In this article: You’ll learn how to choose the correct helmet size before purchasing and how to fit your helmet properly after receiving it.

Difficulty

★☆☆ Easy

Estimated Time

1 - 5 Min

Choosing the Correct Helmet Size

Step 1. Pre-Purchase: Measure Your Head For Sizing

How to measure:

1. Use a soft measuring tape. 
2. Measure around your head: 
   • Just above your ears 
   • About 1 inch above your eyebrows 
   • Keep the tape snug but not tight.

Lumos Helmet Sizing Chart

Notes:

• Most adult riders fit the standard M/L size.
• Lumos Nyxel helmet is available in Small and Large. Contact customer support for assistance in placing an order for either of these variants.
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Bern Youth Helmet Sizing Chart

2. Post-Purchase: Fitting Your Helmet

After you receive your helmet, follow these steps to ensure a secure and comfortable fit. 

Step 1: Place the Helmet

1. Loosen all straps and the rear adjustment dial. 
2. Place the helmet on your head. 
3. The helmet should sit just above your eyebrows and level on your head. 
4. Reference A/B/C diagram for common positioning: 
   • A – Correct Fit: Level, just above eyebrows, snug. 
   • B – Too Far Forward: Front of helmet too low, may block vision. 
   • C – Too Far Back / Too High: Sits above eyebrows, exposing forehead.

Step 2: Adjust the Rear Fit Dial

1. Turn clockwise to tighten or counterclockwise to loosen. 
2. Adjust until snug but comfortable. 
3. Shake your head gently—the helmet should remain stable.

Optional: add aftermarket padding if desired for enhanced fit.

Step 3: Adjust the Straps 

1. Fasten the chin buckle. 

2. Adjust side straps to form a comfortable "V" under your ears. 

3. Ensure the buckle does not press against your jaw. Ears should remain uncovered.

Troubleshooting

• Display won’t power on → Make sure the green Julet connector is fully seated and the arrows are aligned. Verify that your battery is properly connected and charged before testing again.

• Display turns on but doesn’t respond to buttons → Double-check that the control buttons are securely plugged in and that the connector pins are not bent.

• Display flickers or restarts while riding → Inspect the display cable for loose connections or tension near the handlebar. Make sure the cable is not pinched under the stem or zip ties.

• Display moves or tilts while riding → Loosen the bolts, reposition the rubber pads under the clamps, and retighten evenly to secure a firm grip on the handlebar.

• No pedal assist after replacing the display → Power off the bike and reconnect both the display and button connectors. A loose or partial connection can interrupt communication with the controller.

FAQs

• What is the standard Lumos helmet size MOD BIKES sells? 
  Most Lumos helmets sold by MOD BIKES use the standard M/L size option, which fits head circumferences from 54-61 cm. 

• Can I order a smaller or larger Lumos helmet? 
  If you need a smaller or larger size helmet, please contact our support team and we can assist you with that. 

• Do Lumos helmets include extra padding? 
  No. Extra padding is not included with Lumos helmet purchases and is not currently available separately in our store. 

• Which Lumos helmet size should I order? 
  For most adult riders, the standard M/L size fits comfortably and is what we recommend first. It is included in our bundled packages. 

• What if my helmet feels slightly loose? 
  Try tightening the rear adjustment dial and experimenting with aftermarket padding before sizing up or down. 

• Can I swap helmet sizes if needed? 
  Helmets are a final sale item and cannot be returned/exchanged, but your safety and comfort are very important to us. If your helmet does not fit correctly, please contact MOD BIKES Support before riding, and we will help determine the best solution.
  
  
  

Warning

⚠️ Important Safety & Liability Notice

Always wear your helmet properly fastened while riding. A helmet that is loose or improperly adjusted may not provide adequate protection.

Never ride with a helmet that does not fit correctly. Check rear dial and strap tension each time you put it on.

Local laws may require helmets—always follow regulations in your area.