I have a 99 ranger and wandering what r the biggest tires i can put on the factory rims with a 4cyl engine

 

Umm biggest do you mean not rubbing or that you will have the power to move down the highway with.? I think you can get 30's in there but not sure i have 235-75-15's on my 4x4 with plenty of room to spare.. Are you going to go offroading? If you are or arn't and just want big tires leveling springs will get 31's up front with no rubbing.

 

With bigger tires you may find that a gear change will be needed with a 4 banger.

 

31x10.5x15 on stock rims. If you don't have a 4:10 rearend then I
would go with 30x9.5x15. I have 31's on my 4-banger with a 4:10 rearend and it does OK going up hills but.................

 

How about 245/70/15's????

 

If my calculator worked right 245/70/15s are 28.5" in diameter which would only be 1" bigger in diameter so you would only see little change.

 

An even more important question is "What am I going to have to change AFTER I change the tire size?"

Three things I can think of that can cause you grief.

1. The Speedometer.
2. The Anti-Lock Brakes.
3. The Computer.

All of these are calibrated with a certain tire size in mind. Changing the tire size will most certainly throw these off.

Personally, if it is just a normal everyday truck for work/transportation, I would keep the factory sized tires on it.

Larry

 

The only grief will come from the speedo being off. The cheap ABS system ford puts on the ranger isn't intelligent enough to care about tire size and it won't affect the computer other then the speedo being off.

>An even more important question is "What am I going to have
>to change AFTER I change the tire size?"
>
>Three things I can think of that can cause you grief.
>
>1. The Speedometer.
>2. The Anti-Lock Brakes.
>3. The Computer.
>
>All of these are calibrated with a certain tire size in
>mind. Changing the tire size will most certainly throw
>these off.
>
>Personally, if it is just a normal everyday truck for
>work/transportation, I would keep the factory sized tires on
>it.
>
>Larry

 

The computer can be adjusted with a OBD-II scanner to correct for tire size and gear ratio changes. It will affect the speedometer, odometer and the shift points on an auto trnny.

 

Regarding the difference between 235/75/15's and 245/70/15's. Depending on the exact brand of tires (all manufacturers are just a little different) those two sizes should be virtually the same height. Using the simple formula: width * aspect ratio * 2 + rim diameter, the 245's come out 28.5 inches, while the 235's come out 28.8 inches. This by no means takes into account variables in tire design between manufacturers, or even tire designs from the same manufacturer. The 245's would be a little wider, but less than half an inch.

Likewise, most "30 inch" tires aren't really 30 inches tall. But they'll still be about an inch taller than the stock tires.

 

My 99 Sport had 225-70-15s stock. I replaced them with 235-75-16s. These are 29" tall. The speedo is right, don't know how it did that! ABS. computer, etc, are all fine with it. They rub a little bit at full lock, otherwise fit fine. Steep hills at 70 mph are tough on the 2.5. above 75 though, it rolls. Just got to keep the Rs up.
Dave