Spare Tire Strategy

[sfbayjay]

Hypotetical question for discussion related to flat tire, spare tire, and AWD. Hoping for some fun discussion from this one!

Say you're on the freeway somewhere and have a flat or blowout or whatever. You've been running stock 235/70R16 tires on stock rims for like 35K miles on your truck. Good about rotations, etc., so they're all wearing evenly.

EXCEPT, your spare tire hasn't been in the rotation program.

So, you've got a pretty new spare tire and some decent, but somewhat worn tires on the ground.

Now, you have to get to a tire shop or whatever for a repair. Figure you're in Nevada or something where you'll have to drive for awhile.

If you put on the spare, you'll have one tire that's slightly bigger than the rest.

This is a bad scenario for an AWD or 4WD Auto vehicle, right?

So here's the questions:

(1) Where is the best place (i.e., front or rear axle) to put the bigger spare tire for your run to the repair shop if you want to avoid damage to your drivetrain?

(2) I just learned (from other posts on this forum) that you can defeat the 4WD module by removing power fuses (under hood) 17 and 18. Would pulling these fuses and putting the larger spare on the front axle be a good strategy? Would it make any difference?

Only curious here -- haven't actually run into this problem, but I've been researching new tires for my XLT and it got me thinking...

Look forward to responses!

 

[tv4fish]

My opinion - Not that big of a deal - put the spare on the place where the flat is. I believe if Ford was concerned about that being a problem, you would have all sorts of "Warnings" in the Owners Manual, stuck all over the spare tire, etc.

 

[rrgone]

Yeah, you would think there would be warnings in the Owner's Guide...

I would just put the spare on in place of the flat and drive it a bit to see if it sets off the 4WD. If it does, then pull the fuses or disconnect the module until you can get the flat repaired. If you are in a snowstorm somewhere at the time then put it into 4 High until you can get out of the storm and/or fix the flat.

 

[jrford]

just to differentiate between 4WD (Switch on the Dash) and AWD (no switches). There is some difference in how they operate and thus how they affect the drivetrain.

4WD - depending on the difference of tread depth it might try to activate the 4wd. Note this 4x4 systems uses a full lock of the transfer case and turns off as needed, many times a minute. You might burn that motor up. Here i would pull the fuses. . . but it may not care so then all will be fine.

AWD - this is always on and engaged, the clutch plates will slip as need but lockup if the they are allowed to spin freely in relation to each other. With a different sized tire long term there has to be some wear on those plates, how much and how long before it wears out i don't know. But that Viscous clutch is over $600 alone, not including the rebuild. Chrysler a few years back with their AWD minvans found a lot of premature failures of the Xfr case. Their system was similar to viscous AWD system in the Ex, What they reportedly found was people who didn't rotate their tires at all were the ones that had the xfr case replaced under warranty. Rotation is very good in this case.

I would think unless it starts behaving badly right from the get go, i would expect you could get across Nevada but imho i wouldn't make it a round trip. . .to much to lose in the long run.

To try and eliminate the negative possibilities i just bought and put a full spare/stock rim and its in the rotation (4k for me with the oil change). I also discovered a side benefit, rotation is a lot easier as i only need one jack, before i had to use two for one side and rotate front/rear.

Hopefully someone will post their findings from experience. . .i'm trying to remember last time i had a flat. . but i don't want to jinx myself. lol

 

[rrgone]

Good post Jim. I wasn't thinking about AWD at all, even though the OP asked about it.

 

[tv4fish]

Appreciate the post/info Jim - BUT I will stick by my first post. Don't you think that if it REALLY were a concern - (esp. in our litiguous society) that Ford WOULD have addressed it? Also - does anyone have any documented data that shows at what point the tire size difference kicks in the 4WD motor? Not being argumentative here - but at some point common sense has to enter the picture ??

 

[briwayjones]

It seems that from what people have been posting lately about problems with late model Explorers with 4wd and tire size difference is that would be enough to cause problems on a late model 4wd Explorer.

 

[Gus Gorilla]

1/2 inch difference in circumference is the recommended max amount. But what it takes to bother AWD or Advance Trac? Who knows.

 

[Thelt]

What if your spare is a 235/75/16 and your tires on the ground are 265/75/16?

 

[jrford]

Great questions tv4fish, :biggthump:
As to the Size difference there must be some spec, but I have yet to find any definitive answer either.
But the owners manual does state (’04): “5,000 rotation, . . . make sure all tires and wheels are of the same size type tread design, brand, load-carrying capacity and speed rating because it can affect the safety and performance, etc . . . .pg268, 271
So the spare should also match.

The powertrain warr. Is only 36k, which is not much time for anything to go wrong, no matter what you do to it, then when it does fail after that time, its your responsibility.
If you have an extended warranty and one fails, I don’t know what they will say, never been there. My guess if they can pull that quote out they will, that also could be an individual call depending on the circumstances.

In another forum, not to be mentioned here, (if you search on ‘247 to 242 swap’ you’ll find some good reading), I’ve been following that forum for a few years, and I’ve read about many 247 failures from 60k on up , they can last a long time, but it seems that more of premature failures seemed related to tires in some fashion. Their Viscous nv247 is similar in function to our AWD (no switches) so it kinda relates to ours. They also go sooner than their counterpart the nv242 which is similar to our 4WD but with the BWM too, it has an additional 2wd mode, tire size is not an issue with this type, heck sometimes the spare is only a donut on the non LSD models.

After reading about those failures, checking on the cost of the rebuild $600-1200, they are not cheap, plus time and hassle, I’d kinda of want to error on the paranoid side of things and keep the 4k 5tire rotation, who knows in the end, I may be stuck rebuilding it anyways at a 100k??? lol.

 

[coghij1]

I know this is an OLD thread, but hey, what the heck...

While reading some other threads on this forum about the limited slip differentials and 4x4 auto with the selector switch on the dash, I heard quite a bit about the importance of matching the tire sizes as best as possible. I can't recall off the top of my head at what difference problems start to occur but I CAN share an experience I had a couple years ago.

I have an 02 XLT V8 with the limited slip diffs and auto 4x4 and was running oversized 20" wheels and tires all around. One day, I got a flat in one of those tires (front passenger side) so I pulled into a parking lot to throw the spare on. The circumference difference between the two is actually a LOT more than one would have with one new and one used of the same tire. Immediately upon attempting to drive away, I experience some very obnoxious clunking type noises. I can't remember exactly what it sounded like but it wasn't good. I pulled over again and had a buddy drive me to get my tire fixed, put the 20" back on, and problem was gone.

After this I learned'd myself all about the limited slip and the transfer case function. To eliminate the possibility of being stranded somewhere again with a flat tire, I did the brown wire mod, which is similar to pulling the fuse you mentioned. Now when I need to thro the spare on I can flip a switch and dissable the transfer case from sending power to the front diff.

In regards to the BWM, I never use it for any other reason. I've heard of people using it to try and improve fuel economy but I don't mess with it. The transfer case will load 95% to the rear and 5% to the front during optimal traction and "light" throttle, and when needed it can split the load in increments up to 50/50 front and rear.

Geez, I really didn't mean to ramble on here. Sorry. Just thought I'd share my $0.02 in a dead thread.

 

[huntman58]

Old post but I will add some info to it any way as who know it may help some one some day!

On a limited slip rear end a deference of only 3/4 inch was enough to destroy my dive axel set up (limited slip)! This was after I cut three tires (side walls as I was aired down to only 15psi) on some obsidian in eastern Oregon deer hunting some years back. Got a ride to town and all they had was three tires. They were a deferent brand then mine but labeled as the same size so I thought I was okay after all there the same size right? Wrong! So after getting towed in to town and paying to have the rear rebuilt I learned, as I was shown the deference and what happened and why. Lesson I will not forget! can not speak on a AWD but I do know on some you can pull a fuse and it turns it into a 2wheel drive normally as a front wheel drive. Told my son this and he has tried it on a Subaru and it dose just that no power to the rear just the front and in fact it’s what there manual tells them to do when using there space saver spare.

 

[Tarpman]

I've been woundering about this myself. Would it help if you have done the BWM (brown wire mod)?

 

[joney]

Hypotetical question for discussion related to flat tire, spare tire, and AWD. Hoping for some fun discussion from this one!

Say you're on the freeway somewhere and have a flat or blowout or whatever. You've been running stock 235/70R16 tires on stock rims for like 35K miles on your truck. Good about rotations, etc., so they're all wearing evenly.

EXCEPT, your spare tire hasn't been in the rotation program.

So, you've got a pretty new spare tire and some decent, but somewhat worn tires on the ground.

Now, you have to get to a tire shop or whatever for a repair. Figure you're in Nevada or something where you'll have to drive for awhile.

If you put on the spare, you'll have one tire that's slightly bigger than the rest.

This is a bad scenario for an AWD or 4WD Auto vehicle, right?

So here's the questions:

(1) Where is the best place (i.e., front or rear axle) to put the bigger spare tire for your run to the repair shop if you want to avoid damage to your drivetrain?

(2) I just learned (from other posts on this forum) that you can defeat the 4WD module by removing power fuses (under hood) 17 and 18. Would pulling these fuses and putting the larger spare on the front axle be a good strategy? Would it make any difference?

Only curious here -- haven't actually run into this problem, but I've been researching new tires for my XLT and it got me thinking...

Look forward to responses!

Yes it's an OLD thread, but - I've got 4wd on my 98 XLT and NO spare...just the rim. PO sold it that way. Tires all match and seem to have at least 3/4 of the tread left. A new one of what I have isn't real expensive - but it would be bigger around. Suggestions?

 

[Gary Crist]

I hope you do not take this wrong. Why not measure the tires with a piece of string?

Just because it says 235/70-16 etc. not all tires even new are the same size (in circumference)
from manufacturer to manufacturer sometimes in house too.

Some mfgs. will give a REV per mile too to help in one's selection.

Here is a story from when I ran a tire store in Anaheim CA.

A customer came in to buy a set of retreads, 225 78-15 for his Caddy. I did not
have any repops in his size so, I sold him a set 235 78-15 instead.

Several days later, he came back in and tipped me $20 for selling him these "special"
tires! ????????? "Special ?" I asked.
"Yes, those new tires shortened his trip to Vegas by several miles"!

Oh well take the money and run.......

 

[joney]

I hope you do not take this wrong. Why not measure the tires with a piece of string?

Just because it says 235/70-16 etc. not all tires even new are the same size (in circumference)
from manufacturer to manufacturer sometimes in house too.

Some mfgs. will give a REV per mile too to help in one's selection.

Here is a story from when I ran a tire store in Anaheim CA.

A customer came in to buy a set of retreads, 225 78-15 for his Caddy. I did not
have any repops in his size so, I sold him a set 235 78-15 instead.

Several days later, he came back in and tipped me $20 for selling him these "special"
tires! ????????? "Special ?" I asked.
"Yes, those new tires shortened his trip to Vegas by several miles"!

Oh well take the money and run.......

Looping a string around the tire halfway up and across the hub so it's centered, I hope will give me a measurement, I have some garden wire that won't stretch. Would be an odd measurement but hopefully I could duplicate it across all 4 tires, and on any spare that I'm looking at - IF it's on a wheel. Could get the actual circumference if I jack up the truck. Thinking of going to tire shops where they have used ones. Thanks for the idea, funny story too!

 

[TechGuru]

IMO the spare should go on the front when possible as the front diff does not have a LSD and the rear does (usually). If your rear don't have a LSD then it don't matter.

 

[jamie8470]

I've been woundering about this myself. Would it help if you have done the BWM (brown wire mod)?

Can anyone confirm/deny this theory? I don't want to put a 235 spare on if it will wreck my truck.
I have 265s with a 235 spare and I'm thinking about doing the BWM.

Is it possible to just fit a 265 tire in the spare tire holder anyhow?

Thanks

 

[joney]

Looping a string around the tire halfway up and across the hub so it's centered, I hope will give me a measurement, I have some garden wire that won't stretch. Would be an odd measurement but hopefully I could duplicate it across all 4 tires, and on any spare that I'm looking at - IF it's on a wheel. Could get the actual circumference if I jack up the truck. Thinking of going to tire shops where they have used ones. Thanks for the idea, funny story too!

As I hate a thread without an ending, I ended up getting a random spare, with the correct numbers, from a towing place, took it to a shop to have it mounted, and found the mechanism that lowers/raises the spare tire, actually still worked. Put the new old spare back under the truck. As I have a compressor and jack now, not worried that the spare may not be the same exact diameter - in an emergency, should get me to somewhere I can have the original flat repaired, should it come to that. And another friend has the same exact tire I have, going to get it from him as a backup.