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 + 12.5 to 16.5
Alpha One 14" 3 to 5 13.5 to 16.5 13 to 16.5
Alpha Two 16" 4 to 6 16.5 to 22
15 to 22 
Alpha Three 20" 5 to 9 20 to 23 17.5 to 23
Alpha Four 24" 7 to 11 24.5 to 28 23 to 28
Zulu Three 20" 5½ to 9 22 to 26 20 to 25
Zulu Four 24" 8 to 11 25 to 29 23 to 29
Speed Silver
Power Purple
Braap Blue

73 reviews
Speed Silver: In Stock
Power Purple: Back in Stock Late Mar
Braap Blue: In Stock

Wheel Size
20 inches

Approx. Age Range
5 to 9 years


Easy Shifting
RAPIDFIRE+ shifter &
Smart Cage Derailleur

$15 Shipping
in the Continental USA

Shipping Terms

Checked and Tuned
Each bike is checked & tuned prior to shipment.

Easy Assembly
Includes all the tools you need & easy instructions.

1% for the Planet
Prevelo donates 1% of sales to planet worthy causes.

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 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.


Kid Centric Features

kids sized bicycle crank

Kid Engineered Crank

kids bike wide span gearing

8 Speed Shimano Drivetrain with Wide Span Gearing

Internally Routed Cables

prevelo kid size brake and shift levers

Kid Size Hand Brakes and Easy to Use Shimano Rapidfire Shifters



Sealed Bearings

Quick Adjust Seat Height

Built Kid Tough

Confidence Inspiring Geometry




Customer Reviews
5.0 Based on 73 Reviews
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Filter Reviews:
    Casey W.
    United States
    Magic Bikes

    I have a daughter that is very small for her age and Prevelo bikes are sized perfect for her. My seven year old daughter had grown out of her 16” Bike but when she got on her older sister’s 20” Bike she was super stretched out and super uncomfortable and scared. Enter the Alpha 3. Since we got it she has had a seamless transition to the larger sized bike. Jacob definitely has the magic touch when it comes to the dimensions on these bikes. The brake levers are adjustable for small hands and the gear range is great for climbing the hills around our house. I now own 3 Prevelo bikes and have zero regrets. If you want your kid to enjoy riding, buy one of these and you will get much more enjoyment than tears.

    United States
    Great bike, great purchase.

    Had some anxiety about this purchase-that completely went away when I saw the quality of this bike and most importantly how much my son loves it. Worth it. By a long shot. I have a fairly confident rider that started on a balance bike at 2, and never had training wheels. But, I wouldn't describe him as a shredder and honestly was just kind of indifferent about riding. Well, he is all about his Alpha 3 24/7. Wants to ride as soon as he gets out of bed. Picked up the gears and hand brakes quickly, w/in minutes. We have logged a couple miles every afternoon for a week..As a gearhead myself, I am very impressed with the quality and build of this bike. Just can't say enough good things about it.

    Anonymous verified customer review of Alpha ThreeAnonymous verified customer review of Alpha ThreeAnonymous verified customer review of Alpha Three
    Michael Z.
    United States
    Great Setup, Great Value

    I purchased the Alpha Three for my 5-1/2 year old son after researching pretty much all options in the 20” kid bike category. I settled on the Alpha Three because it had the best combination of all the attributes important to me – a good gear ratio, lightweight, trigger shifting, and accommodating standover height, all for a reasonable price tag. I really like the gear ratio Prevelo chose with the 32T up front and the 11-34T in the rear. A wide gear ratio including low gearing was important to me considering the hilly terrain we live in. Needless to say, my son (not the strongest kid) can power up hills much steeper than I thought possible for him. All of the comparable bikes, other than the pure mountain bikes, have gear ratio ranges that are very narrow and are more for flat, less hilly terrain. In my mind, it is more important for a little kid to easily get up a hill than attain top speed on the flats. My only recommendation would be to maybe even go a bit further to something like a 30T in the front and 11-36T in the back for even more range and good climbing ability. The trigger shifter was also another must for me. The main choice in shifters for kid bikes is either the trigger or twist grip. The reason I like the trigger is because that is what most big kid/adult hybrid, fitness, and mountain bikes use, not grip shifters, so why not learn to use what just about everyone else uses? My son is on the smaller side with small hands and he had zero issue with using the trigger shifter on the Alpha three. I think the combination large gear ratio and trigger shifter offering on the Alpha Three is a huge differentiator because no other comparable bikes come close. Really great bike that a kid can confidently ride on the pavement and the dirt/gravel at a great value for the components you get. I agree with the other reviewers in that the interactions I had with the Prevelo team were great – very prompt, helpful, amazing customer service, and the assembly of the bike was a breeze. Keep up the good work!

    Kate F.
    Absolutely Brilliant Bike

    I wish I had found Prevelo sooner. The bike we bought our youngest son (aged 5) today is light weight, designed perfectly for him and had him riding within minutes. He has had a gliding bike for a few years, and is over the moon to finally be pedalling and keeping up with his 10 year old brother. It’s an absolutely brilliant bike, well worth the money, and I highly recommend it.

    Jason L.
    United States

    My son loves this bike. He’s four years old and we ride the beginner trails at the bike park together almost daily. The only thing that’d be better is if my son was tall enough for the Zulu Three. Unfortunately he was a few inches shy of the mark when he needed a new bike. But the good news is my son was tall enough for the Alpha 3! It was the only bike with 20” wheels that I could find to fit him this spring. We upgraded from a Woom 2 with 14” tires and single speed so, initially, it was a big jump up. However, my son quickly adapted and the bigger tires and gears made a huge enjoyment in our biking together. We’re riding about 100 miles per week in serious mountain terrain. Many of the trails we are riding now are rated as intermediate XC trails. This bike has made it a ton of fun to ride together. Everyday he’s keeping up better and better. My son has become my little shredder. On DH trails, he purposely finds every rock he can to ride over and even with multiple hits to various components it’s still going strong. This bike stands up to some serious punishment. We’ve had it for a number of months now with very hard daily use and it holds up. If I’d bought a department store bike it’d be trashed in a week of our riding (not to mention how unsafe it’d be for this type of riding). This bike just keeps going. In contrast to the Prevelo, I’ve seen many “name” brand kids bikes (even those made for 7 - 10 year olds) fall apart on these trails and parents constantly shelling out to fix them over and over again. That means down time from riding (and all the tears/frustrations those kids suffer) and total cost of ownership skyrocketing past the cost of our Prevelo bike. My kid may be the exception at 4 years old doing hardcore mountain biking, but he doesn’t have to be. With a little patience and a passion for biking any kid can become your best biking buddy. I wouldn’t trade anything for the memories my son and I have made this summer riding at the bike park and XC nearly everyday. If you’re hardcore like us and your kid can fit the Zulu, go for it. If they aren’t as hardcore as us and/or can’t fit the Zulu, then get this bike. You won’t be disappointed.

    Jason L. verified customer review of Alpha Three