Capricorn Posted August 31, 2011 Share Just for my own understanding (and appologies, I'm an accountant, not an engineer), so if you put a bigger rotor on, are you actually generating more stopping force, or does it only feel that way, because the force that you need to exert via the brake levers is less to get the same stopping force? Not sure if I'm making sense? the torque required to counteract the rolling of the wheel, aka the braking torque, is a function of the stopping (or Braking) force and the distance of the application of that force from the center of the rolling center, that is from the center of the axle to the point where the brake pad surface touches the brake disc.As Patches nicely explained, the formula for what I described is T = F x d.T = braking torqueF = force applied by the brakesd = distance from brake pads to center of rolling, the axle. So even though the braking force is the same (cos the brake is the same and used in the same way by the same rider), the braking torque increases because the distance d increases (bigger rotor). so for the same pull on the brake lever, a larger rotor will give you more stopping torque than a smaller diameter brake rotor. That clear it up Banna? Edited August 31, 2011 by Capricorn Link to comment Share on other sites More sharing options...
banna Posted August 31, 2011 Share the torque required to counteract the rolling of the wheel, aka the braking torque, is a function of the stopping power and the distance of the application of that force from the center of the rolling center, that is from the center of the axle to the point where the brake surface touchs the brake disc.As Patches nicely explained, the formula for what I described is T = F x d. So even though the braking force is the same (cos the brake is the same and used in the same way by the same rider), the braking torque increases because the distance d increases (bigger rotor). so for the same pull on the brake lever, a larger rotor will give you more stopping torque than a smaller diameter brake rotor. That clear it up Banna? Awesomeness! You okes should become teachers! Link to comment Share on other sites More sharing options...
Captain Fastbastard Mayhem Posted August 31, 2011 Share Just for my own understanding (and appologies, I'm an accountant, not an engineer), so if you put a bigger rotor on, are you actually generating more stopping power, or does it only feel that way, because the force that you need to exert via the brake levers is less to get the same stopping force? Not sure if I'm making sense? More stopping power, yes. Basically due to the torque that is exerted on the hub from the braking point being further out. If you compare a 203mm rotor and a 160mm - you exert exactly the same amount of force on the levers, with exactly the same set ups and pressure settings etc etc (basically the EXACT same set up, apart from the rotors, no differences whatsoever) and the force seen at the hub WILL be different. Ergo, the 203mm shod wheel will stop far faster than the 160mm shod wheel. Thus: The hub with the 203mm will have more force exerted on it at the rotor mounting points than the hub with the 160mm rotor, given equal forces on each braking SYSTEM. However: What that also means though, is that in order for a wheel to stop at the same speed on the 160mm shod bike and the 203mm shod bike, is that you need to pull HARDER on the brake lever itself in order to slow the wheel down at the same speed as the 203mm shod wheel. Thus: At the same BRAKING forces (ie - the same contra-rotationary force at the disc mounting points) less pressure will be exerted on the lever of the 203mm shod bike than the 160mm shod bike. EDIT: Banna - I'm a Financial Advisor - not an engineer... so your excuse isn't valid... Edited August 31, 2011 by cptmayhem Link to comment Share on other sites More sharing options...
Big H* Posted August 31, 2011 Share Could somebody please do the following ( I do not have a bike here or I would have done it myself) 1) Turn your bike upside down2) Loosen QR3) Spin tire4) Apply brakes Do that a few times at increasing rotating speeds and please report back to what happens. If the QR is removed there should be no forces involved the wheel should stay put in its place. Would really know what happens? Link to comment Share on other sites More sharing options...
banna Posted August 31, 2011 Share More stopping power, yes. At the same BRAKING forces (ie - the same contra-rotationary force at the disc mounting points) less pressure will be exerted on the lever of the 203mm shod bike than the 160mm shod bike. Thx Mayhem. It's amazing how the new XT brakes are so much stronger than the old one's. But that's obviously brand new technology doing it's thing. I will have to run 203mm rotors on the old XT's to hopefully get to the same stopping power as the new XT's with 160mm rotors. Link to comment Share on other sites More sharing options...
banna Posted August 31, 2011 Share EDIT: Banna - I'm a Financial Advisor - not an engineer... so your excuse isn't valid... Ok dammit, I plead low IQ and 4 years of alcohol abuse at varsity... sheesh you happy now? Link to comment Share on other sites More sharing options...
Tieffels Posted August 31, 2011 Share Could somebody please do the following ( I do not have a bike here or I would have done it myself) 1) Turn your bike upside down2) Loosen QR3) Spin tire4) Apply brakes Do that a few times at increasing rotating speeds and please report back to what happens. If the QR is removed there should be no forces involved the wheel should stay put in its place. Would really know what happens? At sufficient speed the wheel should come out. Your point being? Link to comment Share on other sites More sharing options...
Captain Fastbastard Mayhem Posted August 31, 2011 Share Could somebody please do the following ( I do not have a bike here or I would have done it myself) 1) Turn your bike upside down2) Loosen QR3) Spin tire4) Apply brakes Do that a few times at increasing rotating speeds and please report back to what happens. If the QR is removed there should be no forces involved the wheel should stay put in its place. Would really know what happens? This used to happen before the days of "lawyers tabs" or, more colourfully "lawyers lips" were introduced to keep the wheel in place. There are forces in play, and because the disc itself isn't running in a dedicated channel, and thus is free to move about should the wheel come unfastened, the braking force COULD have caused the wheel to pop out of the QR tabs. Basically, when the braking force is applied, the disc is encouraged to rotate around the brake pad, not the hub. As such, the wheel could be forced out of position A) the braking force is strong enoughB) there is no tethering system in place to hold the wheel where it should be. Now, seeing as brakes are getting stronger and stronger, it could be argued that if the lawyers taks weren't introduced, we could have been seeing an ever-increasing occurrence of the wheel popping loose under hard braking. But since the lawyers tabs (and new QR designs such as trhu axle and QR15) there is enough tethering force in place to negate the effect that the brakes has on the wheel. Therefore, this does not often occur anymore, and will only really happen if there are no lawyers taks, or some flunky forgot to tichten their QR. Link to comment Share on other sites More sharing options...
Big H* Posted August 31, 2011 Share I searched for this and found it, an email from Marzocchi From: techinfo@marzocchiusa.com Dear Customerin reply to your technical question: Is the 8" rotor compatable with the standard QR version of the Z1FR? --------------------------------------------------------------------------the reply is:--------------------------------------------------------------------------It will definitely fit onto the fork. It is recommended that an 8" rotor is not used on a standard axle fork because the forces exerted on the wheel can potentially pull the axle out of the dropouts. So, it will physically fit, but it is not recommended for aggressive riding. Best Regards,Marzocchi Staff661-257-6630 Link to comment Share on other sites More sharing options...
Captain Fastbastard Mayhem Posted August 31, 2011 Share Thx Mayhem. It's amazing how the new XT brakes are so much stronger than the old one's. But that's obviously brand new technology doing it's thing. I will have to run 203mm rotors on the old XT's to hopefully get to the same stopping power as the new XT's with 160mm rotors. Yeah... It's also a difference in the pads, and the way the calliper & piston is designed. More cooling is going to the pads, so they perform better for longer. More power can be transferred to the pads with the same force as before, due to enhancements in the master cylinder and piston design. So it's a bunch of different things. Get yourself some good rotors, pads and a new adaptor for your 203's. Then later get yourself some braided hoses. You'll be stylin! Link to comment Share on other sites More sharing options...
Big H* Posted August 31, 2011 Share Go and read here, I found the email above here. http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/ He may be rambling a bit but interesting. Also do a search for "warning not to use 8" rotors with QR skewers" a lot of hits with interesting reading. Mayhem have you done the test I asked for or are you just guessing? Link to comment Share on other sites More sharing options...
Captain Fastbastard Mayhem Posted August 31, 2011 Share I searched for this and found it, an email from Marzocchi From: techinfo@marzocchiusa.com Dear Customerin reply to your technical question: Is the 8" rotor compatable with the standard QR version of the Z1FR? --------------------------------------------------------------------------the reply is:--------------------------------------------------------------------------It will definitely fit onto the fork. It is recommended that an 8" rotor is not used on a standard axle fork because the forces exerted on the wheel can potentially pull the axle out of the dropouts. So, it will physically fit, but it is not recommended for aggressive riding. Best Regards,Marzocchi Staff661-257-6630 That's also their stock-standard anti-litigation speak. They're covering their own asses with a two-bit reasoning and the assumption that everyone is stupid and doesn't fasten QR levers properly. If the fork has lawyers tabs, and you tighten the QR properly, there is no way the wheel will come out unless the QR itself fails. Which will NOT happen as a result of how hard you brake, rather the hits that you take and whether you tighten your QR with a 10lb hammer to get the cam to close... Link to comment Share on other sites More sharing options...
Big H* Posted August 31, 2011 Share I searched for this and found it, an email from Marzocchi From: techinfo@marzocchiusa.com Dear Customerin reply to your technical question: Is the 8" rotor compatable with the standard QR version of the Z1FR? --------------------------------------------------------------------------the reply is:--------------------------------------------------------------------------It will definitely fit onto the fork. It is recommended that an 8" rotor is not used on a standard axle fork because the forces exerted on the wheel can potentially pull the axle out of the dropouts. So, it will physically fit, but it is not recommended for aggressive riding. Best Regards,Marzocchi Staff661-257-6630 The above is for 30mm stanchions, it may be a completely different kettle of fish with the newer 32mm stanchions. Link to comment Share on other sites More sharing options...
Big H* Posted August 31, 2011 Share That's also their stock-standard anti-litigation speak. They're covering their own asses with a two-bit reasoning and the assumption that everyone is stupid and doesn't fasten QR levers properly. If the fork has lawyers tabs, and you tighten the QR properly, there is no way the wheel will come out unless the QR itself fails. Which will NOT happen as a result of how hard you brake, rather the hits that you take and whether you tighten your QR with a 10lb hammer to get the cam to close... I had a Shimano QR fail on the rear wheel of our road tandem. It was a brand new bike on our third outing. Luckily we were on a uphill as even then the wheel came out of the dropouts. It snapped with such a force that the QR body was never found. It disappeared into the grass. I only found the nut end lying on the ground. I do not want that to happen to me on a downhill after I tightened my QR with a 10lb hammer. Link to comment Share on other sites More sharing options...
Captain Fastbastard Mayhem Posted August 31, 2011 Share Go and read here, I found the email above here. http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/ He may be rambling a bit but interesting. Also do a search for "warning not to use 8" rotors with QR skewers" a lot of hits with interesting reading. Mayhem have you done the test I asked for or are you just guessing? No guessing... It's an engineering / mechanical force standard. BUT - I've just done it now to prove it to myself once & for all, and the wheel popped 10" out of the QR seat. Loosened the QR all the way, so that the cams cleared the lawyers tabs. Link to comment Share on other sites More sharing options...
Cassie Posted August 31, 2011 Share You are also forgetting that (1) Normally the wheel is NOT upside down - like in Ecc's experiment (2) when braking, normally one's weight is tending to be going forward (and into the ground - thank goodness for shocks!!) thus lessening the potential for the wheel to drop out! Now, on a radical arial manuevre with hard braking in the air... ...do expect your front wheel to drop out!! I also think Marzocchi is just covering themselves legally! Link to comment Share on other sites More sharing options...
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