Disc Brake Gurus?....Sprocket Adapter

Discussion in 'Performance Mods' started by andyinchville1, Jun 27, 2008.

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  1. HI All,

    As you all may know I have been making sprockets for mounting in place of the disc on a disc brake hub....However, placing the sprocket further out (where the disc mounts) has caused some issues for some users (the chain or sprocket would interfere with the rear stays of the bike frame itself).

    A simple solution for most users has been to simply redish or space out the rear wheel....While this has proven to work for some users for some it is still not enough for others (primarily depends on the frame and wheel in question)....Plus extreme dishing can weaken the wheel and spacing sometimes has its own problems (in extreme cases some of the rear cog gears cannot be used)...

    With this in mind, I am designing a "Hub Adapter" to which a 9 hole sprocket is attached (the sprocket with the enlarged center hole (to clear the disc hub) is bolted onto the adapter and the adapter is then bolted onto the disc portion of the disc brake hub....This will place the sprocket, at or very close to where the sprocket would have been had it been mounted using the standard mounting hardware (of course using the hub adapter and sprocket on this disc mount will ensure a more precise alignment and be free from lateral run out or "wobble"...

    While there has been a another design of adapter that somebody had made....My design hopes to not only mount the sprocket precisely but ALSO enable one to retain use of the original disc brake if one choses to....

    Which brings me to my question for you disc brake gurus out there (my bikes are not equipped with a disc brake so I can't check here at the shop)....

    1) The adapter will push the disc of the disc brake out 1/8".....would this be a
    problem or is there some adjustment that can be made (much like a
    rim brake)?

    2) What is the diameter of a disc brake disc?

    3) What is the thickness of the disc brake disc?

    4) How far in towards the spokes does the disc brake caliper (the part that
    grips the disc to slow you down) extend ?

    Thanks in advance for any help on this....I will post pipcs of the prototype soon!


  2. vyzhion

    vyzhion Guest

    My disc rotors (and I believe most others) are 160mm in diameter and 2mm thick. You could move the caliper to accommodate your 1/8" inch just fine but you might need longer bolts depending on your setup. I'm interested in this idea. I just got one of your 34T sprockets from ebay and I have it mounted directly to the disc hub. I am installing it with my Titan so I can adjust the chain to line up perfectly. On most frame-mounted bikes though, the chain doesn't quite line up with the disc brake hub. I wish you luck on this. Please keep us posted on your progress. :)


    PS not to go OT but did you ever get one of the thread-on 5 hole freewheel sprockets from the Grubee HD axle kit to be able to make sprockets to fit those? If not, pm me and I have one I could send you to measure and make a master if you're interested.
    Last edited by a moderator: Jun 28, 2008
  3. meme405

    meme405 Guest

    Disc brakes depend, the best of them are 8-9" butt hey come in 7" and 5" as well. They are not that thick at all...
  4. Demosthenese

    Demosthenese Guest

    just my two cents, i have bolted my sprocket to 3 different disk brake wheels, and all three of them have had different clearences. Two of them were almost perfect distance for the chain to be straight, and one needed the idler to keep it on.

    the biggest problem i had was longevity; the hubs aren't designed to be under load all the time, and the bolts inevitably vibrate themselves out. Trust, i used tons of locktite, different kinds of locktite, different friction washers, different disk brake bolts (some of which are 5 dollars a pop) i redrilled and rettaped hubs for larger more durable bolts, checking and retightening every time i road it... in the end, it didn't seem to matter what i did, the bolts managed to get out over time. So constant retightening and buying new bolts, while still worying about what will happen if on a long ride one or two come out on the same side. The disk brake hubs are not designed to take the prolonged torque the engine is putting out, so if one or two bolts go, it can be pretty catastrophic when u rev that engine, with the sprocket tearing itself right out of the hub or shearing all the remaining bolts off at the hub. both things have happened to me.

    i tried this to death lol. moved on to one of the hd hub kits, its great and sturdy and made for the job. gl andy! if you have better luck then i, let us know what you did.
  5. Bogaurd

    Bogaurd Member

    Interesting that you mention that - I made up a disc hub adapter & have had no issues in the month or so since. I check the bolts every week or so, and so far they haven't loosened at all... I'm not sure, perhaps I'm just lucky! :lol:

    Common disc sizes are 160mm or 203mm from memory, thickness is 2mm. Regarding moving the brake caliper 1/8" laterally, depending on the mount used, this may or may not be an issue - more often than not though, this will probably be an issue. I own several bikes with discs, even the high end gear I have with the most adjustment doesn't allow for such a large offset.

    Here is a photo of a rear disc mount - the top two bolts can be loosened to allow offset adjustment, but generally moving more than 1mm or so either side is unlikely. The bracket which attaches the caliper to the frame could potentially be machined thinner to make allowance for this offset, but mountings may vary from frame to frame & caliper to caliper - most bikes use IS (International Standard) disc breaks & mounts, though other standards exists.

    I will post some pictures of my own frames tomorrow morning if you'd like. :smile:

    Here are some PDFs provided by Hayes with schematics for disc mounts:
    Rear International Standard Mount
    Rear International Standard Quick Release Hub
    Last edited: Jun 28, 2008
  6. Demosthenese

    Demosthenese Guest

    keep checking those bolts my friend, and do report on longevity, especially if u find a longterm succesful mod. engine probably makes a difference too. i was using a "90"cc engine with a 36 tooth sprocket, so the force would be more then on a 49cc with a 50 tooth for instance. nothing would make me happier then to understand why mine kept failing; the first time could have been negligence, the second time could have been overuse on a single day, but the thrid time it happened to me i swear i was checking that thing pretty hard and babying it all the time. id be nervous for it whenever i rode, so i know it was in perfect condition the day the bolts failed. im the first to admit i don't fully understand why; i could understand a lifespan for the hub, but not one that short when disk brakes can stop you for years at high speeds; the hubs must be reasonably strong, intuitively it seemed like they'd be strong enough.

    keep experimenting everyone. ultimately this solution was too inconsistent and weak for my application, but i'd love to hear more tales of success!
    Last edited by a moderator: Jun 28, 2008
  7. HI Guys,

    Thanks for the input so far....

    1) Regarding bolt strength....It is true that the bolts holding the sprocket to the disc brake hub are substantially smaller (not to mention fewer also) than the bolts in the 9 hole mount...While I have not personally heard of any bolts shearing because of lack of strength, I have been looking into using Titanium bolts.....Titanium is WAY stronger than the the material which is probably used as the standard mounting bolts...

    2) As far as loosening is concerned....I am not sure why this has been a problem especially with liberal use of Loctite or similar product....It should be noted though that when using some products....More is not always better .....Perhaps Loctite is to be used sparingly for maximum performance? (of course parts should be clean and grease free before use....I'll have to find my Loctite and read up)....Perhaps...Loctite AND good old fashioned lock washers could be used to prevent the bolts from loosening...

    3) Yes, there are many variations on disc brakes and disc sizes as well.....My biggest concern at this point is not necessarily the 1/8" that the disc would be moved outward....as mentioned earlier....some adjustment may be possible even if it requires minor grinding or filing of the caliper mounting points on the bike frame....I am somewhat more concerned that the caliper itself on the inboard side (the ones closest to the spokes) would be thick enough to cause possible interference with the sprocket if it is mounted in roughly the same position as the 9 hole factory mount (this is where I ultimately wan the adapter to place the sprocket)....I could do some additional machining on the adapter itself in the hope of gaining enough clearance for the caliper to fit in between the disc and sprocket without interfering with the sprocket or chain....of course if it is a really tight fit that barely allows the caliper to fit in one could play with sprocket and disc sized to prevent possible interactions.....but that probably wont be necessary since the caliper would probably be closer to the sprocket than the chain would anyways....

    Tomorrow I will try to visit a bike shop to get a feel for clearances.....I will post pics soon!

    Keep the pics and info coming!.


  8. azbill

    azbill Active Member

    I have 1200 miles on my disc mounted sprocket
    these are all 'hard-riding' miles, most of them pulling my grandkids in their trailer :D
    see "my Jag" thread in the pics forum
    (I mounted it and then painted everything black, so I would see any movement as showing the silver, no movement yet :D)
    Last edited: Jun 28, 2008
  9. Hi All,

    Well, I took a trip to the local bike shop earlier today (it was a spontaneous trip while I was doing other errands so I forgot my calipers / tape measure etc...) and checked out some of their disc brake equipped bikes.....Upon closer examination of everything, it was as I had guessed....the brake caliper itself would pose the largest obstacle to making things work (i.e. being able to run a disc mounted sprocket AND disc brake at the same time) BUT I think the solution would be to mount the brake caliper to the OUTSIDE of the frame rather than the inside of the frame and space out the disc even further (my current spacer is 1/8 inch but I think we'll have to go 1/4 or 5/16 to make up for moving the brake caliper OUTSIDE the frame....Then I may still have to machine the adapter a little so the bolt heads holding the sprocket onto the adapter itself wont interfere with the relocated Caliper....I'll take some measuring tools with me next bike shop visit!


    PS - I don't know if the "tabs" to which the disc brake calipers mount are of a standard thickness or not, so for all you disc brake people out there....if you could measure yours and let me know how thick it is I'd appreciate it.....Thanks!
  10. HI Bogaurd,

    Thanks for the pic....yes any extra pics you have would be appreciated!


  11. Demosthenese

    Demosthenese Guest

    there was a really cool motorbike built for discovery's motorcycle mania i think, anyway, this guy engineered a combined rear sprocket/disk brake. if only you could make ur own caliper lol...

    also, the bolts i were using, don't know what they were, but i went to the local mtb store and told them about it then asked for the strongest bolts available. they cost like 3 bucks each, so i know they were strong :) and i did use lock washers too.
  12. Bogaurd

    Bogaurd Member

    Hi Andy,
    I'll get some pics for you tonight.

    However, regarding the caliper mounting, I don't believe mounting the caliper on the outside of the frame will be a feasible solution to the problem - the frame mount is often such that the tubing etc will prevent the caliper from being mounted on the wrong side.

    Seeing as you have access to a machine shop, I would think a better option would be to look at designing a dual purpose adapter - that is a disc which acts as both the braking surface & has the appropriate drilling to accommodate the drive sprocket. In this way it would be a painless conversion, and would suit more bikes. Infact, there's at least one user on the forums who has successfully mounted his drive sprocket to the disk brake. :smile:
  13. Hmmm....Mounting a sprocket off a disc...now that is thinking out of the box.....I'll have to look into that idea too....

  14. Bogaurd

    Bogaurd Member

    Sorry for the long time in taking the pics, but I've now put a few shots up at www.bogaurd.net/brake/
  15. Thanks for the Pics Bogaurd....Great close ups!

  16. souloution

    ok first off discs come in 120, 140, 160, 165, 180, 185, 186, 203, 205, 225, 230, and 256 mm sizes w/ many manufactures making theirs afew mm off from the standards of 140, 160, 185, 203
    second there is a 4.5 mm difference in offset from a front or rear post mount adapter and one size rotor too. Hence a you can use a adapter for a front 185 mm rotor for a rear 160
  17. HI,

    Thanks for the added info....I think we have "solved" the problem with the Top Hat Sprocket Adapter....;-)


    PS - I ha no idea there were so many different size discs out there! WOW
  18. for the record andy I run a 20t cog sandwhiched between 2 160 rotors so that they act as chain guides. this is extremely effective and allows me to run some slack in the chain so it is not strining such massive side load on out put shaft and wneel. the wheel itself as it suported on both sides isn't such a issue but it can strain the outp9ut shaft considerably when it is sitting dormant in one position. now what I would like to know is what is the smallest you can make your cogs that fit your hat?
  19. HI Married,

    I am not 100% sure of the smallest sprocket that can be run with the Top Hat Sprocket Adapter but I think a 27T would be close. (Maybe a 25 or 26 would work BUT at some point the chain will start to ride the bolt heads of the 9 hole adapter mount....I haven't tried to verify for sure though)....FWIW I am pretty sure we can make a 18T to fit to the disc hub itself! ;-)

    Hope this helps you.


    PS - I like your idea of your chain guides!
    Last edited by a moderator: Aug 28, 2008