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  1. #1
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    will a 8 or 9 speed cassette fit on a bike that came with a 7 speed

    My question is will a 8 or 9 speed cassette fit on a bike that came with a 7 speed, i understand i would have to get new hubs and shifters but would the cassette fit or will it be to wide that i cant even mount the rear tire and rim. Thanx Guys!!!

  2. #2
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    measure and see(135mm), you can pull the stays apart and force it in it is close

  3. #3
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    Im sorry but im kinda a noob could you explain what you mean. Thanx

  4. #4
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    upgrading a 7 to an 8

    I had a 7 speed that I had upgraded to an 8 speed a couple of years back the rims were cheep and I was warping them left and right and wanted to go to a decent double wall rim. all the 7 speed rims were single wall junk and to get an 8 speed ment going thru the rebuild or special order process. the shop where I have my work done had some 8 speed stuff left from someone elses upgrade that he sold at a decent price, here is what we did.

    replaced the rim with a double wall model which came with a hub that would suit an 8 speed cassette. put on an 8 speed shifter. readjusted the original rear derailer to suit the new cassett.

    I didnt need to make any other modifications to the bike that I can recall. pretty sure that is all that is needed, the 7 and 8 speed use the same size chain so your chain and front spockets will be fine along with the front shifter and derailer. the rear derailer worked fine after we adjusted it as to the spacing being different for the 7 & 8 speed cassett I am pretty sure most of the bike manufactures sold the same frames with either 7 or 8 speed component packages.

    I found the upgrade to the 8 speed cassett was well worth it becuse it gave me a much lower gear than what I had with the 7 speed. it made a lot of difference in my climbing ability especialy on the rocky technical stuff. that and I stopped distroying rims every other week. if you weigh over 200 lbs single wall rims dont last.

  5. #5
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    Quote Originally Posted by byerlytaylor
    My question is will a 8 or 9 speed cassette fit on a bike that came with a 7 speed, i understand i would have to get new hubs and shifters but would the cassette fit or will it be to wide that i cant even mount the rear tire and rim. Thanx Guys!!!
    yep, i converted a 7 spd to 8 a couple of years ago...it was quite a struggle to get the wheel between the chain stays...needed an extra pair of hands to get the wheel off to fix a flat

    Also, had to change the RD from a SIS-7 to an STX (8), needed a new shifter, and added 4 (maybe more) links to the chain

    didn't make much of a difference to the ride

  6. #6
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    so what yall are saying is that a 8 speed will fit you just have to force it between the chain stays. Thanx Guys!!!

  7. #7
    JmZ
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    There are mainly two rear sizes for rear wheels. 130mm, and 135mm.

    7 Speed is either 130mm or 135mm
    8 Speed is 135mm

    You can force a 8 speed (135mm) wheel into a 130mm rear spacing wheel. It will only spread the stays by 2.5mm on each side. I wouldn't worry with a steel frame, wouldn't want to do it with a aluminum frame.

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  8. #8
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    Well guys im not sure if it is 130 or 135mm, because i actually dont have the bike yet, its a Trek 3700, i know its not a bike thats up to yalls standards but it will make a good begginer bike for me, it is a 7 speed, but the next step up the 3900 comes with an 8 speed, from what i understand the frames are the same so maybee the 3700 is a 135mm, if anybody knows what it is please post. Thanx Guys!!!

  9. #9
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    i hope you dont mind me asking...why you want to switch to 8 speed?
    why don't you save me some trouble and kick your own ass?

  10. #10
    All 26.5" all the time!
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    130mm mountain frames died out about 17 years ago. I'd bet it's 135mm spaced.

  11. #11
    Ebo
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    No. The 8 spd cassette will not fit on a 7spd hub. Wasn't that the question all along?

  12. #12
    Ebo
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    Also, the Trek 3700 is spaced at 135mm so a 8/9 speed hub will not have to be forced in. Hope this helps.

  13. #13
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    what you need is

    an 8spd/9spd free hub ( they are the same). If you have a shimano hub changing them is easy, just need a 10mm allen key and a bit of patience. If the rear triangle is 130mm, speading to 135 is not a problem. Someone will tell you it is not a good idea, but I have done it a few times with no ill effect. Your bike shop can supply a spacer if you use 8 spd on the 9spd feerhub. jim

  14. #14
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    Quote Originally Posted by jimbo2k
    an 8spd/9spd free hub ( they are the same). If you have a shimano hub changing them is easy, just need a 10mm allen key and a bit of patience. If the rear triangle is 130mm, speading to 135 is not a problem. Someone will tell you it is not a good idea, but I have done it a few times with no ill effect. Your bike shop can supply a spacer if you use 8 spd on the 9spd feerhub. jim
    +1...easiest thing to do is to pick up a used wheel with an 8-spd cog set...but the cog set, RD, and shifter must be compatable...if you mix Sram and Shimano, the ratios vary, so if you have an indexed shifter, make sure it lines up the RD on the correct cog, or you'll be hunting, especialy in the 3-6 range (Sram= 2:1, Shimano= 1:1)

    easiest fix is to use those cheap thumb lever friction shifters

    Also, when I made my conversion, i should have replaced the 7 chain with an 8-9...its a little thinner and fits better on the cogs.

    But as a previous poster asked...why change?. the 7 and 8 cog sets are probably both 11-32's, so there will be no difference in the high and low gears...i used an 11-34, but it was no big deal.

    What made the biggest difference is that i swapped my wheels from 26" to 28" with 28x1.75 tires...made one fast bike (there's a thread with some pics here someplace...think from summer 2005 july-august-sept?)

    happy trails

  15. #15
    Ebo
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    You can't just change the freehub body, which is what you would do with a 10mm wrench. Will not work....

  16. #16
    Ebo
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    Yes you CAN use Sram shifters. You just use the one's that are Shimano compatible and are 2 to 1. The 3.0,7.0,9.0 & 10.0 are all 1.1 and will not work. The Sram shifters without numbers, such as the Rockets,Attack,Centera, etc, will work and are 2.1. In addition, the 9spd chain is narrower than an 8spd chain. Had my 1.1 and 2.1 backwards in my haste. Sorry.
    Last edited by Ebo; 08-03-2006 at 01:53 PM.

  17. #17
    Ebo
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    Are you sure you are using 28" tires? Too funny...

  18. #18
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    Okay hold on a sec, you may not be too bad off....

    most modern bikes come with 135mm spaced rear hubs, as noted earlier the 130mm rear spacing for MTB died out quite some time ago. Now when you get the bike remove the rear wheel and then remove the cassette. If there is a spacer about 2mm thick under the cassette you can switch to an 8 speed cassette no problem, just leave out the spacer. Most current mountain bikes come with 8/9speed compatable rear hubs. Most manufacturers don't even bother with using the older 7 speed specific hubs anymore, it's much cheaper and more cost efective to simply add a spacer to an 8/9 speed hub than it is to stock a 7 speed specific for bikes speced with a 7 speed cassette.

    And yes you can use SRAM shifters on the bike. Just make sure as mentioned before that they are Shimano capatable. As JMO1 stated. Just one correction to his info. SRAM uses a 1 to 1 acctuation ratio, Shimano uses the 2 to 1. Not a big deal, just make sure you get Attack, Rocket, MRX, TRX, and Centra shifters will all work.

    Also, just to help you out a bit, Trek has been using what they call the Mega Drive cassette for the last few years on the lower end MTBs with 7 and 8 speed specs. The cassette starts out with a pretty normal range in like a 12-28. But the 1st gear cog is a 34!!! That's a serious drop from that 34 tooth 1st gear to 2nd gear. I work for a Trek dealer, and while they shift okay, it makes for some serious lag time when going from 1st to 2nd or vise-versa. If you can afford the upgrade it is a good idea to go to an 8 speed and get a more sensible gear range in the back.

    Anyway, as long as the bike was made after 2000, which it should have been, I doubt that you will have any problems. The rear spacing is most certainly 135mm, and the rear hub is most likely a spaced 8/9 speeder anyway. If not you still only have to replace the hub. An added expense for sure, but easily done. There shouldn't be near as much hassle with this conversion as this thread would lead you to believe.

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