Skip to main content

When Size Matters

When Size Matters

Getting bike and helmet fit right for kids

By: Prevelo
Posted: August 26, 2022
Kid riding a bike over a wooden feature
Photo courtesy of: SDMBA

Before you get your little one on a bike, it’s important to make sure their bike and helmet are a good fit.

Bike sizing

If you are confused about how bikes are sized, it's not your fault. The bike industry has different sizing conventions for different types of bikes. Mountain bikes, road bikes and kids bikes are all measured differently. 

Kids bike frames typically indicate the diameter of the wheel in inches. So when you see sizes like 14, 16, 20 or 24, those numbers indicate the diameter, which is the length of a wheel running through the center.

The problem is that wheel size is a pretty vague indication of size. As evidence of this, check out sizing guides for adult bikes. Many adult bike manufacturers will size a bike for an adult that is less than 5 feet tall and an adult that's over 6 feet tall using the same wheel size, but changing the frame geometry. So, while kids bike sizes are indicated by wheel size, wheel size alone is not a reliable indication of whether a bike will fit your young rider.

The solution here is to use a size chart, which most reputable kids bike brands provide. There are two factors that are taken into account when considering sizing–rider inseam and rider experience

Rider Inseam

At Prevelo, we think the most important measurement is inseam. If the bike is too big for the rider's inseam, then the rider will have difficulty getting their feet on the ground - a fit which we don't recommend for many young riders. If the bike is too small for the rider's inseam, then the rider will be cramped, uncomfortable and inefficient. So this is really a critical measurement for children.

There are other measurements that are significant. For example, the rider's torso length and arm length impact reach. However, if the bike fits the rider's inseam, reach is seldom outside of an acceptable range. Further, a child can ride a bike with suboptimal reach, but if height is not within an acceptable range, the bike is likely to be unrideable.

How to measure inseam and size guide

Rider Experience

The second element we look at is rider experience. There's a progression that occurs with children on bikes. 

  • When children are first learning to ride they are most confident and safest if they can get their feet flat on the ground while seated in the saddle. We call this the Learner Fit
  • Once a child is comfortable riding, they can be fitted so they are on their tip toes while seated in the saddle. We call this the Pedaler Fit.

Fitting for the best experience

Helmet sizing

Wearing a helmet is good practice. But if a helmet doesn't fit well, it may be less effective at protecting the rider. Here's our handy guide to properly fitting a bike helmet.

Note: If the owners manual for your helmet tells you something different than what you see here, follow the owners manual. The people that made your helmet know it better than we do.

  1. Check Helmet for Damage. Inspect the helmet for any cracks in the shell or molding, worn straps and broken buckles. If any damages are found, it’s time for a new helmet.
  2. Position helmet on the head so that the front of the helmet is just above the rider's field of vision.
  3. As a guideline, the front of the helmet should sit approximately two finger widths above the rider's eyes.
  4. Tighten the retention dial until the helmet fits snugly on the rider's head.
  5. Adjust the helmet straps so that the "Y" sits just below the rider's ear.
  6. Adjust the chin strap so that it is snug (but not too tight) against the rider’s chin. As a guideline (1) the strap should push against the rider’s chin when the rider's mouth is fully open and (2) you should be able to just barely fit three fingers between the chin strap and the rider's chin.
  7. Have the rider shake their head vigorously.  The helmet should remain snug and tight on the rider's head.

Ready to go on a ride? Celebrate Take a Kid Mountain Biking Day all throughout the month of October.

IMBA's Take a Kid Mountain Biking Day (TKMBD) is celebrated annually on the first Saturday in October. This year, TKMBD is on October 1, and events are happening throughout the month of October.
Find an event near you

Organizations that register their events with us by August 31 will have a chance to win prizes from our event partners. We also have a toolkit and special swag for to give away to participants of events registered by September 16.
Register your event

"Side by side comparison of 14-, 16-, 20-, and 24-inch bikes"
About the author
Animated version of Jacob Rheuban

Prevelo is a bicycle company focused on making kids’ bikes hat are as confidence inspiring, easy, and fun to ride as possible. The inspiration for the company came to Prevelo founder Jacob Rheuban after researching bikes and teaching techniques, and watching his kids and their friends ride.

View complete profile

Ride Vibes

Positive trail vibes for all

Responsible riding is a simple and powerful tool that all mountain bikers can use to create a positive trail experience for all. We can make trails places of respect, inclusivity, safety, and enjoyment.

Spread good trail vibes
Two people riding mountain bikes on a trail
Photo courtesy of: