Alpha Three

Size Guide

Prevelo Bike Sizing

Getting your kids the right size bike is important and, fortunately, also easy. You just need two pieces of information about your little rider:

  • Inseam
  • Rider Experience

Measuring Inseam

  1. Have the rider stand against a wall, hold a book between their legs so that it is firmly against their crotch (the same place their bicycle seat will be).
  2. Measure the distance from the floor to the top of the book.

Rider Experience

Children who are learning are more sensitive to bicycle height than children who already know how to ride a bike. For this reason, our recommendations for bicycle sizing vary slightly based on the experience lever of the rider. The chart below takes into account the fact that experienced riders tend to adapt better to a bike that is slightly larger. For this purpose we categorize young riders as either "Learners" or "Pedalers"

  • Learner: riders who either have not yet learned to ride a pedal bike, or are still frequently putting their feet on the ground while riding.
  • Pedaler: riders who can ride confidently and only put their feet down to stop.
Model Wheel
Approx. Rider Age
Learner Inseam
Pedaler Inseam
Alpha Zero 12" 1½ + 9.5 to 13.5
Alpha One 14" 2½ to 4½ 12.5 to 16 12.5 to 16
Alpha Two 16" 3½ to 6 16 to 18 with short seat post
(21.5 to 24 with long seat post)
15 to 17.5 with short seat post
(20.5 to 23.5 with long seat post)
Alpha Three 20" 5 to 9 18 to 23 17.5 to 22.5
Alpha Four 24" 7 to 11 24 to 29 23 to 28
Zulu Three 20" 5½ to 9 21 to 26 20 to 25
Zulu Four 24" 8 to 11 24 to 29 23 to 29

Get young riders on gears earlier.
Wheel Size:20 inches
Approx. Age Range: 5 to 9 years
USA Customers: In Stock - Ships Free and Fast!
Canadian Customers: Available in Canada Soon. Click to be notified.

20-Inch Wheels | V-brakes | 8-Speed

  • The 20" Alpha Three is our smallest geared bike. The 8-speed Shimano drive train and 11-34T wide range gearing is the real deal and gives growing riders truly usable gear range. It features:
    1. Prevelo confidence inspiring low and narrow geometry. Prevelo geometry keeps the rider low, balanced and in control.
    2. Lightweight 6061 aluminum frame with custom formed tubing.
    3. Lightweight aluminum alloy fork with chromoly steerer.
    4. Tektro front and rear v-brakes.
    5. Quick release front and rear wheels for toolless wheel removal.
    6. Three piece crank with squared taper bottom cartridge bearing bottom bracket and ultra narrow Q factor.
    7. Custom made cranks. All Prevelo cranks are sized specifically for each model bike, down to the millimeter.
    8. Shimano ALTUS 8-speed drivetrain. This 8-speed derailleur has a SHIMANO Smart cage. This unique pulley cage permits the use of a shorter pulley cage without comprising gear ratio width. Because kids’ bikes have small wheel diameters, rear derailleurs on kids bikes hang low and close to the ground. The Prevelo Alpha bikes use Smart cage derailleurs to keep things high and away from the ground.
    9. Shimano ACERA RAPIDFIRE Plus Shift Lever. Small hands have a hard time using twist shifters. We use reliable silky smooth thumb shifters. They are easy for small hands to operate, have an indicator display, and operate just like shifters on high performance bikes.
    10. 95% assembled. Just install the handlebar, seatpost, front wheel and pedals.
    Weight (including pedals) 18.9 lbs / 8.6 kg
    Minimum Saddle Height 20.7 in / 525 mm
    Maximum Saddle Height 25.5 in / 648 mm
    Bottom Bracket Height 8.1 in / 205 mm


    A Wheel Size 20"
    B Wheelbase 32.9 in / 835 mm
    C Effective Top Tube Length 17.4 in / 443 mm
    D Head Angle 69°
    E Seat Tube Angle 71.5°
    F Chain Stay Length 13.8 in / 350 mm
  • Components

    FRAME 6061 heat treated aluminum alloy custom formed tubing
    FORK Aluminum alloy blades with chromoly steerer tube - 35mm rake
    SEAT CLAMP Aluminum alloy with toolless adjustment
    FRONT BRAKE Tektro aluminum alloy V-brake
    REAR BRAKE Tektro aluminum alloy V-brake
    FRONT BRAKE LEVER Tektro aluminum alloy
    REAR DERAILLEUR 8-speed Shimano Altus double servo with Smart cage
    CRANK SET Prevelo anodized alloy 3-piece square taper with 110MM crank length.
    SPROCKET 32T with double chain ring guard
    BB SET Sealed cartridge
    HEAD SET 1 1/8" threadless
    RIM Aluminum with grinded sidewalls
    FRONT HUB Lightweight alloy 1-piece forged CNC with quick release
    REAR HUB Lightweight alloy 1-piece forged CNC with quick release
    TIRE & TUBE Kenda Small Block Eight Pro 20 ×1.5
    SADDLE Prevelo big kid saddle
    HANDLEBAR Prevelo aluminum big bore - 580mm width x 40mm rise with 31.8mm to 22mm taper
    HANDLEBAR STEM Aluminum 60mm extension
    GRIP Kraton rubber
    PEDAL Composite with 9/16 chromoly axle
  • Trying to decide between the Alpha Three and the Zulu Three? Click here to learn the difference:  Alpha Series vs. Zulu Series



What people are saying

Bottom line: We’re big fans of Prevelo’s Alpha Three, and highly recommend it for riders ready to step up to a 20″ bike!

- Wild Tales Of




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  • Reviews (3)

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Chad R.
United States

Great little bike for a growing cyclist

I bought this bike for my 5 yr old son who started on a 14" wheeled bike. Height wise he is just at the minimum for this bike, both in height and inseam. I didn't want to spend the money on a 16" wheeled bike that he might quickly out grow. The Alpha Three's frame is very accommodating, and will fit him as he continues to grow. It is truly a gorgeous looking bike. Right out of the box everything worked great. I only had to adjust the reach on the brake levers for his smaller hands. The shifting works great, and I like that the bike uses QR skewers and a traditional seat/seatpost design. I lowered his seat and moved it forward. I'm so glad I found out about this bike as there was nothing else out there this flexible with rider size. I wish the brake levers had more of a bend in them, so he could reach them a little better without straining his hands, but I do understand that this style will be more flexible in the long run. Thanks for an amazing bike, an easy shopping experience, excellent customer service and super quick shipping.

Alpha Three
Brian Y.
United States

Rocking the Alpha Three

My 5-1/2 year old daughter absolutely loves her Alpha Three. The kid-friendly brakes made the transition away from coaster brakes a snap. Understanding the gears and timing took minimal coaching and then it was ON. A couple clicks of the thumb you’re climbing up a hill with ease, push back with your index finger and you’re racing Daddy home! My daughter absolutely loves her Alpha Three and I would highly recommend the Prevelo line of bikes for all stages of young riders. You won’t be disappointed. Thanks again Prevelo! -Brian and Avery

Alpha Three

Best bike!

We got this bike for my 5 year old. He had been riding a two-wheel pedal bike for over a year. The bike he had was getting boring for him. Not to mention, he wouldn't stand and pedal when going uphill. As soon as he got this bike, the excitement came back for him. He loves being able to switch gears! On top of that, for some reason, he has better form (stands when going uphill etc). This bike is amazing and it was worth every penny. I like for my boys to get outside and do some physical activity and this bike helps motivate him to get out there. It's well made, easy to maneuver and most importantly, fun!!