hhk25

I’m tuning a friend’s bike and I notice a hop in the front wheel. I put the wheel on a truing stand and I noticed this piece of metal embedded in the rim exactly where the hop is. Someone marked it in the past with sharpie.

Obviously it’s going to cause premature pad wear but it’s a cheap bike for a casual cyclist. I don’t want my friend to spend money unnecessarily but I’m concerned it’s a safety issue. Perhaps the integrity of the rim is compromised.

Thoughts?

bblair

It looks to me as though the wall of the rim has worn so thin that a small piece has begun to break off.

Don't think he should ride this.

rm -rf

"a hop in the front wheel": I'm not sure what you saw.
I think of a "hop" when the tire tread has a bulge or other high spot, or the bead isn't evenly seated, causing a low spot.

Is this braking pulsing, or is it an out of round wheel or tire?

What is that on the braking track? My first thought was a nail embedded in the rim, but how would it get stuck right there? Take off the tire and look at the inside of the rim.

EDIT -- from the previous comment: a worn rim? Now I'm noticing the braking track has evenly spaced grooves. Those aren't wear indicator grooves, but I think they are too consistent to be grooves from bits of metal stuck in the brake rubber.

FBinNY 

That it's at the hop is pure coincidence. And there's no safety issue. IMO you have two choices.

1. Use a file or sand paper to smooth it flush with the surface.

2. Ignore it and let normal brake use smooth it out.

mpetry912 

that sidewall looks pretty badly scored.

here in the Pac NW we have seen the black crud from winter riding become an abrasive and wear thru rim sidewalls over several seasons.

I know of at least on rim that failed, blew apart.

But in this case, just try to knock that peice out, true the rim, keep riding it

/markp

hhk25

Those are actually two grooves that are machined into the rim, maybe for water evacuation. Rim does not appear badly worn. I’m going to remove the tire and see what’s going on. Will report back.

FBinNY 

The grooves are brake track wear indicators. When they disappear, the rim has reached the wear limit and needs to be replaced.

smd4

Rim looks like it took a pretty good pothole or curb blow at that location. Seems flat. I vote for filing too.

Iride01 

Why would it be unsafe? What catastrophe are you imagining?

The braking surface on the rim does look funny in the picture. So that would be more of a concern to me. But the picture might just be at the wrong angle, lighting and depth of field to tell anything for certain.

I might try to flick that imbedded looking chunk of metal out with a sharp pointed pick. But I might also find that it's part of the braking surface that wore thin and crumpled up. But if the bike brakes well for the moment and that chunk isn't felt, I might not be in too big a hurry to replace it depending on what I'm going to use the bike for.

Kontact

Completely disagree.

I have seen this before - the rim takes vertical hit, the rim bulges out into the brake track, then the brake pads wear down the high spot. Eventually the super thin aluminum gets brittle (work hardening from the impact and heat) and a chunk falls out.

If you take off the tire you are likely to find that the inner width is wider at that spot and that there is a tiny hole shining through.


And even if I am wrong, the tire and possibly rim tape needs to be pulled off to at least inspect that area. If this is what I think it is, it's going to fail during a fast descent where there is a lot of braking friction and the air pressure in the tube has gone up from the heat, and then it will jam in the caliper locking up the wheel at 40mph.

hhk25

Pretty much what the comment below you said. I’ve experienced front wheel failure at speed and I wouldn’t want to wish it on anyone.

Kai Winters

I agree with two of the posters who say it has taken a blow and the 'hop' is really a 'flat spot' on the rim.
IMO it is time to replace the rim...just in case...or ride it as it is and hope for the best...

FBinNY 

FWIW --- An alternate theory.

It might be my age, but I don't see any kind of rim dent deep enough to account for the artifact. Also, the OP said hop, not dip, so I'm thinking high spot, but either way it really doesn't matter.

As for the artifact --- I believe it to be a terminal burr, caused when (possibly) a stone got embedded in the brake shoe and gouged the rim.

To understand, imagine dragging a stick in the dirt. You'll make a groove and push dirt ahead leaving a small mound where you stop.

So, the stone left a small burr where the wheel stopped, or vwhere the stone was finally ejected, then future braking smoothed it over.

So, IMO, the issue isn't the burr or dent(?), but the groove itself. How much it matters depends on its depth, along with other factors.

From what I can see, it seems OK, but the OP might seek an opinion from someone who can properly assess the depth.

As I said, it's only a theory based on what I saw, but it is consistent with what I've observed on many scored rims.

Kontact

That may well be what happened, but I don't know why you would presume it can't be a safety issue.

The right thing to do is look inside the rim.

mpetry912 

Like wear bars on a tire ! so I guess that rim has lots of miles left in it

/markp

Bill Kapaun

File/scrape it off.
The tire will likely handle the slight dip in the rim.

BTW, look exactly opposite of the valve stem.
See the rim joint with a slight dip?

Kontact

Don't know what you're seeing. The damage is over a spoke hole, not between them.

Crankycrank

Seems to me measuring the brake track thickness is a good idea to at least rule it out if it's fine. If OK just sand or file it down as has been mentioned. It does look like a small dent from an impact and if when you say "hop" in the wheel are you just saying you can see the bulge in the truing stand or does it actually have a vertical hop when rotating?

Bill Kapaun

I agree. You don't know.
I didn't say I saw anything.
Read what I'm writing.

Kontact

You are using the word "look", but not at anything you can "see". Thank you for the brusque correction.

I don't think anyone, including the OP, actually is concerned with the flat spot's effect on the tire. Which is why I didn't follow why you were talking about other potential flat spots.

smd4

He’s suggesting that most rims have slight flat spots where they’re joined.

Bill Kapaun

I wasn't talking to you in the first place, but as usual, you have to insert yourself to apparently up your post count.
That's why you have been on my ignore list for years.
Back to totally ignoring you for 5 more.

Kontact

You didn't address anyone specifically.

I don't know what my post count is. I participate on this forum because I enjoy bikes and helping people with mechanical problems.

I won't ignore your posts when you make illogical or unsafe suggestions, but that's fine if you don't want to reply to such posts. Bye!

FBinNY 

Looking inside the rim won't tell you anything about the depth of a gouge on the outside.

My earlier belief that it's not a safety issue was based on a tiny cell phone image where the groove wasn't as visible, along with the OP asking about the burr(?), without mentioning the gouge.

However, as I said in the post you referenced,-----

From what I can see, it seems OK, but the OP might seek an opinion from someone who can properly assess the depth.

Kontact

Again, I have to disagree. You can't assess the remaining thickness of a possibly bulged rim without looking at the inside of the bulge.

And you may see the inside of the damage seen on the outside.