizes up, but good overall.

Initially bought medium as that's never done me wrong before, but the thing couldn't get over my thighs. While not skinny legged, my legs aren't disproportionately huge either. Returned with no fuss and exchanged for a Large, these are also surprisingly tight around the thigh, but just about enough give to be wearable. They are designed quite short, with some rubber around the leg to grip on, which does work well, but means that you have to wear them like very short trunks, almost briefs. If you prefer undershorts that stretch most of the way to your knees, or that will cover your legs if your shorts ride up while cycling, I'd recommend getting a different style. The padding itself is decent, it definitely makes cycling more comfortable, I generally use them for 1-2 hours per ride, and feel the benefit compared to riding without. Probably wouldn't be as much use if you're really roughing it, but better than nothing.


Great pair of shorts, fantastic cushioning

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Advise you to check actual sizing

These are pretty decent undershorts for the price. I see that there has been a lot of complaints about the sizing. I would usually order a L or XL based on a 39-40 inch waist but when I looked at the detail on the sizing chart I ordered a 2XL which was perfect.

Bike underwear

Great quality and comfortable

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Brilliant shorts

Brought the shorts as my padding fell out of my cycle leggings. Brilliant still using them now

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True To Size (TTS)

After reading reviews I went a size up and purchased an XL, which I then returned for a L which is my natural size. I play football as well as cycle. I have somewhat of an athletic shape. Sizing can be difficult as it all depends on your waist, bum and quads. I’ve used them on 4 occasions now at 2 hours a ride and they are comfortable (no chaffing or soreness). I’d prefer them to be longer undershorts with more/additional padding under the glutes where it meets my hamstring but it does it’s job. I’m due to buy another pair.

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Size Guide

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Additional Product Information


Main fabric: 100.0% Polyethylene Terephtalate ; Padding - Inner fabric: 100.0% Polyethylene Terephtalate ; Padding - Outer fabric: 80.0% Polyamide, 20.0% 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


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