There’s no maximum permitted size for brake rotors but bigger = heavier of course, so it’s down to the smallest that will do the job.

OK, same as for push bikes then, except weight is less of an issue when you have an engine. So if a single 185mm rotor does fine stopping a 140kg – 160kg motorcycle and rider from 40 – 50mph, it’ll probably work ok on a push bike with big wheels.

go on then ben, put the OP out of his misery, from what did you fab the dual rotor mount hub?

Wasn’t a Hope – it was someone who made a prototype for BMX I think got the shell through BikeBiz, then hand to turn a custom axle.

i have a pair of Z1 bams with the dual disc brake mount but sadly not the right hand side caliper 🙁

This sounds ace!
Are you planning on trying to make it a thing of aesthetic beauty too?

Thanks ben, looks like its custom or bust then. or 120 front axle.

Alex – I plan on making it not un-rideable in terms of handling and braking. If I can buy the tubes then beauty may come into it, may not though, some pretty shoddy looking 36″ers around.

Talk to Ted James (Ted James Designs) maybe, he has a workshop in Stroud and has made hub shells for his own projects from scratch.

I had a set of the Z1 Bombers with dual disk mounts. I bought them when I lived in Boulder, Colorado. Paid buttons for them too (in uk terms)

The Disk mounts IRC weren’t standard size and I’d a helluva time getting an adapter to make Hope and then Shimano XT calipers fit. I never liked the feel of the forks either.

The kicker was when selling no one wanted them because of the double mount.

Edit: Again, my memory may be failing me, but I think Goldtech made a dual disk hub back in the day.

Why is one caliper mounted on the front of the fork?

won’t the dish (or lack of)caused by two discs on a 100mm fork dropout, combined with the wheel size, make for a horrible and fairly weak wheel?

paul – because otherwise youd probably foul the spokes.

faustus – having spoken to my favourite wheel builder he said he has seen similar builds and they have been fine, see mountian unicyclists and the stuff they ride, with 14 gauge stainless spokes I should be fine. I am also thinking of running 120 up front.

Why is one caliper mounted on the front of the fork?

Because nobody makes mirror image calipers. Really, the front of the fork leg is usually a better place to put the caliper anyway.

My motorbike weighs 160kg, + 60kg of Northwind, and stops very nicely from warp speed with only one rotor. Admittedly, a rotor the size of a pizza, but still.

Considering the stupendous power of the best brakes these days it does seem like you’re overcomplicating things but I do like a mad project.

“Just because” is a perfectly valid answer…

any updates maximus? : )

He’s still doing a superman from the first time he pulled the brake lever 🙂

He’s still doing a superman trying to pull his head out of the brick wall from the first time he pulled the brake lever

😉

I remember when V brakes first came out. People would go on a test ride, and we had to warn them about the braking! Riders used to heaving on the anchors with cantis would grab the same handful of lever with a V and stop rather suddenly!

Riders used to heaving on the anchors with cantis would grab the same handful of lever with a V and stop rather suddenly!

I had almost the reverse issue. Having ridden only disks for years I switched to a canti-braked cross bike. First time I braked on a wet, chalky downhill it took me ’til I was half way up the next hill to stop.

Same when I’d let my cousin try my mtb. He’s French and grabbing a handful of ‘back’ brake to do a skid didn’t quite have the effect he intended 🙂

Jamie – This is as far as I have gotten so far.

Spacing between disc and spoke flanges has changed since I rendered the image. 110 OLD with 4 sizeable bearings, need to grind my own QR15 axle and also need to find somewhere for custom 14G spokes in the 370-380mm range else my flange diameters get huge.

Also depends entirely on the dual crown geometry (that I am yet to get hold of) and how much bodging would be required. Reasons for not using a double fixed hub are sealing issues but surly seem to do a double fixed 120 OLD with cartridge bearings so if this custom one doesnt work, those may be worth a shot, but the flanges are pretty tiny.

Mainly it depends on spoke lengths at the moment.

Full set up Ebay last year
There’s more info on retrobike if you search

P20 – based on yours going for 300(!!!) it’s unlikely to fit such big wheels in I don’t think I’ll be looking for those forks (although the hub looks good!) seems pretty rare as well, probably quicker to make my own.

thanks maximus.
love what a slow burner this is. and how totally overengineered it sounds, tho not in a position to pretend i can do the ‘math’
doesn’t sound like it’ll break tho, or you’ll have trouble stopping

what about the rest of the bike?

Jamie – The rest of the bike is on a back burner, I have a very good idea of what I am going to do for tube sets etc I just need to decide on rear axle spacing and head angle/mechanical trail to try and get it to handle like a 26″ bike. My other project is coming first (shameless plug) as I would like a 29er before the 36.

I ask questions like this as I want to do a stupid amount of research to make sure I don’t get further down the design stage for nothing.

But so far its looking like 110/120OLD front hub, Hope pro2 trials rear hub (or SS specific so 135OLD but may go to fatbike 190OLD), 100mm BB and a 31.6 post. Going to keep ATC as small as possible and it will of course have a 1.125″ headset with a 44mm HT. I also want it to have 15mm axle up front and a 12mm axle out the back (if possible with the given hubs) with pinch bolts on each for extra security.

Decided against hydro brakes for the front at least as the piston movement in the lever is designed for one caliper, leaving me getting half the braking force at each caliper so not improving anything (apart from heat dissipation and resistance to the power mode of failure). The mechanical levers will be much easier to bodge either 2 lever bodies to one lever or incorporate a cheater system into the cable run to increase pull. Although I do still have concerns about the force still being halved or a huge amount of set up to get anything worth while.

As I said, its all in my mind atm and I have it down on paper in a few places but the 29er project is coming first in the funds department which is hindering the 36″ project.

the lever is designed for one caliper, leaving me getting half the braking force at each caliper

Hope V twin/TRP Parabox with both outputs sent to the front wheel?

You can get cable splitters for mechanical brakes – eg pull one lever which goes into the splitter and then pulls two cables for the calipers.

V-twin/parabox needs two cables going in so you could use a splitter as above but you’re not really gaining anything other than having a semi-hydro setup.

This thread may be useful:
http://singletrackworld.com/forum/topic/bike-brakes-for-people-with-one-hand

this being the splitter EDIT – it’s actually called a ‘doubler’.
http://problemsolversbike.com/products/cable_doubler/

Clubber-very useful thread!

It seems no mater which system I use the force will be halved, just means heat build up is less likely to fail the pads, which is no bad thing. Maybe Ill use that mechanical puller and get on the squash balls for grip. It will be a lot simpler than either dual hydros or a semi hydro system.

need to find somewhere for custom 14G spokes in the 370-380mm range else my flange diameters get huge.

Well that’s easy at least. Ben will remember my saga trying to source spoke blanks to make a double ended spoke – I eventually found a source at http://www.unicycle.uk.com/unicycle-parts/spokes.html – 371, 375 or 376 available, or they’ll cut and thread custom length ones.

Well you’re only providing X force at the lever so other than through leverage, you can’t change that unless you have some sort of servo assist 🙂

But as we discussed a while back, I don’t think it’s really an issue – you’re overengineering it IMO – a single, large brake would be fine.

aracer – I have looked at them and my calculated spoke lengths are ~378, I know you can get away with 1mm either side of that but am yet to speak to the person I would get to build the wheels if using longer nipples would be appropriate (I don’t like to pester him with too many questions, I imagine I get annoying after any period of time). Those penny farthing spoke blanks are something I hadn’t considered though, and in the correct gauge.

clubber – yeah, thinking about it properly (and not being a numpty) I don’t need the same force in each caliper to equal a standard one, together they will equal a standard one, it’s the equivalent rotor size I am after, dual 120’s would give me the perfect rotor size but to make sure I don’t gather too much heat in the pads and glaze them over or cause power absorption failure I have been advised for 160’s.

Admittedly yes, dual discs are overkill, but it does cancel the reaction forces out and mean I don’t need a custom rotor (which I am more worried about designing and making than a hub) or custom caliper mounts. All the safety critical bits are not my problem 🙂 .

Bit more info that may be helpful:

Here

&

21 pages on a similar project here

http://cdn.mos.bikeradar.com/images/news/2014/03/09/1394323671389-15urnkwyut0ww-670-80.jpg

thats from my post below.
I was going to link that photo when i saw it but i had issues with the hub…. i.e. missing spoke hole.

Doesn’t help with the hub, but Magura do a setup with one lever to 2 calipers:

http://pedicabshop.com/blog/perfect-twin-disc-brakes-big-magura-twin.html

I had some reverse hubs on mavic 325 rims a while back that had mounts for 2 front discs. Lovely set of wheels that I only parted with due to the acquisition of a dh bike and needed a wider rear hub and part ex’d mine

http://m.pinkbike.com/photo/3457391/

An update with graphs, drawing and picture on where I am at the moment. But making my bike frame jig had priority at the moment!

You’re sure the Zee lever has twice the volume/pull as std levers?

AFAIK 4 pot calipers often use smaller pistons and hence the same lever.

Not sure at all, working off the assumption of larger piston area at the calipers so would be more suited to run two than the standard lever. Not an unfair assumption I dont think, hopes bores seem similar although that doesnt mean jack all about the piston area depending on the design as Ive never had one apart.

Ive got an adaptor for a non disc hub to convert it to a disc. Its made up of a flange that bolts the the hubs original flange with a 6 bolt disc part to bolt to. Ill try and dig it out and get a photo up.

kevs, something like this I assume, it could solve my 4 cross spoke length issues.
http://www.sjscycles.co.uk/images/products/medium/nuvinci-disc-brake-adapter-IMG30971.jpg