Originally Posted by
dglevy
Hi all, I have a friend who is looking at a 2003 steel framed bike to purchase. The description looks good. If the bike is still available, we are going to go look at it tomorrow. I will inspect the frame for cracks, of course, but I'm wondering how to check to see if it's bent. I found
this thread on BF. The consensus is to measure both sides with string but I don't want to get into that if I can avoid it. One comment was that one can ride the bike with no hands on the handlebars and, if it won't track straight, then the frame is bent. Is this a reliable measure?
do the string thing. Measurement is minimal, so it’s really quick. Tie the string to the rear dropout on one side, loop it around the head tube and tie it off taut to the other dropout. Compare the distance between the string and the seat tube on both sides (this is the measuring part). If the string is the same distance on each side, you’re good. If they differ by more than 1-2 mm (I’m using this as the limit of resolution of a quick&dirty measurement), there’s something up. You could also bring a sharpie and mark the string at a specific point wrt the frame on each side, and also at the midpoint on the head tube. Remove the string, bend it in two at the head tube mark, and the other two marks should line up. Again, more than a few mm out and there’s a possible problem. This might sound like a faff, but it’s basic due diligence when buying a used bike.