driving on spare tire

[Mr. Wizard]

I just put on a new matched spare and I'd guess there's about 1/4" difference in the tread depth vs the used tires on the other wheels. I'd like to use up the other tires some yet before I buy a new set but the dealer told me that it could damage rear end parts with all the sensors/controls in the newer trucks. I drive an 05 F150. Should I believe him and get the new set now?

[Jack Peterson]

Over the past 7 years working in a mechanic shop, I've seen a lot of weird things. Having one new tire on a truck isn't necessarily a good thing, but I personally wouldn't worry about it. I've seen different size tires hurt transmissions, but that's because people accidentally ran two different size tires on their front wheel drive car. If you trust your mechanic, go with his opinion. If they're doing their job, they should be out to help you, not just make a buck.

[Big Buck Buster]

I would not recommend it if your truck has a limited slip rear end in it.

[Jeremy airjer W]

You would be in much better shape with two new tires on the rear and the other tire mounted as the spare.

[BobT]

Really? Today's vehicles can't handle different wheel rotational speeds? How do they handle cornering? Isn't that what a differential is supposed to do? Sounds like a step backwards to posi-traction.

[Jeremy airjer W]

How often do you spend making tight turns?

How often do you drive in a straight line?

You should see how the old AWD fords react to new tires in the back and almost worn out tires in the front. A difference of a 1/4 inch and the thing is hopping all over the place.

Most tires start out at 10/32". 1/4" = 8/32". So he has one brand new tire and one almost worn out tire. That's a pretty big difference.

[BobT]

I guess I can go home now. I learned something. Would have never guessed it would matter that much.

[Macgyver55]

It can also (sometimes) affect ABS systems because of the difference the wheel speed sensors pick up.

[Jeremy airjer W]

  Macgyver55 said:

It can also (sometimes) affect ABS systems because of the difference the wheel speed sensors pick up.

Ford wynstars with early TPM systems where notorious for setting of low tire lights when tire tread was not uniform!