7 and 8 string scale length

[amadeus]

Alright i was looking at gettting a 7 string and an 8 string and i was wondering what scale lenght is needed to get my guitar intonation perfect for these tunings

7 string: (floyd bridge)
ADGCFAD
8 String: (1 full step + drop D formation on 8)
DADGCFAD (low D/not tuned up on the 8th)

iv used 25.5, 26.5 and 27 inch scale lengths seven strings so im comfortable with any scale lenght but i dont want intonation problems.

what im aiming towards the schecter c7 and c8 if what im planning on doing with it wont work then ill look at other companys (I.E agile, Ibanez, Esp)
any thoughts on whats the best for intonation purposes?

 

[Explorer]

To correctly intonate my three 25.5" 8-strings with a low E1 and Hipshot bridge, I had to buy the shorter saddles from Hipshot, but beyond that, no problems.

You might not have that much flexibility in terms of total available movement on a Floyd.

 

[Dayn]

I can get a low E intonated fine on an RG2228 with an .080 (27"). D may not work well on the fixed Edge III-8, also depending on how thick you go. I'd use a .090 at least, though I think by that point the string starts to get too big for my guitar.

With the thickness of the string, you may fret it sharp or flat, so I think if you get the intonation reasonably well enough, it's just up to you to develop your technique so you can fret it fine at the proper pitch.

 

[amadeus]

To correctly intonate my three 25.5" 8-strings with a low E1 and Hipshot bridge, I had to buy the shorter saddles from Hipshot, but beyond that, no problems.

You might not have that much flexibility in terms of total available movement on a Floyd.

when it comes to intonation with lower tuning do you find that your moving the saddles further back (away from the pickup) when the notes get lower?

 

[Explorer]

It's not just for ERGS that one must move the saddles back for the larger strings.

Electric and acoustic six-string guitars have saddle compensation...

...as well as other fretted stringed instruments like mandolins.

I'm not sure if there's a formula for determining when you'll be in the ballpark for intonation at a given scale length, pitch, string gauge and tension. My guitar tech looked at my Ibanez 7-string acoustic, and figure out that the saddle had to move back a quarter of a inch, but I don't know if she was just eyeballing it and taking a guess, or if there's some secret knowledge which generated the exact distance.

I'm a little fuzzy right now, but hopefully someone will come in and explain why lower notes need more compensation....