Varying tire tread depths will damage drive terrain

[ignis]

I just got a call from my mechanic. He claims the tire treads are all at different depths which is a very bad thing and could ruin my drive terrain b/c I have a 4WD vehicle (2002 Ford Explorer). So, he wants to sell me 4 new tires.

I'm thinking B.S!

I'd love to hear the thoughts from the members of this forum?

 

[v8mouse]

I think he or you meant drive train! LOL
Terrain is what you drive over.
If the tires are within the safe limit for tread depth I would say b.s
If they are bald I would buy new, most important part of the car I say!

 

[robeyster]

My father inlaw is a mechanic at the local ford dealership he has told me if I replace the tires on my explorer I should buy four new ones because the truck has automatic 4 wheel drive the different tires will offset everything the trucks computer reads. I think this mechanic is not BS you.

 

[cybergasm]

we just went through this in a another thread here:

http://www.explorerforum.com/forums/showthread.php?t=279366

if the tires differences are Minor then you should have no issues. I you are running different sizes then you could have a problem then.

 

[EasyRhino]

I say BS.

I do not measure the tread depth on my Explorer, but as the tires on my C6 Corvette are 300+ each, and being a sticky compound tend to wear out quickly (only got 28K out of my last set of front tires) I do measure them 2x/year.

Here's what I have learned (this is all for the C6): The tread depth is about 10/32-11/32 when new, and at 2/32 the tread wear/low tread depth indicators go solid, leaving 8/32-9/32 of wear available to sue from "new" to "replace". That translates to a total tire diameter reduction of 16/32 to 18/32 over the life of the tire, or approximately 1/2". Since the tires are 19" on the rear and 18" on the fronts (that's wheel size of course), and the sidewalls are about 3-4", the overall diameter of the tires is about 23" which is reduced to about 22.5" when worn out (BTW, that's why speedometers are off typically, as tires get smaller, your distance/revolution goes down, therefore, per shaft speed actual car speed goes down - but that's another posting). Anyway the delta between the distance travelled from new to old tire is about 2% for the Corvette.

Where I am going with this is that NO car traction control system is reasonably calibrated to respond to a delta of the range of 2%.

The way to sort out your tire situation is:

(1) assuming all tires are identical (size).

(2) (public service announcement) - rotate them and you won't have an uneven wear problem.

(3) as long as the front to back are all within normal range (one axle set is brand new and the other within the non-worn out range) I would do the calculation to determine the delta % rotational distance travelled. First, if the tires are all the same kind and replaced the same time, then in the worst condition what are the chances that one axle is worn down significantly and the other set is brand new from a tread weat standpoint? (This is why I called BS).

(4) Once you determine the delta %, ask the dealership what percentage is okay (you'll stump them on this, uncovering their sales tactic - they'll have no clue). If they try to get technical, ask them at what x/32 difference front to rear does Ford recommend replacing the tires (and ask to see the technical guidance)?

(5) If there is such a huge delta, then why doesn't the dealership recommend trashing the low set and keeping the newer ones, only replacing two?

(6) The guidance in the book is to use mtaching tires, not to match the % wear, for crying out loud.

(7) Find a new dealership. I hate places that take advantage of others to transfer money from other's pockets to theirs.

(8) Tell them why you are taking your business elsewhere.

(9) Post the name of the dealership here so we can know to avoid there.

(10) Let them know that you are going to post thier name here.

Enjoy

 

[tv4fish]

I agree ---- TOTAL BS -- Rhino - excellent post

 

[mikeinri]

Yes, I'm thinking BS too. Even if you had AWD, I can't imagine the remaining tire life making that much difference.

Mike

 

[gbranh]

I have a 2002 Explorer, AWD. We replaced the front two tires last fall. They were dimensionally the same as the rears (265/60 r17, or whatever the stock size is), but a different brand. As soon as I got it on the road, it ran like crap; lurching, tires grabbing the pavement in turns, etc. It was a mess. I took it right back to the tire shop, and the manager said the AWD computer was getting fouled up due to differences in overall diameter from the front to the rear tires. I asked him why he let his tire jockeys put only 2 tires on my truck if he already knew this, and I also asked him why my tires were different overall diameters if they were dimensionally the same, according to the sidewall numbers. He said overall diameter varies from manufacturer to manufacturer. The put the old front tires back on, and sure enough, no problems.

So, I went home, got on tirerack, and looked at the specs on my front and rear tires. Sure enough, there was about 1/8" difference in overall diameter, and with the rear tires being a bit worn (but not too bad), the total difference in overall diameter from the front to the rear was less than 1/2". But, that equates to something like 700 revolutions per mile, so yeah, even a small difference in diameter can screw up the computer.

If you haven't rotated your tires in a long time, and you have, say, really bad wear on the fronts but not the back, then I could see his point.

Greg

 

[jrford]

looking for my slide-rule to double check the math. . .just kidding. LOL.

Good write up, i was almost going to say i agree for the most part with easyrhino with CommandTrac (Dash Switches, BW4411). . .but i do keep reading experiences like gbranh above. CommandTrac is activated as needed so most of the time 4wd is off. I'd like to know what the mfg spec is but haven't found one. Your calculations seem on the money.

A little off topic of the OP i don't think he has AWD but rather 4wd. On the other hand with AWD (which is commonly misused but there are no switches on the dash, also known as the BW4410 with a Viscous Clutch). This critter might be a little more sensitive as the system is always on and/or the clutches work 100% of the time. They have to slip in turns and lock up when it gets slippery.

But from reading the heep forums with their Quadratrac (similar in function to the BW4410), i thought the rule of thumb is no more than 1/2 inch difference, but are they talking diameter or circumference - not sure. Also there was reference to a problem Chrysler had with their minivans and AWD. They had to replace a large number of viscous units under warranty, got to be expensive so they investigated. The discovery was the minivan moms where not rotating the tires, which caused premature failure of the viscous.

The thing i'm doing to reduce the chance of frying my viscous is a 5 tire rotation every 4k miles; 5 tires in case one blows out 3 years from now, i'll still have 4 fairly even wear tires, in theory. From what i've read those viscous are expensive and hard to find.

Diameter will give you the circumference, what might be more helpful is to find the circumference, by marking a line on the pavement and one on the tire, rotate the tire one revolution and measure the difference, repeat for all 4, once you have all the measurements you can go from there.

just some thoughts.

 

[safn1949]

I discussed this with my shop and he confirmed that on the AWD it is a must to have evenly matched tires.I just bought the 2000 so I am taking the front tires on my 94 with 700 miles on them and switching them over to the 2000.Putting a new set on the rear of the same tire.It has 2 different brands of tire on it now and a lot of driveline vibration.

I'm not going to take a chance of tearing the front end and transfer case up as he said he's seen over and over.Plus the rear tires on the 2000 are crap anyway and I'm going to put 31's on the 94 next year.My advantage is the tire shop does lifetime rotate and balance if you buy from them.

So,2 new Goodyear Wranglers,235/75/15 and remove 4 tires,mount 4 tires,toss 2 tires...$300

 

[Beachbum_va]

t

 

[Beachbum_va]

I have a 2002 Explorer, AWD. We replaced the front two tires last fall. They were dimensionally the same as the rears (265/60 r17, or whatever the stock size is), but a different brand. As soon as I got it on the road, it ran like crap; lurching, tires grabbing the pavement in turns, etc. It was a mess. I took it right back to the tire shop, and the manager said the AWD computer was getting fouled up due to differences in overall diameter from the front to the rear tires. I asked him why he let his tire jockeys put only 2 tires on my truck if he already knew this, and I also asked him why my tires were different overall diameters if they were dimensionally the same, according to the sidewall numbers. He said overall diameter varies from manufacturer to manufacturer. The put the old front tires back on, and sure enough, no problems.

So, I went home, got on tirerack, and looked at the specs on my front and rear tires. Sure enough, there was about 1/8" difference in overall diameter, and with the rear tires being a bit worn (but not too bad), the total difference in overall diameter from the front to the rear was less than 1/2". But, that equates to something like 700 revolutions per mile, so yeah, even a small difference in diameter can screw up the computer.

If you haven't rotated your tires in a long time, and you have, say, really bad wear on the fronts but not the back, then I could see his point.

Greg

this is the only post you should read, the others are t well informed and the mechanic is correct!!!!!!!!!!!!! My 2004 eddie baur 4.6l had the same issuee and it did cause the drivetrain to lurch,,when quoted witth t he cost of tire replacement I was not happy nor did I think it w ould fix my issues,,,,,had plannedd on scamming a new set of t ires for free when it didntt fix it even. Well it did repair it and there was no possible way with the nekkid eye to see a difference in tread in any of the 4 used ones,,,turned out that the difference in tread wear causedd the transmission to lurch into and out of 4wd,,,,at 80 mph on the interstate it felt as though the ttransmission was going to fall out of it,,,either listen or dont it is your choice and your checkbook when the transmission hoses you in the not to distant future.

Good luck and BTW for those thinking still bs I did not have this issue until I had the service dept roate my tires, the next day it appeared,,,my explorer is a 4wd and d oes not have the traction control so this is not the answer,,I was told that that slight variance would and will ruin a 4k transmission

 

[imp]

AWD vs. 4X4 AUTO

I discussed this with my shop and he confirmed that on the AWD it is a must to have evenly matched tires........

Well, after all the posts here, I finally view this as good reason to opt for, if possible, "4X4 AUTO" rather than "AWD", if a choice is possible. As I understand V-8 Explorers were not given the 4X4 AUTO type normal driving set-up, insisting on a V-8 requires acceptance of the "4 identical tire diameters" requirement. imp

 

[Curtis]

Well, after all the posts here, I finally view this as good reason to opt for, if possible, "4X4 AUTO" rather than "AWD", if a choice is possible. As I understand V-8 Explorers were not given the 4X4 AUTO type normal driving set-up, insisting on a V-8 requires acceptance of the "4 identical tire diameters" requirement. imp

My 04 V8 is 4x4 Auto...

 

[imp]

My 04 V8 is 4x4 Auto...

Do you then have the choice of manually picking 4X4 HIGH or 4X4 LOW by pushing the appropriate button? As I understand it, the "AWD" version has no such choices available at all. imp

 

[Curtis]

Do you then have the choice of manually picking 4X4 HIGH or 4X4 LOW by pushing the appropriate button? As I understand it, the "AWD" version has no such choices available at all. imp

Correct, I have the 3 buttons to the left of the radio.

4x4 Auto
4x4 High
4x4 Low

And yea the AWD versions have no buttons, If memory serves me right, there are no electronics involved in the AWD system, just a viscous coupling that engages the power. Maybe someone else can confirm or correct me. I remember a thread about 2 guys, one with a 2wd explorer and one with a AWD mounty, and they were considering switching all the components as no computer changes were involved.

 

[manaen]

There was a series of gen3's that had AWD, 4x4, 4x4 Low

Either way, even the 4x4 auto could have problems with tire size differences. It goes like this. The computer uses the speed sensors in the wheels to determine if the rear tires are slipping (spinning faster then the front) if they are it varies the voltage sent to the TC to engadge the 4wd system and send power to the front. I personally do not know what the percentage of speed difference must be to engage the 4wd. However my mounty has the auto 4wd and it shift very fast . To the point that I almost at times don't even know the thing is engaging in offroad situations. At one point I thought about trying to create an indicator light driven by the voltage at the shift motor to see if I could create some indicator of the TC's status. But I have more pressing things to do with my truck right now so I decided to put the idea on the back burner.

Anyway my point it depending how different your tires are I would say that it could be absolutley true. One thing to consider is to always make sure you have the largest diameter tire mounted on the rear so they will always be spinning slower then the front which should in theory eliminate the problems on a 4wd auto equipped vehicle.

But I am hoping someone has some more insight on the technical details of the computers shift data.

 

[rhauf]

I just got a call from my mechanic. He claims the tire treads are all at different depths which is a very bad thing and could ruin my drive terrain b/c I have a 4WD vehicle (2002 Ford Explorer). So, he wants to sell me 4 new tires.

I'm thinking B.S!

I'd love to hear the thoughts from the members of this forum?

this is only true on some ALL WHEEL DRIVE vehicles (which is very different from 4 wheel drive).

you're 4 wheel drive vehicle is actually only 2 wheel drive unless you have 4 wheel drive engaged. (and even then mismatched tires aren't a problem unless they are way, way off).

time for a new, more honest (or smarter, or both) mechanic.

 

[DVRDOWN]

I say no B.S. I've got an '02 with BFG Rugged Trail's same as OE. When i bought new tires a few years ago, i only bought 3, and reused the original spare tire for the 4th. There was a TSB on the tires when i was at Belle Tire, because BFG slightly redesigned the tire, and the overall dimension was just slightly different. I installed them anyways. No issues for quite awhile, but as my tires wore down i started having issues. I rotated my tires in a manner that i had both an old and new tire on the rear of the vehicle, and my truck went nuts. I had very bad lurching, especially at highway speeds, as my computer was sensing different wheel speeds and engaging, and disengaging (i am assuming) my 4WD. Once i figured that was the problem, i rotated the tires back so that an old and new were at the front, and all problems stopped. So my 2 cents is that its not b.s., but if you've never felt any issues then i wouldn't worry about it!

 

[manaen]

this is only true on some ALL WHEEL DRIVE vehicles (which is very different from 4 wheel drive).

you're 4 wheel drive vehicle is actually only 2 wheel drive unless you have 4 wheel drive engaged. (and even then mismatched tires aren't a problem unless they are way, way off).

time for a new, more honest (or smarter, or both) mechanic.

Keep in mind the newer 4wd vehicles have Auto 4wd which will automatically shift into 4wd on the fly (started on some Gen2 models). What you said is true for the older style 4wd that is normally in 2wd until you shift it into 4wd. However with the computer controlling the TC shifting by using the speed sensors tire size could be a problem.

Anyone really worried about it could do the infamous "brown wire mod" which basically disconnects the computer from the shift motor and eliminates the AUTO 4wd setting and makes your truck true 2wd again.


There are also TC's in Gen 3's that have AWD, 4WD, 4LO selection in this case it is even more crucial to match tire size.