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  1. #1
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    Cassette swap - 24" Specialized Hotrock

    Just got my son a 2008 Specialized Hotrock 24" 7 speed. He had a 20" prior and it's gearing combo was just right for our hill climbs here in central NC. I've noticed that the 28t granny gear on his 24" takes a little more pedal power with 24" wheels. I'd like to add a 12-32, 7 speed cassette. I've seen cassette swaps on this bike but I'm not sure if it's a direct bolt up on to the wheel and if a different length chain is required.

    The specs for the cassette I'd like to add: SRAM PG-730 7 Speed 12-32 Cassette

  2. #2
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    You'll need a freewheel (screws directly onto hub) not a cassette (slides onto the hub). You probably will need a longer chain. It is possible that your derailleur would not extend out are enough to accommodate a 32-tooth cog.

    I wonder whether freewheels going to 32 teeth are even made.

  3. #3
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    You would also need the tools to remove the old freewheel and break your current chain.

    I took a look at Jenson USA. Their freewheels max out at 28 teeth.

  4. #4
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    Shimano MegaRange freewheel. 14-34. The 34T is a very large jump though. I've used it before, while I'm building up a wheel.


    Shimano MegaRange 14-34

  5. #5
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    Thanks for the info so far. The 34t might do the trick. We just got back off a 10 mile single track ride at the White Water Center in Charlotte, NC. The climbs are short but steep and he went down once near the top of a climb. I'm sure he would have made it with some better suited gearing.

  6. #6
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    Quote Originally Posted by IAmHolland View Post
    Shimano MegaRange freewheel. 14-34. The 34T is a very large jump though. I've used it before, while I'm building up a wheel.


    Shimano MegaRange 14-34
    Quote Originally Posted by rollis View Post
    Thanks for the info so far. The 34t might do the trick. We just got back off a 10 mile single track ride at the White Water Center in Charlotte, NC. The climbs are short but steep and he went down once near the top of a climb. I'm sure he would have made it with some better suited gearing.
    Just a fyi, you need a new rear derailleur and chain for that mega range.
    13 Lenz Lunchbox punkass

  7. #7
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    IRD makes a top quality 7 speed 13-32 Freewheel

    IRD Freewheels

  8. #8
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    I think the IRD is the way to go. I bet it may even shed a little weight.

  9. #9
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    better gear ratios too. if i weren't going to rebuild an old 20" wheel I have, i'd get that one. i'm not sure about lighter though, but it would be good to get the weight when you pick it up.

  10. #10
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    I'll weight the difference if I can find the gram scale.(former weight weenie here) Even it doesn't shave any weight at all I still know for certain it will help him. He wants to do some racing this fall so I've upgraded his seatpost and bars and plan on a set of 24" Kenda Small Block 8 kevlar's and will keep it at that.

  11. #11
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    Shimano Freewheel

    I just pulled the Shimano Freewheel off this Hotrock 24 I culled from Craigslist last week.
    The good news is the bike came with Alex Ace20 rims and Forte Team brakes and levers.

    The bad news is it still had enough heavy parts to weigh over 26 pounds.

    The Shimano Freewheel weighed over a pound. The IRD part has got to be lighter.




  12. #12
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    Quote Originally Posted by alex_sdca View Post
    The IRD part has got to be lighter.
    Not necessarily. Freewheels are heavy. The stock Hotrock 24 7 speed freewheel is 13-28T I believe. Going to a 7 speed 13-32T has larger steel cogs. It should come in over 500g. I believe the IRD 7 speed 13-24T is around 400g.

    There's only one way to find out for sure.

  13. #13
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    I'm having some reservations on the freewheel swap. I've been seeing some not so great reviews on the IRD's. I'm tempted now to get way off topic and upgrade the crankset instead. I have seen FMF crank arms with 110mm BCD, 33t chainring and will require a 68x113 ISIS bottom bracket. It would run about $60 for the complete set-up (not including chain if needed) It would be a 3 tooth drop so I wonder how much a difference it would make?

  14. #14
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    I think rear gearing is more of an effect than the front chainring.

    The FMF crank can't run a bash. I milled it a bit with a dremel so I could put a BBG bash on. It's not very pretty but it works fine.

    If I had to do it again, I would use a Sinz, which can be run double sided.

    For freewheels, I use the Shimano. Hunt around, it can be had cheap.

    For your case, with a 36T chainring. Your son came from a 20" 36T chainring with 28T rear. The gear inches are about 2.0. To get a 2.0 gear inch with a 24" bike you need a 36T chainring with a 34T rear. You cannot achieve it with just a chainring change at 110BCD.

    If your desire is to get the same effort level, then the freewheel is your best bet.

    Tree fort bikes has the Mark 4 IRD. I can't say if it's better, but it's the newer version. I too have read the same problems with IRD freewheels, that is they stop working and spin freely. I saw someone said they "fixed" it by lubricating it, but others said that the spacer for the highest gear cracked, and there's really no fix for that.

    Again, no experience with IRD, but the Shimano have held up very well.

  15. #15
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    Quote Originally Posted by TwoTone View Post
    Just a fyi, you need a new rear derailleur and chain for that mega range.
    What derailleur would be a good mate?

  16. #16
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    Quote Originally Posted by rollis View Post
    What derailleur would be a good mate?
    Any of the newer Shimano ones will be fine. Just look for the capacity of it. The newer Shimano Tourney can handle 34T. You should be able to pick up an Alivio or something fairly cheap as well from older adult bikes.

  17. #17
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    What rear derailleur would be recommended for the 34T Mega Range?

  18. #18
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    Quote Originally Posted by rollis View Post
    I'm having some reservations on the freewheel swap. I've been seeing some not so great reviews on the IRD's. I'm tempted now to get way off topic and upgrade the crankset instead. I have seen FMF crank arms with 110mm BCD, 33t chainring and will require a 68x113 ISIS bottom bracket. It would run about $60 for the complete set-up (not including chain if needed) It would be a 3 tooth drop so I wonder how much a difference it would make?
    Here is a better crank setup if you want to go that route

    Truvativ IsoFlow 175mm MTB crankarms Shortened to 153mm

  19. #19
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    OP, does the current chainset run 26/36/48 tooth rings? I hate that so many kids bikes come spec'd that way. Most adults do not ride 26/36/48 on trails. I don't understand why companies put such high gearing on a bike for children. Mtnbiker72's suggestion is worth a look. Get a set of 22/32/42 rings.

  20. #20
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    Here's quick video. I messed and used the memory card that can't write fast enough for the cam so it' freezes about 10th frame or so and makes us look a little slower but try and overlook it. You'll see where he could use more granny at the end of the video. It's so much steeper than the video appears!
    White Water Center 28t - YouTube

  21. #21
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    Quote Originally Posted by mtnbiker72 View Post
    Here is a better crank setup if you want to go that route

    Truvativ IsoFlow 175mm MTB crankarms Shortened to 153mm

    I use that but in 140mm! It's good work.

  22. #22
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    Quote Originally Posted by rollis View Post
    What rear derailleur would be recommended for the 34T Mega Range?
    It depends what you want to use. It's hard to say, as all modern mountain bike derailleurs support 34T, even some older ones do. I have an old long cage derailleur from 1990 that supports 34T just fine. The docs for your derailleur says 28T is the max, but you can try it, move the arm and see how far it goes.

    However, when I change the gears, I tend to use SRAM stuff. I have a SRAM X7 derailleur on my son's 20" bike right now. It works, but I wouldn't go crazy unless you want to.

    This works, but it's not the lightest, just make sure the mounting works for you. You can also shop EBay and look for something.

    Nice vid, btw.

  23. #23
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    I used these lasco cranks on my son's 24" bike. I replaced the big ring with a BBG. The small/middle rings are steel. With a sinz expert chromoly bottom bracket the set weighs about the same as a shimano slx crankset, just under 900 grams. Not as light as sinz cranks, but more versatile with the granny ring (necessary for our trails). 152mm is a good fit for a bike this size.

    Utah Trikes - Lasco 152mm Short Triple Crank Set

  24. #24
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    I've got the 14-34t installed along with a new chain. I had an older XT rear derailleur laying as the stock Tourney was too compact and could not handle the 34t jump. I had concerns prior to installation that the jump from 24t (gear 2) to the 34t (gear 1) was not going to very smooth but I was wrong. It's changing just as quick and smooth as the rest. Now they are calling for rain here next couple days...dang it!

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