Homepage Forums Rodney’s Repair Center How To’s On Repairs and Maintenance Need help with a 5yr old’s new bike

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    I hope all you dads and/or Rodney can give me some tips on a good set up for my son. I have no experience with the Mini / Junior bikes.

    He is 5 years old (b-day was January). He is 4 feet tall and 52 pounds. He is one of the tallest, if not the tallest, kids in his pre-school. He is always in the 96-99% box on the doctor’s chart.

    I recently got a Diamond Back Junior for him from Rich Farside. It’s a tad big for him, but he rode on it pretty well last night for the first time. Since we just got him off training wheels, I am not expecting big things this year. Rich said he’d probably would grow out of a mini before his next birthday based on how tall he is and the Junior should work now with some slight modifications.

    It currently has the Junior bars with no cross bar. I’m sure the first time I bring it to the track someone can tell me if he would be better off with the shorter mini stem and lower mini bars. I pulled the bars back so he could reach them comfortably, but it looks funny.

    My other concern is the gear and crank size. It currently has a 42-16 with 165mm cranks. What size cranks do most kids this age/size ride? They seemed a little long for him, even though he was getting them around okay. What about the gear? Any thoughts on that as well?

    Last question: Brake levers. Do they make a smaller lever for smaller hands? I hope so, cause he can barely grab the one thats on there. It made for some tense moments last night.

    Thanks in advance for the help!!



    You could try rotating the stem 180 degrees so that it extends towards the seat. This should make the top tube length a little shorter if that is a problem. I think I have 150mm or 145 mm cranks on my daughters mini. The gearing sounds OK for a start. The brake lever is a tough one. I am using a vintage DIA-COMP one that came with MX 1000’s. It has the adjustment screw for little fingers. Hope this helps.



    How tall is your daughter?


    DK makes a 30mm stem that is shorter than most, light and cheap. Crupi has a 0 offset stem as well. I think reversing the stem will make the bike handle funny, but it will get the bars much closer.

    Sinz makes a mini lever for 9 dollars.

    Look on a chart from Dan’s or J&R for the crank length, but I would buy up since you aren’t worried about results. Most of the min cranks are expensive to replace every year.

    I am trying to build a bike for my 3yr old so I have been researching for awhile.



    Craig, my kids are running 41-16 gears-they are 6 and 8. Colin (8) can pull 42-16 at HC, but he says he likes the 41. The 8 year old is on 150mm cranks, I just ordered a set of 140’s for the 6yr old to try out. Dotek cranks are only like $30 from Dan’s or J&R. They were both on 155’s until a few weeks ago. I am certainly no expert at this either, alot of it has been other people’s advice and some research and alot of trial and error! If you bring him out to HC he can certainly try out my kids bikes. Kyle has a mini, Colin has an expert which he is finally growing into. Both Haros, FWIW.



    This is helping out alot, thanks.

    Dan’s has the 0 offset stem, JR does not, but they have the DK mini Kev mentioned, plus that Sinz lever.

    I’m gonna measure my kid’s inseam and see how it matches up with the size chart. I think 140’s may be a good place to start seeing how its definitely longer than the stubbies on his little 16 inch bike that he’s been riding up to now.


    sounds like you got some great advise so far. i would get the lowest mini bars you can get and by all means cut them a little off each end… to make sure his hands are gripping on the part that is equal with his shoulder width. they shouldnt be out too far that would make him unstable as far as balance goes. my husb always trimmed the bars a little bit..dont worry you will always get your moneys worth out of them when you sell them. they are custom and there is always someone who has a little guy who is looking for them.

    agree to turn the stem around facing the seat to shorten the tt length.

    a jr frame seems a bit large for his size but with the modifications it should be fine. the cranks seem a bit long. if his hips are moving up and down(choppy) when he pedals they are prob too long.i would try 145-150’s.

    building a bike for a little guy is an education in itself. unless you have done it you have no idea…. its confusing at best but always ask there are plenty of dads/moms who have been there done that.

    remember in bmx never buy a bike that your rider will “grow into” it should always fit him for this season. what we used to do is get the frame/ equip handed down from someone we trusted who took care of their bikes… then you sell your outgrown items and buy the next size up.. always consult other parents but see what feels comfortable on your son, after all he is the one who is riding.

    hope this helps- my son started when he was 4 1/2 on a 16″ heavy hand me down and we got lots of help building his first “race bike” that didnt have to break the bank either… remember he is 5…not going to the olympics…


    also gear size depends on the diam of the wheels if he is on 1 1/8″ or 1″ that makes a big diference rather than if he is running 1 3/8 which is on many jr bikes that come stock.

    check your gear chart and let him run an easy gear that gives you about 54 give or take a few…. let him spin if he can i wouldnt start with big gear ratios esp if he is young he prob dosnt have great leg strength.


    Thanks for all the advise. Wow. I got a lot to learn.

    The bike came with 20 x 1-3/8 wheels, as you said, stock on a Junior. Still, you have to see my 5 year old to appreciate him. He is big for his age. Tall and lanky.

    Based on my expectations, I think he’ll do just fine on the Junior, but I won’t rule out a Mini frame if I come across one for the right price. If nothing else I have a head start on his next bike!


    CRAIG let me know if you need anything I can get almost anything FMF , ANSWER , ODYSSEY , CRUPI , PROFILE ,S &M , just to name a few . I can give you a good deal since you bought stuff from us in the past , very far pricing, can deliver to local events ( flemington)let me know !!!!


    Keep the higher junior bars. The mini rise bars will put too much of his weight over the front end, especially if the frame is long. I have a Crupi 0 degree offset stem on JDs bike but I have been thinking of moving him to a conventional stem as he has been growing and is jumping pretty hard now. You can try it out and see if it helps his stance on the bike. JD is running the junior bars btw with the no cross bar.

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