A good lugged steel frame can outlast its first owner by decades. When one does fail, it's usually at a joint, or from rust inside a tube that no one looked at. You can catch most of it from good photos, and the rest on the day it arrives.
Why the joints are where it happens
On a lugged frame, the tubes slide into steel sockets called lugs and are brazed in place. The joints carry the most stress, they were heated during building, and the edge of each lug is where a stiff joint meets a thinner tube. Water also collects at joints and in the bottom bracket shell. So cracks and rust tend to start at the same handful of places on almost every frame, whoever built it.
What a crack looks like in a photo is a thin line in the paint that follows the edge of a lug or runs across a tube, often with a rust stain running from it. A crack in the paint can be just paint, so treat a fine line as a reason to ask for a closer photo. A line with rust weeping out of it is more serious.
The seat cluster
The seat lug holds the top tube, seat tube and seat stays, and it takes the seat binder bolt. Look at the binder ears for cracks around the bolt, and at the slot behind the seatpost. Rain runs down an open seat tube into the bottom bracket, and rust often starts here first.
Ask the seller whether the seatpost moves. A seized post is common on old bikes. It can usually be freed, but it's work, and forcing it can damage the frame.
Aluminium frames have their own version of this. On the bonded aluminium Vitus 979, the seat lug ears around the binder bolt cracked often enough that Vitus redesigned the lug in 1985.
The head tube and the front of the frame
Look behind the head tube, on the underside of the down tube and the top tube. Ripples or a kink in the paint there are the classic sign of a front-end crash. The fork takes the hit and the force bends the tubes just behind the head lugs. Look at the fork from the side too. Its blades should curve smoothly forward. A fork that's straighter than its partner, or bent back, has been hit.
Check the head lugs themselves for cracks along the edges, and ask whether the headset turns smoothly. A notch at center can be a worn headset, which is an easy fix, or a sign of a hard impact.
The bottom bracket shell and chainstays
The bottom bracket shell is where the down tube, seat tube and chainstays meet, and it takes your full pedaling load. It's also where water ends up. Ask for a photo from underneath. Look for cracks along the lug edges, rust around the drain hole if there is one, and rust stains around the cups.
Follow the chainstays back from the shell. The chainstay bridge, the short tube between them, is a spot where small cracks and rust can start. The drive-side chainstay also takes knocks from a dropped chain, so chips and gouges there are common. Most are cosmetic, but a deep gouge is a weak spot.
The rear dropouts
The rear dropouts hold the wheel and the rear derailleur. Look at where the stays meet each dropout for cracks in the braze. Check that the derailleur hanger isn't bent. A bent hanger makes the derailleur hang crooked, and while it can usually be straightened, a crack there is a bigger problem. Ask the seller to look down the rear of the bike from behind. The derailleur's pulleys should sit in line with the cogs above them.
Rust inside the tubes
Rust you can see on the outside is easy to judge. The rust that matters most is inside, where you can't see it. Take the seatpost out on arrival and shine a flashlight down the seat tube. A little surface rust is normal. Thick flaky rust, or rust water running out, means a frame that sat wet for a long time. Pull the bottom bracket during the tune-up and look up the down tube and seat tube from below. A frame saver spray inside after cleaning helps it last.
Repaints
A fresh repaint can cover cracks, filler and rust. Plenty of repainted frames are sound, but a repaint earns a few more questions. Who painted it, was it stripped first, and are there photos from before? A shop that blasted the frame to bare steel will have seen any cracks. A spray job over old paint shows nothing. See our eBay red flags guide for how to spot a repaint that's sold as original paint.
Checking alignment
A frame can be crack-free and still bent. You can check the rear triangle with a piece of string. Run it from one rear dropout, around the head tube, and back to the other dropout. Then measure from the string to the seat tube on each side. The two gaps should match. If they don't, the rear triangle is off center and the bike won't track straight.
Check that the rear dropouts are parallel too, especially after a crash or if someone has spread the frame for a wider hub. A good framebuilder can cold set a steel frame back into line. Don't try this on aluminium or carbon. Our wheel guide covers spacing and cold setting in more detail.
On a test ride, a straight bike will roll hands-free in a straight line on a flat, quiet road. One that pulls to the side, with the wheels true and centered, may be out of line.
Where the bikes we cover need a closer look
Every frame has its own weak spots. Sheldon Brown's own Raleigh Professional frame came to him cracked between the seat tube and the down tube, which is why the bottom bracket shell earns a close photo on any bike. Chrome needs its own look. The Peugeot PY-10 has a chromed fork crown, fork ends and rear stays, and rust that starts under chrome is hard to fix. Thin tubing dents easily. The Colnago Mexico is built from very thin Columbus Record, so ask for raking-light photos of the top tube and down tube. And on a lugless frame like the Peugeot P8, there are no lug edges to read, so look for cracked paint at each joint instead.
A quick photo checklist
- Seat lug and binder ears, close up.
- Both head lugs, and the tubes just behind them from the side and from below.
- The fork from the side.
- The bottom bracket shell from underneath.
- The chainstay bridge and both chainstays.
- Both rear dropouts and the derailleur hanger.
- A note on whether the seatpost and stem move.
If the seller sends all of that and it looks clean, you're buying a frame you can trust. Browse our catalog for the frame-check notes on each model, and see the Reynolds 531 and Columbus SL pages for how those tubes were built.