Disc brake rotors go out of true from normal use all the time and will rub your brake pads eventually. It is not a matter of if but rather when. Things like heat build up from using the disc brakes will warp the rotor and the rotors have zero side strength and easily flex and get bent if you touch them with anything.

Even with a perfectly true disc rotor, a thru axle is required for disc brakes in order to not have rub because even just a little bit of flex at the axle is enough to cause rubbing of the disc brake.

There is no easy way to fix a rubbing disc brake and you cannot increase the clearance between the disc pads and rotors since this small clearance is an inherent property of the self-adjusting O-rings inside the disc caliper and not something that can be changed at all. You have to manually bend an out of true rotor with a wrench and use Allen keys to loosen the bolts holding the disc caliper to realign.

This is not correct. The focus on through axles for disc brakes is to have better and more repeatable wheel/caliper alignment and, more so for the front, to prevent disc brake braking forces from pushing the wheel out of the dropout when the brake is applied.

---

Advanced Aero TopTube Storage for Road, Gravel, & Tri...ZeroSlip & Direct-mount, made in the USA.
DarkSpeedWorks.com.....Reviews.....Insta.....Facebook
--

Thx. You mention thru axle is a requirement, yet so many road and cross bikes now have discs, without the thru axles.

I've worked on disc bikes with skewers, and those were much more sensitive to rotor alignment. Had to make sure the wheel was in the drop outs perfectly, and skewer clamping force was consistently the same. Pain.

The majority of disc bikes are now thru axle. Very few are still made with skewers. Much easier for consisten alignment.

And yeah, sometimes you have to manually bend the rotor to get ride of minor rubbing.

---

Alex Arman

Strava

I don't think any new road or cross bikes with disc brakes use QR skewers anymore. All new disc bikes I see are using thru axle. Using QR with disc brakes is a huge mistake.

The only time my mtb rotors have rubbed or gone out of true was because a stick got jammed in there somehow. In the past year, riding offroad (~2000 miles), I've only had to true my rotors once or twice. It's easily done with a crescent wrench, and it takes about 30 seconds.
I've had to adjust the toe-in on my rim brake pads just as often.

Another person to substantiate that very little of this is true.

Discs rarely go out of true. I've had to re-true them maybe 3 times in the past 5 years (each instance was because of something happening (got knocked while packed in team-trailer etc)). Each event was more a fine-tuning than an unusable set-up. In fact, because of broken spokes, I've had disc brakes save a ride (Twice) vs. Ruin a ride (Never).

Both of my Current Cross Bikes (Sworks Crux) run QR's and disc brakes. It works fine. To say you need to be careful about alignment is to say that you just need to put your wheel in correctly. If your wheel is misaligned in any bike, it is inappropriate. Yes a disc brake will let you know sooner than a rim brake, but frankly that's probably a good thing!

To answer the original question: I've never had an issue with disc brake drag. I currently have 2 cross bikes and 2 mountain bikes with discs. I've owned 8 disc brake cross bikes from Specialized and Focus, plus spent significant time riding Giants. Never any issues on CX or Road or Gravel terrain.

---

I talk a lot - Give it a listen: http://www.fasttalklabs.com/category/fast-talk
I also give Training Advice via http://www.ForeverEndurance.com

The above poster has eschewed traditional employment and is currently undertaking the ill-conceived task of launching his own hardgoods company. Statements are not made on behalf of nor reflective of anything in any manner... unless they're good, then they count.
http://www.AGNCYINNOVATION.com

They never have for me and I've had them extremely hot descending hills. It's not clear why rotors would warp if they're not bumped. I have QR wheels on my MTB and never had any issues. I don't put the wheels in any more carefully than a regular wheel and they've never come loose from braking.

Uh oh... I've been making a huge mistake then for the last 3 years riding both a Trek Boone and Cannondale Synapse with discs and QR skewers... I'd estimate 10,000+ miles in total and not an issue with either bike.

I think it's important to recognize that disc brakes are nothing new, just old tech being applied to a new genre of cycling.

Some contact between pads and rotors is common, but it should so little that it really does not noticeably (or effectively) increase rotational drag. However, it does cause quite an annoyance when the callipers or rotors are out of alignment and adding drag. Years ago, I had a friend who could not seem to get rid of a constant disc rub from his MTB and was constantly was taking it back to the shop for adjustment. I was happy at the time that I still had v-brakes!

From what I have seen, the design of many cable-actuated disc brakes tend to be prone to weaker braking performance and annoying rubbing issues. I actually think that the type of calliper is more relevant than the type of axle supporting it. I'm specifically referring to the less expensive, single-sided piston callipers, which are known to have all kinds of issues maintaining consistent clearances/alignment.

Thru axels do appear to support greater wheel stiffness which may reduce unwanted disc brake friction when doing things like climbing out of the saddle (or similar). But to me, thru axles are an overall improvement, but also a little 'over-kill' in the application to road / tt bikes. The only annoyance that I see with thru axel is that wheel changes seem to take a little more effort to get the axel all lined up to start threading it in.

The only disc warpage I have seen from major manufacturers is from ham fisted types cranking hard and unevenly on 6 bolt rotor types and using discs designed for looks not use.
Modern discs from legit manufacturers use carefully placed holes and disc shape to counter any possibility of heat induced warping.

Aftermarket discs made to be super light or have little figures cut into them are shite.

The only bent disc I own was from a crash, never had a problem other than that.

I've used (counting on my fingers here...) five different MTB disc brake setups over the past TWENTY years (first ones were the AMP/Rock Shoe D1) and I only recall having a warp issue once, with the D1. That was because AMP was a little too much into light weight in the infancy of MTB disc brake technology, and as I recall the rotor got landed on by another rider. As noted by the other poster, a crescent wrench resolved about 99% of the problem.

I've had closed-system Hope brakes that actually had a dial on the lever that would tweak the free play at the caliber - very handy. All but my last two MTB setups were QR skewer - my commuter bike still has a regular front skewer, and I have never had a problem with things going out of alignment due to braking. You need to make sure that the skewer is tight, and that the axle is bottomed in the dropout, and then there is no problem. I built one bike with two wheel sets, with two different brand hubs, and the rotor alignment was THE SAME, allowing me to switch out wheels in no time. The through-axle forks improve the system operation, but they are not essential.

All of the horror stories related by hybridlete have, at some point, occurred to someone, but current brake, hub, and fork technology has advanced to the point where you are unlikely to actually have any of these issues. Anyone that is having persistent problems with disc brakes (especially hydraulic setups) needs to look to their mechanic because the issue is likely with the installation (or the operator) and not the brakes themselves.

---

Less is more.

Yeah...and that's BS.

Up until I upgraded the frameset on my "all-road" rig to something that came with a thru-axle fork (Fuji Jari), I was perfectly happy using QRs on it...one caveat is that the Salsa fork I was using was smartly designed using forward facing dropouts. Bottom facing dropouts on disc fork are aligned with the "ejection force" caused by braking, and are most likely the real reason for rotor misalignments occurring while riding. Forward facing dropouts prevent that movement. Even so, I've never had any problems with the QR fork on my MTB, which has bottom facing dropouts...but I pretty much remove and reinstall the wheel on every ride of that thing, so the skewer is constantly being put into place and tightened adequately.

BTW, if you look at the structure of a quick-release and axle vs. a thru-axle, it's pretty obvious that they don't really add any torsional stiffness in a rigid fork...on a suspension fork with independent lower legs, maybe...

On the rear of a bike, I find thru-axles to be a royal PITA to swap wheels as compared to QRs, so I'm glad that my disc bikes all still allow QR setups. If the fork on my Fuji still allowed QR, I'd still be running one there too.

---

http://bikeblather.blogspot.com/

Public Service Announcement:

I strongly recommend that Hybridlete not be taken seriously on any topic.
He has demonstrated that he cannot be trusted to accurately represent his knowledge on a subject, and appears happy to state as fact, that which is nothing more than uninformed opinion or speculation. From what I've seen to date, his assertions are mostly incompetent and often misleading.

agreed,

my first disc was a hardtail cannondale that i rode for 4 years in the city and single track racing. it had QR and i had the occasional rub when i didn't align it properly. but i probably put 5-7k hours on the bike and i didn't have a single issue with a warped rotor.

i just picked up my first road bike with disc brakes a few months ago. i've already put over 1k miles on her with transportation inside my car, tossing the bike in there with bags on top of it etc. not a single issue.

it's a 1mm thick piece of metal, it doesn't just warp that easily.

john