STRINGING THE FRAME SET

Believe it or not, with these few tools, coupled with a bit of understanding and a tape measure, a frame set can be checked for straightness and, in some cases, even repaired.  Though some of the frame straightening/inspecting tools look to be pretty crude, they do the job.  Most people will have immediate access to a string and a ruler.  That is all that is needed to check to see if the frame set is straight.  There is, of course, a great deal more to checking if a frame set's structural integrity but these simple tools will help the average person get a feel for the frame's condition.

Be warned, this test in by no means accurate if the drops are not parallel to one another.

Simply put, a string is secured on one rear drop, run around the head tube and secured again to the opposite rear drop, mirroring the attachment point of the first.  Since I measure quite a few frame sets each year, I found that it was easiest if I don't actually tie the string at any point.  Knots could throw the mirror position off a wee bit and this whole process is already crude enough.

Once the string is secured to the left drop, run the string up and around the head tube.  I will be taking more than one set of measurements when checking the frame set.  One set of measurements are taken with the string at the top of the head tube.  The second set, with the string at the bottom.  Any differences in these two sets of measurements will indicate problems forward of the stays, suggesting misalignment in the main tubes. Correcting misalignment of the main tubes is beyond the scope of this procedure.

With the string tautly strung around the bottom of the head tube, measure the gap between the strings and the seat tube on each side of the seat tube.  The measurement for each side will be pretty close to equal if the frame set is straight but that doesn't matter at this point.  Now, move the string to the top of the head tube and measure again.  If these two sets of initial measurements are not the same, it means that the head tube and the seat tube are not in line with each other.  Or, put another way, the main tubes are bent and beyond the scope of this repair.  I should add that it is infrequent that I run up against a frame set with bent main tubes.  Most alignment problems are associated with the stays and rear drops.

If satisfied that there is no misalignment in the main tubes, move you attention to the stays.  Measure the distance from the seat tube to the string.  Repeat this measurement on the other side of the seat tube.  Compare these two measurements.  If they are the same, the stays are probably in alignment with the center line of the frame.  If the measurements differ by more than a millimetre, chances are the chain and seat stays will need a bit of tweaking.  In fact, any difference in the two measurements should be eliminated by "cold setting" the stays.  "Cold setting" is a fancy term for bending, in case you are interested.

The measurements for this old frame set are not the same, suggesting that the frame set is bent somewhere.  Based on the gaps measured, 129mm on the left and 131mm on the right, the diagnosis would be that the stays are bent towards the right side of the bicycle.  Of course, the question that comes to mind is what to do with this frame and fork set.  Can it be straightened and is it worth straightening?  In my opinion the damage is minor and I will attempt to straighten the set.

The measured difference between the left and right side is two millimetres.  But the actual misalignment will only be half of that amount, or one millimetre.  To me this is a repair that seems reasonable to attempt.  I should add, based on my experience with quite a few vintage road bicycle frame sets, this sort of misalignment with the seat and chain stays is very common.  Few bicycles that I find are perfectly straight.  If the misalignment is minor, I take a shot at repairing the damage.

NEXT - CENTERING THE STAYS