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Mountain Bike Undershorts EXPL 500 - Black

Sale price: $34.99 Regular price:

With its thick pad and breathable fabric, the ergonomic foam pad on these men's undershorts absorbs vibrations and prevents chafing and irritation.

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Sale price: $34.99 Regular price:

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San Francisco, 735 Market St. Options

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Model: 8580800

Product Videos

Product Features

Mountain Bike Undershorts EXPL 500 - Black | These mountain biking undershorts were designed for your mountain biking rides lasting 3 hours on average

With its thick pad and breathable fabric, the ergonomic foam pad on these men's undershorts absorbs vibrations and prevents chafing and irritation.

A photo of the Mountain Bike Undershorts EXPL 500 - Black in use

Seat comfort

Ride comfortably for up to 3 hours with the ergonomic foam pad (13 mm).

Moisture wicking

Actively wicks away perspiration to the outer surface for quick drying


Fitted cut without compression, very elasticated waistband


Elastane in the fabric to guarantee ease of movement.


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


170 g in size L.

Product Customer Reviews

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370 Reviews
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Mountain Bike Undershorts EXPL 500 - Black,black
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I offered these undershorts to my husband for his BD. He loves them: they are fitting perfectly, they are comfortable, and they prevent any soreness. I like them too because they go in the washing machine and they dry in a sec. Highly recommended

ST 500 mountain bike undershorts

Great short for the price . $25 for a pair of bike shorts can’t go wrong.

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Sizing is a bit weird. I went for a size larger than I normally have and that seems to fit ok. They are very comfortable though and have good padding. Cheap too, what’s not to love except the bonkers sizing.

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Sizing is nonsence - big waist ultra skinny legs

I recently bought 2 pairs of these to replace my old MT500 undershorts that are excellent, especially for the cost, and fit extremely well, but worn out now after years of use. Likewise, I have an old and new pair of the MT900 undershorts - and it is the same issue with crazy tight legs.bottom sizing (cannot get them on) but waist stated way larger . As the issue on the latest MT500 and MT900 is the same, below I paste the issue from the MT900 as its the same. As others have said, the latest (2021) version of these are sized/cut for a stick insect. Dont buy without trying on in store. Likely uou will need to size 2 times up and take the waist in. Decathlon, PLEASE fix the weird 'large waist/ultra skinny legs' fit - its mad! I have a 32" Waist, and like the pair of these I got years ago bought Large, which used to be for 82-89cm and fitted well 32-34" with a slim athletic legs/hips. The latest version Large MT500 now state on the label they are for 98-104cm (38-41")!! However, despite the claimed size being way bigger than my waist, I could barely get these on my thighs/bottom, they are so tight around the thighs and bottom, my legs started throbbing! And I have a slim athletic shape legs/bum - not a 'Chris Hoy' figure. Friends keep telling my I need to eat more and put on weight, so its not my shape, but the new cut of the shorts. The waist might just at a push stretch to 41" - but there is no way anyone with that waist would get them above their knees. The shorts themselves (my last pair) are excellent especially for the price, brilliant - the pad is fabulous, comfy, light. Such a shame they have totally ruined the cut. I am going to have to try an XL (for my slim build & 32" waist!) in store and hope I can then take the waistband in - as they are otherwise great value undershorts. Maybe these were a mis-manufactured batch - however I also have the excellent MT900 undershorts - and also an old pair - and its exactly the same issue. You would need absolutely pipe cleaner legs, no bottom and a huge waist for the cut to have the correct snug but comfy fit.

Poor stitching

Poor quality stitching; after 8–10 uses, stitches come out.

Hello Vinay

Hope you are doing well.

Thank you for taking time out to review our MTB shorts. I apologize as our product did not meet your expectation. At Decathlon we ensure our customers are satisfied with our products and service. We have a 2 year warranty on the stitching of our apparels. I request you to please visit the nearest Decathlon store where our team of sport advisors will be able to guide you further.

I stay available incase you need any further assistance from my end.

moubt bike short

It makes my bottom feel numb instead...not comfortable.

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Hi Thomas,

Thanks for your feedback about our ST 500 mountain bike under shorts. I'm sorry to hear that they are not comfortable for you.

If you're dissatisfied with the shorts, you may return them at any of our stores. Our product designers are riders themselves and monitor the reviews, so please rest assured that they are continuously working to improve our products.


Digital Sport Leader

Cycling & Roller Sports


Value for money

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Чудесен продукт!

Липсват му джоб/ове

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Благодарим Ви, за отделеното време да споделите обратната си връзка за нашия продукт!

Като спортна компания, която се стреми да направи спорта достъпен за всеки, нашата цел е винаги да предоставяме качествени и функционални продукти.

Спортни поздрави,

Екипът на Декатлон България


Velká spokojenost

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Gumové manžety na nohavicích příliš těsné

I přesto, že použitý materiál včetně polstrování vypadá slušně, tak kraťasy jsou pro mě nepoužitelné, protože gumové manžety na nohavicích jsou až příliš těsné na danou velikost. Bohužel nohu "škrtí" a nedokážu si představit, že bych v nich měl vydržet vyjížďku.

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Dobrý den, Radime,

děkujeme za Váš čas věnovaný recenzi tohoto produktu. Každá zkušenost je velmi cenná a pomáhá nám s vývojem nových modelů.

Chápeme, že ne každý střih kraťas vyhovuje všem naším zákazníkům. Z těchto důvodů máte vždy 90 denní bezplatnou lhůtu na vrácení pouze vyzkoušeného zboží. 

Za způsobené komplikace se velice omlouváme.

S láskou ke sportu


Gute Radhose

angenehm zu tragen, gute Polsterung

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Auf dem Bike, meinen wir natürlich 😁

Sportliche Grüße,



Ich habe vor Jahren die ROCKRIDER MTB Innenhose ST 500 Herren schwarz in 2xl gekauft und die ist sehr weit. In XL bekomme ich sie gar nicht erst an.

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Hallo Marcus,

vielen Dank, dass du dir die Zeit genommen hast, um deine Erfahrung mit uns zu der Mountainbike-Innenhose ST 500 MTB Herren schwarz von ROCKRIDER zu teilen.

Wir bedauern, dass du Defizite bei der Größenwahl feststellen musstest. Wir arbeiten mit einem internationalen Team kontinuierlich an optimalen Größenangaben. Dein Feedback werden wir an den zuständigen Projektmanager der Marke ROCKRIDER weiterleiten, um die Auswahl weiter zu verbessern.

Solltest du weitere Fragen haben, steht dir unser Serviceteam (service[at] jederzeit zur Verfügung.

Wir hoffen, dich in Zukunft wieder von unseren Produkten überzeugen zu können und wünschen dir noch einen schönen Tag.

Mit sportlichen Grüßen



Guten Preis-Leistungsverhältnis

Sitzt perfekt, sehr leicht,

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Additional Product Information


Main fabric: 87.0% Polyester, 13.0% Elastane ; Foam: 100.0% Polyurethane ; Yoke: 86.0% Polyester, 14.0% Elastane ; Lining: 100.0% Polyethylene

Undershorts support.

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.

A second skin with comfort to boot.

The pad has been designed for more regular users looking to progress in MTB. The support foam is also soft but more dense. It protects pressure zones for up to 3 hours. The foam is soft and the stretchy outer layer hugs the cyclist's body so the pad can follow their movements. Foam thickness: 13 mmFoam density: 100 KG/m3Foam firmness: 25 KPa

Shorts, undershorts.

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.

Care instructions

You can find detailed info on looking after your mountain bike clothing on our website

Product tests

Our team of product designers based at the B'Twin Village in Lille is continuously working to make cycling more comfortable for our users.Our obsession is to create products that meet the specific cycling needs of our users and eliminate hindrances to a good cycling experience.

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.

Storage instructions

Store in a clean and dry place.



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