Change Tire Sizes?

[wintermute]

Here's a question for the car guys...I recently got a used 2004 Grand Cherokee w/ 16" rims. It came with really crappy 225/75R16 tires. I want to throw Bridgestone Dueler All-Terrain Revos (great experience with these) on the sucker, but they don't come in that size, they come in the "alternate" size for the Jeep, which is 245/70R16.

The question is, how bad is this going to screw up the speedometer and odometer? thanks.

 

[BlackHills]

Probably not enough to make a difference. In theory the 225s are 29.3 inches tall and the 245s 29.5 inches though calculated size doesn't always equal actual size. 2/10ths of an inch isn't much as far as the speedo goes.

http://www.5speedtransmissions.com/calculators.html

 

[JatMat]

You will have that much change as the tread wears off, don't concern yourself with the difference.
Just my .02
Ain't worth much,
Jim

 

[wintermute]

sweet. thanks. i was deeply concerned that it was going to take some doing to get this thing ready for off-road (beach driving for fishing).

 

[STR]

It won't matter. Changing rim sizes totally or really putting a tall tire on might but what you are talking about is of no concern.

STR

 

[alex]

If you have or can borrow one of the car GPS units like a Garmin 550 or any other you can see exactly what your car speedo reads at different mph settings against what the GPS speedo is reading both before and after changing tire sizes. On my F150 with the factory delivered tire size there is at most about a half mile per hour difference at almost any speed up to about 80mph. Easiest way to check is if you have cruise control and can maintain constant mph setting for a couple of minutes.

 

[Sid Post]

I went with tires 1.5" taller then stock on my Toyota Tundra. They are pretty wide as well. The only thing I had to deal with is possible rubbing of the inner fender well. Since I put a 3" lift in front to level the pickup, they fit like a charm.

My speedometer accuracy was not effected enough to notice any difference. They only issue in general I would consider is the power of the engine. Bigger tires on a strong V-8 is a don't care in general (if people stay with reasonable tire upgrades). A weak engine will have trouble rotating the larger mass and dealing with the greater distance covered in one tire revolution - that's why jacked up 4x4's typically run much lower ratios for street use (off-road ratios are typically even lower for torque and control).