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I was recently in an accident where a car pulled out on me. I hit the car around the front wheel and me and the bike went over the bonnet and landed on the road, the other side of the car. I was travelling around 20mph.

The bike is in one piece but I'm super-wary of it.

Several people have suggested getting the fork and frame X-rayed to check for fractures. How exact is this science? How certain can you be that the frame is road-worthy?

The bike has an Aluminium frame with a carbon fork and Alloy wheels.

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  • Are there any visible fractures and can you provide a picture?
    – Ambo100
    Jul 6, 2011 at 17:43
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    What type of frame/fork are we talking about, here? Carbon Fiber, Aluminum, Steal?
    – Jack M.
    Jul 6, 2011 at 17:45
  • @Jack M. I've added details of the bike.
    – Greg B
    Jul 6, 2011 at 19:02
  • @Ambo100, The bike is still at the Police station and I haven't had a good look at it but I remember it being in one piece the last time I saw it at the road-side. I'm looking for general advice, assuming there is no visible damage.
    – Greg B
    Jul 6, 2011 at 19:03

5 Answers 5

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The easy way would be to get a qualified bike mechanic to take a look at your bike for less noticeable problems.

  • It's not safe to ride a bike if the frame has been noticeably disfigured.
  • Re-adjust the wheel to be aligned to the handlebars. The wheel tends to twist after crashes.
  • Go through the final safety inspection you would normally go through, check the tyres, brakes. Replace the brake cables if they are frayed.
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    This. Put the bike in the hands of a trusted local mechanic.
    – Stephen Touset
    Jul 6, 2011 at 19:06
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    Yes, but how can one tell if a mechanic is knowledgable in this kind of post-mortem?
    – Goodbye Stack Exchange
    Jul 6, 2011 at 19:36
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    @NeilFein: That's probably another question...
    – Ambo100
    Jul 6, 2011 at 19:46
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    @Neil Fein: you can't, but you can be pretty confident that none of them have had formal training in doing so as the only definite information I've ever got is from training providers who don't provide it :) Mostly they just check the obvious stuff, but because they see more failures than the average punter they've got a better idea what to look for.
    – Мסž
    Jul 7, 2011 at 0:18
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    @NeilFein get two or three analysis done by different bike shops. Its like medical docctors consolting with colleagues, peer review.
    – Criggie ♦
    Nov 4, 2015 at 21:42
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Sorry to hear about your accident - be prepared to take a while to physically recover even if you want to get back on the bike now.

You will have the option to chase things up with the driver's insurance company, but honesty is the best policy and you should only go for the 'write off' claim if your bike is truly mis-shapen. You also have to be aware that chasing up an insurance claim takes time and effort, time that you could be using more productively. A claim can be emotionally stressful and I personally prefer to walk away from following that avenue because an accident does not need to be re-lived, just moved on from.

As for judging whether your bike is truly pranged, straighten up the bars and go for a small, low-speed ride in a car-free area with smooth surfaces, e.g. a car-park after hours. Take your hex-wrenches with you.

Ride around and feel your bike. There may be brake levers out of place and other parts that can be adjusted back. These parts are surprisingly resilient but not totally crash-proof so inspect any parts that you need to reset. Your hands should have their own memory of where the bars were and you should know (and be able to double check) if the bars have been bent.

The wheels also survive reasonably well considering how they are constructed out of a few bits of wire and a 20mm or so wide rim. Make sure they are centered in the frame/fork properly and that they are true. If off-centre then you may have a damaged fork - double check this by taking the front-wheel out and putting it back in turned 180 degrees - if it is still off to one side then you have a sideways-bent front fork. As for the back wheel, that can be out of track, a similar process of checking is needed to determine that.

Look down your head tube and how the forks meet up. Are they parallel to the head-tube like they used to be? Is the steering more twitchy? If so then the fork could be pranged, but not necessarily, the frame could have bent instead. Examine where the top tube and down tube join the head tube - are there any bulges underneath or paint that is flaking off/wrinkled? If this is the case you have a damaged frame, damaged but not necessarily unsafe, aluminium does not catastrophically fatigue after being bent once and, although a different shape, may not be any weaker. I have ridden front-stacked frames for a long time after the incident and even preferred the added twitchy-ness.

Next you will need a bit of string. Wrap it round from the left-hand rear dropout to the head-tube and back down to the right-hand rear dropout. Now check that the seat-tube is in the centre of the two bits of string. If it is not bang-centre then you have a tracking problem - either historical or fresh from the crash.

Run through the gears and make sure you do not get any noises from the front derailleur. Check the rear derailleur is perpendicular to the ground when the bike is vertical.

With that initial inspection over you should double-check your carbon fork. Generally carbon forks are a lot stronger than their alloy/steel counterparts but they have a different failure mode.

Not all carbon forks have a carbon steerer, some can be a clumsy mess of glued together bits hidden in the head tube. Your stem is easy enough to remove, pop it off and have a look at what is going on around the lower bearing race. Give it a good clean and inspect for cracks.

X-ray scanning will not be able to detect any of the problem areas that you will be able to see for yourself in a quiet car-park with a bit of string.

For a second opinion ask at your LBS, preferably one that deals in second hand bikes. Shop staff that assess trade ins should be able to spot crash damage at fifty paces, your regular mechanic at a new-sales-only shop may not be so tuned into checking this.

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  • A great list and in the spirit of "how can I tell"
    – Joe Bronikowski
    Jul 21, 2011 at 23:06
  • I know that bicycle accidents bad enough to possibly damage the bicycle are serious and scary things. But I hope that nobody will mind if I say, as a resident of North America, that I love the word "pranged"! I've never heard it on this side of the pond.
    – rclocher3
    Nov 12, 2021 at 2:36
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While may be funny to remind, check also if the "low importance" parts are still in place and ok.

Once a car driver managed to hit my rear wheel (the mudguard over it, to be precise) while himself driving backwards. Both car and bicycle initially looked undamaged.

However the rear mudguard stay internally broke off from the mudguard blade. This was not visible being covered by the mudguard itself, a good check would require to move it by hand. After the attempt to continue the journey, the stay disengaged completely and got caught between the chain and jockey wheel, requiring significant repairs and replacements.

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    FYI, the term for what I think you mean by "holding wire" is stay, used similarly in the case of seat stay or chain stay (these are frame tubes on the bike). The holding bolt is probably better called the boss or the mount - the bolt screws into the mount.
    – Weiwen Ng
    Nov 8, 2021 at 18:11
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Should have dragged it with you in the CT scanner when you went through!

A really good set of trained eyes will do the best to inspect it.

Xray will not find tweaks, bends or stretches, which could turn into cracks later on.

If you wish to build your own bike and have expensive hardware on the crashed one, you can probably salvage a lot of non critical parts.

When in doubt get another bike, its not worth the risk.

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Always be careful about carbon fiber and collisions. Carbon fiber is light and strong, but it's very fragile and can break unexpectedly because you can't always see the cracks. In one of my collegiate mtb short track races, a guy snapped his carbon fiber handlebar at the stem after a 1' drop because the handlebar took abuse over time. When it lost all strength, the effect on the equipment was catastrophic. So in your case, if the crash was strong enough to throw you over the hood of the car to the other side, it probably messed up the carbon fork, even if you can't see it. When riding bikes, I've found the fork to be particularly useful, so certainly have the fork checked out, but be prepared to junk it for your own safety.

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