I ended up in a bad crash due to front wheel coming off during the ride. It all happened so fast without warning, there was no time to react or even understand why I fell.
Initially though I was clueless why the wheel came off, but once I researched the link between a disk and QR on the front wheel it is now clear to me what transpired.
I was lucky to not have ended up with broken bones, just concussions and bruises which kept me out of action for full 3-4 days.
YES there is a risk of a disk brake loosening a QR causing a wheel to come off. In my case my ride was a hybrid with disk brakes (Montra Helicon D - from TI cycles), but this can happen with any bike which has disk brakes with QR.
Take a look at the below picture of my setup (image courtesy Amazon listing)
Does it cover all the bad engineering in one shot?
- Dropouts pointing downwards in the direction of the rotation of the wheel - a free fall off in case of loose QR latch.
- A loosened QR would yank the wheel off the drop out in case of hard emergency braking
- QR and the disks on the same side. In theory if the latch gets into the rotor, it would be catastrophic.
- No secondary fail safe mechanism to prevent a wheel from coming off.
Now that we examined why the design is lame, here is a little bit of physics and mechanics that will play its part in the rider crashing. (The below is how a friend explained me and he is a Trans-Am finisher, so his opinion is worth weight in gold)
In theory, it goes like this:
A bike's wheel rolls around its axle, because rolling resistance (on
the axle and on the tire-road contact) is so small when compared to
the sliding friction at the tire-road contact.
What happens when we apply brake?
Braking works because of three forces: pad-rotor contact point (or
pad-rim in case of non-disc). Note: pad is fixed to the fork.
axle-dropout fastened by a QR. tire-road contact point (a strong
sliding force) All the three contact points are on the wheel one way
An effective braking requires that all the three contact points can
withstand the forces. In the worst case, the tire-road contact SHOULD
be the first to give up and cause a skid. Second worse case is for the
pad-rotor to give up and slip the braking.
What happens if the worst case scenario turns out to be a give-up in
the axle-dropout contact point? Or why would this even be the case in
the first place?
When the pad-rotor contact point is fixed and tire-road grip is
strong, there is a massive force at the axle-dropout contact point,
with the axle pushing backward. Try to imagine without the dropout on
the fork. The wheel will try to rotate around the pad-rotor contact
point. If the rider+bike has sufficient momentum (speed), this can
cause enough force for the wheel to rotate around the pad, specially
if the dropout is somewhat on the circumference of the circle drawn
with the axle around the pad and in the direction of rotation of the
wheel. If the dropout directly is completely opposite of the direction
of rotation of this circle of axle around the pad, then the only way
the axle can come out of the dropout is to break/damage the dropout.
It so happens that a Montra helicon dropout can easily cause the axle
to come out. Apparently, there were so many recalls in the US on this
faulty design of the dropout. I compared this bike with my KHS 650B.
There is literally no room for the wheel to come out in case of KHS
650B (you can google for images of both).
You should check if your fork dropout is designed safe enough. I WILL
RATE THIS A VERY HIGH RISK CATEGORY FAULT.