robbyville

I've noticed that when climbing hard (standing on pedals), I hear a slight rub of brake pad against rim on each revolution. I just centered my brakes a little better to see if that will help but when I clenched the wheel and moved it from side to side it moves a little (as does the front), just normal flex I assume. The hub itself does not seem to have any excess play. I suppose it could be that I have my pads set quite close and that the flex is normal. Is that the case?

The hubs are Chris King, I have not looked into how to adjust yet but I'm told it's pretty easy but as mentioned there does not seem to be any play in the axle.

thoughts, normal, weird?

halfspeed

Some movement is normal. What kind of rims. What kind and how many spokes?

Homebrew01

And are the spokes nice and tight ?

robbyville

38mm carbon rims with sapim cx-ray spokes 24 spokes. Wheel is within 1mm of true and only has 200 miles on it. So long as some play is normal. Once snow melts and I can ride again ill see if my re-centering helped, maybe I need to open the pads a tiny bit

robbyville

Seem to be but will check in the morning.

FLvector

Sounds like normal rim flex. If you aren't a lighweight and the wheels aren't particularly stiff, its normal to have some flex as you stand and grind. Open up the pads.

November Dave

https://chrisking.com/files/upload/in...cR45Manual.pdf

You may need to adjust bearing preload tension. You're trying to get to a point where you have just enough tension to prevent play, and not enough to put excess load on the bearings.

King hubs, properly adjusted, are exceedingly stiff.

Brake rub can actually be a sign that your rims are really stiff. Soft rims flex below the hub, where stiff rims can transfer load across the axle and to the top of the wheel. Getting bearing load just right will minimize that. King hubs are capable of handling that torque. They're great hubs.

Sorry for brevity, typing on phone.

rpenmanparker 

Could be bottom bracket flex. The whole bottom section of the bike (bottom bracket and chainstays) could be rocking from side to side. That would tilt the wheel alternately toward each brake pad on the two halves of each stroke. That used to be common (along with chainring rub on the front derailleur) in light weight steel bikes, early aluminum frames like Vitus, etc. Not so much nowadays. I hope that is not the case, but you have to wonder.

Robert

StanSeven

That's just normal flex, especially if you are big, strong, and generate a lot of power. Open up the pads a little. If you are concerned, take it into a shop if you aren't experienced with adjusting tension.

robbyville

Thanks Dave (and all others), I will check the preload as well tomorrow.

robbyville

may need to. I certainly would not classify myself as either big or strong but maybe the slight rub should act as an ego boost!

November Dave

A possibly unrelated note on brake setup. Many people set their brakes up too close to the rim, which is less than ideal from an ergonomics and modulation standpoint. If your brake pads contact the rim with like the first mm of lever pull, then your hands/fingers are going to be still extended far out when you are at max braking. Imagine how much more pressure you can exert when squeezing a baseball than a softball - you want your hands/fingers to be in their max power range when you are really hitting the brakes. My general rule of thumb is that for 21mm rims, I want to be able to remove the wheel with a 23mm tire on it without having to open up the brake quick release, maybe giving a light bump on the tire to make it clear the pads. With a 23mm rim, when undo the skewer, the wheel drops out easily clear of the pads. This is with SRAM or Shimano brakes, which is what 99% of my experience is with.

If you divide the range of brake lever pull into quarters, my pads make contact at the end of the first quarter, and stops at the end of the third quarter. I don't start braking right away in the pull, and my levers don't bottom out at my bars.

rpenmanparker 

Dave, I agree with you completely, but remember that with modern brake levers that include reach adjustablility, there may be less travel when set up for a person with small hands. I'm not sure, but I suspect it could be hard to leave pads as wide as you recommend without bottoming out at full actuation under those circumstances. Put another way, with the lever adjustablility it may not be appropriate to use the wide spacing as you have already set up the levers to start the hard braking at a point where the hand grip is optimized.

Robert

November Dave

Sure, absolutely. That's why I included the "divide into quarters" thing - if your absolute range of your throw is less because you've got your levers dialed in (and mine are dialed in quite a few mm), then you still want to start feeling pad contact at about the end of Q1 and get to lock up at about the end of Q3. It's also self correcting to a degree, since hand size correlates at least somewhat with power output for most riders. Less lever throw b/c small hands probably = less need for pad clearance.

I've got a good friend who can not be convinced to leave more than 1mm (seriously - the width of the blade of a CX Ray) between his pads and rims. It's incredibly evident when you see him ride, too. He does the herky-jerky all day long.

robbyville

Great recommendation once again thanks. I do have my reach adjusted down a fair bit for my tiny tot hands, but definitely engage within the first quarter, maybe a tad early. Looking just now, there is no way that either pad is more than 1-1.5mm away from the rim especially with a little bit of toe in. I'll adjust a bit and see what happens. When I pull hard on the levers they don't bottom out on the bars but with cable stretch the shift part of the lever would definitely come up against my knuckles assuming I was in the drops at full skid!

Hey Dave, somewhat separate but since you're on this thread... I have hears that some brake squealing on carbon rims is normal, I have none on the rear but some on the front if braking medium-hard on a decent (I know I'm trying to learn good braking technique), is this just break in time, toe-in, or normal? I've never had squealing before but this is my first carbon rim.

November Dave

If you're using the Black Prince (just figured out who this was - not much gets by me! j/k), which I've been using, yeah I get some squeal sometimes. Scrubbing speed for a turn I get no squeal, but like coming to a stop at the end of a downhill approaching a stop sign, I got some out of the front the other day. I think it's also got to do with how cold the air is, but that's an educated guess. It seems like if they're warming up from having been cold (i.e. after a long climb and screaming downhill when it's 35* out as happened Saturday), then they squeal as they're becoming warm. I've never had squeal on a warm day.

My thought is they are such good brakes that I don't really care about a little noise. Check out what kind of howls you get out of disc brakes and metal pads on a cold day, it can wake the dead, but you stop when you want to.

robbyville

true enough! I was a little worried when people would comment on braking with carbon rims but so far it's been as good as any other wheel that I've ever had. The pads are great and the DA 9000 calipers are incredible.

thanks again to all for the advice.