Have a 2004 Dodge and noticed it had 3 tires that were 275/60/20 and one was 275/55/20 - been that way for about 4k miles - I have 120k miles on my truck and it is having a hard time going into 4WD - would this be the problem? Off size tire was on right front, what other damage could this do?

 

I would say that tires will wear uneven. The 4wd is probably a another issue in itself.

 

The size differential won't have an affect on wear. You do have a 1" diameter difference. The 4x4 won't like it much, just like you can't run two different gearsets. "... hard time going into 4WD..." What does that mean? It won't engage, or it makes bad noises? Cheap enough to fix unless something's really hurt - buy a used 275/60x20 tire. Shouldn't cost more than $50 or so. If you have the scratch, replace 'em all.

 

The tires you have are the same width i.e. 275
The heights are different 60 vs.55 which is a % of your width of the tread
so you've got mismatched tires on w/20 inch rims.
If they were really mismatched your truck would be pulling to the right.
Sounds like you should check your fluid levels : transfer case, tranny and such...

 

The tires are NOT the same height. 275 is not the height, it's the width of the cross section. A 1" diameter difference isn't a great deal, but it does mean one wheel is rotating a fair bit faster than the other.

 

You have your explanation reversed. The 275 is the section(tread) width. The 70, 60,40 etc is the ratio of the side wall to the section width so it directly affects the height. If both are on the rear and you have LSD, it will cause additional wear. If no LSD, it will not affect much except that corner will be 1/2 inch lower. 4WD shoud only be used when there is slipage. Different tires have different road matters so it could affect handling.

 

Well, almost. Section width and tread width are not the same unless the tire is mounted on the wrong-size wheel. The section-width is measured at the "bulge" or widest part of the tire between the wheel and the tread.

 

If they're both on the rear and you have the LSD, it is not happy!

 

Thanks Mike, you are right. I get confused because two tires of the identical size but different manufacturers vary both in height and width. Add to that was my last truck, a rice burner had BFG AT size 31.5X10.50R15. The section width was 10.5" and the tread width was 9" and some change. I do realize the metric sizes are a different animal. Even there it is misleading as the rim size is still SAE, stated as inches. I go back to when a standard tire was 7.75x14, then they started using letters before the so called metric. It's getting harder to teach this old dog new tricks.

 

As mentioned earlier, the difference in diameter is 1.1 in, however the most important thing is the tire circumference which is in your case is 3.4 in. Such difference will result in different overall tire rotation within the same axle and definitely affect 4WD.
Due to the difference of tire speed, 4WD engagement / disengagement while on the move will be difficult, also under 4WD mode; you will feel that the car will steer to the right under acceleration.
My advice is change the tire immediately if you use 4WD mode otherwise you will end up destroying your front diff.