majmt 

In your first photo, it looks like you position the rear hub at the forward end of the dropout in your frame device. That’s the way my Masi was set up below. Is that the normal design position? If I recall correctly, there were comments earlier in this thread suggesting moving the hub further into the dropout. Seems like that would slope the frame back a bit. Just curious if it matters much in your opinion.

repechage

I own a slew of these, some from new, others with original paint.
the into the shipping box configuration was axle all the way forward, slight adjustment as required to center the rear wheel.
note that the filing of the dropout was an uncontrolled surface. Judgement.

John Barron had an unboxing image set of a NOS Italian GC that showed the rear wheel all the way forward. If you wanted to run a 28t cog you might need to pull it back depending on the small cog and large chainring teeth count.

Road Fan

Actually I don’t think any of the tools I use have to be digital. I’ve used roof angle gauges ($10.00 at Ace Hardware a few years ago, and i can make the differential measurements I mentioned with a metric scale - also about $10 from Ace. And if one purchased a digital caliper at Harbor Freight those are or were in the $29 range.

Is TT slope a real problem? I think it depends how you measure angle. If you measure with a mechanical angle finder, the pointer on its scale is read with respect to a weighted pointer, where the weight is responding to the position of the center of the earth, not the angle of a top tube. So if I read 73 degrees with respect to a force vector always pointing at the center of the earth. Similarly for a digital angle finder such as a Wixie or a carpentry app downloaded to an iPhone. In the electronic case a chip uses a laser-based gyro function to maintain a reference of “up.” For a digital protractor where you move a pair of arms from parallel to represent the angle between two objects, there the reading could be affected by the TT angle, at least if the protractor does not also contain a laser-based gyro to allow the software or firmware to compensate that error.

One could address the TT slope possibility by checking it before removing the fork. One can put a set of good wheels with matching inflated tires on the bike and stand the frame on the floor. Measure the angle of the floor (I learned a decent method from my house inspector when he verified the runoff draining pitch of my driveway), then the height of the front of the TT and rear of the TT respectively from the floor represents the amount of slope. If you know your trigonometry you can calculate the angle of the TT. Write down those numbers, because you will need them to combine with the measured head tube angle from TT to get the actual head tube angle to the horizontal. I guess it does get a little convoluted, but this is how real-world measurement can work out. Every engineering project I’ve been involved in has this sort of detailed work when you are trying to measure real parts on real systems, such as automobile radar sensors on cars or trucks, solar array pivot locations on space satellite mockups, and instrument installation details on particle physics instrumentation. Same for frame elements for bicycles. In this case after I measure the TT slope, I still have to pull the fork and follow my first procedure to measure the fork offset.

If it’s too convoluted for you, find a different method to get the data you might want. That’s the reality. I find this kind of approach works, you just have to take pains to be consistent.

But how big is the error introduced by the sloping TT? Let’s assume the TT end point at the front is 10 mm higher than the endpoint at the rear, and the length of the actual TT is 55 cm. Let the angle from the TT center to horizontal be called alpha. If you solve the resulting right triangle, the angle of the TT is the arc sine of 10/550, which is 1.04 degrees It’s not a lot, though it is critical to building a frame to the precision it needs. But I think the effect of that error on the riding properties due to trail is most likely negligible.

But I’m not giving mitering instructions to a master frame builder. I’m not going to build a frame anytime soon, so I don’t have to worry about that, though it is truly an error. It’s just that for my purposes, I believe it worn’t matter.

Doug Fattic 

In my case I originally didn't realize the top tube had a slope so when I measured the angles they were not the same as they would be if measured against level ground. I used what I thought was the same angles when I designed my 1st frame and of course they were off by half a degree.

How important one degree makes depends on the circumstances. As I have aged a 73º seat angle no longer works for me. My aging body likes it to be 72º or less. I require a shorter stem raised higher up. Otherwise I am not as comfortable as I can be. I need my saddle to be back far enough so I am balanced over the pedals. That takes my increased weight off of the handlebars. I also like Brooks leather saddles that require even more setback. In my case 1º matters a lot if it prevents me from placing my seat and handlebars where I require. On the other hand, in some circumstances it is possible to adjust the stem and saddle to be at or close enough to their optimum position so it won't matter.

I'll give another example. I took over to Ukraine a sport touring steel Trek as my personal ride. Its seat and tube top tength are within a mm or two of my own custom frame. However the seat tube angle is 73º while mine at home is 72º. I am used to things being exactly right for me (the advantage of being a frame builder) and I can notice and prefer the shallower seat angle. I can tolerate the extra weight on my hands but I certainly like less with a shallower angle. YMMV

repechage

Sloping top tube means nothing to the performance/ handling of the bike.

it does expose the approach and what is, is not important.

the potential error could approach a degree, take one of mine where the top tube rises near 10mm, assume its level and of one measures the frame and fork independently, there will be confusion to sort out.

repechage

Surfing around early early today, I found this-
this is an image from a current ebay auction.
The Masi is from the “breaking away” era, same color, different size, same graphics as the movie bikes, wrong equipment, showing a Dura-Ace EX caliper. These were normal reach.
note the pads are all the way down in the slots.
almost always other than this era on most bikes the reach is at the other end with a standard Record Caliper. I have seen this before, it is curious. The recipe book was tossed for this bike and a few others.