dsentel

Tire shop says all 4 tires must be replaced even though rears are much more worn than fronts. It seems to me that the rears are worn enough extra that the current tire diameter is already off. Replacing them with new tread will be similar in tire diameter differential (only rears larger now) as the current situation. In fact, the rears will probably now catch up with the fronts at some point.


Does anyone have the definitive answer for this question the tire installer brought up?

super7pilot

Why would your 4matic be eating rear tires? The power bias is 60 front 40 rear. And are you rotating your tires?

I was told by my MB dealer that 3 or 4/32" F/R difference is where stress will begin to mess with your 4matic system. You DO NOT want to break that as the transfer case & transmission are one unit. Very, Very expensive.

I made it a point to replace my OEM tires with a non-directional pattern tire. That way I can do an X rotation, Thus getting even wear on the inside & out side as well as wearing the individual tread blocks evenly front & back from reversing tire spin every rotation. Which makes for a much quieter tire.

dsentel

Not sure why the rears would wear so much more than fronts, seems opposite to me. The wear is in the middle, so it was not real apparent but I should have checked more closely and rotated much more.


I read somewhere else that others have the same problem with excessive middle wear on rear.


Thanks for the reply, I guess I will play it safe and replace the entire set and then start rotating....

super7pilot

Wear in the middle is generally (well actually always) an indicator of too much pressure. I keep mine at 32-33 PSI.

I also switched to regular tires as run flats are mostly rubbish, far too expensive & ride like a hardtail chopper. And one is up the creek anyway if you have a flat in the middle of the western US and have to limp into the local redneck tire shop that is 100 miles away. Said shop is usually lacking a supply of 19-20 inch runflat tires. May as well just buy regular tires, join AAA and call for a free flat bed ride. Or carry an emergency compressor and a tire plug kit.

ble2716

I am quite sure as the GLK is rear wheel drive bias, so your rear tires would wear out much quicker than the front tires.
I have replaced the rear tires only on my GLK before and it's fine.

3.5L

I replaced the OEM Continental tires on our 2012 GLK 350 4 Matic 2 weeks ago. We bought the car new and got almost 45k miles out of the original tires. I had those tires rotated at every yearly service and it seems to have paid off in even wear across all 4 tires, plus reasonable mileage (they were not quite worn to the wear bar indicators).

I think tire rotation as well as proper inflation is key to achieving even wear on all 4 tires.

For what it's worth, my new tires are Michelin Premier LTX and I love them. Same size as original (235/50 R19 M+S).

Mmr1

I don't believe that 3-4 32nd matters. I purchased a certified used Glk with new rears and fronts at 5/32. 5/32 is the minimum MB can sell a car under the certified program. As far as needing to replace all 4 tires. That isn't true. You just want the better tires on the rear for saftey in emergency handling situations. Put on a better set of tires than the stock Continentals, the continentals are crap when compared to the top Michelin or Pirelli and others.

super7pilot

Holy crap! You should call my MB dealer (509-736-1600) and inform them that MB Hq is wrong.

I have been down this road before when one OEM runflat was damaged and I had to replace all four. Yes it sucked and cost me a bunch. But that's the price you pay if you want AWD.

This is what my MB service center told me:

If the diameter differential of the front Vs rear tires on the MB 4-matic is greater than 4/32" It can & will cause a lot of wear on the center diff clutch pack. This is why it is so much more important to do a rotation on a 4matic MB. I do mine every 5K (which is done for free at Les Schwab)

The front/rear torque bias is 45% front, 55% rear on the Car based 4matic systems. The GLK is a C-class car based chassis. The G, GL 4matic is 50/50 torque split.

Mmr1

Then that statement , rule of operation is in writing somewhere. But I don't think you will find it! Needing to buy 3 extra tires? Sounds like a scam well planned. Did they also tell you you can't fix a Run Flat? Another scam by all dealers. If single tire or a pairs wear was critical it would be in your warranty! Wouldn't it. I went through that same run flat BS scam with BMW for years. They wouldn't fix them, only replace them. But the tire man I've used in Chicago , 42 years! Yes the owner of Associated Tire in Oak Park Illinois fixes them perfectly. The reason dealers don't fix them is there is no money in it. I've found many other tire dealers to be totally crooked, doing whatever they can to just sell you a new tire. Me call your dealer? They don't care. Crooks.

super7pilot

Can you imagine if a "fixed" runflat failed and caused that car to have an accident. Most tire manufacturers state that runflats not be fixed or are subject to the sole decision of the dealer after an inspection. The hard part for the dealer is this: Did the driver tell the truth when they said they only drove for 10 miles at 30 MPH on that run flat to get to the dealer. And is it worth the dealers trouble being sued after they "fix" a run flat that actually went to far at to high a speed? You know that if an accident were to happen, The customer would "claim" that they said they had went to far, But the dealer fixed it anyway. So in this sue happy culture the dealer will be ultra conservative. Even if they did want to fix it. It's not worth the risk.

Pirelli says: A tire should always be changed and not repaired after a loss of pressure, as it is not always possible to establish the time and conditions under which the tire has been used with insufficient inflation pressure.Damaged Run Flat tires, or Run Flat tires that have experienced a loss of pressure should be replaced immediately with another Run Flat tire of identical size and service description.

Bridgestone says: Reparability of run flat tires depends on the tire damage, amount of pressure loss, and vehicle operating conditions. Contact a Bridgestone retailer for details.

Michelin says: If a tire loses all or most of its air pressure, it must be removed from the wheel for a complete internal inspection to be sure it's not damaged. Tires that are run even short distances while flat are often damaged beyond repair. Most punctures, nail holes, or cuts up to 1/4 inch -- confined to the tread -- may be satisfactorily repaired by trained personnel using industry-approved methods.

So Mmr1. It's not so clear cut (no pun intended)

On my GLK. The run flat took a sheet metal screw right in the curve from tread to sidewall. So it was DOA and the diff. In tread depth of a new tire and my old tires was too great to not cause damage to the center diff clutch pack.

Mmr1

Every day they sell 4wd certified used with tires not equal. My Glk had a warranty, I got an extended warranty. My tires were 5/32 different front to rear. I even brought it up as a complaint at purchase. No where have I seen in writing this "Tire issue" they told you about. If they can't give you a written factory warning, they owe you for 3 tires. I think tire scams are everywhere. Small claims is cheap!

Mmr1

True and not true, an experienced tire guy can check for damage, knows how to check for damage. But I agree if you drove on it flat that it's a risk, in my case we had maybe 6 repairs done but on most we noticed the leaks and got them fixed before it even got low. The point is if you go in to the dealer and it's only loosing a pound a week and it's at 33 and never run out of air , your dealer still won't fix it. Now that's Bs.

super7pilot

This is for you Mmr1, Being the sort that believes in fair play. I have no issue admitting when I'm wrong.

In this case I was at least partially wrong. Out of curiosity I called a very large German auto specialist shop in Portland, Or and talked to a guy that knows the 4matic system very well. When I posed the OP's question. He stated that while there is no documentation at MB about tire size differential.

And said that the size difference wouldn't immediately torch the center diff clutch plates, It would however cause unnecessary accelerated wear. As the clutch pack is designed to prevent binding (gear train wind up) when cornering (short duration event) and not slip 100% of the time while going straight down the road. Akin to riding the brakes lightly.

So I guess it could boil down to picking ones poison.

I guess the tire shop issue is a sticky one. Taking a customers word as to how far & how fast they drove on a deflated run flat could come down to how much a shop wants to start gambling with lawyers.

Mmr1

I'd have to see something in writing from MB to think a front - rear tire size difference (of tire wear) matters at all. Another point is front tires wear faster, and for me in the city I think I'll trash a set of continentals in the front, in 10000 miles. My point is the fronts for me will always wear and be a bit smaller, I just don't think it matters.

Sure if you drive a run flat with zero air for miles, it could be best to replace it. Only once did I drive a flat, all the other times it was a slow leak the dealer refused to fix, so I had a tire shop I've used for over 40 years repair it. And the owner of the shop was not worried about liability, he is the same owner I met in 1974! My point is, the refusal is profit motivated.

Mmr1

How many miles were on your tires , what was tread depth?

Here is something interesting. A friend bought the full tire insurance for maybe 1700. They had a slow leak, the dealer replaced one tire. Vehicle had 15000 city miles. I don't know how worn they were.

i wonder what the dealer would have done if you had the extra warranty.

super7pilot

Mmr1, I of course had the rubbish Bridgestones. The screw I took happened at only 10,000 miles and the tread depth differential of the new one was already 4/32nds. Those OEM stones were wearing fast as heck. As I have the 250 Diesel, it's no hotrod and I drive it like a diesel & mostly hiway miles. Except when we drove to Croatia over the Austrian alps, That was a bit twisty & steep. So I was very shocked at the rate of wear.

The screw went through the apex of the transition zone from the tread/sidewall. Having worked years ago at a goodyear dealer, I knew that even a non run flat would be toast from a puncture at that spot. Never did care for run-flats any way. So I was glad to be rid of them.

bop11

This vehicle does not have locking differentials. Traction control and anti lock are accomplished via sensors and application of the brakes.Tire rotation differences across the axle is taken care of by the differentia since they are "open". A slight difference in tire diameter between a new and a some what used tire of the same type does not strain the transmission. Most roads have a crown which causes the car to be steered up the crown. This is accomplished by the correct alignment so the driver feels he is driving straight. All turns cause the inner wheel to rotate slower than the outside wheel and most roads are not straight so you are almost always causing one wheel to turn faster or slower than the other. Replacement of a wheel on an axle with a new wheel of similar tread and traction characteristics should not affect the wear of the transmission. Replacement of one tire with a new tire of different tread pattern would definitely affect the stability characteristics of the vehicle and should be avoided. Even with significantly different diameter and tread, such as the inflatable doughnut spare, driving can be tolerated by the differential but should be used only for short distances because the handling is greatly affected.

vonriess

I was in a similar situation as the original poster; one of my tires received a sidewall puncture and needed replacing. I bought two new Cooper Zeon RS3-G1 tires online, which were the same size as the original tires 245/40R18, and planned on having them installed at a local tire shop. After calling around and visiting a few shops several said they would not install two tires on a 4Matic (I have a 2013 E350 Wagon) because it could possibly overstress the center differential and cause damage.

I eventually found a small shop to do it. But they would only put the two new tires on the front, stating that they would wear faster there and become compatible with the worn rears quicker. Also, they wanted me to sign a waiver exempting them from any possible damage that might happen (I didn’t sign a waiver as they said they didn’t have any more. Did they ever?)

I understand in principal how using tires of different circumferences make rolling distances longer/shorter and could make a full-time AWD work more. But if this is such a major issue why isn't the need to keep tire circumference tolerances close mentioned in the vehicle's owner's manual or posted on Mercedes Benz's website? I feel like most of the information driving this thinking is coming from tire shops.

If driving with tires that have 4/32" difference in tread is such a major concern then why would Mercedes Benz provide me with a compact spare? Since the spare is a different size than worn tires that it’s paired with, that action by Mercedes seems to counters what is being mentioned. Also, the difference in tire wear between front and rear tires over time in many cases is more significant than 4/32". How is that accounted for?

Are we hearing about center differential/transfer case failure much at all? Of such failures can it solely be attributed to difference in tire size? I think that would be hard to prove.

I know that the engineers at Mercedes Benz are smart and surely they realized how to deal with differences in tire circumference when they designed such a system and developed real world tolerances into the 4Matic system. Otherwise I feel that we would be hearing of a slew of problems about 4Matic cars, which have been built since 1987, and I don’t see that happening.

googuse

Who is your go-to guy in Portland?