Originally Posted by bccycleguy
I've been entering the details of my Lemond Sarthe frame (hand built, TIG welding in the USA) into the on line version of BikeCAD and have been surprised at both the difficulty and frustration in reconciling the differences between the published geometry/specs and what I am able to measure.
I don't know anyone's background here, but just being logical about it, if you're comparing your measurements with published specs and they don't agree there several possible explanations:
1. The published specs are disingenuous, i.e. not seriously representing the product, aka, just not valid.
2. The frames are not built to match a valid spec, either due to loose QC, or it's just the way they do it.
3. The measurement technique or instruments are not capable of adequate accuracy to be compared to the published specs.
I've tried very hard to measure bike frames, and I don't think it's easy to be accurate and consistent. Can you measure the same bike several times and come up with exactly the same results (I usually can't, BTW)? If not, your technique is not consistent (after all, the frame didn't just shrink 2 mm). And if it's not consistent, how can you say its not your fault if your numbers do not match those of the bike company?
If it is consistent, how did you test if it was accurate?
I come at this from an engineering background, not a frame builder's background. I've found I don't measure consistently, so I know this problem can be real. For me, accuracy is not the issue, since I'm not even consistent.