Mountain Biking - QRs not up to the job?

Has anybody heard anything more on this issue of QRs not being up to the job of holding the wheels on under hard and repeated braking with disc brakes? :eek:

Uhm... no.

Yeah, I read an article. Someone here posted a link. Honestly, I think is unsubstantiated. I honestly think if a QR comes loose on you, it's because you were too stupid to put it on right!

This country has become to litiguous and no one is taking responsibility for their own actions. My guess is some idiot didn't put enough tension on his QR, rode some trail beyond his ability, got hurt and is going after some deep pockets like Shimano.

If I've offended you by stating this, TOO BAD, that's how I feel! Idiots are going to drive the cost of bikes and bike parts through the roof as manufacturer's have to cover their expenses from frivolous lawsuits.

L8R

Saw this and wondered

http://www.singletrackworld.com/article.php?sid=1005

"Idiots are going to drive the cost of bikes and bike parts through the roof as manufacturer's have to cover their expenses from frivolous lawsuits."

They must have started a long time ago... these things cost an arm and a leg. For the amount you spend on a $3500 bike and a $3500 motorcycle which one do you think you get more on?

-Joe

You aint kidding. I stopped in a Harley Shop down here, and was just looking around. I found a front CNC'd wheel on sale for $269.00 and thougt, HOLY SMOKES, that's cheaper than my mtn bike wheel!

L8R

Crooks. I mean crooks... woops, well you get the point.

-Joe

This was supposed to be an issue with the rear brake/wheel, correct? I have to ask: how much braking force does the rear wheel have, barring bikes with huge amounts of weight on the rear (tandems)?

I tighten the hell out of mine, personally. I've never had ANY problems. I do know some people that don't even put it on correctly. They spin the lever part instead of the knob to tighten it down, resulting in a seriously dangerous condition.

We have quite a few tandems out there(biggest tandem dealer on the west coast) and I have never heard of this happening on one of them. Or on any bike we have ever sold.

I wouldnt use an 8" rotor on a standard QR fork simply because the breaking force "IS" enough to tear the skewer right out of the dropouts regardless of how tight you make them. Ive even heard of big rotors breaking skewers and sending riders flying over their bars to impending doom.

Originally posted by BurlySurly
I wouldnt use an 8" rotor on a standard QR fork simply because the breaking force "IS" enough to tear the skewer right out of the dropouts regardless of how tight you make them. Ive even heard of big rotors breaking skewers and sending riders flying over their bars to impending doom.

While no engineer, I find it difficult to believe that hard application of a brake creates enough shear force to create this problem. Obviously the speed, weight, forward velocity and the ability to have the tire assembly lock up to shear the skewer is a 1 in a million. I haven't been mountian biking that long but I have not yet locked up my front brake. I can't imagine a time when one would.

I can see how this could happen, but in reality how often does it happen I think is a different story. You have the downward pressure against the QR, but then you have your weight pushing up on the QR.. and the brakes themselves clamping down on the disc holding them from going down.. There are ALOT of forces in many different directions. I think in reality play it safe tighten up you're QR properly, and check condition of it periodicaly so use standard common sense.

Originally posted by Kev
I think in reality play it safe tighten up you're QR properly, and check condition of it periodicaly so use standard common sense.

Marzocchi and the other fork companies would disagree, as they do NOT recommend using qr with 8" rotors for this very reason. You go for if you want.

Do they NOT recommend it because of problems or from FEAR of potential lawsuits? I honestly don't know. Plus, since I've started using a 20 mm thru axle for my front hub, I'll never go back to a standard QR, not for fear of the QR letting go, but more for the rigidity the 20mm provides.

L8R

A2,

Is it that big a diff over qr20? And in that case can I fit a 20mm into my current qr20 hub?

I'm not sure the article linked to above explained. Did the skewer come out of the dropouts or did the QR skewer shear off? That would be pretty important. It's amazing how much force those ordinary skewers take.

Hey Mael, a QR20 is just Marzocchi's name for it. I have a Rock Shox Psylo with the Tullio QR. Same thing different name!

Both 20 mm thru axles.

L8R

ok...:D..thanx

The original work linked from the "Singletrack" article talks about 2 failure mechanisms. One is pulling the QR out (forces greater than the ISO test for QR integrity), the other is loosening of the QR induced by variations in braking force. The calcs are for the former mechanism. The second, however, seems to be fairly common.

We are talking front brakes only, here.

In fact, larger rotors "ought" to be better - max force is the same in all cases (wheel lock-up) but there is a lower moment about the front axle, thus less chance of pulling it out.

Quite a lot of discussion on the Singletrack forum on this issue. No-one is quite sure how bad this is or whether certain QRs / forks are better/worse. Needs a bit more investigation though, as James Annan (original author) points out.

From my experience, though, I've never had this happen but that doesn't make the analysis any less valid.