You recalibrate it because bigger tires mean different speeds... for example, lets say your car had 14 inch tires... and your speedometer is saying that you are going 50, if you add 20 inch tires which is 6 inches bigger, you might be going around 60-70. No need to get a speeding ticket. Bigger tires cover more road then smaller tires, for example for ever 1 turn from a 20 inch tire is like 1 and ahalf turns from a 14 inch... Hope Ive helped you understand why :)
slightly bigger tires
On most newer vehicles t is done with a scan tool.
Yes, they do.
I have never found a way to "adjust" any speedometer.
when you get bigger tires, or different rear end gears.
Have you installed tires smaller than the OE tires? If so this is the problem.
You can only do this if you have a LUFKIN SLIDE RULE made in Kosmonia. Get one ; and email me back and I'll tell what to do with it.
Jet Accu Speed Speedometer calibrator. It adjusts your speedometer for bigger tires or gear change. Only works on automatic transmissions.
The 99 tires are much bigger than the 90 tires. With the smaller tires on the 99 you would be going slower than indicated on the speedometer.
Could be that the wrong size tires are installed, or that somewhere along the line, a different rear-end gear ratio was installed.
The size of tires can effect that accuracy of a speedometer. Larger tires will cause the speedometer to read less than you are actually going.
Putting larger tires on your car will give you higher top spee with less torque. However, changing the tire size will make your speedometer inaccurate.