05-28-2014, 04:32 AM
I'm sure I'm going to get crap for this, but here is the math.
If you take a tire put a mark on it and rolled it along the ground until you got back to the mark that would be the circumference of the tire. This is also Pie*Diameter or 3.14*D. The sensor is measuring revolutions of the wheel. It doesn't matter that the location it is measuring this is inside the outer diameter it is still just measuring the number of revolutions. If you put a mark on the ring the sensor was looking at it will always be in line with the mark you made on the tire. So if you took that number of revolutions multiplied by the circumference of the outside of the tire you would get the distance you have traveled. Remember the bike is doing all the math (Rev*3.14*D) now if you change the diameter significantly, but don't let the bike know it still does the same math. So even though you would travel a different distance, based solely on revolutions, it still thinks you went the old distance.
Example time.
So say you went from a stock 25" tire to a 30" tire. What the bike is reporting is 25*3.14*Rev*0.0000157828 (the last bit is just to get it from inches to miles). What is actually happening is the outside of the tire is traveling 30*3.14*Rev*0.0000157828. What this means is by the time you actually have traveled 1 mile you have made 672.6 revolutions of the wheel. Since the bike is still using the old formula it reports you have only traveled .83 miles.
This is true if it is measuring the revolutions of the wheel, or some part of the transmission. The only time it would not be true is on the old style bicycle style odometers that used a direct drive mechanism that made contact with the outside diameter of the tier, this would be accurate no matter what size tire you used.
And also like CIP pointed out, the difference in outer diameter with this particular tire is so small, it really doesn't matter at all.
I know that was way more educational in tone then this forum is used to (or probably wants), but I hope it helped.
If you take a tire put a mark on it and rolled it along the ground until you got back to the mark that would be the circumference of the tire. This is also Pie*Diameter or 3.14*D. The sensor is measuring revolutions of the wheel. It doesn't matter that the location it is measuring this is inside the outer diameter it is still just measuring the number of revolutions. If you put a mark on the ring the sensor was looking at it will always be in line with the mark you made on the tire. So if you took that number of revolutions multiplied by the circumference of the outside of the tire you would get the distance you have traveled. Remember the bike is doing all the math (Rev*3.14*D) now if you change the diameter significantly, but don't let the bike know it still does the same math. So even though you would travel a different distance, based solely on revolutions, it still thinks you went the old distance.
Example time.
So say you went from a stock 25" tire to a 30" tire. What the bike is reporting is 25*3.14*Rev*0.0000157828 (the last bit is just to get it from inches to miles). What is actually happening is the outside of the tire is traveling 30*3.14*Rev*0.0000157828. What this means is by the time you actually have traveled 1 mile you have made 672.6 revolutions of the wheel. Since the bike is still using the old formula it reports you have only traveled .83 miles.
This is true if it is measuring the revolutions of the wheel, or some part of the transmission. The only time it would not be true is on the old style bicycle style odometers that used a direct drive mechanism that made contact with the outside diameter of the tier, this would be accurate no matter what size tire you used.
And also like CIP pointed out, the difference in outer diameter with this particular tire is so small, it really doesn't matter at all.
I know that was way more educational in tone then this forum is used to (or probably wants), but I hope it helped.