Re-calibration of Speedometer for Aftermarket Wheels

[MIK3]

Just curious as to how many people re-calibrate they're speedometer after upgrading to 16" or 17" wheels and tires, assuming we all know that different overall wheel and tire radius will give us an innacurate reading of the speedometer. This might be a good excuse for the officers who say you're going 50mph in a 40mph zone. You're speedometer will read 40mph, but his gun will pick up 50mph due to your greater sized wheel covering more space per rotation than a stock wheel would. Tell him that you just got new wheels and don't have the money to recalibrate your speedometer! Heh. So has anyone done this, or spent the money to do it?

[shepherd79]

if you get tire matched to your wheel. you shouldn't see diff in speedo.

[hondamanlxi]

well ok, but what if.....he got 17s wit big tires or 18s?

[MilTownSHO]

This might be a good excuse for the officers who say you're going 50mph in a 40mph zone. You're speedometer will read 40mph, but his gun will pick up 50mph due to your greater sized wheel covering more space per rotation than a stock wheel would. Tell him that you just got new wheels and don't have the money to recalibrate your speedometer! Heh. So has anyone done this, or spent the money to do it?

Be warned now, that excuse will not work. For one you had knowledge of it!

[SteveDX89]

It's call plus sizing. As you're wheel gets bigger, the tire sidewall gets smaller. The diff. in your speedo should be 1 mph at the most.

[deadlight]

Be warned now, that excuse will not work. For one you had knowledge of it!

Miltown's right, it didn't save me in court unfortunately, when I mentioned I had aftermarket rims and tires, he said, "So you knew the speedometer would read inaccurately" Much stuttering followed.

[MIK3]

Yeah, I guess that's part of the reason we have low profile tires when we upgrade wheels to bigger sizes. I guess this is more of a truck questions if anything, knowing they don't ride on low profiles usually if they are lifted, they're more up in the 35"-38" range, bigger than stock in most cases.

[Morpheus]

It'll throw it off enough, you can pick up one of these.
http://www.nordskogperformance.net/marine.html
GPS guages, go in cars too.