I got a flat tire the other day, actually while sitting in the garage. I guess I picked up a nail on the way home, good thing too because I have a custom sub box in the spare tire well. My spare tire is kept in my shed. Anyway, before mounting it, I thought I would put it next to the normal tire and the spare is about 3/4" smaller in OD, and that is with my tires nearly bald.

If I put this on the rear, I am sure this would wreak havoc on the LSD, so I switched the front tire to the rear and put the spare on the front. It was brutal to drive! It pulled to the right very hard, so I had to have a firm grip on the steering wheel at all times.

I can't believe Ford would design a spare tire that very much so reduces the driveability of the car. Anyone else had this experience?

PS, the wheels and tires are the factory ones, the 20" ones are off the car for the fall/winter.

 

They make the tires like that for a reason, and it is because of small women and older people that have a hard time handling a full size wheel/tire. Plus reduced overall weight of the car, and easier to design a place to store the smaller tire.

 

Interesting points. Don't forget cost, which is always the primary factory.

 

 

Yeah the stock spare tire can't be good for the LSD thats why i replaced it with a one of my old wheels and tires when i got my deep dish black bullitts.

 

Some have suggested that the small tire reduces overall weight. Personally I would have preferred the normal tire size as a spare.

 

The outside diameter of the tire could be the same as the factory tires and still be lightweight. I am only talking about 3/4" . The width is smaller too, but that is no big deal to get from A to B. The diameter difference is bad for the car when installed, I would love to hear from Ford on this one.

 

The owner's manual does say to only put the spare on the front. It is double the work, but it saves your limited-slip from wearing out quickly. Some cars, like the GT500 and Corvette, don't even have a spare anymore, just a can of fix-a-flat and an air compressor to get you to a tire store.

 

Most of the new Vette's also come with run-flats, don't they?

 

but they still have to handle the full size tire.

 

I think run-flats are standard on the Z06, and optional on others. Not totally sure though. They are expensive tires though, run flats are around 300 bucks each depending on size.

 

Will the normal size tire (235/55/17) fit in the trunk well??


Mike

 

looks like it'd fit but probably not if you had the shaker. don't think much else would fit though.

 

well, its 300 for the fun flats, but the stock tires that the corvette comes with (eagle f1's) are like 400 apiece themselves. If I can help it, Ill never use the fix a flat junk, past experiences have told me that it doesnt work. I just keep an air compressor and a plugger kit, and hope that keeps her up, till I can get to the tire store.

 

Hey, I got a question while we're on this topic. I punctured my rear tire a few months back and replaced just that one tire with a new one. So now I have 3 tires with 20,000 miles on them and then the new one (on the rear). Would this little difference between a new and half-life tire mess with the differential? The guy at the ford dealer said it wouldn't and actually recommended putting the tire on the rear since it would likely pull if I put it on the front.

 

I speak from personal experience using the spare tire. it sucks. It takes literally NO effort to spin the **** thing in the rain. All you have to do is let the clutch out a little too fast. It definitely is a smaller diameter and will completely muck up your handling to an unsafe point, even at around town speeds. Its only meant as an emergency resort to get you in for service as quick as possible. I had it on the rear and it pulled bad. I don't want to imagine having to steer with that thing on the front.

From a driveability standpoint, the dealer was right to put it on the rear, but you should always replace tires in pairs so the car doesn't have an uneven amount of traction side-to-side. As far as the differential goes, I don't know. How much of a difference in tread depth can you actually see? A difference in diameters would be like always turning to one side from the differential's point of reference which i can definitely see wearing out the clutches faster.

 

Driveability really has nothing to do with putting new tires on the rear. It has everything to do with maintaining stability based on the amount oif traction the tires provide (new tires are both stickier and have greater tread depth). Unless the tire is a different size (smaller) or has a lower speed rating than the rear then it should be placed in the rear.

This stuff has serious legal ramifications - every tire manufacturer that is a part of the RMA (Rubber Manufacturers Association) has come to the agreement that new tires (except for a few special cases) should be placed on the rear.

New rubber aside, even having 5/32 difference in tread front to rear is enough to jeopradize the safe handling of the vehicle, or allowing your air pressure to go low (as little as 3-5 psi IIRC) can put you at risk. This is mainly in wet weather.

Here's my favorite link
http://www.michelinman.com/tire-care...artire-change/

I've had the good fortune of actually have been to that very test track and experiencing that very scenario first hand where I was able to drive two vehicles back to back with both new tires on the front and on the rear and it was eye opening.

I was able to get the vehicle up to 45 mph before the slide started to occur, with the new tires in the rear it was very controllable, but when you placed the new tires up front the vehicle lossed the sort of progressive control you had with the rear tire placement (intersting observation - SN95 Bullitt wheels work very well on a Ford Fusion in case anybody was wondering).

The instuctor for the course said most people fair well right up into the slide, but fail to plan ahead after the car regains traction ( the key being, you dont react to the slide, but set the vehicle up for the moment after it regains traction) Drifters and Open wheel (mud track) folks are best at this.

 

I ran the spare on the back, it appeared the same overall diameter as stock, side by side. I didn't measure but did eye ball it because it seemed so small compared.

A word to the wise though, if you have a flat and have replaced your oem rims, make sure you check for a hub centric ring. I didn't even think of that and crushed it behind the spare, felt like I was fishtailing and scared the heck outta me before I figgured out what I had done. Otherwise the spare was fine for getting me to the tire shop.