Pro BMX SKills book and gearing for juniors

Hi Lee,

Thank for your fast reply … the download link to the Pro BMX Skills ebook works well! I went through the pages quickly and it is very interesting. It’s very difficult to find this kind of book in France.

I had a question/observation … I’m very surprise by the gearings recommended in the book. For example, the book recommended 40/16 for junior and in France it’s common to have 37 or 38/16. Why this difference?

Thx !



First, thank you for buying Pro BMX Skills. It’s the greatest book nobody’s heard of.

OK, gearing:

Check out this chart from the book:

Adult BMX bikes often come with 44/16 gearing.

Junior gearing is typically closer to 40/16 (or 37/14), which is a bit lower — but not much lower.

At big bike companies, component choices are less about what’s ideal for each rider and more about:

• What can the bike company get at high quantities?

• What can the bike company get at low prices?

• Which parts can be used on numerous models?

From Pro BMX Skills:


At the bike-company level, gearing choices are not about power and spin. They’re about cost and availability. For example, Toby Henderson of Intense BMX says he can’t buy a 43-tooth chainring in bulk, but he can get 42s all day long at a good price.

What’s why aftermarket companies like Sinz Racing and Profile Racing are so useful. They can make every size in every bolt pattern and color.

Less [gear] is more [speed]

I think most kids’ bikes are over geared. Just watch all those groms mash their pedals.

Easier gears (like your 37/16 or 38/16) seem like a good idea because:

• Less strain for young bodies.

• Faster starts.

• Teach them to spin faster.

• When they get going fast, they should focus on pump.

I usually ride/race BMX on a Specialized P3 dirt jump bike with a 1×10 Shimano XT drivetrain. I have my pick of gear ratios, and I use much less gear than a typical BMXer.

This gives me a better start (with less strain on my old body). Once I’m out of the gate, it’s all about pump, high-rev spinning and some sneaky MTB-style cornering (lots of details in Pro BMX Skills).

Have fun out there,


Know more. Have more fun!

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14 replies
  1. Clint says:

    I bn racing 24” with a 43t-18t
    Now I’m about to finish building a 29” and I have no clue what’s a good strong gear to run on it that’s the last two pieces I need to finish the front and back sprockets plZ help

  2. Rob d. says:

    is crank size important to gearing? for instance, if i have 155mm cranks, with 38/14, and i go down to 147.5mm cranks, does that make the rider more of a spinner now because of the shorter crank length?
    my daughter has this set up, 38/14/147.5mm ( down from stock 155mm) , I’d like for her to gain top end speed, should i go to 41/15 and put her back on the 155mm cranks or will 147.5m and 41/15 be OK to use? that is 55.74 rollout with her tires.
    Thanks for any info you can provide.

  3. leelikesbikes says:

    Crank length is part of the equation that dictates how hard it is to push the pedals and how far you go with each pedal stroke.

    The first big questions is, what’s your daughter’s inseam? That will help us determine her ideal crank length. Gearing can be decided after that.

    What’s your daughter’s inseam? In centimeters please.

    • leelikesbikes says:

      According to the Lennard Zinn crank length calculation, your daughter should ideally be riding 117-123mm cranks.

      So definitely keep the shorter cranks.

      1) Teach her to spin faster. This way she gains top speed without losing low end acceleration. The 137.5s should be easier to spin than the 155s.

      2) If that just doesn’t give the top speed you want, then you can start adding gears. The 41/15 will be just barely higher than the 38/14.

      Learning to spin faster really is the hot tip. The shorter the cranks, the easier this is.

      I hope this helps,


  4. Mike says:

    Hi, lee

    So my son rides junior Dk on 150 crank with 37/14. I think we need to change his gears because it seems like he takes off fast at the gate but slows down a lot down the track. It looks like he pedals alot but doesn’t go know where. What do you recommend. Thanks for your time

    • Lee says:

      Hi Mike,

      If he’s getting out of the gate fast, that’s a great thing. I’d hate to bog him down in a taller gear. The first thing I’d do is teach him to spin faster.


      • Lee says:

        The other thing I’d consider is is crank length. Too long is hard to spin. How many centimeters is his inseam?

  5. Chris says:

    Hi Lee,

    Currently my son is on 38/16 gearing and 135mm cranks 57cm inseam with shoes. I have used the Helium Racing Q factor method of crank sizing and technically it puts him at 130mm. Watching him ride he seems to get out of the gate well, but looks like he struggles over some of the jumps. I feel he needs to spin faster out of turns to combat the jumps I am just wondering if I need shorter cranks or different gearing to do this or just training. He is new to the sport has only raced twice and placed in both of them but I feel he could be doing much better. Thank you

    • Lee says:

      Hi Chris!

      It’s almost always best to err toward shorter cranks, then work on both the start and top-end speed.

      I can be a lot more helpful if I see your son ride.

      If you want some quick public feedback, you can post a video link in these comments.

      If you want private, detailed feedback, check out my virtual coaching:

      Have a great day,


  6. Lisa says:

    Hi Lee,

    Our son is new to BMX racing. We are noticing he is slower out the gate and not able to spin fast. His current set up is a ari sun mini (more jr size frame imo), 20 x 1 1/8 tioga powerblocks, 44/16 gearing and 145 mm cranks. His inseam is 50.8cm.

    Would dropping his cranks down to 135mm and change his gearing help with his spinning ? What would the ideal gearing be?



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