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Rockrider ST500 Mountain Bike Undershorts Men's
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.
Free shipping over $49
Final Sale: No returns or exchanges
Free returns
Free pickup
San Francisco, 735 Market St. Options
Select an available color and size to see options.
Product Videos
Product Features

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.
Stability
More support for more comfort thanks to the elastic band and gel bands.
Compatibility
You just need one: these undershorts are compatible with our men's MTB shorts.
Questions & Answers
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Product Customer Reviews

Great price
Thank you for your review!
Jessie
Tient pas en place
Bonjour,
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.
Chloé
Fits well. Good quality .
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Decathlon Brampton Team
Great to wear under regular shorts for cycling. Comfortable to wear and they seem good quality for the price.
Comfortable
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.
Ideal for everyday use.
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.
I use these under normal styles of shorts when cycling shorts are not convenient
Hello Geoff,
Thank you for taking the time to post your review.
Have a good day,
Desislava
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
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.
Great quality and comfortable
Brought the shorts as my padding fell out of my cycle leggings. Brilliant still using them now
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.
Size Guide

Additional Product Information
Composition
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.
Origin
Imported
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
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Research and development
delivers high-quality cost-effective products
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State-of-the-art production processes
minimize manufacturing costs
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Optimized supply chain
reduces retail prices
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Minimal retail footprint
lowers overhead and indirect costs

Rockrider ST500 Mountain Bike Undershorts Men's
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Heavy products return policy
If you return a product you will receive a refund for the purchase price plus any applicable sales taxes, less any non-refundable charges.
Decathlon will cover all shipping costs associated with your return except for items excluded from our return policy such as bikes, basketball hoops, snowboards, surfboards, tents, and other larger / heavier items.
Return costs for heavy products:
Weight Thresholds | Shipping within California | Shipping outside of California |
---|---|---|
> 9 lbs | $20.00 | $25.00 |
> 30 lbs | $50.00 | $65.00 |
> 100 lbs | $100.00 | $125.00 |
> 200 lbs | $200.00 | $230.00 |
If you return a product at any of our store locations, we will gladly help you find the best alternative product or refund you on the spot.
