Adjustable Rear Frame Options- Mtbr.com
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  1. #1
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    Adjustable Rear Frame Options

    What are some other SS 29ers with this set-up... been looking at the El Mariachi? Want to explore some other options before making a decision. Carbon & Ti, not an option for me. Would prefer steel but open to alloy or alloy with carbon rear.

  2. #2
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    Quote Originally Posted by Clobber
    What are some other SS 29ers with this set-up... been looking at the El Mariachi? Want to explore some other options before making a decision. Carbon & Ti, not an option for me. Would prefer steel but open to alloy or alloy with carbon rear.
    What do you mean by "adjustable rear frame options?"

    --sParty
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  3. #3
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    From what I understand, SS bikes come in 4 frame types generally. Because there is no need to shift, which means no rear D, which means no tension arm (on the rear D), which means the chain is tight. All 3 of these layouts allow you to put on a rear tire and then tighten the chain.

    Horizontal dropout-- This frame type has a horizontal slide where the axle slides into and bolts down. You can attach the chain, and then slide the axle back and then lock it down.

    Eccentric Bottom Bracket-- This frame type utilizes a normal vertical dropout like your standard geared bike for the rear axle. The tightening occurs in the BB area. If you look at the bottom bracket area on an EBB you will see that it is shaped different, larger. What happens is that the actual bottom bracket sits in a cylinder shaped frame. In that frame is the real bottom bracket threaded shell, but it isn't in the center, it's offset. You put in the BB, attach the cranks/chainrings and slide the whole thing in a circle which moves the crank forward/back/up/down. The attached pic will help make more sense. There are set screws beneath the EBB that are used to tighten it

    Adjustable rear-- This frame type has the rear axle dropouts on a mechanism that can slide forward and back. Basically you put the chain on the rear cog, and losen 4-8 bolts, and slide a whole mechanism forward and back.

    The 4th type is related to the adjustable rear bikes, but not exactly like them. Some SS bikes have the ability to go between geared and not by use of a rear D hanger, or a SS vertical dropout. In this configuration, you often see Eccentric BB's but sometimes you don't. When you don't, you are expected to adjust your chain as close as you can, and then use the 5 or so mm of play in the vertical dropout to tighten the chain.

    Regarding what is best...well that is debatable. The horizontal slide is the classic way of doing it. When it was the only way, 20mm through axle was used instead of quick releases. In order to make more standard with the 9mm quick releases that everyone loves, a way was sought out to use the 9mm, and then tighten a different way. Incidently, modern horizontal slide bikes accomidate 9mm quick releases just fine.

    Eccentric Bottom Bracket is by far my least favorite type..for a number of reasons. For one, the elliptical motion in the crankset/BB involved in tightening your chain with an EBB means your bike geometry changes based on your chain length. Your pedals can be an inch+ further or back from the seat, higher or lower from the seat, etc. Also, under extreme pressure, that bracket can slide and your chain can loosen. You can tighten it really hard, but it they all end up sliding under heavy use. Lastly, you can't use any bottom bracket with it.

    Adjustable rear allows you to use whatever BB you want. It allows you to use 9mm quick releases. It's the most standard and easy option. Unfortunately, it's the rarest. It exists on nicer frames which cost more money.

  4. #4
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    Quote Originally Posted by Clobber
    From what I understand, SS bikes come in 4 frame types generally... .
    Sounds like you've got things pretty well sorted.

    --sParty
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