Do all carbon rims flex so much that the brakes rub?

[User Name]

If not, then why are all these pros riding with their brakes undone?
I was considering dropping a load on some Zipp Clydes



Cancellara

Haussler


Cavendish


Freire

[Tubes6al4v]

The short answer: No, not all carbon rims are flexy. Some are, but I'd be willing to bet that most pros prefer more laterally stiff wheels. So why are the brakes undone? Even in the stiffest wheel, there is some deflection. And if it is say 5mm, you will have effectively tapped your brakes. In a race, this is very costly, and thus racers open the brakes preemptively. It may not be necessary for every setup, but at least you don't loose a race because you didn't...

[Stockie]

I always thought it had to do with brake pads wear...
If you start with the brakes undone and the pads start to wear due to rain and/or heavy braking, you can stille place the pads closer to the rims...

But i can be totally wrong

[rico]

Many pros will flip their blocks open (or ride like that from the off) if they know they're really going to put the boot in at some point. Climbers do it, sprinters do it, most do it at some point.

Of course you can just turn the adjustment knob to change the spacing, or tighten/loosen the cable. But whenever I get a new bike (or new brakes) I have them open - wrenches always seem to set them up too close.

[Coolhand]

easier flat changes

[mr_tim]

I might be wrong, but I'd have thought it related to the wider rims being used by the pro's you've pictured (rim widths coming in at 24mm+).

Wider rims means the actuation needs to be further out - thus necessitating the brake being left open.

To answer the other question - carbon rims don't flex that much if they are laced up properly. With decent tension I'd be expecting worst to be 3mm under a hard effort... and that's based on my own builds with generic rims.. none of this $$$ high end stuff.

If you've a concern over flexy rear wheel builds, you probably should look at rear hub spacing & spoke counts as well - some hubs really don't give a very good off-set and tension balance, so they inherently build up into a soft wheel. Far less to do with whether the rim is carbon or alu.

If you set up your stuff well and maintain it properly with normal width rims (20mm odd), you shouldn't need to set the shimano lever in the open position.

[$mokeyJoe]

I'm pretty shure that the riders themselves just open the brakes for tuning their brake feeling. Some riders want a flush feeling, others want them to be super sensitive. When the mechanic setup the brakes, he does it the way it should be. When the rider setup his brakes he does it the easy way => opening the brakes.

So do the riders in my team.

[JohnnySea]

Do carbon rims flex - no. I have a number of sets of carbon wheels on which I don't experience any wheel rub.

That being said, I have a set of Lightweight Ventoux's which flex sufficiently to cause wheel rub so when I'm sprinting or ascending out of the saddle I release the breaks. I guess some pro's do the same. I use Campag SR so releasing the breaks as can be done without fuss from the lever.

[rustychain]

I have seen the open brake thing done often on aluminium rims too. Do all aluminium rims flex

My opinion (#1), spoke count is as or more important then the rim regarding flex. Yes deep dish rims tend to be stiffer but even a flexy rim will stiffen up with enough spokes

My opinion (#2), as a big guy I notice that we often tend to do this. Yes some mechanics like to have the brakes as tight as possible so perhaps that is an issue with team mechanics
This not only can make for brake rub with MOST rims for us big guys but can IMO adversely affect braking and have you braking when your trying to shift gears

I also had to do this when using new brake pads on my M5 brakes as they had not enough clearance for some wider rims

Last, some people just forget

[holsen]

I just replaced my Mavic Ksyrium Elites with a set of Tokyo Wheel Epics The epics are so wide I also had replace my brakes. Anyway I've got it all set up and I get brake rub under even light load. There's alot of flex and I never experienced that with the alu Mavics. It doesn't make any sense.to me because the carbon should be.stiffer. I don't know the cause I just know the rub only started with the.carbon wheels.

[Irish]

The pros riding with their quick releases half open are most likely riding wider rims, if they puncture and get a narrower rim from service they can just close it and still have braking.

[Ozrider]

In races with neutral support the bikes get set up to accept the wider rims the team is using ie: Zipp, Bontrager Aeolus etc. If a narrower neutral service rim ie: Mavic or Shimano gets swapped in they can close the quick release partially or fully to compensate for the narrower rim.

And as @ rico said, many sprinters and climbers do it out of habit or to eliminate any potential brake rub.
The big sprinters push out way more power than any of us, so might experience brake rub or flex in the frame we are just not able to replicate.


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[dofman]

Flexing the front wheel under load climbing, yeah...

[hasbeen]

Carbon rims don't flex more but lower spoke count wheels often times do. Spokes are thinner and lighter and spoke tensions remained the same while other wheels like ksyriums and eurus got higher tensions and bigger spokes. So, opening the brakes is a tradition that isn't going anywhere for a while. Its a tradition to open up the brakes on a climb or sprint. Its like taking a drink from a bottle before tossing it away. And as with most things it is mostly mental. Been a tradition since way before my time!

[hasbeen]

is there an echo in here