alternate disk just for "funn"

I managed to wreck 3 sets of Sinz cranks since I got into running disk brakes and found another brand of cranks that I thought would work with the Mountain Uni system for cheep at Chain Reaction Cycles.

Just for sh*ts and giggles I decided to get a chain ring along with the cranks to see if I could use it as a disk. It is an aluminum single speed ring and 3mm thick.

I thought that the cranks would be much heavier than they are but the centre part of the crank is thinner than the rest making them not as good for multiple holes as I was hopping. I think I can still put one extra pedal hole in them without much of a problem and the wide C beam style should be plenty strong with a hole in it.

I took off the old cranks, threw a disk on and installed the Funn cranks. It became apparent that even with no spacers between the disk and crank that the disk would have to move out about 3mm. I started filing away with a bastard file then got wise and took it to the belt sander.

It took me a good hour to get the crank flush and level like I wanted with all the arms within a 0.02mm tolerance of each other.

Next I ran into the problem of the chainring bolts being too long. I ground them down too. (easier said than done)

I was able to put it together and it was perfect with 2 spacers between crank and disk. Once that was established I decided to try the chainring.

Like I said before the chainring was 3mm thick which is quite thick for a disk brake. The MU disks are 2mm and most other disks I have used were 1.8mm. I got a 44 tooth ring because I figured it would be the closest size to 180mm. the top of the teeth are a bit taller than 180mm but not a whole lot and it just fits in the disk calliper without any modifications. I do get some slight rubbing between the disk and the calliper body (not the pads)

The brake seems to work just fine with the chainring instead of the disk but I haven’t done more testing than just in the building. I am curious to see how long it will take to wear down the aluminum, I already am down to 1.92mm (from 2.00) on the braking surface of the disk it is replacing, and it hasn’t seen nearly as much use as my two other ones.

This is a fantastic idea for cheap disc brakes…

I found this stuff on sale and the cranks and chainwheel cost me about $55. Since this seems to work so far (it is very preliminary) I don’t see why you couldn’t do the same thing with other ISIS or square taper cranks and single-speed chainwheels.

The Mountain Uni disks are great and really not that expensive compared to most of the chainrings available. And as a plus the MU rotors are designed to work with brakes and fit without rubbing.

Sometimes it is just fun to use things in ways that were not intended by the manufacturer.

That’s a cool idea!

Can you modify a disc to fit into those cranks? Although I do like the toothy look.

BTW, how did you break the SINZ cranks?

The MU disk would work perfectly well on these cranks once they were ground down some. I haven’t been able to find any other purpose built disks that would be worth modifying to fit. There is one two piece disk by Shimano I would like to take apart and try but it costs more than the perfectly usable mountain uni disk I already have.

When I told my dad I wanted to use a chainring as a disk he suggested a saw blade bight be better. If you can cut and drill one he probably would be right.

I drilled extra crank holes in the Sinz cranks and some bent at the short hole and one just twisted near the hub. (i am still riding that one but will still replace it soon.)

do they squeal when they get hot

I haven’t had an opportunity to get them hot yet, probably wont until summer. hard braking in winter generally results in sliding.

Prepare for the comments:
“Where’s your chain, man?”
“Dude, you’re missing a chain and a wheel!”
Etc. :slight_smile:

We’re working on something like this for fixies. it would give us a market to fuel our uni development.

Have you ever shanked your ankle on the disc with this type of set up?

kb1jki:
This type: http://www.southbayriders.com/forums/attachment.php?attachmentid=390974&d=1324717185
or http://urbanvelo.org/wordpress/wp-content/uploads/2008/04/trackdiskbrake.jpg

or really directly on the chainwheel?

The first one looks sweet!

how are they holding up so far?

I have to disagree - they look a mess to me. And will be far less effective than a brake on the wheel because of the gearing. A proper road caliper rim brake would look far tidier and work better. I thought the fixie craze was all about being so cool you don’t need brakes, rather than “look at me I’ve got a massive brake in a silly place”. Bah humbug. Actually I think disc brakes look untidy on any bike - they make sense on a mountain bike for functionality and to save the rims from grinding away, but I can’t see why anybody would want them for (presumably) looks on a posing-round-town bike. Everybody’s someone else’s weirdo I suppose!