exhausts and tyres

[arfa vmax]

http://i244.photobucket.com/albums/gg23/arfa-vmax/000_1747.jpg http://i244.photobucket.com/albums/gg23/arfa-vmax/000_1746.jpg  http://i244.photobucket.com/albums/gg23/arfa-vmax/000_1748.jpg hi all   the first two pictures are a home made rear exhaust i got from simcha.it fits straight in to the head without the short fittings, and looked like it was part of a 2 into 2 system.the i/d of the port end is 7/8" the merged end is 1 1/4".the third picture is the rear down pipe i removed from my bike tonight.the i/d of the port end is a fraction over 7/8" the merged end is 1 3/8".the diameter of the exhaust port on the head is 1 3/16".right thats all the numbers,my question is......if the ideal i/d for the single pipe is around .8 " as suggested in a previous posting and the mac i saw on simcha's bike looked about this size dose it taper down from the port i/d .the home made 1 has a thick walled end to reduce it down but this must cause poor gas flow.i like the idea of it fitting straight into the head it seams less hassle.the original pipe had been patched up with some stainless steel but the rings on the ends have both broken off.  now for tyres...... on another posting it was said that tyres bigger than 120 could 'nt be used because they grew at higher speeds due to centrifugal force,then rubbed on the swing arm.surely centrifugal force pulls out from the axis and would increase the radius of the tyre not the width,if anything would'nt it pull the sides in in as a result? asking this because i want to fit a 140/90/15 rear wheel from a xv 535      

[kwells]

about tires...I was thinking the same thing actually.  The forces go out to the center of the tire...not laterally.  But, I assume that this does still in fact occur.  I would not recommend exceeding the width rating of your rim because it will change the profile of the tire.

[arfa vmax]

i would change the whole wheel for a 15" spoked one from a virago,it has a 140/90 as standard

[QBS]

I wrote regarding tire growth.  What I meant was that as the tire grew, it grew in diameter and rubbed the middle of the swingarm, not the sides.