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Disc Brakes

Discussion in 'Bicycle Mechanics and Repairs' started by llllllll, 30 Oct 2007.

  1. llllllll

    llllllll New Member

    Bit new to disc brakes, so I hope this isn't too stupid a set of questions. I've got a cheap cable disc (avid something or other) on the front of a chopper, it get's very little use - probably only about 50 miles since new, but the rotor is already warped. Do they warp like car brakes because they get too hot too quickly or is it just a cheap nasty part? Is it possible to true the rotor or does it need replacing and will a more expensive model not warp so easily - any recomendations. Is it possible to fit a bigger rotor or will I need to change the caliper as well?

    Thanks in advance
     
  2. What kind of chopper?

    The rotor is likely bent due to impact, Ive never heard of a bike disc warping through excess heat build up. Unless you live in the Alps...............

    A disc of the same diameter will bolt straight on with no problems, they are available from almost any bike shop. Fitting a larger disc will require either a new caliper or an adapter bracket, probably not worth the effort.

    You could try straightening it, you've nothing to lose, take it off and lay it on a perfectly flat surface, a kitchen worktop will do, and tweak it carefully with a large adjustable spanner.
     
  3. OP
    OP
    llllllll

    llllllll New Member

    It's a Kona Bikehotrod, one of these: http://www.konabikes.co.uk/2k5bikes/2k5_bike_hot_rod.php

    It's definately had no impacts. I thought it may be heat because it's a very heavy bike and we live on a hill so I'm on the brakes as soon as I'm out the door. It's off the road for the winter so I'll give the spanner a whirl. Ideally I'd like to upgrade the brakes anyway because they are woefully underpowered. Unfortunatly it's not got any hydraulic cable guides and most cable brakes seem to be very cheap. Can anyone recommend a good cable brake?
     
  4. bonj2

    bonj2 Guest

    truing rotors is easy - as mickle says use adjustable spanner. I do it while it's bolted on, that way you can fine tune adjustments - see if it's still rubbing on the caliper and if so where and on what side. You don't need to do it very hard - just get the untrue bit on the opposite side to the caliper, grip the edge and move it so that the edge moves by about a centimetre, hold it like that for a couple or three seconds and let go. Spin wheel to test, and repeat if necessary. If you do this and the rubbing is almost gone but you can't get it quite perfect then don't worry about it - likelihood is that the pads will bed in and the very slight untrueness that's left won't cause rubbing once they have.
    mickle might say different (?) but i'd say if it's actually visibly warped i.e. you can tell it's bent just by looking at it it's had quite a bad impact and needs replacing.
     
  5. ransos

    ransos Usual suspect

    Be very, very careful when working on the rotors - far to easy to get your fingers trapped when they're spinning.
     
  6. Bike Hotrod eh? I bought one of those earlier in the year for our roadshows. Got rid of the front brake altogether and just rely on the coaster. Which means of course that I have an unused original-equipment Hotrod disk hanging on my workshop wall........

    Also cut two feet out of the forks to improve the handling, you might want to try it as Im sure you are aware the bike handles like sh!t out of the box.
     
  7. Peyote

    Peyote New Member

    He he, funky bike llllllll, I like it!

    About the brakes, from the spec on the Kona website it says that it's got an Avid brakes, which generally have the best reputation in the cable disc brake market. I.e. they are comparable to many of the hydraulic systems around. Have you tried faffing with the brake lever, changing the cables, or fettling the calliper? I'm guessing that the setup on cable discs is as tempremental as rim brakes! If you've done all that...

    ...I reckon that leaves you with two options, the cheapest is increasing the rotor size and putting an adaptor in between calliper and forks. Cheap rotors can be found for around £15 and an adaptor for less than £10. The increased rotor size should give you more power, maybe a good idea to check with Kona that the fork will be able to hack the increased leverage of a bigger rotor too. Other than that your only option is go hydraulic, which'll cost a bit or a lot more depending on the system you choose!
     
  8. OP
    OP
    llllllll

    llllllll New Member

    :blush: The long forks are the whole reason I bought the bike, no way I'm cutting them up. I have made a few mods. The front wheel has been swapped for a 26in version with a skinny front tyre, and I've put a 3.5in tyre on the rear. This has made the handling even worse, but it looks cool, which is much more important :biggrin:

    Thanks for all the replies, think I'll go for a 200mm rotor and adaptor. The 160mm version on there at the moment looks a bit weedy on the 26in front wheel and the extra braking power will come in handy.
     
  9. bonj2

    bonj2 Guest

    yes, it'd be a great idea to fiddle with them WHILE they're spinning wouldn't it ransos. :biggrin::blush:
     
  10. spivvy

    spivvy New Member

  11. ransos

    ransos Usual suspect


    So you're telling me you've never ever cut or grazed yourself when working on your bike?
     
  12. PrettyboyTim

    PrettyboyTim New Member

    Location:
    Brighton