K2 / Proflex Riders Group
General => Tech Forum => Topic started by: lokomonkey on February 12, 2003, 03:35:09 pm
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I e-mail the guys at Rock shox, and they said tha is OK, it will fit ;D but didi anybody in 'the real world' tried it? anybody out there......
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Sounds like you are talking about mounting an 8" rotor on a standard dropout fork, which is a no-no.
Brake manufacturers don't like this, because the 8" rotor has proven to have enough torque to tear the wheel out of the drop outs in extreme braking. Therefore, they only allow you to setup the 8" rotors with thru axle forks.
I wouldn't suggest trying it.
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I don't know, I'd be willing to bet that most of the 8" rotors out there are being used on normal forks. A lot of people want more braking power. Not nearly as many want a pain in the rear, heavy, non-removable front wheel... Shouldn't the "lawyer tabs" prevent the front wheel from being torn out of the drop outs altogether? Seems like if that were a danger, there would be SOMEBODY who could do it with 6" rotors too...
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Go for it. I would not worry about the brake ripping the wheel out of the fork mounts. I know a lot of guys who ride 8" rotors on standard drop outs and don't have any problems. I also haven't seen any warnings from disk brake companies that say don't run 8" rotors on standard forks. I think you will like the power.
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there are always people who will run stuff together even if its not save...
contact your brake/fork maker about running the 8"/reg axle combo...
there are a list of reasons why u dont see it being done...
not the least of which is the reg axle clamo system WAS never designed to withstand the twisiting forces generated by a 8" hydro...
but if your feeling brave, feel free...
just dont ride behind me, i dont wanna get hit with your tire in teh back of teh head... ahahahhahah
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there are a list of reasons why u dont see it being done...
Maybe you haven't seen it, but a lot of people do it. I just checked MTBR where several people had posed the same question. The response was unanimous in support of 8" rotors on standard QR. One guy even had some physics explanation as to why the 8" rotor puts LESS force on the axle...
The 8 inch rotor puts less force on the axle than a 6 inch, not more.
The max stopping power is dictated by the less of two factors, how much grip your front tyre has and whether you're going over the bars.
Both 6 and 8 inch rotors on good brakes can throw a rider but the 8 inch rotor has 1/3 less force on the caliper and axle than the 6 inch rotor (3 inch lever compared to 4 inch lever).
The brake tabs see the same torque in each case, but may see a higher impact load with the bigger rotor.
Maybe some of our physics teachers here can chime in and explain that... It does make sense though - the axle movement is really only opposed by the rotor in one direction and the tire in the other. All things considered, your tire would lose traction WAY before your rotor ever snapped, and either way, the force at the axle is still just rotational. It's not going to pull out of the dropouts.
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matno your easily convinced..
do me this favor... lossen your QR on your frt tire...
then go ride your disc equipped bike..
nail teh frt brake, tell me again how the axle isnt affected by braknig forces after your bike goes flying...
trust me on this... brake forces applied at teh caliper get directed to teh center of teh fulcrum...
which in this case is the QR...
but like i said lots of people do it anyways (run8" rotors on Qr forks) but it dont mean its safe or advisable..
i wont do it or stand by qiuetly and let others do it....
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I don't know guys if you read the question; I e-mailed the guy at rockshox(fork manufacturer) asking if it was technically possible, he said yes! I asked you guys if putting it in practice (real world) was worth it or what kind of experience you guys got, ;)
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;D yes, threads have a way of shifting direction sometimes! No real world experience here. I've only ridden 6" discs and I've only ridden with guys who have 6" discs. I'm no downhiller, so they're just not necessary.
IFO, I'm not trying to flame you here, you have MUCH more experience with that kind of equipment than I do. I may be easily convinced, but when I can do a 30 second search on the "BrakeTime" forum on MTBR and find 20 people who say "I've been doing it for a long time with zero problems" and not a single person who has had a problem, that sounds pretty good. Generally, the ones who have the most problems are the most vocal on forums like that (or this). I've found the general consensus on that particular forum (the brakes forum, that is) to be very reliable on other issues.
Then again, I've been riding bikes of various kinds for a long time (fairly consistently for about 16 years), and I've never so much as broken a chain. (Unless you count a blown SmartShock as being my fault) I'm just not hard on my bikes. I usually back off before I could do that kind of damage. Blame it on my chicken nature...
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loko, when u contacted Rockshox did u mention your psylo is a req axle version?
the tullio is acceptable for a 8" rotor combo...
p.s. what brake are u thinking of running anyways?
cuz u should also contact your brake maker about their thoughts...
after all its your safety/bike in question not mine or someones elses.... ;)
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no prob Matno...
to bad we cant hook up for a ride sometime...i'd get you riding crazy stuff in no time...
im relentless...just ask some of my riding buddies...
i havent failed to convert someone to teh "Dark-side" yet....
:o
in fact my powers grow more every day, bwhahahaha..... *insert darth vader voice here*
;)
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I am hesitant to weigh in on a topic that obviously has touched nerves, but here goes. IFO, can you tell me where the information against using 8" discs on QR hubs comes from? I would like to understand the arguements.
When braking, the limiting torque is determined by the tire to ground interface. Maximum braking is achieved just before the wheel "locks up." Under most conditions, both a 6" and an 8" rotor can reach this maximum torque. The 8" will require less finger/hand pressure. The 8" rotor will resist fade better and will provide better performance longer. Under extreme downhill applications, it is conceivable that an 8" rotor might torque the dropout a little more (but only if the bite of the tire is so good as to overwhelm the 6" rotor). If you are doing this style of riding, you should probably have the heavier axle anyway. Under these conditions, a larger axle is better for other loading conditions. The braking by a disc is offset to the left side which causes a lateral torque in addition to the braking torque. A heavier axle will resist this much better.
Under anything other than extreme conditions, the 8" disc should work fine with the QR hub. Under those conditions, a QR hub is not the best choice (but only due to other concerns.)
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Well, I DO have those Core Rat arm pads... I just don't use them much. Maybe I should! :)
I would LOVE to ride your neck of the woods sometime. I sort of make it to the "northwest" a couple of times a year. (My in-laws live in northern Idaho, about 30 miles from Canada), but that's still a long way from where you are...
Just got a new issue of BIKE magazine today that has a nice article about hundreds of miles of under-ridden singletrack here in New York state. They even compared it to the Shore! (I have my doubts, although I do know that the trails around here can be fantastic). This time of year, all the trails suck because they haven't been ridden and are covered with leaves. Talk about slippery!
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BTW, IFO, if I can make it your way, I'd like to try the dark side. Doing anything in June?
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Back to the question at hand. I have only used 6" rotors on the front. They provide more than adequate braking for my local hills. I do, however, use an 8" rotor on my rear. This is mostly for thermal performance, since I have a carbon swingarm. It also provides better alignment with the cable to caliper. I feel that I get better modulation and a lighter touch on the brake levers with the 8".
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my info comes direct from the brake and fork manu's....
its not some weird tech thing i dreamed up...
feel free to contact any hydro brake maker and any fork maker...
pose teh question in well worded statements and see what they say...
i posed those same questions to several compaines over a year ago, and got back the info i included...
specifacally, i contacted FOX (forx), and Hayes (hydros), and Zokie (fork)....
and in June im guna be all over Whistler... page me, i'll be on A-line, ahahahahaahah
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You will have no problem running a 8" rotor. I havn't heard of any wheel coming off becuase they have a standard axle. I think you will enjoy the bigger rotor anyways. I have seen pictures in mt bike magazines showing guys from bike companies running 8 inch rotors on standard axles. I don't think they would be showing pictures like that if they were unsafe.
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I just want to be sure you understand my request. I absolutely meant no contradiction to you. I have high regard for your opinions in these matters. As an engineer, I always want to get input from all sources. That's just the way engineers are. I did look into info at Magura, Avid, and RS. I got no information against mixing 8" discs with "standard" hubs. Thanks for your reply. I'll look into the other sources. I think I will try to get up to Whistler if at all possible. It sounds phenomenal!
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Hayes won't sell you an adaptor to run their 8 inch rotor on a standard QR dropout anymore, because of the possibility of ripping the wheel out of the dropout. This is not to say that you can't find the apator anywhere, but respectable bike shops (anyone dealing with QBP directly) won't sell you that part.
That says something to me...
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I gave this issue some thought from the point of view of a manufacturer and I can see why they might have a problem.
As a matter of fact: there is at most 30 to 40% more braking torque for an 8" versus a 6" disc. There are other factors that have at least this much variance between individual applications. My XTR brake levers increase mechanical advantage by more than this, for example.
So the problem is probably not engineering. The problem is demograghics. What type of rider is likely to need to add 8" rotors to their bike? Statistically, a high percentage of riders venturing into downhill or other extreme applications. These riders should have heavy axles anyway, as I mentioned earlier. From a liability/reputation point of view, I can see why the manufacturers might be concerned.
BTW, putting 8" adapters on the standard IS tabs of a front fork does significantly change and increase the loading of these tabs. That is another issue.
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I emailed the various manufacturers and this is what they said:
Avid:
"That question should be directed to your fork manufacturer. I will warn you that many manufacturers draw the line at 185mm for a standard QR.
Thanks,
Dan"
Hayes:
"It is only recommended that you use the 6" disc with a fork with standard quick release. The 8" disc has about 40% more power, and will add more stress to the fork legs.
Sincerely,
Scott
SRAM:
"An 8 inch rotor is fine for a Psylo. It works better on a through axle (less lateral flex in the system but can be used on a standard dropout.
Chris McKenney,
SRAM Dealer Service Representative"
Manitou:
"The only single crown fork that is compatible with an
8" rotor is the Sherman or Dorado SC.
Thank you,
Jon Agnew
Answer Products"
I asked Jon if this also meant the standard dropout version of the Sherman and he said yes. He also said the use of an 8 inch rotor on a fork other than what's approved will void the warranty.
Marzocchi have not answered yet. I'll post them if they answer. It might be like those Lawyer Lips things. The real answer might come out in a lawsuit. >:(
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either way, the makers of the product know alot more about their gear then i do...
so when they say dont do it, i'd listen...
thx for the update...
8)
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I was just at the vancouver outdoor adventure show this past weekend. I really don't have an opinion on this subject, but I did see a few bikes with 8" rotors on standard forks and they were new bikes that were for show from bc companies. And for the emails, they really don't say anything about ripping the wheel out of the drop out. It just talks about the flex.