Road Cycling - Why on earth is there a deep groove in my rim?

I just got an OCR2 and noticed there's a deep groove that runs in the middle of the rim where the braking surface is?

Long story short: What is that thing?!

is it consistent and on the rim when manufacturered? if so - then it is called a machined braking surface.

machined brakings surfaces = better braking

Maybe there once was water there, eons ago...

mine have those too, I'm pretty sure, that if they are consistant throughout, and put in by the maker, they are for better and cooler (temp wise) breaking....they help to keep the surface in tact so the rims will last longer....

Could be the rim wear indicator. When that groove is gone, it's time to replace the rims as the sides will be weaker.

i believe either mavic (i could be wrong) puts those grooves in the new cxp21 rims. no idea why. you'd think if there was an advancement in braking technology, they'd also apply it to the upper level rims as well. i'm not sure if other manufacturers are doing this, but if you're rim isn't a mavic, then i guess so. the groove actually gives you less braking surface, and the parts where the pad actually does contact the rim are going to heat up just as fast.

the "they cool down the rim surface" idea just doesn't wash with me, and unless the braking surface rim wall is thicker there, it weakens the rim. and if they ARE thicker, you just end up with the rim being overbuilt to compensate for this "benefit."

there's a difference between the machining done to an open pro or a CXP33 rim and the machining/groove cutting done to the cxp21s. and honestly, i don't notice a difference between braking on a mavic MA3 which has a machined braking surface and the ritchey rock rims that are on my road bike now (which are not machined). the only difference i notice is that the machined rims look prettier.

That groove is there for a reason. As your brakes contact the rim, the groove has a recording that says, "Buy Mavic, buy Mavic." This is transmitted through the frame and directly into your subconsious.

bling bling, methinks.

That groove is there for a reason. As your brakes contact the rim, the groove has a recording that says, "Buy Mavic, buy Mavic." This is transmitted through the frame and directly into your subconsious.Dang, I like that....

That groove is there for a reason. As your brakes contact the rim, the groove has a recording that says, "Buy Mavic, buy Mavic." This is transmitted through the frame and directly into your subconsious.

"subconsious" = booty?

:D :D :p

That groove is there for a reason. As your brakes contact the rim, the groove has a recording that says, "Buy Mavic, buy Mavic." This is transmitted through the frame and directly into your subconsious.
:lol: :roflmao: :lol:

That groove is there for a reason. As your brakes contact the rim, the groove has a recording that says, "Buy Mavic, buy Mavic." This is transmitted through the frame and directly into your subconsious.

I inadvertently mounted my rims backwards, now when I brake I hear "I buried Paul"

That groove is there for a reason. As your brakes contact the rim, the groove has a recording that says, "Buy Mavic, buy Mavic." This is transmitted through the frame and directly into your subconsious.

The next step is where you can send Mavic an mp3/ATRAC or tape recording of your favourite song and they'll imprint it into your rims. I hope they get the stereo and surround sound channels right between the front and rear rims.

I just got an OCR2 and noticed there's a deep groove that runs in the middle of the rim where the braking surface is?

Long story short: What is that thing?!

The groove is a wear indicator. When brakes wear away too much of the rim, tire air pressure pushes the two flanges apart and the tire blows off. Depending on when it happens, that can ve a very bad thing. As I understand it, a wear indicator for the brake surface is now required by the European version of our CPSC. Some other rims have wear indicators that look to me like somebody took a spoon and dug a chunk out of the inside of the rim extrusion.

The groove is a wear indicator. When brakes wear away too much of the rim, tire air pressure pushes the two flanges apart and the tire blows off.

That would seem like a very dangerous way to implement a wear indicator. It'd be sort of like installing a block of C4 to the bottom of a car that gets triggered when the fuel indicator hits "E".

OMG you guys are joking right?
I'm laughing my ass off at this. Especially the wear indicator comment... That's like, if your engine starts malfunctioning on the freeway, explosive bolts blow the wheels off the car to immobilize you while OnStar calls for help.

The surface is machined but the groove I'm talking about is huge, it's like 1/16" wide by about 1/32 deep. It's wide enough I can stick a dime into and half as deep and it's black. So I have a silver surface with a black ring going around it.

does it look like this?

http://www.alexrims.com/images/tech/Indicator_main.gif

It's more like the red light on the dash that says "service engine soon"

Yeah that's exactly what it looks like.
Please tell me it's not a "wear indicator"/explosive/mind control device.
The former I'm comfortable with, the latter two I'm not. How does the indicator work?

I would think that'll also allow a ridge to form on my brake pads. Meaning if one of em went out of a position for a bit and I didn't notice that now I can't re-adjust them since only that little ridge would be touching the rim.

The thing looks like it's almost 1/3rd as thick as the rim wall itself, it THAT much wears out, I'd think the thing might possibly just explode on me with 110psi when I hit a bump.

Yeah that's exactly what it looks like.
Please tell me it's not a "wear indicator"/explosive/mind control device.
The former I'm comfortable with, the latter two I'm not.

I would think that'll also allow a ridge to form on my brake pads. Meaning if one of em went out of a position for a bit and I didn't notice that now I can't re-adjust them since only that little ridge would be touching the rim.

That's exactly what my Velomax rims look like also. I believe it is a wear indicator. When you see the groove start to disappear, time to replace the rim. And don't worry, the rim isn't going to fail at the groove when it gets too thin. It will fail at the corner, like Retro said, due to the bending stress of the air pressure and bumps you hit. The groove certainly isn't there to make the rim fail!

I've seen some bike rims with the same groove- when the brake pads are rubbing against the rims to the point where the rim is worn.... and at some point, it will be time to replace the rim.

Koffee

I have a theory. It is of course the only correct theory and all other theory's of yours are BS. My theory in not based in fact, or on hard science, or even on a tarot card reading, but if you follow it well you will come to be true believers. Here it is: Like the dimples on a golf ball help it fly further, and multiple blades on a razor help get you a clean a close shave, I believe the “ring around the ring” is there for added aerodynamic efficiency. I believe that at speeds over 48 kph (at mean sea level and at 25 degrees centigrade) the ring starts to break up laminar airflow across the rim and creates a turbulence boundary condition that keeps your rims from "tip stalling." This horrible tip-stalling feature of rims can only be solved by the Hyper-Torrid Mesiostator Ring (HTMS) as they will soon become known after the evil Marketing Department of Mavic reads this. All the most modern and coolest cyclists must have this ring. Next year Mavic introduces the two-ring rim. After all the lemmings buy it the triple will be introduced. The year after that the sinusoidal triple HTMS will be introduced. Then the tour wanna bes will have to get the semi-sinusoidal unobtanium rims with kung-fu grip. Thousands of mindless roadies will solve their previously unknown tip stall problems with these super rims and go on to write federal policy banning cars now that the rims are so efficient that bike can cruise at 100 kph. Now that “rim tip-stall” is no longer a problem we will all eat granola and sup fine wheat beers delivered by cyclists hauling tractor trailers. Reexamination of past Tour-Day-France films will show that the Lance is really a pack a day Lucky Strike smoker with a beer gut, and if it were not for his rims he would be mowing lawns in Austin. It was all mind control and rims courtesy of those evil bastards at Mavic. How many times have we heard that old story? Or, it could be just a visual design thing to make the rims look cool.





Sorry. I just felt weird tonight. :)

I've seen some bike rims with the same groove- when the brake pads are rubbing against the rims to the point where the rim is worn.... and at some point, it will be time to replace the rim.

Koffee

Wouldn't that still interfere with the operation of the brake pad itself, say if the pad needs to be adjusted slightly and now the "groove" has made a nice "ridge" in your brake pad that doesn't fit in the groove anymore because I changed the angle and hilarity ensues as I try to stop from 50mph at an intersection...

Sorry. I just felt weird tonight. :)

Have you been reading http://www.theonion.com/news/index.php?i=2&n=3 ?

I have a theory. It is of course the only correct theory and all other theory's of yours are BS. My theory in not based in fact, or on hard science, or even on a tarot card reading, but if you follow it well you will come to be true believers.

This reminds me of the Monty Python Dinosaur skit.


Host: Now, Miss Elk - Anne - you have a new theory about the brontosaurus.
Elk: Could I just say, Chris, for one moment that I have a new theory about
the brontosaurus?
Host: Er... exactly. What is it?
Elk: Where?
Host: No, no, no. What is your theory?
Elk: Oh, what is my theory?
Host: Yes.
Elk: Oh what is my theory, that it is. Yes, well you may well ask, what is my
theory.
Host: (slightly impatient) I am asking.
Elk: And well you may. Yes my word you may well ask what it is, this theory
of mine. Well, this theory that I have--that is to say, which is mine--
...is mine.
Host: (more impatient) I know it's yours. What is it?
Elk: Where? Oh, what is my theory?
Host: Yes!
Elk: Oh, my theory that I have follows the lines I am about to relate.
(Coughs) Ahem. Ahem. Ahem. Ahem. Ahem. Ahem.
Host: Oh God.
Elk: Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem. Ahem.
Ahem. Ahem. [Impatient noises from Host] The Theory, by A. Elk. That's
A for Anne, it's not by a elk.
Host: Right....
Elk: This theory which belongs to me is as follows. Ahem. Ahem. This is how
it goes. Ahem. The next thing that I am about to say is my theory.
Ahem. Ready?
(Host moans)
Elk: The Theory by A. Elk brackets Miss brackets. My theory is along the
following lines.
Host: Oh God.
Elk: All brontosauruses are thin at one end, much MUCH thicker in the middle,
and then thin again at the far end. That is the theory that I have and
which is mine, and what it is too.
Host: That's it, is it?
Elk: Right, Chris.
Host: Well, Anne, this theory of yours seems to have hit the nail on the head.
Elk: And it's mine.




Sorry. I just felt weird tonight. :)

No problem... but now I'm having flashbacks to all my fluid mech classes from college. It however brought a smile to my face... perhaps because I just got back from dinner and a couple of bottles of wine. :D

Could be the rim wear indicator. When that groove is gone, it's time to replace the rims as the sides will be weaker.

Bingo.

Have you been reading http://www.theonion.com/news/index.php?i=2&n=3 ?

Did I forget to mention that Mavic was founded by that jack ass Heisenburg! I'm so weird the "ONION" reads me!

Real Answer: No, but thanks for the link. It has been months since I stopped by the Onion.