Good morning,

I have a 2003 Grand Cherokee Laredo V8 that I just bought 4 new tires for. I've heard some vehicles can't use a donut or mismatched size spare as it would wreck something with the transmission/differential. Does this apply to my jeep?

Previous Tires - BF Goodrich All Terrain T/A - LT 245 / 70 / R16 with a full size spare
Current Tires - BFGoodrich Advantage T/A Sport LT 225 / 75 / R16

Is the old full size spare usable with the new tires? With distance/speed limitations only to get to a shop or home then get a proper replacement?

Driving style: no offroad, casual commuter car for work a few times a week. I am hoping to upgrade to a new car within the next year or 2 but my wife and I are searching for a house so not making any large changes in credit/debt until after purchase.

 

You’ll Be fine as long as you don’t go too far and fast. Also maybe stay out of 4wd

assuming no traction device like a limit slip dif or locker.

 

First my OCD would never let me do that.
Second not that I would know better but I can't see that be good for the rear.
Open diff or not.
Third on the front and if the the WJ has that Quadratrac thing thinking even worse.

 

Appreciate the thoughts. Correct the Jeep would remain in 2wd and the only purpose would be a single trip to get home/shop and purchase the full size replacement. I'm not familar enough with the car to know about any additional traction device, I'd assume it's stock with no additions. Hopefully I can get away with short-term emergency use but at a distance/not time sensitive situation I'll try to stick to towing it if tire damage is too far for a patch kit.

 

Welcome to the forum.

Your 2003 Grand Cherokee is a WJ, it has the NV247 transfer case.

The tire outside diameter must be within ¼" or it will cause failure of the internal progressive coupler. That part is expensive and transfer case removal, disassembly, reassembly and replacement is not horrible but not much fun. My preference is usage of a transmission jack during removal / replacement to decrease the physical effort and improve safety. Probably due to effects of increased age.

The image is my NP249 on my 1994 ZJ.

My early NP249 was VERY susceptible to tire outside diameter differences. I HAD to use identical tires and tire pressures to avoid damage to the internal viscous coupler.