Longer rear shocks change geometry?

[Excess Impulse]

I've been searching the threads on changing to longer rear shocks as I need to upgrade my 36 year- old originals, and from what I can gather, seems if I wanted an extra 1 1/2" I would also need to lengthen the front fork springs by the same 1 1/2". I'm now rethinking this as that may be more than I need to raise the rear. I see Mike's XS has a 13 3/16" that should fit my 1980 G/SG. (Part # 06-3642)http://www.mikesxs.net/parts/yamaha-xs650-monza-sport-shock-set-13-3-16-black-body-no-caps making the total length only approx 3/4" longer. I know guys here have put 14 1/2" rears on, and my question is,
Does a longer rear shock change the suspension geometry if you leave the front height stock, and how noticeable is it? Will the 3/4" make much difference in ride /handling?
I"m also planning on either running a little thicker fork oil, or changing to progressive fork springs at some time in future.

 

[xschris]

12.5 is the stock rear size. Yes a longer shock will change how the bike handles. The chain can also rub on the swing arm is you get around 13.5 or 14" I can't remember which. Stick to stock for best handling. The guys a Yamaha knew what they where doing. But if you want a "look" than go for it. Also keep in mind spring rates. If you new shock is too stiff it will handle even worst.

 

[Excess Impulse]

12.5 is the stock rear size. Yes a longer shock will change how the bike handles. The chain can also rub on the swing arm is you get around 13.5 or 14" I can't remember which. Stick to stock for best handling. The guys a Yamaha knew what they where doing. But if you want a "look" than go for it. Also keep in mind spring rates. If you new shock is too stiff it will handle even worst.

Not really going for a look with the shocks, but for function, as the old shocks are rough after all this time, and I think the bike looks good even in it's current stage! I do have a small clearance problem with the battery box under the seat, ( looking at it I could shorten it 1" and get clearance) and was specifically looking at those shocks from Mike's, which are only 3/4" longer, not sure if that is significant? I Need to be able to ride down forest roads, handle big bumps on dirt roads, etc. I don't know what the spring rates for those shocks are, I have to find out more...