When I bought my 2012 700X, it had a 170/60 shinko street tire on the rear. I got mid to upper 60's mpg routinely. I put 705's on the bike, 150/70 on the rear and my mileage has dropped by~10 mpg. Has anyone else seen this kind of drop in mileage?
The two tires you describe have different outside diameters and will roll different revolutions per mile. Going to the 150/70 will make the speedometer and odometer read lower than actual, thus your MPG calculations will appear to have dropped. Although it will not account for the whole 10 MPG, it will account for some of the difference.
The solution is to install a speedometer correction device so you can calibrate your speedometer for different rear tire sizes or different final drive gearing. I run a 150/70 rear. I use a Speedo-DRD device, and I’m able to set it up to make the speedometer match the GPS.
Thanks 670. I had checked out the tire size calculators; it looks like there was a 0.9% difference in the diameter -- the 150/70 being larger, in diameter. Perhaps it's a combination of the diameter difference and the fact that I changed them in the Fall and did most of my riding when it's cooler. I like the 705's, so I may try the 170/60 when the 150/70 wears out, or go with the OEM size in another brand.