Workshop: What to watch for when buying a used carbon frame

Our 10-step guide will help stop a sweet deal from going sour

Whatever the material, there are many things to look out for when buying a second-hand bike. However, carbon has its own peculiarities that set it apart and make it trickier to assess.

In particular, there could be hidden damage from a severe impact, which may lead to a sudden failure. Unless you happen to have access to scanning equipment, you’ll have to rely on a more indirect method, along with close visual inspection.

A bit of Sherlock Holmes work will give you a feel for the situation. For example, a mismatched set of wheels, where one or other of the rims has been replaced, might give you a clue as to whether the bike was crashed or involved in a mishap. Also, ask why the current owner is selling the bike.

If you’re in doubt, have the bike checked out by a pro. Bike shop labour charges are around £35 an hour, so expect to pay anywhere from £15 upwards, because the whole process will take at least half an hour, possibly more.

Finally, make sure you’re riding the right frame size at the moment and that the intended new steed is a similar size.

How to assess a used carbon frame in 10 steps

Tools required: Measuring tape; chain checker; torch (flashlight); multi-tool; flat-head screwdriver

1 General inspection

After you’ve determined the bike is the right size for you, lift it up a few inches and allow it to drop, listening for rattles or clunking. With steel, titanium and – to a lesser degree – aluminium, any damage to the frame and fork should be apparent, but that’s not always the case with carbon. First, check the seatpost clamp area, particularly the slot. Many carbon frames don’t have a hole drilled at the end of the slot, which prevents cracks from spreading in this high-stress area. Also, check the seatpost hasn’t seized up: loosen the seat clamp and try to twist the saddle, it should move easily.

2 The frame

Closely inspect the surface of the finish. Have a look at the frame in good light, or using your torch. Sight down the tubes and look for ripples or damage – don’t buy the bike if you see cracks like those in the photo. The front derailleur mounting plate, especially if it’s riveted or bonded, needs to be inspected closely. Bluish-white powdery deposits are sure signs of corrosion and will cause the mounts to break off. Then grab the end of the cage on the front mech and give it a tug – you shouldn’t feel more than 3mm of play. Inspect the top and down tubes for damage from roof and boot racks.

3 Steerer and headset

Do your homework and check how closely the current spec matches the original. If the fork or front wheel have been replaced, ask why. Don’t buy the bike if it’s due to a crash. Check the carbon steerer for damage at the stem clamping point and then ensure the headset doesn’t suffer from a case of steering indexing syndrome (SIS). To do this, lift the front wheel up and allow the bars to swing from side to side: they shouldn’t stop in the centre. If you can, drop the fork out and check the steerer and crown for corrosion. Then check the dropouts for the level of wear caused by the quick release heads.

4 Attachments/rivets

Check all attachments to the frame: bottle rivets, cable stops on both the top tube and rear derailleur, and down tube cable guides, which are often located in a critically stressed area a couple of inches from the head tube. Have a look at the chain suck zone – the area between the chainstay and the small ring. There should be a plastic or metal plate. If there isn’t, ensure this area isn’t gouged. A few surface scratches of the lacquer are okay – they can be touched up with model enamel. Ask for permission to scrape away some paint in badly corroded areas to ensure it’s only skin deep.

5 Bonding zones

Joining methods vary depending on frame design. Even monocoque designs incorporate bonded, riveted or bolted metal elements. Check locations where the carbon or aluminium tubes are bonded into their joints. The combination of dissimilar materials (carbon/aluminium) and an electrolyte (salty road spray) combine to create what is, in essence, a big battery. This can produce galvanic corrosion. A little oxidation or peeling finish is okay, but be wary of large gaps or thick bubbling of paint. Besides the dropouts, check around the bottom bracket and just below the headset cups.

6 Contact points

Contact points are a potential minefield from a safety standpoint. With carbon bars or seatposts, check for the same signs of stress as in Step 2. With aluminium components under normal conditions, a maximum of five years’ use should be allowed for parts under stress, particularly the bar and stem. Under racing conditions, shorten that to two. Don’t risk injury by accepting a bike with parts used for any longer. Now open up the clamp and look for heavily worn spots or grooves, identifiable by worn anodising and exposed raw aluminium. Look for signs of crash damage, such as scrapes on the brake levers, bar ends, saddle edges and rear derailleur. Consider replacement and its cost if you’re in doubt.

7 The wheels

Important for the overall performance of the bike, and crucial for controlling costs, the wheels and tyres need to be true and in good shape, so check for oxidation and cracks at spoke holes on the rim and hub. Also, ensure worn pads haven’t been allowed to score the braking surfaces. Give the wheels a spin and eyeball the gap between the brake pads. A slight out of true of about 1mm or so is okay if it’s gradual and occurs evenly. If it’s intermittent or occurs at a different spot on each revolution then this is a sign of bearing wear, which usually means at least a hub service and often a new wheel. Equally, a rumbling sensation felt in the fork leg or tip is a sure sign of dry or worn bearings.

8 Drivetrain

Now use your handy chain checker to detect any chain wear. If you don’t have a tool to hand, simply lift the chain away from the large chainring as shown. It shouldn’t lift past about two thirds of the way above the valley between the teeth, or you’ll need to replace it. Also, the tooth profile should be even on both sides and the forward edge not hooked. Cranks have a way of breaking at the worst possible time, so check the inside of the crank arms at the point where the specs (arm length, brand and so on) are etched or engraved, since these can lead to cracks. Inspect the pedal thread size engraved near the pedal threads and for gouges caused by a lack of pedal washers as well.

9 Cabling and controls

Inspect the cables in the area pictured below: this is the most frequent spot for fraying and splitting. Now squeeze the brakes and check that they snap back quickly and freely. Give them a firm tug right to the bars to confirm anchor bolts are working well and the cables aren’t frayed and about to fail. With derailleurs and brakes, check for pivot and joint wear or sloppiness in the bushings. Grab the rear mech by the lower end of the cage and move it in and out towards the wheel. It shouldn’t feel too baggy, with the combined play in the top and middle pivot along with the parallelogram bushings adding no more than about 2 or 3mm of deflection, (not to be confused with flex in the material).

10 Test ride

Before your test ride, grab the bars and twist firmly. No cracking or creaking noises should be heard and it should feel firm(ish), offering slight resistance to twisting. Then lock down quick-releases and find a safe, car-free area. Try riding with your hands off the bars to see if the bike tracks straight. Stand on the pedals and put a bit of muscle into it while swinging the bike left to right – there should be no cracking or crunching noises. Test the brakes and try to lock the rear wheel just a bit. Now get a bit of speed going and see if there’s a wobble, caused by damaged tyre or out of true wheel. If you’ve decided it rides well, make an offer well below the asking price and let the haggling begin!

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