- bt1
-
Accessories
- A - Z Accessories
- Bags
- Bells & Horns
- Bicycle Storage
- Bike Racks
- Books & DVD's
- Bottles & Cages
- Cameras
- Car Racks
- Childseats
- Bikes
-
E-Bikes
- Shop By Type
- Electric Mountain Bikes
- Electric Urban Bikes
- Electric Road Bikes
- Electric Folding Bikes
- Electric Cargo Bikes
- Shop By Year
- 2023 Bikes
- 2022 Bikes
- 2021 Bikes
- 2020 Bikes
- Shop By Brand
- Specialized
- Haibike
- Cube
- Giant
- Boardman
- Orbea
- Brompton
- Merida
- Shop all brands...
- Shop By Motor Brand
- Bosch
- Shimano
- Ebikemotion
- Brose / Specialized
- Yamaha / Giant
- Fazua
- Other
-
Clothing
- Shop By Brand
- Altura
- Castelli
- Cube
- Endura
- Fox Clothing
- Giant
- Shimano
- Shop all brands...
-
Parts & Components
- A - Z Components
- Bearings
- BMX Parts
- Bottom Brackets
- Brakes
- Cables
- Cassettes
- Chainguides
- Chainrings
- Chains
- Cranks & Chainsets
-
Helmets & Safety
- High-Vis & Reflectives
- Reflective Tyres
- Accessories
- Clothing
- Bags
- Shop all reflectives...
- Safety
- Bells & Horns
- Mirrors
- Eyes & Face Protection
- Goggles
- Cycling Glasses
-
Tech
- Computers
- Wired Computers
- Wireless Computers
- GPS Computers
- Turbo Trainers
- Turbo Trainers
- Rollers
- Turbo Trainer Accessories
- Shop all turbo trainers...
- Electric Bikes
- Electric Mountain Bikes
- Electric Urban Bikes
- Electric Road Bikes
- Wearable Tech
- Activity Monitors
- Power Meters
- Cranks & Chainsets
- Pedals
- Wheel Hubs
- Components
- Shimano Di2 Components
- SRAM Etap Groupsets
- Turbo Trainers
-
Help & Advice
- Contact Us
- Contact Us
- My Account
- Track Your Order
- Delivery & Returns
- Delivery Info
- Returns
- Useful Info
- Bike Finance
- Shops
- Price Match
- Tredz Ambassadors
- View all
- Buyers Guides
- Bike Guides
- Clothing Guides
- Accessory Guides
- Components Guides
- Lifestyle Guides
- Seasonal Cycling
- Brands
- View all guides
- How To Guides
- Bike Adjustment Guides
- Bike Maintenance Guides
- View all guides...
-
Cycle to Work
- Cycle to Work
- Cycle to Work Scheme
- Get your Online Quote
- Commute by Bike Hub
- Clearance
Smith Optics Mainline Mips Full Face MTB Cycling Helmet

Give credit where credit's due. Thank your mom, your legs, and your gear for giving you the opportunity to land that rocky gap. Made for going big, going fast, or both, the Smith Mainline is our pinnacle, downhill certified enduro bike helmet. Safety innovations like Koroyd™ and MIPS® provide energy-absorbing impact protection so you have the confidence to get aggressive on the trail. It doesn't matter if you're slaying the EWS in Whistler or suffering through the last stage of your local enduro race, you need a breathable, lightweight helmet that pairs well with goggles and fits like a glove. The Mainline integrates with your bike goggles for efficient venting and fog-free vision. Multiple pad sets including liners and neck-rolls let you customize the fit.
Key Features:
- 21 fixed vents for consistent airflow
- Adjustable visor
- Hybrid X-STATIC® / XT2® anti-bacterial performance lining for odor resistance
- Weight: (Size M, MIPS®): 27 oz / 77 g
- Sizes: S - 51-55cm, M - 55-59cm, L - 59-62cm
Protection
- Aerocore™ construction featuring complete Koroyd® coverage for lightweight, energy-absorbing and ventilated impact protection
- MIPS® Brain Protection System reduces rotational forces caused by angled impacts to the head
- CPSC CE EN 178 and ASTM F1952 downhill certified
Fit / Integration
- Designed for ultimate integration with Smith performance goggles for maximum comfort, venting and storage convenience
- AirEvac™ ventilation system integrates with Smith goggles for fog-free lenses
- Three washable cheek pad kits, two crown liners and two neck rolls let you fine tune the fit
- D-ring chin strap fastener for a snug fit
Occasionally, without notice, manufacturers change product design and/or specifications.

Smith Helmet Size Guide
Use the below chart and guide to find the correct size Smith helmet for you.
|
Head circumference (cm) |
S |
51 - 55 |
M |
55 - 59 |
L |
59 - 63 |
XL |
63 - 67 |
How to measure
To find the circumference of your head, place a tape measure in the centre of your forehead, wrap it around above your ears and around the back of your head. If there's a slight difference between two different sizes, always go for the tighter size.

Once you know the circumference of your head, see the available sizes shown on the product and select the appropriate one.
The majority of cycling helmets have some form of adjustment for size, usually in the form of a ratchet adjuster to tighten or loosen the straps, some helmets will also come with different thickness pads to further customise the fit.
Read our clothing size guide for more information on sizing.
Customer reviews and Q&A's are disabled because you declined functional cookies.
To enable reviews and Q&A's click the 'Cookie Settings' button below and enable functional cookies.


Smith Optics Mainline Mips Full Face MTB Cycling Helmet
Christmas Delivery
- this product is available for Christmas DeliveryCycle to Work is a salary sacrifice scheme, where you can save up to 42% off a new Bike and Safety equipment. This means the cost is deducted from your salary as a non-cash benefit, so you save on tax and national insurance.
Here at Tredz, we accept Cycle to Work vouchers from all national schemes. For more information click here.
At Tredz, we’re committed to bringing you the best products at the best prices. If you find a product cheaper elsewhere, simply contact us for an immediate response using our live chat service. Click here to discuss your price match with an agent now for help.
At Tredz, we offer a fast high quality service, with a range of options from free delivery on orders over £20, next day and convenient click & collect from one of our stores. Simply select within the checkout.
When you receive your bike, all you'll need to do is unpack it, attach the pedals, turn the handlebars and ride.
To help you get started we have put together a handy Bike Building Guide, click here.
At Tredz, if you are not 100% happy with your order, then you can use our simple hassle free returns service. Simply return the item new and unused in the manufacturers original packaging within 365 days of purchase. Bikes and larger items are collected by courier.
Love it glad I went with the smith over the fox pro frame really comfortable and stylish very well made not one bad point I can pick up on would recommend to anyone wonting a full face
£5 off voucher
Sign up to our newsletter
Get all the deals and special offers first
- Help
- Contact Us
- My Account
- Buying Guides & Reviews
- Size Guides
- Bike Glossary
- Product Recalls
- Sitemap
- Our Shops
- Tredz Cardiff
- Tredz Swansea
- Giant Swansea
© Performance Cycling Limited 2023. Tredz is a trading name of Performance Cycling Limited. All Rights Reserved Company No. 03398601 | VAT No: 797 0776 69
† IMPORTANT INFORMATION: Performance Cycling Limited FRN: 720557 trading as Tredz & Tredz Bikes are Authorised and Regulated by the Financial Conduct Authority. We are a credit broker, not a lender – credit is subject to status and affordability, and is provided by a panel of lenders of whom we have a commercial relationship. Terms & Conditions Apply. Performance Cycling Limited trading as Tredz is registered in England and Wales 03398601. Registered office: Icknield Street Drive, Washford West, Redditch, Worcestershire, England, B98 0DE. Performance Cycling Limited trading as Tredz is authorised and regulated by the Financial Conduct Authority. Our registration number is 720557. Credit provided subject to age and status.
† Novuna Representative Example: If total purchase price is £4,255.52 and your selected term is 36 months 14.9% APR Representative, Annual Interest Rate 14.9% p.a. Fixed with £0 deposit you would pay £145.38 per month. Total amount payable will be £5.233.68 with a cost of credit of £978.16.
† Novuna Buy Now Pay Later Example: If total purchase price is £4,255.52, payment holiday of 12 months and 24 monthly payments at 9.9% APR Representative, Annual Interest Rate 9.9% p.a. Fixed with £0 deposit you would pay £213.02 per month. Amount of Credit £4255.52, Total amount payable will be £5,112.48 with a cost of credit of £856.96. If the loan amount is voluntarily paid in full before the deferral period ends, interest will be waived but an early settlement fee up to £29 will apply.
Finance is subject to application, financial circumstances and borrowing history. Performance Cycling Limited FRN: 720557 trading as Tredz are authorised and regulated by the Financial Conduct Authority. We are a credit broker not a lender – credit is subject to status and affordability and is provided by Mitsubishi HC Capital UK PLC. Terms & Conditions Apply.
PayPal Credit is subject to status. Terms and Conditions apply. Performance Cycling Limited acts as a broker and offers credit from PayPal Credit. PayPal Credit is a trading name of PayPal UK Ltd Registered Office: Whittaker House, Whittaker Avenue, Richmond-Upon-Thames, Surrey, United Kingdom, TW9 1EH. † Full Representative Example: Representative 23.9% APR (variable), Purchase interest rate 23.9% p.a. (variable), Assumed credit limit £1,200.00.
PayPal Credit and PayPal Pay in 3 are trading names of PayPal UK Ltd Registered Office: Whittaker House, Whittaker Avenue, Richmond-Upon-Thames, Surrey, United Kingdom, TW9 1EH. PayPal Credit: Terms and conditions apply. Credit subject to status, UK residents only, Performance Cycling Limited acts as a broker and offers finance from a restricted range of finance providers. PayPal Pay in 3: PayPal Pay in 3 is not regulated by the Financial Conduct Authority. Pay in 3 eligibility is subject to status and approval. 18+. UK residents only. Pay in 3 is a form of credit, may not be suitable for everyone. Use may affect your credit score or make credit less accessible or more expensive for you. Consider if affordable for you. See product terms for more details.
Learn more about Pay in 3