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-   -   rotors rub when standing up? (https://www.bikeforums.net/showthread.php?t=1171305)

spectastic 04-24-19 01:05 AM

rotors rub when standing up?
 
I noticed no matter how precisely I adjust my front rotor, it always finds a way to rub when I stand up and put power down. this is on a 2016 giant tcx, plenty stiff. I noticed that when I switch the rotor to a different one, the noise would change. the 2 rotors i have are avid hs1 and generic chinese floating rotor, which rubs a lot more than the avid

advice?

dsaul 04-24-19 04:44 AM

Its pretty common on disc forks with QR dropouts. That's probably the main driver behind the switch to thru axles on almost all disc forks. There is not much that can be done. On mechanical brakes, you can space the pads further away, but then that ruins the braking performance.

dabac 04-24-19 07:33 AM

Functionally, it doesn't matter.
W/o any pinch force behind, the friction generated is entirely unimportant for anything but the noise it makes.

Only ride windy days or in heavy traffic.
Hire someone to ride along with you and sing loudly.
Reintroduce your childhood playing cards dragged against the spokes to mask the noise.

Slightspeed 04-24-19 08:44 AM

I have TRP Spyre cable discs and they have a spring to keep the pads off the rotors till you need them. I don't know why the recently more popular hydro discs don't use them too. I never hear or feel any pad rub if the caliper is adjusted properly. I also have two wheelsets, and swapping wheels causes no rub issues, even with TRP rotors on one set, and Maguras on the other. I've had the bike over 5 years, and have normal QRs.

fietsbob 04-24-19 09:08 AM

Magnets can hold steel backed disc pads to the slave pistons .. some use this ..

redlude97 04-24-19 09:55 AM


Originally Posted by Slightspeed (Post 20898596)
I have TRP Spyre cable discs and they have a spring to keep the pads off the rotors till you need them. I don't know why the recently more popular hydro discs don't use them too. I never hear or feel any pad rub if the caliper is adjusted properly. I also have two wheelsets, and swapping wheels causes no rub issues, even with TRP rotors on one set, and Maguras on the other. I've had the bike over 5 years, and have normal QRs.

Huh? Both shimano and sram hydro calipers use a spring similar to the spyres

Slightspeed 04-24-19 10:31 AM


Originally Posted by redlude97 (Post 20898733)
Huh? Both shimano and sram hydro calipers use a spring similar to the spyres

OK.
But I hear a lot of guys complain about pad rub on hydro systems. I've never had hydraulic discs myself, only cable Spyres, and never experienced pad rub.

redlude97 04-24-19 10:37 AM


Originally Posted by Slightspeed (Post 20898787)
OK.
But I hear a lot of guys complain about pad rub on hydro systems. I've never had hydraulic discs myself, only cable Spyres, and never experienced pad rub.

Thats a piston retraction issue having to do with master cylinder and system volume

spectastic 04-24-19 02:27 PM

btw. my bike has thru axles.

and I realize the rubbing isn't a huge power sap. but it's annoying AF. also, imagine trying to attack a group with pining noises. horrible.

shelbyfv 04-24-19 02:43 PM


Originally Posted by redlude97 (Post 20898799)
Thats a piston retraction issue having to do with master cylinder and system volume

Could you explain a little more? A fellow I ride with had rubbing on DA discs after a short downhill. His thought was that the fluid expanded as it heated. Wasn't much of a hill and I know folks ride these in the mtns w/o issues. Thanks

redlude97 04-24-19 02:53 PM


Originally Posted by shelbyfv (Post 20899219)
Could you explain a little more? A fellow I ride with had rubbing on DA discs after a short downhill. His thought was that the fluid expanded as it heated. Wasn't much of a hill and I know folks ride these in the mtns w/o issues. Thanks

especially for road levers and calipers, the master cylinder is pretty small. The way hydros work is the fluid moves as the piston is pressed by the brake lever. Then it retracts when the lever is release and the fluid moves back in the master cylinder. Since this volume is small, and the calipers also have minimal volume and size, the amount of piston retraction is tiny. So the gap between the rotor and pad is very small even for a perfect system. When it gets hot the fluid and/or caliper expands so now the pistons retract even less so the pads sit a bit closer to the rotor. When people say their rotors warp after descending its actually the pistons retracting less and there happens to be a slightly out of true spot on the rotor and that one spot will rub. With mechanical discs you can change the distance between pads/rotors and since the pistons don't automatically move out with wear generally this gap will be larger than on a hydro system so its less of a problem.

tyrion 04-24-19 03:10 PM


Originally Posted by spectastic (Post 20898229)
advice?

Frames flex. I don't think there's anything you can do, other than get a stiffer frame or weaker legs.

edit: I didn't catch that it was the front rotor that was rubbing. I don't think normal frame flex would account for that.

HerrKaLeun 04-24-19 04:29 PM

I was about to start a similar thread for my giant Toughroad with CF fork and QR. A while ago, I started to have a similar problem. Every once a while the rotor makes the "ding ding ding"noise. This seems to happen when I push on the NDs pedal or even if I coast and stand on the NDS pedal. Doesn't seem to happen to DS pedal. I re-seated the axle, re-adjusted the caliper, no resolution. I also tried to tighten the QR very tightly.

Doesn't happen all the time and seems to be limited to specific pedal forces. I recently installed new pads, maybe that put them closer to the rotor. I hope once the pad wears it will get better.

Obviously I don't want to buy a new TA fork and a new hub. I weight 175# and am not particularly strong.

Troul 04-24-19 05:28 PM

Increase the gap, but it'll increase the pull needed. For a front brake, I wouldn't see it as an issue since the front brake ideally shouldn't be doing any of the skid stopping braking.

u235 04-24-19 05:28 PM

I am having a hard time trying to think through a situation where standing and or power would put significant stress, strain, or force on the front axle and fork, separately causing a gap change between the two. Frame yes, but frame flex does not transfer to a twisting force thru the fork and then to the axle. Even extreme equalizing force pulling on the bars to counter crank force would apply stress evenly thru the downtube and not twist the fork. I must be missing something. Only thing that makes sense to me is play or excessive movement of the front hub on the axle and it moves back and forth while standing. Hub and rotor move but caliper doesn't and then rubbing.

spectastic 04-25-19 12:33 AM

what I tired was manually apply a lateral load on the wheel, simulating lateral stress while pedaling standing up. what I saw was that the rotor does indeed move, and very slightly touches the adjacent pad.

Koyote 04-25-19 05:57 AM

I skimmed this thread, and it looks like no one has made the obvious suggestion: check to make sure the rotors are true. Many of them (esp the cheaper ones) become warped, which makes the rubbing more likely.

Also make sure the rotor is centered properly in the brake caliper, which is actually accomplished by moving the caliper. (youtube is your friend on this one.) If all else fails, increase the gap in the pad and just squeeze more/harder on the brake lever when you need to stop the bike.

redlude97 04-25-19 08:53 AM


Originally Posted by spectastic (Post 20899823)
what I tired was manually apply a lateral load on the wheel, simulating lateral stress while pedaling standing up. what I saw was that the rotor does indeed move, and very slightly touches the adjacent pad.

What hubs/ bearings? That indicates play in the axle

Sapperc 04-25-19 07:12 PM

Probably nothing wrong, but you should certainly rule out anything that might need adjustment or replacement. If the scraping is infrequent and only under unusually stressful riding conditions — like pounding out of saddle sprinting and/or climbing — chances are there is nothing to worry about. Manufacturers won’t advertise it, but the unfortunate truth about the current state of the art disc brake systems is that this can and does happen.

veloz 04-26-19 06:35 AM

Had the same problem on my XTC. After years of brake issues I switched to Shimano hydros. No more problems. You might also check wheel bearings for play.

djb 04-26-19 11:38 AM

have you ever regreased hub bearings? If so, then you should be able to check easily to see if there is some play going on.
If its not that, and possible, just put a bit more gap between rotor and pads, and yes, as already stated, check rotor trueness (do that first obviously)

Ive trued a rotor using a cleaned adjustable wrench, worked fine and not hard to true using common sense.

personally I have had this happen, and after checking the diff possibilities, just backed off the pads a bit, no more problem, and I like a brake lever that engages about half way in anyway, better for modulation imo (for my braking sytems anyway, cantis and BB7 mechanicals)

spectastic 04-28-19 01:27 AM

OK... I just spent WAY more time than I'd like testing different wheel/rotor/brake pad setups, and it appears that all 3 can be a contributing factor to the severity of the rotor rubbing when putting down high power. For anyone else reading this and frustrated by the same problem, or to those who are simply curious, here are the results:

brake pads:
I tried 2 sets of brake pads I had in my toolbox. one of them is a bit taller (I think built for mtb), while the other one is a little shorter, but wider at the base (came stock with the cx bike). both are shimano pads. The hypothesis here was that a taller pad has a higher likelihood for the edge of a rotor to making contact. based on my test, this held true. the shorter pad was noticeably quieter during hard sprinting.

rotors:
This was most surprising to me. It made no sense that the shape of the rotor could impact how much it rubs against the brake pads, but in this case, it made a huge difference. the 2 rotors I tested were avid HS1 and a cheapo floating rotor I found on ebay (see below). The cheapo rotor was MUCH louder than the HS1 rotors, regardless of which set of wheels they were on. The two rotors are both 160 mm at the widest parts, and both measure 1.7 mm. I can't rationalize why the cheapo rotor is noisy AF when I'm standing up, and the HS1's are a lot more silent. I did notice that the cheapo rotors were poorly machined and assembled, so while I may have had them perfectly true laterally, they might not have been true radially. Go figure..
https://i.ebayimg.com/images/g/1zsAA...sV/s-l1600.jpg

wheel (or more specifically, the hub):
I tested 3 wheels: mercury gx (good wheels), giant px-2 (sh*t wheels), novatec (just finished building them today, decent hub). the mercury and novatec hubs performed similarly: noisy with the cheapo rotors, silent with the HS1 rotors. However, the giant wheels produced a lot of rotor/pad contact while standing, regardless of the pad/rotor combination that was used. I believe it has to do with the stiffness of the hub itself. These disc hubs tend to have 2 cartridge plugs on either side, protecting the hub bearings from dust. You can remove them by hand, and I believe the excess play in these plugs are what causes the excess flex. All the wheels I tested had 0-200 miles on them btw, so the bearings are good.

so in conclusion:
  • avoid sh*t wheels with sh*t hubs
  • get road specific pads for road/cx calipers
  • get name brand rotors

HerrKaLeun 05-07-19 05:15 PM

I resolved my rotor "ding ding ding" problem. I couldn't adjust the caliper any better. I saw the rotor has a tiny untrueness. I wasn't really able to true it on the bike (or was too impatient). I ended up buying a Park tool DT-3 for my truing stand and I tried it on the stand.
After that I fiddled a bit with the caliper adjustment and not it works perfectly, all noise gone even when I stand on just one pedal.

I guess it was a combination of a bit fork flex and a bit rotor un-trueness and the rotor is the only part I can fix. The hub cones didn't have play and the center-lock was solid.

Hope this helps someone. sucks to pay much money for the DT-3, but worth it to get my enjoyment back.


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