Intonation: flat wound vs rounds

[SteveHenry]

Just bought a beautiful almost-new G&L JB Special from a TB member and the first thing we did was change the rounds on it to flat wounds (LaBella Deep Talkin Bass .043 to .104). When I went to set the intonation I had to crank down all the bridge adjustment screws to about the very end of their reach (shortening the string length). This was very different from the bridge position with correct intonation when the bass arrived with the rounds on it.

I mentioned this to my brother and he said the same is true for his G&L (he also uses flat wounds).

Neither of us understand what causes this. Is it the flat wounds? Can anyone enlighten us?

 

[Eric66]

I have no clue. I can easily exchange flats an rounds on P and J basses without changing intonation.

 

[tangentmusic]

Are the gauges the same from the old rounds to your new flats?

 

[96tbird]

Witness points. You have to bend them over the saddles so they don't form an arc.

Bend the E so it shoots straight at the nut. NO ARC over the saddle. Now it will be flat. Tune. Intonate. The saddle will need to move forward. Bend tune rinse repeat. All strings.

Oh Zooberwerx! Where art thou?

 

[SteveHenry]

Not sure what the gauges of the round wounds were. Would that account for the difference, if they were different gauges?

Bent the strings--didn't seem to make a difference.