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Convert Trek Marlin 4 to disk brake??

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Convert Trek Marlin 4 to disk brake??

Old 06-29-18, 03:36 PM
  #1  
JoelMacDonald
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Convert Trek Marlin 4 to disk brake??

My 12 yo so has a 2017 Trek Marlin 4 and wants disk brakes. I assume I convert the bike to disk brakes? Would it be cost prohibitive or would we be better off trading up? Anyone have information on parts required and instructions on doing so? I'm mechanically inclined, wrench on my own motorcycles and cars, just new to non motorized bikes. Thanks.
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Old 06-29-18, 10:12 PM
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wsteve464
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It is not cost effective, the 2018 model comes with disc brakes and lists for $449 from Trek. If you where to go ahead you would need a new fork with a caliper mount, you would need to redesign, cut and weld the rear end for a caliper mount on either the seat stay or chain stay, new wheels or at least hubs, and a set of disc brakes. I have probably left something out but you get the idea.
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Old 06-29-18, 10:49 PM
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It's not a simple bolt-on retrofit. Disc brakes exert different stresses on different points of the frame and fork than rim brakes, and the frame and fork need to be built to withstand those stresses. (Because the disc is closer to the axle of the wheel, braking torque at the caliper is higher for disc brakes.) Plus, the wheels' hubs need to be built to accept discs.

Considering all the parts that would need to be replaced or modified -- particularly the frame, fork, and wheelset -- it's cheaper and way simpler to start with a bike built for discs.
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Old 06-30-18, 01:16 AM
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Originally Posted by SkyDog75 View Post
It's not a simple bolt-on retrofit. Disc brakes exert different stresses on different points of the frame and fork than rim brakes, and the frame and fork need to be built to withstand those stresses
Pretty much irrelevant when you have to weld anyway, with the current disc standards, there is almost no viability for retro-fitting any bike today with discs, unless you can do it all yourself (a then, if you could, you would just build a disc frame from tubes)
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Old 06-30-18, 09:33 AM
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If your frame was made for only rim brakes, consider building wheels
around drum brake hubs .

makes a fine retrofit.. I have been using mine, [Sturmey Archer], for over 30 years ..
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Old 06-30-18, 11:38 AM
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I wouldn't be surprised if that bike wasn't already set up for disc brake mounting. Frames are often set up to be used for numerous models and extra mounts to facilitate different drive trains. I have a couple bikes with rim brakes and disc mounts. Still probably not worth it when you look at likely needing wheels plus brakes on an entry level model.
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Old 06-30-18, 11:51 AM
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Why does he want disc?
Even semi-properly set up, you should be able to wheel stand the front with V brakes.
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Old 07-01-18, 04:08 AM
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dsaul
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As others have said, it is cost prohibitive to convert that bike to disc brakes. It appears that the frame has an IS(International Standard) disc brake mount, but the fork does not. By the time you buy a new fork, disc wheelset and the brakes/rotors, you have exceeded the original cost of the bike.
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Old 07-02-18, 10:43 AM
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Originally Posted by Bill Kapaun View Post
Why does he want disc?
Even semi-properly set up, you should be able to wheel stand the front with V brakes.
I suspect because he's 12 and discs are cool
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Old 07-02-18, 11:26 AM
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Bill Kapaun
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Originally Posted by Litespud View Post
I suspect because he's 12 and discs are cool
In which case, in a couple years he'll need a bigger bike and can get discs then.
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