These are the first preliminary results - this page will be updated as I get more data. I’m doing this in my spare time, and you can help... Vibration testing:
Part of the theory is that disc brakes cause quick release skewers to loosen off more quickly than they do with other types of brake. To test this, I did the following: My usual commuting bike is equipped with disc brakes. It has titanium quick release skewers, and forks with no “lawyer tabs”. In over a year of use, I have never had to adjust the quick release. It was tightened as hard as I could get it by hand. I retightened the skewer using the “90 degree rule”. This rule is often quoted for quick releases - you tighten the nut so the lever starts to get tight when the lever is at 90 degrees to the wheel (straight out). So this was looser than I previously had it, but still “hand tight”. The lever was on the right side (opposite to where I normally have it, but consistent with advice from SRAM and others).
I then rode the bike on my usual commuting journey - 6 miles per day, on and off road, including cattle grids and speed bumps taken at speed. Every day I loosened then tightened the lever, and recorded the angle at which the lever began to “bite”. This turned out to be an accurate way of measuring the state of the skewer - I also tried using a torque meter on the skewer, but this was less accurate.
I repeated the experiment on a V-brake-equipped bike - the same skewer was used over the same route. The results were as follows: Disc bike: after 3 days, the “bite point” was 80 degrees - the experiment was halted. V bike: After a week of use, the “bite point” was still 90 degrees. Conclusion: From the above, there seems to be an effect from the disc brake which causes the quick release to loosen. There could be other explanations (for example, I tried to brake in the same way on both bikes, but since discs are more powerful, I may have braked harder on the disc bike).
Since this disc bike was used with the same skewer for over a year with no adjustment, it is apparent that this effect only occurs if the skewer is not tight enough. There is a certain critical limit - below this limit, the skewer can loosen - above this limit, it won’t. The limit is dependent on skewer design and rider weight.
It is also important to note that in the experiment I had the lever on the right side, whereas I normally have it on the left. How important this is will need to wait for further tests... Update: Out of interest, I have now been trying a new setup - using hte same QR on the same disc-equipped bike, tightened in the same way, but with the QR lever on the left side instead of the right.
This setup has now been in use for over a week with no loosening. So now I am going to repeat the first experiment to make sure that I did not imagine the loosening that occurred... Want to help? I know that two weeks’ riding does not make for excellent statistics - I could really do with some help to get more data. If you want to help, try repeating the experiment above. Tell me if your bike has discs or V-brakes, what make of fork and skewer you use, and (approximately!) how heavy you are. Tell me how many miles to takes for the skewer to start loosening (if at all). Tell me how you tightened the skewer - the “90-degree-rule”, the “hard as you can by hand rule”, or the “stand on it with all your weight rule”. Was the lever on the left or right side of the bike? Thanks... | 
