Are 140mm rotors any good

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Bentnose
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Are 140mm rotors any good

Postby Bentnose » Sat Sep 29, 2012 9:04 am

I'm looking at this http://www.konaworld.com/bike.cfm?content=rove Kona Rove as a potential new bike but am just wondering on anyones opinions on the 140mm rotors, they seem and look a little small. A 160mm rotor on the front would probably be better, but no one is getting back to me about whether the forks can take a 160mm rotor.
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MichaelB
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Re: Are 140mm rotors any good

Postby MichaelB » Sat Sep 29, 2012 9:55 am

On a road bike - For the rear, maybe.

Based on my experience with 180 or 160mm front rotors over 10,000km

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Re: Are 140mm rotors any good

Postby Crittski » Sat Sep 29, 2012 11:55 am

I have two bikes with disc brakes, a road bike and a MTB. On the roadie (cable), it is 160 front and 140 rear and on the MTB (hydro) it is 180 front, and 160 rear. I have had no issues or probs with either bike, . The only issue I would be wary of (and will be able to report soon - TRP Parabox currently clearing customs) would be the effect of long descents on 140mm rear rotors with hydraulics and the risk of overheating. I am not anticipating a problem but will be keeping an eye out for any issues given many people's paranoia over the issue (non-issue in my book - anyone who boils their hydraulics on descents isn't doing it right in my opinion - esp in the rear...).
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Re: Are 140mm rotors any good

Postby Nobody » Sat Sep 29, 2012 1:04 pm

The primary reason I put a 185 on the front of my CX bike is hand strength operating the levers from the hoods is less than ideal.

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Bentnose
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Re: Are 140mm rotors any good

Postby Bentnose » Sat Sep 29, 2012 6:43 pm

Nobody wrote:The primary reason I put a 185 on the front of my CX bike is hand strength operating the levers from the hoods is less than ideal.

Did you have a 160mm on before? Most disc CX bikes tend to come with 160mm rotors, bit hard to test a bikes brakes out properly without a decent ride.
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Re: Are 140mm rotors any good

Postby Nobody » Sat Sep 29, 2012 8:02 pm

No, I went straight to 185 when I built the bike. I already had issues previously on getting enough power with rim brakes from the hoods, so I didn't want to take the chance. The maths says you'll need 32% more lever force to get the same retardation with a 140 than with a 185. I don't struggle to lift the rear wheel at the moment with 185 from the hoods, but still would not like to squeeze 32% harder to do it. However that would be even better for modulation.

If you buy it, I suggest you try the brakes before you change them, making sure you bed them in properly before forming an opinion. You may like them.

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Re: Are 140mm rotors any good

Postby Mulger bill » Sat Sep 29, 2012 9:32 pm

Weightweenieness? I run 160/160 on the commuter (Kona Dewdrop, BB7r) and think they work fine. IMO, smaller rotors will heat up faster under heavy use and fade quicker.
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Bentnose
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Re: Are 140mm rotors any good

Postby Bentnose » Sun Sep 30, 2012 8:11 am

Mulger bill wrote:Weightweenieness? I run 160/160 on the commuter (Kona Dewdrop, BB7r) and think they work fine. IMO, smaller rotors will heat up faster under heavy use and fade quicker.


I don't know why they specced such small rotors, its never going to be a light bike being all steel. I didn't think brake fade was an issue with cable discs.
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Re: Are 140mm rotors any good

Postby jacks1071 » Sun Sep 30, 2012 8:59 pm

Bentnose wrote:
Mulger bill wrote:Weightweenieness? I run 160/160 on the commuter (Kona Dewdrop, BB7r) and think they work fine. IMO, smaller rotors will heat up faster under heavy use and fade quicker.


I don't know why they specced such small rotors, its never going to be a light bike being all steel. I didn't think brake fade was an issue with cable discs.


I've had serious brake fade on our tandem with cabled Avid BB5's - cable operated you havn't got fluid to boil leaving you with nothing but they will still fade when over heated. Some cable operated brakes have plastic parts on them as well which can melt causing failure.
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Bentnose
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Re: Are 140mm rotors any good

Postby Bentnose » Thu Oct 04, 2012 6:12 am

Kona Tech support got back to me, a 160mm rotor is okay, though I'm now thinking this http://www.cube.eu/en/road/off-road/cross-race-disc/ is a better buy, only $300 more, light and comes with good wheels and Shimano's CX70 disc braked 160mm rotors. Only problem is it doesn't come out in Australia till mid December/early January, waiting is the hardest part, may have to buy a tubeless conversion kit for the MTB to ease the urge to buy something bike related.
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JustJames
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Re: Are 140mm rotors any good

Postby JustJames » Thu Oct 04, 2012 9:20 am

There are three types of 'fade':

1. Green fade - caused by pads/disks not being properly bedded in.
2. Fluid fade - brake fluid (or more correctly, water absorbed by the hygroscopic fluid) boils and the pedal/lever goes mushy.
3. Pad fade - the pad exceeds its design temperature and ceases to be effective.

Green fade and pad fade can happen to any disc set up.

Fluid fade can happen to a disk setup that uses a hygroscopic (water absorbing) hydraulic fluid. It shouldn't be an issue for bicycle brake systems that use mineral oil as brake fluid.
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Re: Are 140mm rotors any good

Postby jacks1071 » Thu Oct 04, 2012 12:45 pm

JustJames wrote:There are three types of 'fade':

1. Green fade - caused by pads/disks not being properly bedded in.
2. Fluid fade - brake fluid (or more correctly, water absorbed by the hygroscopic fluid) boils and the pedal/lever goes mushy.
3. Pad fade - the pad exceeds its design temperature and ceases to be effective.

Green fade and pad fade can happen to any disc set up.

Fluid fade can happen to a disk setup that uses a hygroscopic (water absorbing) hydraulic fluid. It shouldn't be an issue for bicycle brake systems that use mineral oil as brake fluid.


The day we had fade on our tandem it would have been 3. Pad fade. You could smell the brakes burning, brakes were still functional but power was reducing and an increasingly rapid rate - I wasn't left with nothing though. I think if we had hydraulic brakes in that situation the overheated pads would have quickly turned into boiled fluid at which time you'd have nothing.
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queequeg
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Re: Are 140mm rotors any good

Postby queequeg » Thu Oct 04, 2012 1:37 pm

jacks1071 wrote:
JustJames wrote:There are three types of 'fade':

1. Green fade - caused by pads/disks not being properly bedded in.
2. Fluid fade - brake fluid (or more correctly, water absorbed by the hygroscopic fluid) boils and the pedal/lever goes mushy.
3. Pad fade - the pad exceeds its design temperature and ceases to be effective.

Green fade and pad fade can happen to any disc set up.

Fluid fade can happen to a disk setup that uses a hygroscopic (water absorbing) hydraulic fluid. It shouldn't be an issue for bicycle brake systems that use mineral oil as brake fluid.


The day we had fade on our tandem it would have been 3. Pad fade. You could smell the brakes burning, brakes were still functional but power was reducing and an increasingly rapid rate - I wasn't left with nothing though. I think if we had hydraulic brakes in that situation the overheated pads would have quickly turned into boiled fluid at which time you'd have nothing.


Could this also be influenced by braking technique? Down long descents, I can imagine that riding the brakes is not going to do any good to the pads, but if you use the brakes sparingly then they shouldn't overheat. That is, apply to reduce speed and then release.
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