Rule #41 Quick-release levers are to be carefully positioned.
: Quick release angle on the front skewer shall be an upward angle which tightens just aft of the fork and the rear quick release shall tighten at an angle that bisects angle between the seat and chain stays.
It is acceptable, however, to have the rear quick release tighten upward, just aft of the seat stay, when the construction of the frame or its dropouts will not allow the preferred positioning.
For Time Trial bikes only, quick releases may be in the horizontal position facing towards the rear of the bike.
This is for maximum aero effect.
bicycles.stackexchange.com/users/29740/The Bogeyman
Something noone has mentioned is that the QR lever is not to be touching the frame or fork when in the closed position.
Reasons for this are the clamping force is not as high as it could be the frame or fork can slowly push on the lever and loosen it a bit more over time.
bicycles.stackexchange.com/users/19705/Criggie
I'd put both of them in a way they can't be hit by rocks or branches.
I had no trouble aligning them as described below.
So: for the front wheel it should be aligned with the fork.
For the rear wheel I think two possible and secure options are to point it upwards or align with seat stay.
bicycles.stackexchange.com/users/4007/k102
For disc brake bikes specifically, you want to have them positioned in the way that makes them easiest to open without touching the discs.
For the front this is easily achieved by putting the lever on the right (in whatever orientation you fancy), but you can also have it slightly in front of the fork on the rotor side (behind also works if it's not interfering w/ the caliper).
In the rear, I find that just slightly below the chainstay works best for me, making it easy to brace against the chainstay for both opening and closing.
bicycles.stackexchange.com/users/29446/Jamie A
Front QR is to be exactly parallel to the fork arm.
Rear QR is to be positioned exactly half way in between the chainstay and the seatstay, oriented to the inside of the frame.
bicycles.stackexchange.com/users/19106/ebrohman
Mechanically it makes no difference, since the quick-release work any way you position the lever.
The only reason to adjust the levers position is for the ease of use.
The best way is to position the front lever slightly behind the fork (not aligned along the fork, otherwise you cant press the lever down completely and its hard to open because you cant get between lever and fork with your fingers).
Same for the rear: between the two makes the lever accessible most easy.
You can press with the thumb on the chainstay/seatstay and open the lever easy.
bicycles.stackexchange.com/users/29738/michaelsinner
Personally, I think it depends a little on the design of the quick release lever.
I put my front one pointing upwards aligned with the fork.
However, some quick release designs will actually contact the fork before they are fully closed.
In this case I would place it slightly behind the fork.
For the back quick release, I position it between the seat and chain stays.
Again if you have something in the way, you'll have to adjust parallel with the seatstay or even behind it a bit if something is in the way.
I've seen some people position them both facing backwards.
The idea is that they are less likely to catch on something and open as you are riding.
However, I think this makes them more likely to be opened by some other factor when not riding because there is nothing guarding them.
This would be fine if you checked them before each ride, as we probably should, but most people probably aren't consistently checking their quick releases every time they ride.
If they are in a position that they are least likely to be opened accidentally in most situations, then that is probably the safest.
bicycles.stackexchange.com/users/163/Kibbee
Is it best to have the front wheel release lever in front of the fork, tailing the fork, or aligned with the fork? How about the rear; ahead, behind, or alingned with the chainstays, seatstays, or between the two?
What is the proper position for quick-release levers?
bicycles.stackexchange.com
<quick-release>
bicycles.stackexchange.com/questions/43113
bicycles.stackexchange.com/users/29737/grasshopper
Mechanically it makes no difference, since the quick-release work any way you position the lever.  The only reason to adjust the levers position is for the ease of use. Quick-release levers should be put in so that they can't be hit by rocks or branches. For the front wheel it should be aligned with the fork. For the rear wheel the two possible and secure options are to point it upwards or align with seat stay. If they are in a position that they are least likely to be opened accidentally in most situations, then that is probably the safest. The levers should not be touching the frame or forks when closed, as this may mean that they are not fully locked. While the mechanics are not affected by the positioning, it should reduce the risk of getting caught or opening by accident. Another consideration is ease of opening and closing without obstruction or touching brake discs and other fragile components.
The levers should not be touching the frame or forks when closed, as this may mean that they are not fully locked. While the mechanics are not affected by the positioning, it should reduce the risk of getting caught or opening by accident. Another consideration is ease of opening and closing without obstruction or touching brake discs and other fragile components.