DIY single speed disc brake converter……….will I die?

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  • DIY single speed disc brake converter……….will I die?
  • ajantom
    Member

    I have a lovely 1998 Indy Fab SS Deluxe that I’ve been planning on building up and riding again, but it being rim brake only on the back has been putting me off.
    I considered having a disc mount brazed on (or maybe doing it myself), but I decided to go down the non-permanent route.

    I’ve seen similar designs to this on t’interweb, but none that I could actually find for sale. So I decided to have a go at my own using a Boxford milling machine we have at work.

    My only slight worry is that the forces on the dropout might be a bit much. I’ve fitted a 140mm disc to start off with to minimise the braking force a bit.

    CAD designs:

    [url=https://flic.kr/p/223M1zP]SS Dropout 1[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/DL69q4]SS Dropout 2[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/223M1vk]SS Dropout 3[/url] by tom harrison, on Flickr

    Prototypes – first was hand cut and milled in aluminium to get the shape/dimensions, and then CNC milled out of wood to make sure my CAD drawings worked:

    [url=https://flic.kr/p/Fhd3LN]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/FhcS8o]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    Final dropout – finish isn’t perfect, but it’ll do to test with and I can always make a ‘nicer’ one at some point!

    [url=https://flic.kr/p/23nj3bU]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/JtcRbp]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/23nj8MJ]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/23nja7C]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    And fitted ready for a ride/test tomorrow:

    [url=https://flic.kr/p/DL5SiV]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/23njdg3]CNC SS Disc Dropout[/url] by tom harrison, on Flickr

    Premier Icon Bez
    Subscriber

    I’m liking the wood ones 🙂

    ajantom
    Member

    Means you can whack up the speed on the milling machine to test the pattern quicker.

    I might turn them in to Christmas tree decorations for next year 😉

    Nice work!

    As long as the bracket you made is a snug fit in the dropout slot I should think it will be ok. A brace running from the bracket’s upper caliper mount up to the the frames V brake mount would solve any such issues.

    EDIT; Hmm no it probably wouldn’t looking at it again. Something to let it lean on the seat stay right under that upper caliper mount would though.

    Rorschach
    Member

    A lot of torque is generated from the disc caliper.I’d be looking at some way of bracing it to the seatstay to prevent the dropout taking all the force.I’ve seen what a Rohloff can do to a dropout without the torque arm!

    ajantom
    Member

    As long as the bracket you made is a snug fit in the dropout slot I should think it will be ok.

    It is a very snug fit, no movement at all with the brake on and rocking the bike back and forth.

    You’re right though, I am a bit worried by the amount of torque that will be going through the dropout.

    Premier Icon tallie
    Subscriber

    From experience of trying something similar, I suspect it will work but you may get an annoying squeal as you brake… hope I’m wrong!

    ajantom
    Member

    BB7s – they squeal whatever you do anyway!

    Premier Icon JAG
    Subscriber

    I kind of agree with you OP – I think the dropout will be fine but I think your Aluminium mount will get chewed up by the braking torque.

    Just for clarity – a smaller disc will not reduce the braking torque 8)

    Looks good. The A2Z adapter I have also rests on the seatstay where the upper caliper bolt mount is, so perhaps that braces it a bit there too.
    Generally retrofit braze on disc tabs have a brace between seatstay and chainstay. Not something you can do with a bolt-on adapter, I’ve had no issues using the A2Z adapter on a few different frames with 160mm rotor though.

    Premier Icon tthew
    Subscriber

    .I’d be looking at some way of bracing it to the seatstay to prevent the dropout taking all the force

    That was my initial thought too. In fact, both the steel disk bikes I have have a brace between the seat and chainstays to spread the load between them too. Would be a shame to damage that nice frame.

    edit – I was a bit slow. Oh yeah, and nice work too OP.

    ajantom
    Member

    Just for clarity – a smaller disc will not reduce the braking torque

    Will it not?

    I thought that torque = radius × force.
    So if you increase the radius of the disc, braking torque will increase.

    Or am I being dumb (probably!)

    andyl
    Member

    Looking at the drop out area of the frame you could position the caliper in the triangle between the chain and seat stays like the original mounts on the On One carbon 456 ie rotate your mount around 90 degrees anti-clockwise. You could then make some form of extended pad areas to brace it against them with some form of adjuster or adjustable clamp – ie turn the mount into the seat/chainstay brace itself.

    Little bit more work but would look a lot neater and not stick out on the frame so much.

    Did you use the official IS brake mount measurements or work them out from another frame?

    The A2Z adapter has a little foot which rests on the seat stay but i think you could make something better. The problem you do have the the sliding drop out means it needs to be adjustable as you tension the chain and the gap changes but can be worked around.

    andyl
    Member

    Look at B and D options here: https://www.on-one.co.uk/i/q/FSOOCNCSO/on-one-cnc-anodized-swap-out

    The singlespeed design has slots to adjust the brake manually after tensioning the chain.

    noltae
    Member

    Hope it goes well – well done for all your efforts . .

    Premier Icon joebristol
    Subscriber

    https://www.tensile.net/tensile-disc-brake-converter.html#PhotoSwipe1515792930247

    Might be worth having a look at this adapter. I’ve got one on an old hardtail – it bolts through the qr adapter like yours, but then has a bolt that braces it against the seatstay, and a torque arm which goes up to the v brake mount. Works perfectly.

    Rob Hilton
    Member

    Needs more spoons

    ontor
    Member

    No tom!

    Bad Tom!

    Bad! Tom!

    cynic-al
    Member

    I’d be bracing it for sure, especially in a high end frame.

    The torque on it will Shirley vary with rotor size. Simples physics innit. Unless your point is that it’s about traction between tyre and found being the limiting factor.

    Premier Icon Jerome
    Subscriber

    Just use an xtr v brake and get rid of that nicely made monstrosity . I rode miles and miles with a v out the back and disc on front.

    ajantom
    Member

    No tom!

    Bad Tom!

    Bad! Tom!

    Bring a camera along on Sunday Joe and film me going down in a massive fireball 😉

    Premier Icon mintimperial
    Subscriber

    cynic-al – Member

    I’d be bracing it for sure, especially in a high end frame.

    *ctrl-F* “spoon”

    Rob Hilton – Member

    Needs more spoons

    Ah, good, carry on. 😉

    He’s right though OP, I’d not ride that, not very far anyway. I think it will bend or snap and bad things will happen. I bet you could add some sort of triangulation to it to support it without too much modification of the design though, and it looks quite nicely made, well done.

    Premier Icon cookeaa
    Subscriber

    I modelled something very similar intended for my slot dropout commuter, I was going to do it in mild steel though…

    You do have a fair bit of support from the slot faces to react against brake torque so it’s not a given that bracing back to the stay is necessary, let us know how you get on…

    Nice work.

    brant
    Member

    I did design, make and sell something similar for very early on-one frames.

    I seem to recall I had bracing under the dropout too.

    I didn’t use a CNCd lump to locate it. I used nuts from m6 bolts which are 10mm a/f located by 6mm holes. Much easier to fabricate.

    I will see if I can find pics.

    ajantom
    Member

    didn’t use a CNCd lump to locate it. I used nuts from m6 bolts which are 10mm a/f located by 6mm holes. Much easier to fabricate.

    I did think of that – seen some bmx disc converters that use M6 bolts like that.

    Premier Icon Del
    Subscriber

    i’m glad you’re handy on the mill cos i don’t think much of your filing 😉
    i’m also happy you’ve built the indy fab back up. we’ll need something to ride to the bog next time we go camping.

    ontor
    Member

    Bring a camera along on Sunday Joe and film me going down in a massive fireball

    Will do.
    I suspect the dropout will bend given what happened with the torque nuts on the alfine and a similar dropout.

    i’m also happy you’ve built the indy fab back up. we’ll need something to ride to the bog next time we go camping.

    It’s a beautiful bike serving a vital purpose…

    Premier Icon Speeder
    Subscriber

    The torque comes from the wheel at 13″ and ultimately will ultimately get reacted at the dropout as there’s no other load path it can take. What happens between, ie the rotor size is irrelevant. Big rotors are “better” because they can both apply more torque at any given instance, have more surface surface area to dissipate heat and the surface moves slower relative to the pad at a given rpm. All that is only applicable up to the point where you can’t generate any more grip and at the rear that point is quite low due to weight transfer.

    I’d try to avoid skidding over braking bumps and no back hops but there’s lots of similar products being used in BMX right now so you may be ok.

    Good luck, it’s a neat solution to have it outboard of the dropout. Not one I’d have thought of.

    ajantom
    Member

    Brace added…..what do we think? Still a flaming ball of death?

    [url=https://flic.kr/p/22mYAh7]Brace added![/url] by tom harrison, on Flickr

    [url=https://flic.kr/p/23oUzEG]Brace added![/url] by tom harrison, on Flickr

    Rorschach
    Member

    I approve of the P-clip usage!

    ajantom
    Member

    It’s how coaster brakes are braced, so I thought why not!

    Brace added…..what do we think? Still a flaming ball of death?

    That’ll be great, for going backwards.

    I can’t help thinking that any force strong enough to damage the dropout/bracket would open up that clip like a tin of sardines.

    Just a pad to push against the back edge of the seat stay would probably resist movement better.

    ontor
    Member

    bringing the camera…

    Premier Icon mick_r
    Subscriber

    P clip should help, I guess the new extra tab of aluminium also braces against the stay.

    Reverse braking is actually quite a relevant comment – a friend peeled off a disc mount that he’d silver soldered. It happened on a failed attempt at a steep banking, braking whilst rolling backwards. With weight transfer, that is probably the worst loadcase for your mount (but doesn’t happen very often)

    Rorschach
    Member

    Bar adding a spoon….that’ll do pig.

    Big rotors are “better” because … the surface moves slower relative to the pad at a given rpm.

    Eh?

    The outside of a bigger rotor moves past the pad faster at a given rpm.

    Premier Icon Speeder
    Subscriber

    thenorthwind – Member
    Big rotors are “better” because … the surface moves slower relative to the pad at a given rpm.
    Eh?
    The outside of a bigger rotor moves past the pad faster at a given rpm

    Doh! Of course! I worded that wrong didn’t I! 😳 Anyway there’s more contact area per revolution which means better dissipation of heat and better cooling.

    Premier Icon eviljoe
    Subscriber

    So DDay then Tom?

    If you die in a horrible ball of flame today, can I get the Love/Hate frame I sold you back?

    You know, the sensible single speed with real actual disc mounts on?

    Good luck !

    ajantom
    Member

    😉 if I die it’s yours!

    Not sure if I’ll get a ride in today……teething baby + tired wife + snotty 4 year old + pile of books to mark = busy tom 🙁

    ontor
    Member

    Probably for the best. Gives the IF a stay of execution ;p

    ajantom
    Member

    Hmmmm, I’m not feeling the unerring support I’d hope for from a friend here 😉

    They all laughed at the Wright brothers. Same thing.

    Anyway there’s more contact area per revolution which means better dissipation of heat and better cooling.

    That’s better! 😛

    ontor
    Member

    Hmmmm, I’m not feeling the unerring support I’d hope for from a friend here

    You can wear my support as long as you like 🙂

    Missed you out today – next week?

    ajantom
    Member

    Missed you out today – next week?

    Managed to get out, but only for a ride with the gremlin. Hopefully be out next week for a decent ride.

    Annoyingly after dropping a load of cash on the Belter she is insisting on riding her old balance bike. To be fair she did 4.5 miles on it. Which is pretty good going!

    On a positive note (naysayers take note!) I rode the IF with it’s rear disc mod and didn’t explode in a fiery ball of death 😉

    Now obviously a 4.5 mile ride with a 4 yr old, at an average of 3.5 mph isn’t really testing it to the limits. However, I did a few hard rear brakes to try it out and didn’t hold off using it for general braking……and it seems to work. So far.

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