I fi generally fit 19″ frames with a decent top tube if i sized down to an 18″ but with the same top tube length as my current 19″ frame does that necessarily mean that the seat will be 1″ higher than i currently have it.

Apologies for the noddy question but i’m struggling to work out how top tube length affects this sort of thing (if at all) as the head tube height will be pretty much the same for both bikes ie. same fork length/wheel size + or – 10 mm or so for head tube length.

No, you’ll just have 1 more inch of seatpost sticking out.

You see that’s what i thought thinking about it logically, or as logically as i can 🙂

But if i sit on a 17″ frame for example i end up with the saddle much higher than the bars. Since the bar height is relatively fixed as mentioned before i was getting confused as to why the seat was so much higher.

Is your answer dependant on the top tube length ??

Top tube length has nowt to do with how high your seat is. The relationship between saddle height and bar height is only really down to BB height and head tube length assuming you’ve got the same forks and angles. If you leave the head tube the same length and alter the seat tube length to give a different ‘size’ bike, then your saddle and bars will still be in the same place, you’ll just need a longer seatpost.

If your top tube length alters then it may make the saddle to bars relationship feel different as your hands come closer/further away altering your weight distribution even though the bars and saddle are at the same height as before.

The 17 inch you talk of may have a higher BB or a shorter head tube or a mixture of both to give the feeling you describe.