1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
mtn. biking 101
2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    Question on kids bike

    Hello everyone. I'm new here and not too familiar with bikes. So any help is greatly appreciated. OK, so my boy has pretty much outgrown his bike (16"). He's turning 8 in a month is about 48". So I figured an upgrade was in order. Decided on a 20" MTB. Didn't want to spend a lot, want to make sure he's actually going to ride it. So I bought a Diamondback 20" cobra. Seems to fit him well, although seems very heavy. Now the problem I'm having is it seems pretty difficult to pedal even in lowest gear. Its at least as hard as his old single speed. like I said above, I'm not to familiar, but I was under the impression that the geared bike would be easier to pedal up hills. So, is there a problem with the bike, or is this normal. If its normal, I'm just going back to a single speed for him.
    Well thanks for reading and thanks ahead for any help!

  2. #2
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    Hubs correctly adjusted?
    Brakes not rubbing?
    How big is the new front chain ring? Same size chain ring with bigger wheels will be harder to pedal. Fit a smaller front chain ring?
    Duct tape iz like teh Force. It has a Lite side and a Dark side and it holdz the Universe together.

  3. #3
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    Hello, not sure if everything is adjusted right or not, but I was just figuring it was going to be substantially easier to pedal. Front chain rings do appear to be the same size though. Wheels spin freely, so breaks are not catching. What's the use of having a geared MTB if the easiest gear is harder than a single speed. Lol. Not helping him get up hills that's for sure. Guess I'll have to take a closer.

    BTW, thanks for the quick reply. Wasn't expecting any tonight!

  4. #4
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    It is the middle of the day for me

    Manufacturers don't seem to put much thought into building kids bikes.
    Duct tape iz like teh Force. It has a Lite side and a Dark side and it holdz the Universe together.

  5. #5
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    Not sure if its just this manufacturer, or if they are all like this. Can't really justify a MTB, if the first gear is that hard to pedal. Not going to be beneficial for him at all.

  6. #6
    Hi There!
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    this bike has no front derailleur and a 40t, are you sure he is on the biggest ring in the back which is 28t?
    NTFTC

  7. #7
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    Yes, on the biggest ring on the back. Still no easier than his single speed. Wanted him to be able to ride up the hills in our yard, but can't like this.

  8. #8
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    Check out the Families and Riding With Kids forum here for tons of good info on kids' bikes.

  9. #9
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    Let's say the old bike has a 40t front and 28t rear, the same as the new. That same gear ratio will be harder on the bigger wheel.
    IMO 48"-54" rider height is the trickiest. Not quite tall enough for an adult bike, yet too tall/long for a kids. IME the crank arm length is usually a problem. If one of my kids friends comes over and wants to ride but has no bike, I'll put them on my wife's 26" wheeled 13" frame if there's enough standover, and without fail, within a few minutes, they are faster, better, and leave thinking they need a new bike. Of coarse the bigger wheels make it easier to keep momentum and roll over stuff, but think the longer 170mm crank arms make the most difference. Especially when it's time to stand and grind or get off and walk.
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  10. #10
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    Quote Originally Posted by theMeat View Post
    Let's say the old bike has a 40t front and 28t rear, the same as the new. That same gear ratio will be harder on the bigger wheel.
    IMO 48"-54" rider height is the trickiest. Not quite tall enough for an adult bike, yet too tall/long for a kids. IME the crank arm length is usually a problem. If one of my kids friends comes over and wants to ride but has no bike, I'll put them on my wife's 26" wheeled 13" frame if there's enough standover, and without fail, within a few minutes, they are faster, better, and leave thinking they need a new bike. Of coarse the bigger wheels make it easier to keep momentum and roll over stuff, but think the longer 170mm crank arms make the most difference. Especially when it's time to stand and grind or get off and walk.
    Your words have thunder....When my kids were little, I bought a cheap hardtail frame and built it up using inexpensive parts but I was able to control the final product. It was a 26" which was a bit big, but it came in under 25 pounds and had low gearing. A multi gear wont be easier than a single speed if the lowest gearing is the same.

  11. #11
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    So I imagine all the 20" MTB's are pretty much the same? I just can't see him ever using even 2nd gear let alone any of the others. Was riding in the yard today and was having trouble with just the little hills. Was wondering if any of the other 20" may have better ratios for easier pedaling? Or should just get a single speed which is lighter?

  12. #12
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    I had a 10 speed 20" bike that came geared too tall to be of any use, I took off the smaller chain ring and replaced it with a even smaller ring. You might be able to do that or replace the cassette with one that that has a larger low gear. Those bikes aren't really designed for off road use just like other department store bikes. A new or used real bmx bike bike might be the way to go ,light and you could change the gearing to whatever you want.

  13. #13
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    I built my son's last two bikes. The 20" had useless department store gearing. I replaced the crankset with a set from Sinz and used a 34 tooth chainring. The rear wheel got an old 8 speed Shimano XT hub and a cassette with 32 teeth on the largest cog. Worked well...
    Then I bought a Craigslist 24" bike that weighed a ton but I wanted the alloy frame. Again, Sinz cranks, Salsa 34 tooth ring but this time, I built the wheels with current Shimano Deore hubs and put a ten speed cassette out back with a 36 tooth large gear. He climbs most anything.
    I like turtles

  14. #14
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    For comparison, I went to this gear-inch calculator. His 40/28 at 20" diameter is almost the same as running a 29" with the same size ring and cog -- on mine it would be the big ring and big cog, or little ring and fourth-from-biggest cog -- not real low.

    How many teeth does his 16" have? You can see if the new one is really higher-geared or not.

    Bicycle gear inch calculator

    I'm wondering if the front ring could be replaced. Maybe someone else will know if the crank is standard. It wouldn't hurt to post a picture of the crank and ring.

    Also, measure the Bolt Circle Diameter -- hopefully it is something standard. For a 4-bolt pattern it is the distance from the center of one bolt to the center of the opposite bolt -- easy to measure if you have a caliper to reach around the crank. But just measure the distance between two adjacent bolts and it can be calculated or looked up on a table.
    Sheldon Brown's Bicycle Glossary Bo--Bz
    (The picture shows measuring from the center of one hole to the center of the other. It is easier to measure from left-side to left-side. You don't have to remove the ring of course --- just measure the distance between bolt heads).

  15. #15
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    If this would fit...
    Amazon.com: Shimano MF-TZ20 Tourney Freewheel (14-34T 6 Speed): Sports & Outdoors
    Amazon shows other 6-speed cassettes including the 14/28, and they look similar. Would cost $15 to find out!

    May need a new rear derailleur tho. But here it shows it in third-to-largest and seems to have plenty of capacity. Worst case, add a few links to the chain then lock him out of the smallest cog or two with the limit screw.
    Diamondback Bicycles - Cobra 20

  16. #16
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    Well I really don't want to be tearing apart a brand new bike. Pretty sure its going back. Was at my parents house today and they had an old huffy 20", don't think its been ridden for years. Boy rode it just as good as the DB I just bought. Thinking that's going to be his summer bike this year.
    I was searching the forums before I posted, but didn't see many complaints if any about this. Maybe it's just me but I just can't imagine what these bikes would be useful for, other than flat paved trails. Guess I'll just keep my eyes open on craigslist for a used one that I can tinker with alittle.

  17. #17
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    Yeah, I searched too and couldn't find anyone else complaining about the gearing either. I guess most of them are ridden to school and that sort of thing.

    People knock Huffy etc., but that's basically what I rode for a year as an adult on some real trails--given to me by a relative. I was glad to get rid of it, but for a kid, it would have been great. Plus I think the old ones are better. Rigid fork? Better than a pogo stick -- that's what mine had.

    Go for it!

  18. #18
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    Re: Question on kids bike

    You are not alone. I bought my son a specialized hotrock 20 last year when he was 5 assuming it would actually be ready for real off-road use. I was sorely disappointed! I therefore quickly replaced the bottom bracket, cranks with smaller chainring, larger rear cassette, and longer deraileur to accommodate the cassette. Sounds like a lot, but aside from the cranks everything else was inexpensive compared to the prices of the "adult" versions.
    With those changes, he is riding real singletrack out here in Utah and it was definitely all worth it (now 6, and hanging pretty close to his 10 year old cousin who obviously rides a lot less! ). He has a younger brother who is even more into cycling so I know the bike will get plenty of use going forward as well.


    Sent from my SCH-I535 using Tapatalk 2

  19. #19
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    Glad I'm not the only one! I just don't think I should have to fix up a brand new bike just to make it easier to ride. I would think someone would make one that already is. I just figured I'd have him riding around in like 3rd gear o familiarize himself with the new bike, then shift it to make it easier to clime the hills. Until he learns to shift on his own. Pretty bad when I had to start him in 1st.

  20. #20
    turtles make me hot
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    I know what you mean. When I bought my son a 20" Gary Fisher Precaliber, I thought I would be getting an off road ready bike. The fork completely sucked, it was pretty heavy and the gearing was wrong. My wife almost had a cow when I tore apart the brand new bike and completely rebuilt it.
    It was worth every penny. He's eight now and loves trail riding. He's outgrowing his 24" bike and we're already starting to gather parts for his 26" build.
    I like turtles

  21. #21
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    I guess I'll have to look into rebuilding one. I've just never worked n a bike before and don't want to ruin anything. Wife would really be happy about that! Think I'll look for used and try fixing it.
    How did you change that 20" to make it more hill friendly, and approximately how much $ ?

  22. #22
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    Once again - check out the Families and Riding with Kids sub-forum - all the info you are looking for is there, plus more.

  23. #23
    turtles make me hot
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    Quote Originally Posted by VinnniV View Post
    I guess I'll have to look into rebuilding one. I've just never worked n a bike before and don't want to ruin anything. Wife would really be happy about that! Think I'll look for used and try fixing it.
    How did you change that 20" to make it more hill friendly, and approximately how much $ ?
    Hmmm... I think I paid 40 bucks for the crank arms, 25 for the chainring, another 30 or so for the chainring guard and 10 for the Jumpstop which keeps the chain on the ring since there's no front derailleur. I had the XT rear hub and rear derailleur and shifter. I laced it to a Velocity Aeroheat but don't remember what the rim and spokes cost...
    I then Ebay'd lighter handlebars, seatpost and XT Vee brakes and the bikeshop got me a deal on a fork with better action. Also, 80 bucks on Tioga spider web pedals that he fell in love with.
    Bike wasn't cheap but he loves it. Last summer when I stepped him up to the bigger one I asked what do we do with the red bike? He said I want to keep it for my son to ride someday. Pretty cool.
    I like turtles

  24. #24
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    Thanks. Sounds like a lot more time and $ than I really care to spend on it, especially not knowing what I'm doing. Lol.
    Although I'm sure I could find some great help on it in these forums.

  25. #25
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    Don't give up so easily. Count the teeth of the small front chainring of his current bike (does it have 1 or 2 chainrings up front, btw?).
    Though you will get a bigger improvement by putting a new crankset with smaller chainring up front, even replacing the rear cogset to one of these will give a much easier granny gear than what he currently has. 2nd gear on, however, will not change, so it really only helps in giving an easier easiest gear.... but it is cheap to do.

    If staying 6-speed:
    Amazon.com: Shimano MF-TZ20 Tourney Freewheel (14-34T 6 Speed): Sports & Outdoors

    The only thing is, I'm not 100% sure that you will be able to use the current derailleur with that cassette - it may not have the range to go up to the huge granny gear. This derailleur looks ridiculous on the bike (very long cage) but has been trouble free even with real singletrack use:
    Shimano Tourney TX75 6/7 Speed Rear Derailleur : Amazon.com : Sports & Outdoors

    This one may not be as long but supposedly will still work, though I cannot guarantee it;
    Shimano RD-TX35 Tourney Rear Derailleur (SGS Long Cage 6/7 Speed Regular Mount) : Amazon.com : Sports & Outdoors


    So $28 gives him a MUCH easier first gear, though doesn't change the rest.


    If changing to 7-speed:
    Shimano MF-TZ31 Tourney Freewheel (14-34T Mega 7 Speed) : Amazon.com : Sports & Outdoors

    If changing to 7-speed, you will need new shifters as well:
    Shimano Acera SL-M310 Rapid Fire Shifter, Right (Black, 7-Speed) : Amazon.com : Sports & Outdoors

    Maybe a new chain too, though this chain state 6/7/8 speed, so maybe your 6 spd chain will work anyway:
    Shimano CN-HG50 6/7/8-Speed Chain, Black : Amazon.com : Sports & Outdoors

    I can't find the cog tooth count to compare the number of teeth on the second largest cog of the 7-spd vs 6-spd cogsets, but when I try to count on the picture I guess they are both 24t ring, so the 2nd easiest gear wouldn't change. Therefore, if you want the easiest, cheapest thing to try - get the 6spd cogset. If the derailleur doesn't accommodate the massive granny gear, get one of those too.

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