What's wrong with my wheel? Thumping feel when braking (Possibly resolved)

[makoti]

I thought it was the rim, but it looks true and is smooth on the brake track. No obvious seam issue. Ok, thought maybe it was my brake pads so I swapped them over to another bike. It was unrideable on that bike. Thumped, shimmied, and grabbed with that brakeset. I don't feel any unusual play in the hub. Front wheel, if that makes any difference.
WI hubs (Campy)
Pacenti rims

[AngryScientist]

Originally Posted by makoti

but it looks true

Do you have access to a truing stand? I think the first step has to be actually checking true/round...

If you were local, I'd be happy to look at it for you.

Edit: A lot of Pacenti rims (though usually pre forza) had cracking issues. Take a close look at all your nipple holes, etc to see if you can spot anything...

[makoti]

Originally Posted by AngryScientist

Do you have access to a truing stand? I think the first step has to be actually checking true/round...

If you were local, I'd be happy to look at it for you.

Edit: A lot of Pacenti rims (though usually pre forza) had cracking issues. Take a close look at all your nipple holes, etc to see if you can spot anything...

Good call. These are Forza, bt I'll take a look at that. I'll toss it in my turning stand, but for this kind of action, it would almost have to be visibly out of true.

[thwart]

In the old days I would wonder if you had some Accelerade dried on the rim.

Do they still sell that stuff?

[raven]

Not 100% sure based on your description, but is there any chance your tire isn't seated perfectly on the rim or has a high spot? If so, it could be the tire hitting under the fork crown.

[chismog]

First thought would be broken or loose spoke, but you said the rim looks true.

Look/feel for a bent spot on the rim, maybe just one side? Sometimes you'll see extra brake pad residue at the problem point on the brake track as well.

[tv_vt]

Originally Posted by raven

Not 100% sure based on your description, but is there any chance your tire isn't seated perfectly on the rim or has a high spot? If so, it could be the tire hitting under the fork crown.

My thought, too.

[Tandem Rider]

A "flat spot" caused by hitting something hard and making a slight dent into the rim will cause the rim to actually be slightly wider at that spot than the rest of the rim. This will cause braking to be unnerving, especially if it's the front wheel. Can you try another front wheel on the bike to test? Often taking off the tire and looking closely at the rim in a truing stand will help you spot the issue.

[oldpotatoe]

Originally Posted by Tandem Rider

A "flat spot" caused by hitting something hard and making a slight dent into the rim will cause the rim to actually be slightly wider at that spot than the rest of the rim. This will cause braking to be unnerving, especially if it's the front wheel. Can you try another front wheel on the bike to test? Often taking off the tire and looking closely at the rim in a truing stand will help you spot the issue.

OR, if the rim is really old, a portion of the sidewall may be separating/bulging due to the tire pressure.

[makoti]

So I took it to the shop. He looked it over. Cleaned the rim real nice, adjusted the hub, said the tire was old enough to be starting to dry rot, and he thought there might be too much sealant in it, but nothing seemed to point to a reason for the thumping. I took it home, and the thumping continued. I decided to drain a little of the sealant out, just in case that was a weird reason for it.

As I did and was cracking the bead to drain it, I felt something firm in the tire. INSIDE the tire. If it was alive, I'd have thought it had a tumor. Well, it kind of did.

You couldn't tell to ride it. It gave enough that the wheel ran smoothly, No hop every rotation. 67g of old sealant. I pulled another wheel, about the same age as this one, and only got 22g of old sealant out of that one. My guess is the tire had been on for maybe 2 years. Front, so didn't wear as quickly as it would have on the back. Never flatted, so never needed to pull it before this.

[Mark McM]

Originally Posted by makoti

As I did and was cracking the bead to drain it, I felt something firm in the tire. INSIDE the tire. If it was alive, I'd have thought it had a tumor. Well, it kind of did.

You couldn't tell to ride it. It gave enough that the wheel ran smoothly, No hop every rotation. 67g of old sealant. I pulled another wheel, about the same age as this one, and only got 22g of old sealant out of that one. My guess is the tire had been on for maybe 2 years. Front, so didn't wear as quickly as it would have on the back. Never flatted, so never needed to pull it before this.

But that doesn't explain why you only felt the thumping while braking. Unless somehow the excess dried sealant cause the tire to bulge out a bit, causing it to rub against the brake (pad or arm).

[makoti]

Originally Posted by Mark McM

But that doesn't explain why you only felt the thumping while braking. Unless somehow the excess dried sealant cause the tire to bulge out a bit, causing it to rub against the brake (pad or arm).

I'm guessing that the weight in one spot caused the forces of braking (don't ask me what they technically are) to be thrown all off kilter, and possibly it did bulge a little under the braking forces. Not sure. I did say "possibly", since I haven't remounted the tire and it going to be raining for the next 3 days, so it'll be a bit before I can verify.
It quite possibly could turn out to be an incidental finding

[Peter P.]

"It is not a toomah!"

Yet another reason to use tubes.

[thwart]

Originally Posted by peter p.

"it is not a toomah!"

yet another reason to use tubes.

+1000.

[redir]

I used to put sealant in my tubular tires and stopped doing it for that very reason.

It looks like a snake shed its skin.