Speedo correction with CT

Brand spanking new Darksider here.
I just put a 205/70-15R General Grabber on my VTX 1300R. Have not had it on the road yet. I wonder how this will affect the speedo. According to my calculations, the new tire is .6in taller than the original Dunlop (170/80-15). This change makes the circumference of the new tire 1.85in greater. That is an increase of 2.3%. Would it be reasonable to expect that it would create a 2.3% disparity between the speedmeter reading and the actual speed? Any thoughts?

According to this tire calculator you will be going 1.49 mph faster.
IE: if you speedo shows 65 you will actually be going 66.49 mph.

TRY IT:
http://www.discounttire.com/dtcs/infoTireMath.dos

Hope this helps?

Dont forget if your R is like mine the spedo was off by 10% to begin with. At 70 on the spedo I was actually running 63. Best thing I could recommend, is follow a cager and have them hit there turn signal at the speeds you want to check, make sure they maintain the same speed for awhile so you can get a good reading. Or do like I do, ignore the spedo and drive the way you want.

Jerry

Does the VTX have the speedo through the back tire?

On my shadow the speedo goes through the front tire, so no matter what I put on the rear, it won't change my speedometer reading. Do VTX bikes use the back wheel for this?