Newbie here - so forgive the question if it's a dumb one.

New gravel bike with GRX400 group. Mavic allroad wheels. 12x100 front TA.

Rotor was rubbing on one side (drive side). I loosened the brake caliper a bit, re-centred and pulled the brake, tightened, still rubbed. Next I took off the wheel, pushed the pistons back (shouldn't have been the cause with a new bike?, but just in case), and when I was tightening the TA things lined up perfectly, spun the wheel afterwards and no more rub. I tried that again, had the issue, and then again and it was fine. I realized that depending on how I hold/support the wheel (bike on a stand) when inserting and tightening the TA I can accidentally shift it a bit to one side, causing it to go slightly off centre. Never had this happen before with other bikes with disc brakes, but I don't have much experience with them.

In future I will simply check that the rotor is between the pads when putting the wheel back on and tightening the TA, but I was wondering if this means there is a bit of play in the thru axles with this bike (front at least)? After I've tightened it there is no slop and it seems fine (been out a number of times and it rides fine). Or is this common with most thru axle bikes and you just learn by trial and error, as I did?

Thanks!

No...there should not be any play when the axle is tight.

With the axle tight, there doesn’t appear to be play (no side to side movement). But I didn’t expect that I could inadvertently misalign the wheel when tightening the axle just by holding it less than perfectly straight.

You should not be able to mis-align the wheel with a thru axle. That's one of the primary reasons for using them.

CXwrench is right, a primary purpose of thru axle is to allow the consistent realignment of the disc rotor in the caliper, the hub should barely be bigger then the axle so there isn't room to wiggle the wheel when tightening. When installing the wheel I either have the bike upside down and once the thru axle starts to thread in the other side I let go of the wheel or I have it in the stand and same thing. The result is always right where it belongs. Although it shouldn't matter, since it does, make sure you're not holding the wheel causing it to shift. It may be if a factory hub its not a perfect tolerance or the thru axle isn't quite right. If the current solution is to just not hold the wheel then go with it.

You should not, and I can't feel any play with the 3 bikes I've ridden with through axles.

However, in all of them experienced what the OP is saying. Play may be imperceptible, but it's there and, if the rotor is close enough to the pads, it can make it rub the pads.

In my opinion, the issue is that the hole where the axle goes through is obviously a little bigger than the axle itself (otherwise it wouldn't fit) and allows some degree of movement. It's not that the axle is moving constantly, it's more like it slips to a slightly different position when you start riding the bike and stays there. And in my experience, it happens even with a really tight axle.

I have experienced this with a Suntour fork with Q-LOC axle, with a Fox Rhythm 34 fork, and with the rigid carbon fork on my road bike.

Thanks everyone. What you’ve said and tips provided make a lot of sense.

Your experience brings up a practice that I train into every person we hire as a mechanic. When inserting a wheel into place, the bike comes out of the stand and is set upon the floor for alignment before tightening a thru axle or a QR. The bike then goes back into the stand for final brake adjustment be it a disc brake or caliper brake.

Interesting approach although it would require a lot more taking down and putting the bike back on the lift. For me I just make note of the alignment of the brake pads and the position of the wheel in the dropouts before removing the wheel, and if the pad alignment looks good then I make sure the wheel goes back in the same position when it is put back on. For rim brakes if the brake pads are perfectly aligned (from all angles including being equidistant gap on each side of the rim, pads contacting the center of the rim, not too high or low, and the pad following the arc of the rim) before removal, and the wheel is properly positioned in the drop outs before removal, then it should be the same after the wheel is removed and put back on. For disc brake pads again the gap between the pad and the rotor should be about equal on each side and the pad should not rub when rotating the wheel. When putting the wheel back on I make sure it goes back where it started, make sure the axle is in the same position in the dropouts, and the brake pads are aligned the same as they were at the start of the process. For most bikes with a quick release axle and mostly vertical drop outs all this means is making sure the wheel is placed up all the way into the dropout before securing the quick release. This is for bikes that come in that require the wheel to come off for any kind of service. However, there are many times someone asks for us to look at their bike where the front brake is rubbing and I just look at the brake pad alignment, see it is off, and with the bike still on the ground I just open the quick release, allow the axle to settle properly and all the way up into the dropout (again assuming vertical dropout) and then close the quick release and check pad alignment and this usually centers the brake pads and stops the rubbing. Of course bikes with more horizontal type dropouts are a little more tricky because one must make sure the wheel is centered between the chainstays as well, and all of the foregoing assumes the frame is not bent.

I have been doing that very same thing since the early 1970's. It only takes a few seconds and gives you repeatable wheel placement every time

I always do that, but I've found that the position the axle assumes with the bike on the floor is not exactly the same it assumes after riding for a while and passing some bumps.

If the rotor clearance is really tight, it can start to make noises after riding for a while, and sometimes it can be temporarily solved by loosening the axle and tightening it again, which means that, somehow, the axle / wheel can get slightly displaced after riding.

While in theory a through axle should tighten in precisely the same position every time, in my experience it is not always the case. It is damn close, and usually close enough for disc alignment, but not always.

What I have always done for wheels that sometime give me grief, is do the final tightening with the bike on the ground with a little bit of weight on it. Just enough that if there is some wiggle room, the axle will settle in to the deepest part. It just helps with consistency.

It also makes a difference what brakes you are using.... more specifically, the pad clearance.

The recent posts were really good - I love this level of detail around your experiences and expertise as it helps my understanding. This is something lacking in the YouTube videos I perused when looking for vids around disc brake pad alignment, thru axles, etc. I'll be sure to come here for help in the beginning when diagnosing anything in the future. Thanks.

Oh, If you watched the videos about caliper alignment you have seen the videos about: loosen the cliper, press the lever, and tighten again.

That's crap in my opinion.

It's way easier and more precise to position the caliper manually. You just get behind the caliper and with slightly loose bolts, move it until you can see light on both sides of the pads, then tighten it. You'll probably notice that when you tighten it it tends to move slightly because of the torque of the bolts, so you have to hold it in place when tightening, or account for the movement beforehand, if you want a precise adjustment. This is one of the reasons why the "press lever and tighten" method is crap.

You'll also notice that most rotors are not perfectly flat, so you'll probably have to reach a compromise when aligning the caliper. You'll have to rotate the wheel several times during the procedure to make sure it works during the whole rotation. This is another reason why the "press lever and tighten" method is crap.

If you discover you can't align it because it always touches somewhere, the rotor is bent and it's time to grab an adjustable spanner and straighten it.

And what’s so frustrating about those ‘crap’ videos is they make the process look easy, so when you follow it and your problem isn’t resolved you’re even more frustrated.

I like the recommendation to position the caliper manually. I’ll try that next time, though with everything currently dialed in I hope that’s a while from now!

Cheers

It's not that difficult to do if the rotor is decently straight, unless you have the old avid brakes that had round washers, in which case is a complete pain. What I can't understand is why the method of "press the lever and tighten" is so popular when it doesn't work at all. At least, it has failed miserably on all 4 disc equipped bikes I have.