What's wrong with running different size tires?

[Walker]

I see plenty of pickups around here running those big mud tires in the back and smaller tires in the front. I know its fine on a 2x, but plenty of em' are 4x4's. I like the look and it'd save me a lift kit to get big meats under the front end.



Is it that the gears are turning at different speeds that cause more wear?



I'm also aware of the "spare tire" and "rotating" issues. But, what's the bigger down side?

 

[WadePatton]

Axle windup

When you're in 4WD you'll have the rear-end pushing the front-end because the ratios are effectively different. It's okay in really loose/slick stuff because tire slippage releases the tension. But if you encounter good traction you're going to load up the driveline.



I know- I ran a 3. 50-4. 10 once. Long story, but not recommended. And probably much more significant difference than a tire mismatch.



So if you must have the LOOK, just remember not to use 4WD.



You'll have to do a lot of backing to unlock the hubs too.

 

[Chipstien]

Your U-joints and transfer case will wear out fast if you try it. Not recommended.

 

[nickleinonen]

if you don't use 4wd with the tire mismatch, it won't matter at all. if you do, the difference in tire size changes the effective gearing. if you had 3. 73:1 gearing front and rear, and had 35" in the rear and 33" in the front, your rear gearing will be 3. 73:1 effective, but your front gearing will be 3. 977:1 due to the tire being shorter. small differences up to 10% are ok if you are in an area when using 4x4 that the wheels can slip. [that's why part-time 4x4 is not recomended using on dry surfaces like concrete and pavement]



i run different tire sizes on my tahoe for looks, but they are pretty close to the same size. my fronts are 285/75/16 that according to goodyear are 32. 7" tall. in the rear i run 305/70/16 that are 33" even according to goodyear. those rears are probably pretty close to the fronts for the diam. . i had the tires "shaved" down in the local parking lots. . . lol. .



now if you really wanted to run different tire sizes full time on a part time 4x4 truck, you could stagger the gearing. say you wanted 35" up front and you had the 3. 55:1 gearing and you wanted 37" tires in the back, you would need 3. 753:1 gears in the back to match the effective gearing. it can be done, but is it worth the cost and functionality?

 

[LarryG]

..... not to mention what it is going to do to your fuel consumption and tire wear with the front end of the truck fighting the rear... ... .....

 

[Mick2500]

It could also cause faults in your ABS system if you have the 4-wheel ABS.



Mick

 

[J Shocik]

Along with the possible gearing problems, you also have to worry about the anti-lock brake system if your truck is so equipped. The different size tires could throw off the sensor readings, possibly causing problems.