I recently purchased a new 2004 Ranger Edge 4x4 Super Cab 4 door, I was somewhat surprised to find that the factory equiped spare tire is a different brand/size/profile than the 4ea. P245/75R16 Good Year Wrangler RTs. The Spare is a P 235/70R16 Continental SUV. I questioned my dealer and was accuratly informed that this size spare was the standard Ford "limited duty spare tire size " for that 16' wheeled vehicle. When I questioned the logic of using a spare with a different sidewall profile (R70 vs. R75) I was reminded it was limited duty. When I then questioned the affect of using a single 2" smaller diameter/ 6" smaller circumfrence tire with the three larger would have on the ABS and 4x4 tracking, I was again reminded it was a "limited duty spare". And, the Ford design engineers had considered those factors into the decision to equip the vehicle with that size spare!

Does this sound safe and correct, or am I being too obsessive in questioning Fords judgement to use a smaller "standard" Continental P235/70R16 for a limited duty spare on a truck equiped with larger tires?

Thanks for your opinions,
Jerry

(Click Here to find out why email addresses are removed from posts.)

 

I think you are looking for an answer where you've been given one. The spare is meant to get you far enough to get a replacement tire on the other wheel.

-Jim

 

At least now you do get a 16" wheel. My '99 4x4 off-road had a little tire on a 15" wheel for a spare! Just don't drive far on it...not a good thing for the rear end if you have limited slip.

 

The real reason Ford uses a smaller spare is that the rear frame rails are too narrow to mount a full size spare between the rails. The smaller spare has been tested for vehicle dynamics, ride and handling, braking, etc. The limited spare is a lot better than the mini spare you get on new cars.

 

WxBoy - with a limited slip rear end the difrent tire sizes do not matter. Makes the truck ride/handle a little funny, but it will work fine. If you have a locker, or posi-trac rear end, you must use the exact same tire size, but on a limited slip it does not matter -

 

I don't agree. If you have a large tire on one side, and a small tire on the other side....that means the smaller tire is going to have to spin faster than the larger tire to keep up. It would be the equivalent to driving around a curve non-stop. That will cause the clutch-pack in the rear differential to slip constantly, and that surely will put lots of premature wear on the unit. So don't drive far on the spare if you have L/S in the rear end.

I personally think that Ford should give us a full-size spare...it will fit, I've seen people put them under there.

 

Wxboy - buddy not trying to be rude, but you are wrong. Think of this, why would the manufacturer (FORD) give you a spare to use that would prematurely ruin or wear out your rear diferential unit? Spare me the doom and gloom answer of them making work for themselves, you would not have a smaller spare if it was not ok to use. I know what I am talking about here, it is ok to run to difrent size tires on a limited slip rear diff because it a one wheel wonder. Traction only goes to the tire of least resistance, it is not putting power to both of your rear tires, just one. Like I said earlier a locker, or posi, detroit true track or track lock, (I'm not sure what the torsen rear end requires but I am guessing it is a full size spare because it's mechanics are similar to or the same as that of detroit true track), anyway not ok with those types of rear diffs, you need to run the same size spare as what is on the other side. For a short run on your spare to a shop to repair the original, you are not hurting anything on your limited slip. I'm not talking out of **** on this subject this is pretty common knowledge stuff here. Why not call your local Ford Dealership and ask them to explain this to you if you think I am trying to feed you a load of kaka. I do agree with you though that I think it would be better if we all had full sized spares with real tires on them and not some crappy donut.

 

Well here's my opinion. A posi and limited slip are the same, both have clutch packs. Different size tires on he rear end would cause the tires to turn at different speeds and this would cause the clutch packs to slip, allowing the different rotational speed of each tire. Short distances.... yeh it will wear the packs a little but so does every turn, long distance isn't going to be a good thing. If I was buying a truck that had a smaller diameter tire and a posi.... and the correct diameter spare would fit... I would stop the deal right before I signed and tell them to put the right size spare there before I signed.

 

Ken - ok maybe we are not talking about the same thing then. When I speak about a "limited slip", I am talking about an open carrier. Like a standard 7.5" ford rear diff on most 2x rangers. When I refer to a posi - that is a rear dif where both rear wheels have power applied to them, but has clutch packs to diferentiat the turning speed while cornering. Are we just not talking then same language? I agree - a posi, needs the correct size spare, but a limited slip or open carrier rear end - this type of diff does not require the same size spare.

 

When i bought my o1 4x4 in janurary. My spare wasn't even close to the right size. I told the dealer about this He got me a full size spare. It fit fine. My 98 ranger came with a full size spare from the dealer

 

To me.... a limited slip and posi are the same thing, they have clutch packs and both wheels will aplly power. An open rear only applies power to one wheel.

 

Yes, Limited Slip has clutch packs, and a small spare will wear it out. What Waves is thinking of is an "open" differential. I guess those wouldn't be hurt too bad. But a Limited Slip, which is the only thing Ford offers as an option really, would not get along too well if you had to use the spare out on the Interstate or something.

 

Actualy what I "think" of as a limited slip is this:
It is a diff that the power is applied to the tire of least resistance. I other words should you ever have one wheel in the air and one on the ground the wheel in the air spins and the one on the ground you need to turn does not. A torsen, track lock, or detroit true track work the oposite of a limited slip. When moderate power is applied the rear diff, through a series of worm gears (not clutches) diferentiates the power back and forth, but to the wheel of most resistance. For instance you are driving in soft sand as a tire starts to spin, more power will be applied to the other side, as that side starts to spin, it reverses back to the other wheel. Very usefull in sand, can go a long way in 2x in soft sand with this setup. In a posi power goes to both rear wheels. Posi's have a clutch pack, they diferntiate wheel spin when you go around corners through the clutches. Now a locker or lock-right both rear wheels spin all the time. Some systems have a mechanical type method to disengage when not under power to allow for diferntiating wheel speed when cornering. Ok now that we have that - a posi, a locker, torsen, track lock, true track - these types of rear differntial untis require you to have a spare tire that is of the smae heighth at your existing tires on your truck. This way those types of diffs are not ruined by one wheel traveling at a difrent speed. A limited slip, one wheel wonder has no issues by you bolting on a smaller than full size spare in order to drive to a place you can have your problem tire fixed. Once again call a dealer if you don't beleive me, I knwo Fords not perfect but they aren't setting you up for ruining your rear diff if you ever have a flat -

 

You're getting the terminology wrong. You say limited slip but you should be saying open diff. It's not a "tomayto - tomahto" issue. No flame intended.

But back to topic, using mismatched tires is even bad for open diffs. It causes side gears to work all the time, rather than intermittently like rounding a curve, or changing lanes, or hitting pot-holes. It is basically a VERY VERY SLOW one wheel peel. Run like that too long, and you'll blow your diff.

Granted, Ford is saying their spare is limited use. That covers Ford legally. It doesn't cover negligent owners. If I were in that predicament, I'd go back to the dealer and get a proper sized tire. Even better, I'd get a fifth rim, with the proper sized tire, and do a 5 wheel tire rotation. You'd get even more miles out of your tires.

That said, you guys are saying you got 16 inch rims, with an undersized spare. I've got 15 inch rims, and a "full sized" spare.

 

"Limited Slip", the term I am using, is what the sticker said on my last Ranger. The one I have now I bought used, but it has the same type of diff. The mechanic that re-geared and replaced my "limited slip" or one wheel wonder, with a lock-right used this terminology(limited slip, just like on the window sticker). I assume the guy who re-gears and re-builds rear ends for a living is an expert in this field knows what he is talking about when he uses this terminology. As I stated before - it's ok to use the smaller spare with your "limited slip" rear diff to just get to a place you can repair the damaged tire. It's not going to ruin the rear diff. Now if you drive with something like this for an extended period of time - maybe that's another issue, but that's not what we were talking about. We were talking about using a smaller sized spare in order to get to a place where you could repair/replace the damaged tire. Personally I have a full sized spare because of the type of diff I had made, I have no other choice.