Would a Psylo or Z1, or Vanilla 125, Sherman with a regular QR feature be strong enough to handle an 8" disc rotor up front?
Or would those only work well on thru-axle forks?
Or would those only work well on thru-axle forks?
8 inch disc brake on a QR front fork? Too strong?
- Thread starter MMcG
- Start date
It'll WORK, but it's not ideal. I ran 8" rotors on my QR Jr.T for about a year, no problem.
I'd be suspect of it only if you're a big dude, and do the blast-into-corners-and grab a handful of brake at the last possible second type of riding, or real heavy-duty DH stuff.
I'd be suspect of it only if you're a big dude, and do the blast-into-corners-and grab a handful of brake at the last possible second type of riding, or real heavy-duty DH stuff.
Hayes says not to do it b/c the mounts will flew too much. Probably more of a factor on a Psylo than a Jr. T?
Um, I can't be the only person that knows this but an 8 inch rotor puts LESS force on the fork and more on the hub for the same brake squeeze. Think about your simple machines and the lever in particular. The longer your lever (or rotor in this case) the less force you have to apply to get the same result on the hub. The difference between the two is that with a bigger rotor, you use less pressure on the brake fluid/pads over a greater distance around the circumference of the rotor for the exact same stopping force on the hub. That's why 8 inch rotors exist on big bikes. To get the same stopping power out of a smaller circumference/rotor, you need a greater force on the lever/fluid/pads. This greater force on the pads puts it on the caliper which puts it on the fork.
On side note, if I wasn't clear above; I've been using an 8" rotor on my manitou black fork for a year of jumping/mtx and everything is hunky dory.
On side note, if I wasn't clear above; I've been using an 8" rotor on my manitou black fork for a year of jumping/mtx and everything is hunky dory.
I was wondering why waranties would be voided since my last post and just realized there is something I forgot to consider.....the mounting location on the fork. It doesn't change when you use a bigger rotor. The larger adapter for an 8" disc still attaches to the same eyelets so you actually do get a greater leverage force on the fork since the longer adapter will act as a longer lever. It IS applied to the same place so there was an error in my thinking. If there was a caliper mount higher on a fork for a larger rotor I would have been right but obviously that's not the case.
Thanks for making me think about that though. I feel like I'm in South Park......." I learned something today."
Thanks for making me think about that though. I feel like I'm in South Park......." I learned something today."
Folks - EVERYBODY says not to do it or it'll void the warrantee. I'm pretty sure if you look at the warrantee for your bike, it's "void" if you use the bike for racing, or for drops, or stunt riding. That doesn't mean you can't do it, and it doesn't mean you'll necessarily lose your warrantee.
Basically, it comes down to this - if you wanna do it, you'll be fine, just don't go pulling stoppies from speed all over the place like some stupid Biker-Fox reject.
You are 100% correct. However, you also can use the 8" rotor to apply MORE stress to the mounts than a 6" rotor - but it'll stop you waaaaay faster than a 6" rotor. For a given stopping distance from a given speed with a given rider weight, 8" is less stressful. The problem arises when you use the 8" rotor to exceed the stopping capabilities of a 6" rotor. Personally, I don't think I use the 8"s on my bike to stop me any faster than a 6 (I can skid my front wheel with a 6" or pull a stoppie), but rather to do it with less finger pressure. Which is just fine as far as my brake mounts are concerned.
Basically, it comes down to this - if you wanna do it, you'll be fine, just don't go pulling stoppies from speed all over the place like some stupid Biker-Fox reject.
So I guess the message here is as long as you're going the same speed and doing the same stop, the 8 incher puts less stress on the fork but it's the temptation and subsequent enactment to go much faster that gets you? I think I go just as fast on my xc bike as my dh bike but maybe do in fact stop later with the bigger bike. You may have a point in regards to sudden vs gradual stresses.
So I looked at my black fork when I got home and I think the manitou mounts would be immune to any change in leverage from a bigger adapter hanging way out there. The manitou one seems to push it straight out. The marzocchi adapters however DO put the caliper way out there and make a bigger lever of themselves. I also used to run an 8 on an old z1 and never had any problems with stress cracks or anything but I would think the marz forks would be more suseptible with it. Just throw one on and if you have any problems/damage just lie to the warranty department. How's that for moral relativism?
So I looked at my black fork when I got home and I think the manitou mounts would be immune to any change in leverage from a bigger adapter hanging way out there. The manitou one seems to push it straight out. The marzocchi adapters however DO put the caliper way out there and make a bigger lever of themselves. I also used to run an 8 on an old z1 and never had any problems with stress cracks or anything but I would think the marz forks would be more suseptible with it. Just throw one on and if you have any problems/damage just lie to the warranty department. How's that for moral relativism?
You guys are missing the point.
-Fact
--The caliper mounts on a QR fork or Thru-axle fork are the same
only the drop outs are different.
-Personal Opinion
--Braking puts force on drop out that can destroy the drop out, or overcome clamping force of squewer, basically braking applies a force on the non drive side axle towards the ground below the bottom bracket area of the bike.
*Notice how I stated what I knew for a fact, and what was my personal opinion (Not that anyone was doing that in this post just tired of people doing this in forums)
-Fact
--The caliper mounts on a QR fork or Thru-axle fork are the same
only the drop outs are different.
-Personal Opinion
--Braking puts force on drop out that can destroy the drop out, or overcome clamping force of squewer, basically braking applies a force on the non drive side axle towards the ground below the bottom bracket area of the bike.
*Notice how I stated what I knew for a fact, and what was my personal opinion (Not that anyone was doing that in this post just tired of people doing this in forums)
It might be wise to convert to a bolt on axle,that will likely keep the axle in the dropouts,but it won't make the dropouts stronger.
You do run the risk of breaking the dropouts off the fork.If you constantly are removing the front wheel to transport your bike I think you run a bigger chance of wearing down the dropout and weakening them.
You do run the risk of breaking the dropouts off the fork.If you constantly are removing the front wheel to transport your bike I think you run a bigger chance of wearing down the dropout and weakening them.
Thanks for everyone's input, the reason I was asking is because so many brake sets come up for sale here, but it seems lately that most are 8" front, 6" rear combinations.
This came out from Specialized a couple days ago:
http://www.safetyalerts.com/recall/p/02/p0013424.htm
http://www.safetyalerts.com/recall/p/02/p0013424.htm
Eat my butt.
Everything I say is PURE SCIENCE. Any time my fingers type, it is the absolute gospel which cannot in any way be refuted!!!!!!!!! In fact I invented physics. Not the mathmatical representations but the behaviors of the universe itself.
Now be nice or I'm gonna kick you in the PeePee.
I use 8" Hayes on my Zocchi MX Comp forks. No problem and I'm a big guy. Friend of mine uses 8" Hayes on Psylo 2003 QR, no problem either...
what the adaptor looks like or how much material is around the disc tabs on the fork is irrelevant. What actually happens is that the added leverage of the longer adaptor can twist the fork leg enough to break the dropout in torsion. A 20 mm drop out will not break because it is significantly thicker and the 20 mm axle further serves to strengthen the dropout.
I don't believe that an 8" rotor will pull the wheel out of the drop out any more than a 6" rotor because even if the skewer were rediculously loose the wheel is going to want to move in a circular arc, the caliper being the center point. Moving the caliper from a 6" position to an 8" position only makes the arc's path more horizontal and less vertical. If that makes sense.
I know that all flies in the face of what people want you to believe, but it's true. I am glad that people are finally realizing what I have been saying for a long time about the force at the hub being irrelevant. That is like saying that using a 3" torque wrench will break more bolts at 20 ft/lbs than a 3' wrench at the same torque. Fact is that the tire will start to skid with the same torque at the hub with either an 8" or a 6" rotor and that is the maximum force attainable.
I don't believe that an 8" rotor will pull the wheel out of the drop out any more than a 6" rotor because even if the skewer were rediculously loose the wheel is going to want to move in a circular arc, the caliper being the center point. Moving the caliper from a 6" position to an 8" position only makes the arc's path more horizontal and less vertical. If that makes sense.
I know that all flies in the face of what people want you to believe, but it's true. I am glad that people are finally realizing what I have been saying for a long time about the force at the hub being irrelevant. That is like saying that using a 3" torque wrench will break more bolts at 20 ft/lbs than a 3' wrench at the same torque. Fact is that the tire will start to skid with the same torque at the hub with either an 8" or a 6" rotor and that is the maximum force attainable.
You're right. Stoppin = Stoppin for a given mass at a given velocity. The only difference is is the amount of pressure on the brake lever/fluid etc required for the same stoppin. You'll need less squeeze at the lever with a big rotor for the same stoppin at the hub. By the same effect you get more stoppin with the same squeeze just cuz you got a bigger torque wrench.....I mean rotor.
I got into this whole thing thinking about the force on the fork as a whole, not just the dropouts. And since this started about a month ago, how's that 8 incher workin for ya MMcG? Broke anything yet?
I got into this whole thing thinking about the force on the fork as a whole, not just the dropouts. And since this started about a month ago, how's that 8 incher workin for ya MMcG? Broke anything yet?
I see your point, and it makes a lot of sense, but as I recall, the rear fork of the dropout, failing by breaking off has been a typical failure caused by running 8" rotors on QR forks. How would this correspond to a torsional force on the adapter leg? My intsincts (although probably wrong) still lead me to believe that an 8' rotor applies more force to the axle somehow than a 6".
When a caliper clamps on the rotor, it wants to spin around the rotor but is held in place by the dropout. Lengthening the lever by placing the caliper father from the axle would increase the force at the axle which is in turn fixed by the dropout therefore increasing the force on the dropout. The direction of this force I guess would be 180 degrees of the direction the caliper wants to spin.
I have experienced my front wheel on a qr zocc creeping out of the dropouts when practicing front brake tricks, with a 185mm rotor, and sasla squewer.
When a caliper clamps on the rotor, it wants to spin around the rotor but is held in place by the dropout. Lengthening the lever by placing the caliper father from the axle would increase the force at the axle which is in turn fixed by the dropout therefore increasing the force on the dropout. The direction of this force I guess would be 180 degrees of the direction the caliper wants to spin.
I have experienced my front wheel on a qr zocc creeping out of the dropouts when practicing front brake tricks, with a 185mm rotor, and sasla squewer.
I think you have to realize we are talking about very small deflections when we assume that the caliper does anything to the fork. It's not like you could take a picture of somebody riding and say "woah look at his fork, his caliper is at almost 90 degrees to where it should be." The hub is sliding out of the dropouts or the dropout breaks because the fork is twisting and the hub doesn't so something has to give, either the axle pops out of the dropout or the dropout breaks.
Here's a rough sketch to illustrate the difference between an 8" and a 6" rotor, the 8" clearly seems to be the ideal location as it pushes the axle into the back side of the dropout more so than the 6" rotor.
Here's a rough sketch to illustrate the difference between an 8" and a 6" rotor, the 8" clearly seems to be the ideal location as it pushes the axle into the back side of the dropout more so than the 6" rotor.
Attachments
Ignoring the argument, I'm switching my Hayes with 8" rotor from a Psylo to a Marzocchi Z1, both QR.
Anybody know the correct Hayes part number for the adaptor for 8" on the Z1?
J
Anybody know the correct Hayes part number for the adaptor for 8" on the Z1?
J
I got it like this:
http://www.pinkbike.com/modules/photo/?op=view&image=137565
6" I.S. -> 6" Postmount + 6" Postmount -> 8" Postmount
http://www.pinkbike.com/modules/photo/?op=view&image=137565
6" I.S. -> 6" Postmount + 6" Postmount -> 8" Postmount
Hmm, my buddy recently destroyed a Psylo fork and front wheel. He had the Psylo with the standard 9mm QR axle. I have the Psylo w/20mm axle, not a problem. My bud distinctly remember the front wheel/fork going into "pretzel" mode on the berm dropin at the WG.
I was standing onside of the apex of he berm....not a pretty sight. I would suggest a fork with 20mm axle on 8"ers.Okay, correct me if I am wrong here, but i thought the issue was with breakage of the dropout, not the axel slipping out. Since torqe is Force X Radius, the torque on the dropout caused by an 8 inch rotor, with force remaining constant (this force being the maximum amount of force you can apply to the brake lever) would be about 33% higher then with a 6 inch rotor.
I think the issue is that fork manufacturers only made there QR dropouts with 6 inch rotors in mind, not overbuilding them enough to deal with the higher torques of 8 inch rotors. Thru Axel forks, on the other had, are built up enough to deal with torque just because of the type of riding they are generally intended for. If you think about it, this makes a lot of sense, as thru axel drop outs are generally wider and thicker then QR drop outs. like Kornflake said, the QR axel is not going to slip just based on the direction of the torque.
So i guess that what Im trying to say is that the issue with 8inch rotors and QR forks is more of a strength issue in the dropout then a slipage issue.
Well, I'm doing this on my Black Elite. Time will tell whether it was a mistake or not....
see my reply on the tread below this one
So surfing revealed the following info:
"SRAM has received a number of inquiries lately regarding RockShox fork and disc brake rotor sizes. Following is a list of all RockShox fork platforms and the maximum recommended disc brake rotor size.
Fork Platform...Maximum Recommended Rotor Size
GPS...165mm
Judy...165mm
Pilot...165mm
SID...165mm
Duke...210mm
Psylo...210mm
Boxxer...210mm
SRAM tests the structural integrity of all RockShox forks to that of the 210mm disc brake rotor size. However, other factors, including fork stiffness, bushing design, and intended use are considered when determining maximum rotor size.
RockShox can be reached at (312) 664-8800."
Not that I think this bears on the discussion of whether you should run a certain size rotor on a certain RS fork, but you can at least see what the manufactuer believes to be an acceptable disc size for their products.
"SRAM has received a number of inquiries lately regarding RockShox fork and disc brake rotor sizes. Following is a list of all RockShox fork platforms and the maximum recommended disc brake rotor size.
Fork Platform...Maximum Recommended Rotor Size
GPS...165mm
Judy...165mm
Pilot...165mm
SID...165mm
Duke...210mm
Psylo...210mm
Boxxer...210mm
SRAM tests the structural integrity of all RockShox forks to that of the 210mm disc brake rotor size. However, other factors, including fork stiffness, bushing design, and intended use are considered when determining maximum rotor size.
RockShox can be reached at (312) 664-8800."
Not that I think this bears on the discussion of whether you should run a certain size rotor on a certain RS fork, but you can at least see what the manufactuer believes to be an acceptable disc size for their products.
whenever i see this topic i think of moment arms..
like someone said this is my opinion of what happens
Force*distance
x*6 is less then x*8 which = the moment acting on the dropouts.
however the force x applied on the 8in would typically be less than the force applied on a 6in. the problem then is when the force on the 8in roto is increased...ie. hard stopping/braking/heavy rider
take is as you will.....
like someone said this is my opinion of what happens
Force*distance
x*6 is less then x*8 which = the moment acting on the dropouts.
however the force x applied on the 8in would typically be less than the force applied on a 6in. the problem then is when the force on the 8in roto is increased...ie. hard stopping/braking/heavy rider
take is as you will.....
most companies say don't do it but all of the comanies test the froks to be able to use 8" rotors.
not a good ideal but can be done
not a good ideal but can be done
If applying the brakes creates a torsional load on the fork leg....enough to break it.....wouldn't that torsional/twisting load transfer to the hub? Why doesn't my bike pull to the left when applying the brakes???
I'm not sold on the torsional theory yet.
As far the given load being the same for the 6"and 8" rotors. Your right, a given rider,at a given speed and braking rate will produce the same load, regardless of rotor size. But.....that load is at the caliper, that load is transfered to the hub through a lever (the mounting bracket). The 8" rotor will require a longer lever (or bracket) making the load at the hub higher.
8" rotors will create more load at the hub than a 6" rotor.
Just trying to makes sense of it all.
I'm not sold on the torsional theory yet.
As far the given load being the same for the 6"and 8" rotors. Your right, a given rider,at a given speed and braking rate will produce the same load, regardless of rotor size. But.....that load is at the caliper, that load is transfered to the hub through a lever (the mounting bracket). The 8" rotor will require a longer lever (or bracket) making the load at the hub higher.
8" rotors will create more load at the hub than a 6" rotor.
Just trying to makes sense of it all.
I have been running 8 inch rotors with QR with no problems for the last year and a half.
Is a Z1 2003 with QR strong enough for 8" rotor usage? I ll be having a Hopexc hub.
I had an Avid 8" mechanical brake on a 2001 Z-1 with regular (non-20mm) axle. Couple runs on the North Shore ended up twisting the axle loose, as well as actually twisting one of the stanchions in the crown.
Talked to local guys at DownhillZone, said that the torque on the rotor can twist the entire fork, and that its never a good idea to put an 8" on a non 20mm axle.
Im not sure if that was the original question, but, figured id pitch in my personal experience.
erin
Talked to local guys at DownhillZone, said that the torque on the rotor can twist the entire fork, and that its never a good idea to put an 8" on a non 20mm axle.
Im not sure if that was the original question, but, figured id pitch in my personal experience.
erin