Geometry 700c to 650c

Just wondering how much a difference changing the front wheel from 700c to 650c will change the riding style/geometry and advice from someone who's done it. theoretically it will lower the BB by 1inch, how much difference would that make? (the bike won't be fixed so the fixed pedal strike issue shouldn't arise)

I think your theory is not correct.
If you do 0.5 x (28" - 26"), you'll find that the wheel radius is 1" less.
In casae you keep the 28" fork, the head tube drops around 1", but the rear wheel axle stays in the same position.
So, the BB lowers just by approx. 0.5".

However, if you also change the front fort to a 26" model, the head tube lowers another 1".
In that case the BB axle goes down by approx 1".

This is pure theory. I've never measured it. Measuring in real life will be the only correct way.

Besides the drop of the BB, also the seat angle gets steeper. Perhaps that can easily be corrected by sliding the saddle backwards on the post (or taking another seat post with more setback. But perhaps you will like the more forward saddle position and you don't have to change it at all.
Perhaps you also want to make the saddle deck level, because the nose goes down a bit.

With the smaller front wheel, the steering angle gets steeper.
The smaller front wheel has already effect on the trail, thus steering of the bike.

700c wheel diameter is 622mm, 650c is 571mm, not including tyres.

Does anyone know what will happen if I change my 27 1 1/4 wheels to 700c on my road bike. A bike mechanic told me it was not recommended because my bottom brackets would drop lower and scratch the groud- especially in turns. Any advice?

Well it would be your pedals striking the ground, not the bottom bracket. And it's unlikely, unless you have a low BB and long cranks. So you can probably do the conversion, but you'll need longer drop brakes too.

Should be fine. I rode 700C's in 27" frame for about a year, with 170 cranks. No pedal strike. But I would recommend 165's for peace of mind. And clipless pedals (spd's or atac's) so there's less pedal edge. Bah, this is overkill... it's fine and done all the time.

This is my old bike:
http://www.lfgss.com/picture.php?albumid=486&pictureid=2840

Thanks for the tip! I'll try and report back to the forum

Im about to start getting my Basso tt to look abit more like it used to back in the day (classier re spray and parts, suggestions welcome) during the process I have the bikes original forks. they are to fit a 650 wheel but everyone iv spoken to seem to think will regret changing it to that.

Thoughts?
Ridden one?

you're riding a frame designed for 650c with 700c?

and as such, putting a 650c on the front you will fix the geometry and thus your ride should be improved dramatically.

Whether the change in riding position is comfortable/suits you is another matter entirely.

Yeh its just the front one. been 700 for a LONG time. Yeh true suppose its opinon. Just wondered how its worked out for the thread started too?