Forum home Mountain biking forum MTB buying advice

Disc size and shape

mattie007mattie007 Posts: 98
edited August 2010 in MTB buying advice
Just about to order some Clarks S2 brakes for the rear but there is so many options! I currently have 160mm discs on the rear and i'm wondering if I can fit the 185 or 203mm discs?

Is there an advantage to the bigger discs and will they fit? Also, would you go for round or wavy? I have a Giant Terrago if that helps.
'07 Giant Terrago - Gone but not forgotten....thankyou Center Parcs...... :(

'11 Giant Talon 0

Posts

  • Joe_PineapplesJoe_Pineapples Posts: 1,718
    To fit a bigger disc you'll need a bigger caliper mount.
    Going from a 160 to a 185 shouldn't be too much of a problem, but do you feel like your bike is woefully underbraked? I'd check the Giant website first if I were you, some manufacturers specify a maximum disc size.

    Going to a bigger disc gives a faster moving disc surface and more braking power.
    Wavy discs are a bit of a fashion item, but they work fine. Their 'wave' design is supposed to help clean your pads, stop the glazing and aid cooling, but nice, round, drilled ones work just as well.

    203mm discs are generally the preserve of downhill bikes or heavy-hitting "all-mountain/freeride" rigs.
    A decent 185mm front/160mm rear setup will still have tons of braking power.
  • Bar ShakerBar Shaker Posts: 2,313
    I wouldn't go bigger than 160 on the back. It will just lock up.
    Boardman Elite SLR 9.2S
    Boardman FS Pro
  • Any brake will lock up if you grab enough of it. Moving to a 185 on the back should work ok, but it's debatable how much of a difference you'd notice, given that your front brake does more of the work.

    ....and a 185mm disc is more than enough on the front.

    By the way, what brakes are on your Giant, are they Giant's own MPH brakes?
    They're actually very good stoppers.
  • Thanks for the advice. I currently have Giant MPH on the front and rear. Been on since I got the bike 3 and half years ago without any proper servicing so they've done well!
    I'll stick to 160 on the rear but im now thinking if I should just get the brakes serviced.....
    Trouble is, it will probably be cheaper to buy the S2's than fit new pads, oil and labour charges on my old ones!
    '07 Giant Terrago - Gone but not forgotten....thankyou Center Parcs...... :(

    '11 Giant Talon 0
  • *AL**AL* Posts: 1,185
    Wavy discs are a bit of a fashion item, but they work fine. Their 'wave' design is supposed to help clean your pads, stop the glazing and aid cooling, but nice, round, drilled ones work just as well.

    I fail to see any benefit of the wavy discs at all.

    I appreciate that holes or grooves on discs allow the gasses and heat build up whilst braking to escape, reducing brake fade (I have grooved and drilled discs on my car, I have experienced the difference)

    But as the wavy discs pass through the pads there is less disc touching the pad, which will require greater braking force to attain the same stopping power as a normal disc, and obviously applying more force to the pads will increase the temperature that the discs are designed to reduce ?
    A decent 185mm front/160mm rear setup will still have tons of braking power.

    This also (assuming the pads are correctly bedded in)
  • I have round discs on the car and wavy on the motorbike. Ive ridden motorbikes with round discs and cant really tell a difference!

    Think i'll just get the wavy for the looks!
    '07 Giant Terrago - Gone but not forgotten....thankyou Center Parcs...... :(

    '11 Giant Talon 0
  • Bar ShakerBar Shaker Posts: 2,313
    Holes and grooves were only put on car discs to vent and clean asbestos pads. These were banned years ago. They are there now for cosmetic reasons only.

    In a former life I worked with Brembo and AP on car brake design. Anyone who watched the start of today's F1 would have seen Lewis Hamilton's discs... with no holes or grooves.

    The pads grip to the metal, so the more metal, the more grip. Discs on bikes are slotted or drilled because we don't need much metal and to save weight and look good.
    Boardman Elite SLR 9.2S
    Boardman FS Pro
  • Good point!
    I never fell for grooved discs on cars, I just wanted good brakes!
    '07 Giant Terrago - Gone but not forgotten....thankyou Center Parcs...... :(

    '11 Giant Talon 0
  • joec1joec1 Posts: 494
    i have 203 front and rear (on a Specialized Pitch)

    before you upgrade, realistically think about how fast you ride, and how often you would need to brake hard and often (to heat up the surface area of the disc)
    www.settingascene.com - MTBing in Wilts and the southwest, join up for info and ride details.
  • .blitz.blitz Posts: 6,588
    I've used a 203 on the front of my Rize and if you like the feel of motorcycle brakes, you will like the bigger rotor. There is more power and bite at the expense of modulation but TBH I was overbraked :) for UK conditions.

    Gone back to a 185F/160R.
  • AnonymousAnonymous Posts: 28,799
    *AL* wrote:
    I fail to see any benefit of the wavy discs at all.
    The idea is to increase surface area, making the disc cool down quicker.

    I never knew grooved discs were banned on cars. I thought the groove was there on performance brakes, to help remove the gas build up when they got really hot? :?:
  • myopicmyopic Posts: 692
    *AL* wrote:
    I fail to see any benefit of the wavy discs at all.
    The idea is to increase surface area, making the disc cool down quicker.

    I never knew grooved discs were banned on cars. I thought the groove was there on performance brakes, to help remove the gas build up when they got really hot? :?:

    Think he means asbestos pads were banned
    You don't need eyes to see, you need vision
  • jaysonjayson Posts: 4,606
    I have 203mm rotors front and rear and love the ability to stop pretty much on a point any and everytime i want no exceptions whthere its wet or not.

    Some people might say its abit overkill but i prefer to know ive got excess available just in case than have to struggle tryin to stop headed for somethin heavy or immovable.
  • nickfrognickfrog Posts: 610
    Yes but surely you're limited by the friction that the tyres have on the ground and in the wet I can't see the point of more power as I assume it will lead to early lock up and potentially less modulation, particularly at the rear ?
  • supersonicsupersonic Posts: 82,708 Lives Here
    Max decelleration, assuming you can lock the wheels, is indeed governed by the tyres.

    Some people like brakes set up with little throw and a very light touch to do this. I like mine with a longer,softer throw and progressive power so I can 'feel' this point better. All about your prefs. This is why I also like V brakes, as there is good adjustment here.

    Some wavy rotors were said to shed mud from the caliper better.
  • jaysonjayson Posts: 4,606
    nickfrog wrote:
    Yes but surely you're limited by the friction that the tyres have on the ground and in the wet I can't see the point of more power as I assume it will lead to early lock up and potentially less modulation, particularly at the rear ?

    Its like using anything, you learn how it works then use it within those limits and its perfectly fine.

    I use my brakes alot and haven't yet managed any squirelly moments due to my over exzuberence withthe levers.
  • rhextrhext Posts: 1,639
    I thought most of the advantage on larger rotors was heat dissipation. Having suffered from brake fade on a very steep descent, am seriously considering upgrading myself!
  • What is meant by 'modulation'?
    '07 Giant Terrago - Gone but not forgotten....thankyou Center Parcs...... :(

    '11 Giant Talon 0
  • Brakes with no modulation would lock up as soon as you touched the lever.
    Brakes with good modulation allow you to brake progressively and have finer control over them.
  • I see, thanks for the reply.
    '07 Giant Terrago - Gone but not forgotten....thankyou Center Parcs...... :(

    '11 Giant Talon 0
  • shieldsy94shieldsy94 Posts: 342
    you want around 185 on front a 160 on rear so you have good power/modulation ratio
Sign In or Register to comment.