Rotors replaced

Discuss light weight issues concerning mountain bikes & parts.

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TheRookie
Posts: 910
Joined: Wed Jan 18, 2012 4:23 pm
Location: Midlands, United Kingdom

by TheRookie

Stopping the grinding is precisely what the springs are for, make sure they are fitted correctly and working as intended!
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

Cif
Posts: 36
Joined: Tue Oct 02, 2012 8:36 am

by Cif

Well after a lot of fiddling around I managed to get the rotor and pads in a good position.
No rubbing when the bike is tilted. But I have no idea what I did to get rid of it.
Just took off the caliper and the rotor and started all over.

Front brake is still not as sharp as the rear. Will see if it gets better, otherwise new pads will be mounted
Cannondale Bad Boy 4 (2012) Original weight minus 1541 Gram

by Weenie


02GF74
Posts: 562
Joined: Thu Jan 13, 2011 4:04 pm
Location: Sunny UK

by 02GF74

Firstly if those are 160 mm disc, then a pair of KCNC Razor will weigh 150 g - be similar price too.

I'm about to stir up a can of worms but how can the braking with a disc that has more holes then metal be ever be as good as one with more metal? The coefficient of friction between air and brake pad material is pretty much zero - that is the price you pay for losing weight - do not be surprised if your braking does not get anny better.

Also some design of ligtweight disc will cause the forks to judder due to the pad grabbing the metal then releasing as the disc rotates - I had Gator discs fitted and they were unusable with a pair of SIDs so I fitted Hope floaters and they are fine - the Hopes have the holes stagggered so they are not in one place.

Steve Curtis
Posts: 162
Joined: Thu Jul 31, 2008 12:20 pm
Location: Hampshire UK

by Steve Curtis

That is true but doesn't account for the front to rear difference.

Cif
Posts: 36
Joined: Tue Oct 02, 2012 8:36 am

by Cif

Well did a nice 40k through the woods this morning, and seems like theres nothing wrong with the pads now. Maybe a lot of braking did the trick.

As for better braking, it may be so that the old ones are slightly better. And for a downhill bike I would do it. But this bike is for cyclocross and light cross country and they work brilliant for me.
Cannondale Bad Boy 4 (2012) Original weight minus 1541 Gram

TheRookie
Posts: 910
Joined: Wed Jan 18, 2012 4:23 pm
Location: Midlands, United Kingdom

by TheRookie

02GF74 wrote:I'm about to stir up a can of worms but how can the braking with a disc that has more holes then metal be ever be as good as one with more metal?


Did you pass physics? Area is not a value in the calculation for friction, (Fr = Mu x m) I notice no difference going from near full discs to alligators, except the 'gaters squeal more.

For a different explanation, if you halve the contact area you double the pressure for that area remaining.....which is why area isn't in the calc.
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

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devinci
Posts: 3039
Joined: Sat Jan 03, 2009 9:43 pm
Location: Canada

by devinci

how many ride should it take before new rotors are broken-in and start braking correctly?

I have a new 29er, 160/160 with XO brakes and it sometimes lack braking power, a lot, im only 150lbs. Yesterday I went back on my 26er 160/140 with XX brakes and I was shocked at how much braking power the bike had...

I have 5 rides on the new 29er so far.

Cif
Posts: 36
Joined: Tue Oct 02, 2012 8:36 am

by Cif

I did about 40k on the road and 45k offroad before they were fine and I must say they are superb now.
I tried to get as much of heat as possible in them. Riding 10-15kmh with front or rear brake slightly on.

Thats how I did it, no idea if its correct, but it worked.
Cannondale Bad Boy 4 (2012) Original weight minus 1541 Gram

TheRookie
Posts: 910
Joined: Wed Jan 18, 2012 4:23 pm
Location: Midlands, United Kingdom

by TheRookie

The Shimano tech doc reckons on 20 medium rate stops in quick succesion, you need to get some heat into the discs, so you caould do 100's of miles under the right (wrong?) circumstances and never bed your brakes in.
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

Kennyg
Posts: 22
Joined: Mon Oct 22, 2012 5:30 am
Location: Santa Monica, ca

by Kennyg

What do you think is the best value in a light weight rotor? I am looking for something that isn't too expensive.

TheRookie
Posts: 910
Joined: Wed Jan 18, 2012 4:23 pm
Location: Midlands, United Kingdom

by TheRookie

Alligator, sub £20 (US $30) each for a 160mm, about 82g each for a 160.
Impoverished weight weenie wanna-be!
Budget 26" HT build viewtopic.php?f=10&t=110956

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