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Avid Juicy 5 - rotor size upgrade?

Stuey01Stuey01 Posts: 1,273
edited August 2008 in MTB workshop & tech
Hi guys,

I recently had a SC Chameleon built up by Evans to replace my old Rocky Mountain that now serves as a commuter.

I specified 160mm rotors on the Juicy 5's on the basis that I had never had disc brakes before and they would be a significant upgrade in performance over my V's... I'm quite heavy, weighing in at 14.5st, and I think that these brakes are underpowered for me - in fact they perform worse that my XT v's dating from 1996. I'd like to upgrade to 185mm rotors on the front (160mm will do on the back).

My forks are Pikes so they are ok with the size upgrade.
I'm running Hope Pro2 hubs with a 20mm thru axle if it makes any odds!

What do I need to do this? and how difficult is it to do?

hoping not to need a full new brake kit, but if I do then the 160s could go on my commuter.

Thanks for any help!
(I did do a search but could not find anything about rotor size upgrades)


Not climber, not sprinter, not rouleur


  • nicklousenicklouse Posts: 50,675 Lives Here
    new adaptors and discs.

    thats it.

    oh and how long have you had them?

    they do need some bedding in.
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  • Stuey01Stuey01 Posts: 1,273
    I've not had them long, I did notice a significant increase in performance after a few hours at Swinley Forest. A few more hours later and no more improvement - still not quite enough.
    The 160mm looks pretty weedy too...

    I'll pick those spares up this week and give it a go at the weekend.

    Not climber, not sprinter, not rouleur
  • dave_hilldave_hill Posts: 3,877
    Stuey01 wrote:
    I've not had them long, I did notice a significant increase in performance after a few hours at Swinley Forest.

    The ones on my Orange were exactly the same - they took a LOT of bedding in. Last weekend's trip round Kirroughtree seems to have done the trick though.

    They still aren't as on/off eye-ball shattering as my old Hayes 9s, but they have a lot more feeling to them.

    Be aware that if you want the caliper adaptor to fit a Pike, DON'T get the 20mm version but use a standard q/r one instead. The 20mm version is too thick - I speak from experience.
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  • stevieboystevieboy Posts: 704
    Yeah, give them time, my 180mm fr 160mm r set up took ages to bite and felt way under-powered for my 10st weight on the Scale
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  • Stuey01Stuey01 Posts: 1,273
    stevieboy wrote:
    Yeah, give them time, my 180mm fr 160mm r set up took ages to bite and felt way under-powered for my 10st weight on the Scale

    I weigh almost 50% more than you! I'm definately thinking that 160mm is too small...

    I think I'm gonna buy a full 185 set and then transfer the 160mm over to my commuter so I can fit some disc only carbon forks.
    Not climber, not sprinter, not rouleur
  • AnonymousAnonymous Posts: 79,667
    i was running juicy 5 with a 203 disc on the front and sintered pads, absolutely brilliant stopping power (but i am 19 odd stone)
  • BikerbaboonBikerbaboon Posts: 1,017
    i dont know about the disk size but im 12st and i can lock hte front easly with the 160mm rotor, also im felling prity good about my 12st now thanks to all that have posted there weights :lol::lol::lol::lol:
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  • amt27amt27 Posts: 320
    I have these on my Stumpy FSR 08, 185 rotors,
    they bedded in pretty quickly and were great for about 2 months, then i went on a long downhill and fried the rear big time, the brake worked but just didn't stop the wheel,
    fixed it with some advice from the bike shop to soak the pads in meths and clean the rotors, brake is okay now and but not as good as it was,
    then i found the front pistons only worked on one side of the caliper, bike shop fixed it and bled the brake, but i get problems on some downhills where the lever pulls all the way to the handlebar,
    so basically i have lost all confidence in the brakes,
    i have bought a bleed kit to try and rectify the problem, i prefer to do my own repairs and understand the problems rather than take it to the shop every 5 minutes,
    i weigh 14.5 st too,
    there are lots of complaints about these brakes on other sites, however it is a popular brake, most reviews complain about them easily overheating
  • dave_hilldave_hill Posts: 3,877
    I often think that a lot of "problems" that people experience with brakes can be down to poor braking technique as much as the actual brakes themselves.

    I used to hear a lot of bad press about Hayes 9s, but I've had mine on my Giant for over 3 years and they've never given me any problems.

    Overheating of brakes is caused by dragging them - that is, grabbing a handful at the top of the hill and not letting go until you reach the bottom. That's just poor form and guaranteed to fry your pads, warp your discs and boil your fluid. The same heat build up wil damage seals and other parts. This will result in reduced performance and ultimately breakdown.

    It is true that any brake needs to be warmed before it operates to it's full potential but they shouldn't be as hot as possible - there's an optimum range.

    The most efficient way to brake is to cadence brake on the rear - i.e. pump the lever firmly and smoothly. That way, you allow heat to build up in the pads and discs but by releasing pressure on them at the same time you allow them to operate at their optimum temperature. At the same time, you should barely touch the front brake, just use it to feather your speed.

    The drivers amongst you can try this in your cars to show how it works. Find a long stretch of straight, quiet road, build up to a good speed then hammer on the brakes (without locking the wheels) - you'll be surprised at how long it takes you to stop. Now try again, but this time pump the brake pedal very quickly two or three times so that the pads barely begin to bite, THEN hammer on. You'll be amazed at how much quicker you stop.

    The same applies to cars, motorbikes, push bikes and any other vehicle - you can't just grab the lever or push the pedal and hope for the best. There's technique to braking just like every other aspect of riding!
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  • you will be surprised with the increased performance a 180mm disc can give though - just be careful when bedding in. i made that mistake when i was bedding in my new 180mm rotor for my J5's :oops: :roll:
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