# Does Tire size matter?



## rockws

I was in Arizona and had a couple of flats on different days and had to go to different shops to get new tires. They did not have the same size as the tires I had on the vehicle and said that it did not matter if I put these rear tires on. I have a Jeep Grand Cherokee and have not driven it in 4 wheel drive since I changed the tires. I am wondering if this is going to hurt anything. On the front of the vehicle I have P225/75R16's and on the rear I have 245/70R16's. I have driven about 10000 miles (from Arizona to Wisconsin and around Wisconsin since than) since the tires were replaced. I recently had to replace the sensor and cylanoid(sp) in the tranmission, don't know if this had anything to do with the tires or not? I am going to have any problems becuase of this????


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## rockws

After looking around the internet a little and doing some figuring the difference in the tire's diameter is .21". The width difference is .79", I don't think this will matter but will the overall diameter matter?

Thanks


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## octaneman

Hi rockws


Tires do matter, incorrect tire sizes can cause serious damage to your vehicle not to mention a safety hazard. Putting on the wrong size tires on some cars and trucks will destroy the transmission cause damage to the suspension. Newer cars today have many sensors hooked up to the computer that determines the car's speed, and drivability. Remember, the tires are the only thing on the vehicle touching the ground, the wrong tire size will affect steering and braking distances.


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## Wrench97

What brand and model are the tires, what counts is the overall Diameter of the tire, the 245/70 is a wider tire then the 225/75 but depending on brand and model could be very close to if not the same diameter.


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## rockws

wrench 97 

the diameter of the tires are .21" difference from front to back


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## rockws

octeman

Both of these tires are what the Jeep Grand Cherokee's came with, when I checked some websites that tell you the tire size you should have on your vehicle both of these size's are acceptable.


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## Wrench97

That's less then a quarter of an inch you'll see more then that between new and worn tires, it will be fine.


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## octaneman

rockws

The internet posts many things, but there is no substitute for the vehicles I.D tire tag. Unless the truck's I.D tag SPECIFICALLY has that particular size written on it, then it's ok, you can use them.


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## waynecleary

I would have done the same thing temporarily in the fix you were in...but matching tires are necessary for your vehcile to run safely and efficiently...


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## firefightjason

Remember if you have 4x4 to use the same sized tires front AND back. Or you'll destroy your transfer case.


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## rockws

I have not driven it in 4WD since the tires were put on. So your saying that even though its only about .21 inches in diameter that it will still wreck the transfer case when we do drive it in 4WD? We only use it about 5-10 times in winter for short distances.


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## pat mcgroin

As wrench said above that 1/4 inch wouldnt be any different from an old and new tire.
I think youll be fine in 4wd.
The 1/4 inch only equates to .8 inch if you were to roll both tires one full revolution.


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## wolfen1086

rockws said:


> I have not driven it in 4WD since the tires were put on. So your saying that even though its only about .21 inches in diameter that it will still wreck the transfer case when we do drive it in 4WD? We only use it about 5-10 times in winter for short distances.


Might only take a few feet to totally wreck a transfer case. Along with keeping the same size tire front and back rotate them every 6000 miles, to keep tread wear even.


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## SABL

Best to keep all tires the same size front and back or never engage the transfer case. 
.8 inches doesn't seem like much but will stress the chain/gears and will destroy something on dry surfaces.
With an "open" differential side to side mixing may not hurt if the difference is not great and the same size is put on the same side. Sounds crazy, but how many posters remember the old farm tractors with a larger tire in the left side?? This was done to put the larger tire in the furrow when plowing..... haven't seen that for ages. Just a memory.

SABL


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