Tire Size/ Speedometer Question [Archive] - Glock Talk

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TxTech
05-28-2008, 19:45
On my Grand Cherokee I went from 235/65/17 to 245/75/17. A tire calculator I looked at said when my speedometer says 60MPH I am actually going 65MPH. Does this change throughout the speed range or am I always 5MPH off?

knightkrawler00
05-30-2008, 18:23
It will change throughout the speed range. The faster you go, the bigger the difference will be.

IslandHopper
05-30-2008, 19:25
...Does this change throughout the speed range or am I always 5MPH off?

So when the car isn't moving, you're actually going 5mph... :upeyes:

Bowtie
06-02-2008, 17:00
It will change throughout the speed range. The faster you go, the bigger the difference will be.

Why is that? Do the tires get bigger as he goes faster?

Ashton
06-02-2008, 17:10
If he's off by 5% of 50 MPH that's 2.5 MPH - at 100 MPH the variance would be 5 MPH. Yeah the added circumfrence will make the speedo appear slower than actual. measure the tires though - tire manufacturers are like shoes and jeans - actual measurements may vary - you may be better or worse off than you think you are - depending on the real measurements.

Why did you up the sidewall? Add ground clearance??