Bicycle Mechanics - Can a bent rim cause tire failure?

Hello everyone,

Thanks for taking a look. Here's my question:

The wheel (without a tire mounted) was accidently dropped onto concrete from a height of 6'. This caused a very slight flattening of the rim at the point of impact, measuring a half inch at most. Otherwise, the wheel is round and true, according to the truing stand. The flat part is barely noticeable by eye, but can be felt by hand, and is obvious on the truing stand.

Mounting the same maxxis tire on this rim at ~110 psi resulted in the tire bead coming off the rim while riding. The second time it happened, it resulted in a KABOOM, shredding the bead and the tube. The rubber around the bead exploded, revealing the threads. I am confident that the tube was not pinched and the tire was seated correctly, as best as i can tell. Running a Continental tire on the same wheel at ~80psi caused no problems on a flat 50 mile ride.

My question: Is the slight bend in the rim causing tire failure at high pressures, or was the failure the result of a defective tire?

Thanks for your insight in advance.

My question: Is the slight bend in the rim causing tire failure at high pressures, or was the failure the result of a defective tire?

A half inch flat spot isn't a slight bend. That's a major bend. It can certainly cause a tire blow off. You need a new rim.

Yes that could cause the tire to blow, and I would never have mounted a tire on that wheel after such an incident.

I would love to hear the story on how a wheel was dropped about 6' though!

Booooo. :)

so no chance for repair? a new rim is the only option?

Yes, the rim is toast. Now on with the story.

Yes that could cause the tire to blow, and I would never have mounted a tire on that wheel after such an incident.

I would love to hear the story on how a wheel was dropped about 6' though!

The wheel was hanging from a nail while i worked on the bike. Bumped into it, and KABOOOONK onto the floor. I was soooo bummed. I was hoping that it was still rideable. It seems like at low pressures its ok, but that's no real solution.

Yes, the rim is toast. Now on with the story.

all right all right, the real story is that i got a flat in a bad part of town. I pulled over, stupidly, next to a run down house with a black mongrel, part lab, part newfoundland, all mean, drooling, barking, madness in it's eyes. I squatted down and removed the wheel while noting the thin chain that attached to a spiked collar around the beasts neck--the midevil torture device kind with the sharp teeth that dig in with each pull. suddenly, the chain snapped, the beast leaped over the wobbly chain linked fence straight for the neck. Like Atreyu from Neverending story, I reacted, swung the wheel at the devil hound and caught him square on the snarling incisor. I snapped his tooth in half and he retreated with a yelp. I ended up with a slightly bent rim.

all right all right, the real story is that i got a flat in a bad part of town. I pulled over, stupidly, next to a run down house with a black mongrel, part lab, part newfoundland, all mean, drooling, barking, madness in it's eyes. I squatted down and removed the wheel while noting the thin chain that attached to a spiked collar around the beasts neck--the midevil torture device kind with the sharp teeth that dig in with each pull. suddenly, the chain snapped, the beast leaped over the wobbly chain linked fence straight for the neck. Like Atreyu from Neverending story, I reacted, swung the wheel at the devil hound and caught him square on the snarling incisor. I snapped his tooth in half and he retreated with a yelp. I ended up with a slightly bent rim.

I love it!

I don't know how old you are but I'm personally inviting you to post in 50+. Whatever you lack in age you more than make up with your ability to tell colorful lies. That, after all, is what 50+ is all about.

thanks for the invite RetroGrouch. Glad you liked the story, I'll check 50+ out (i have some ways to go before i reach your ironman stats. Awesome :thumb:).

So i'd like to keep my original hubs. Is the thing to do to order a new rim and have a shop build it? should i get new spokes as well? I could try building it myself, but i've never done that, and i don't have a way to measure spoke tension. How much should a wheel build cost?
thanks again!

So i'd like to keep my original hubs. Is the thing to do to order a new rim and have a shop build it? should i get new spokes as well? I could try building it myself, but i've never done that, and i don't have a way to measure spoke tension. How much should a wheel build cost?
thanks again!

Unless your new rim is a near duplicate of the one that you have, your existing spokes won't be the right length. If you're paying somebody else to do the work, they'll want to cut the old spokes off because it's so much faster than de-constructing the old wheel and cleaning up the old spokes.

Building a wheel is about an hour's work so figure $50.00 labor plus $32.00 for spokes plus whatever your rim costs. Honestly, it's usually cheaper to buy a prebuilt wheel. That's how new bikes come equipped.

The second story was much better. Yes, you can order the same rim and swap it over, but as mentioned, it might be cheaper to buy a prebuilt wheel.

have the widths of the front hubs changed in the last 25 or so years?

this is a Saturne rim with a specialized hub from the mid to late 80's, i think...

have the widths of the front hubs changed in the last 25 or so years?

this is a Saturne rim with a specialized hub from the mid to late 80's, i think...

Modern road front wheels are 100 mm across the fork dropouts. Try measuring yours, probably the same.

Al

is that from the inside to inside or outside-outside?
ie. inside the fork blade or outside?

inside to inside

A little after the fact, but did the tire fail at the bad spot of the rim?
You do mount the tire label at the valve hole, don't you?

Take it to a local wheel builder. They can check the rim to see if the "flat" spot isn't just the rim slightly flared out. That can be fixed using a cresent wrench and carefully bending the flared out rim back into position. Also, a good builder will be able to use some jigging with the spoke tension and straighten out a flat spot somewhat. Give it a shot and make sure the person is a long time wheel builder and not a local wrench who has limited experience. Good luck.

As a wheel builder, I would never do that. It would mean the wheel will come out of true more often, run a greater risk of spoke breakage, and possibly even lead to an accident should the tire come off while moving. Just saying that I wouldn't take on the liability.

I am not a wheel builder. I reader on some post where they used the wheel building calculator database of rim diameters to find a new rim for the old hub and spokes that was effictively the same size as the old rim. They then taped the rims togehter and transfered the spokes. Then they took it to be tensioned and trued. It struck me as a good method for a newbie in need.
Eric

Whatever you lack in age you more than make up with your ability to tell colorful lies. That, after all, is what 50+ is all about.

Truer words were never spoken!

The older I get, the better I used to be!

I've straightened rims out with a wrench and judicious use of "Dr Hammer" before - and wouldn't recommend it! Buy a complete new or used wheel for peace of mind!

consider the usage of the 2 tools attached in pictures. If you want it easy and cheap, just buy a new wheel.:thumb:

You keep the dog's tooth around your neck, right? And it prevents crashes , but for its one weakness: Deep Vs with Andre the Giant spoke cards?

Unless your new rim is a near duplicate of the one that you have, your existing spokes won't be the right length.

That's correct. As I build (and repair) more wheels, I'm learning that certain components allow greater margin of error than others. For example, deeper, double wall rims can safely tolerate some spoke threads clearing the top of the nipple. There's a valid concern that you can bottom out the threads before reaching the desired tension - so what I've done is have an LBS with a Phil Wood spoke machine roll an extra 5mm of threading. This has saved me a few bucks and made some otherwise tricky repair scenarios possible.

Also, in a pinch I have laced a front wheel 2x instead of 3x to make use of shorter spokes that I had on hand. None of these suggestions are optimal, but they can be useful improvisations.

Dude, that is hilarious!! you have me cracking up!

:roflmao2:

honestly, the flat spot is so small that these tools might not be of use (but i have no way of knowing). The impact (with the hound's tooth, of course) was such that it caused a slight flattening of the rim surface, and also, perhaps, a slight bend of the rim outward. Regardless, thank you everyone for all your help. New rim and hub are on the way! i could have gone a little cheap but decided instead on a mid grade mavic open pro and campy veloce hub. Thank you again everyone!