Do the front tires always have to be a bit larger?
Or as long as they are within a certain % is it OK even if smaller by that %?

For example stock they are 1.2% larger in front
What if you flipped that and made the rear 1.2% larger instead
Would the 2.4% "swing" in front to rear bias in the transfer case be bad ie: did they design it to know the front was always 1.2% larger tire and rolling slower?

asking for a friend (lol)
<whistling innocently>

Googling like mad and asking AI too, it seems 2% front/rear or rear/front (ignoring any "swing") will wreck the 4matic. Anything over 1% is "risky". Is this correct?

My new setup is 2% larger in the rear, and I'm worrying. I ran it for a couple months last year and <knock on wood> no damage yet.. but.. could this take out the transfer case?
For reference everyone running 305/275 is at 1.4% front/rear vs my 2% rear/front

 

It's a good question I do not know the answer to but curious to hear what others have to think.

 

3% is the rule with 4matic. There cannot be more than a 3% difference in rolling diameter between the front and rear tires. It does not matter if it is front or back biased. There will always be some bias as the tires wear differently from front to back and you cannot rotate the tires.

 

Ideally, you want an identical rolling diameter front to rear, but the system does allow for a degree of variation from front to rear.

Older systems (apparently) allowed 2%-3% variation, whereas newer (like the 9-speed 4Matic in the W213/S213) apparently has a ~1% tolerance for variation front to rear.

The factory option 20" tyre/wheel combo on my E43 is 245/35R20 front and 275/30R20 rear, which has a 1.2% variation (fronts larger). On the "stock" 19" tyre/wheel combo (245/40R19 and 275/35R19), the variation is 0.7% - again, fronts larger.

I've been looking at 255/40R18 tyre on an 18x9 ET35 setup, but likley going 19x9 as people are concerned about 18" wheels clearing the calipers.

 

.

 

so unlike other 4matic systems

The 4 matic+ is rear biased (ie can send 100% of the power to the rear) which makes the fronts sizing not as important.

WITH THAT Said. that is only for the 4matic sub-system,

The ABS system on the other hand will have a panic attack due to the sizing difference and that will impact ABS, traction control and all the nannys for traction.

 

Copilot, ChatGPT, Gemini, all give different answers different times of the day. Some days "It's well within specs" other days they say "YOU WILL DIE".

One AI told me "Mercedes engineers have stated no more then 1.6% difference" so I asked "Show me where Mercedes Engineers stated this" and it said "Actually there is no document from Mercedes but these experts stated" and the Experts were people arguing on Reddit.

ECC just had to rebuild a transfer case for mis matched tires, it was in one of their you tubes so I am wigged out. They did not mention the sizes.

I'm getting nervous and will probably change up the tire sizing to be closer to 1% unless I can find definitive proof 2% is ok.

 

I had AI make a chart to see what Mercedes does

 

I made a chart with the tire options to run. Highlighted is what I have mounted and ready to go on now.
I also have 3 x 295 PS4S's in the basement.

Get 1 x 295/30R20 PS4's and run 295 square for 0% difference. But, the rear rims are 11" and front 10.5" so I'm worried one maybe be able to see that the front tires are "chunkier" looking vs. the slightly more stretched rears. It's only 1/4" a side, who knows. This leaves 4 barely used ECS02's to get rid of.
Get 2 x 305/30R20 PS4's and use 2 of the 295's I have already on the front. This leaves 4 barely used ECS02's and one PS4S to get rid of.
Get 2 x 295/35 ECS02 and run those with the 285 ECS02's on the front. This leaves me with 3 used PS4's and two ECS02's to get rid of and keeps the taller tire height look.

Now I totally realize why everyone runs 305/30 and 275/35. Because the experts figured all this out back in 2017.
HAHAHA.
What an exercise this has been!

 

So as you well know being in IT... AI is really a bot and that bot parrots answers on what it is fed.

The motto still applies, Garbage in, Garbage out.

Without direct access to StarTek, WIS, etc. It is guessing based on anecdotal information of public forums.

 

Well Grok has this to say:

The ~2% delta (15 revs/mile difference) between the Continental ECS02 305/35R20 (731 revs/mile) and 285/35R20 (746 revs/mile) is not too high for a 2023 Mercedes-AMG E63 S 4MATIC+ and is unlikely to cause immediate or catastrophic damage to the transfer case.

The 2023 E63 S 4MATIC+ (W213) comes factory-staggered with 265/35R20 front (761 revs/mile, ~27.3" diameter) and 295/30R20 rear (770 revs/mile, 27.0" diameter). This gives a built-in front-to-rear rolling diameter/circumference difference of **1.1–1.2%** (rear spins slightly faster). Mercedes designs the 4MATIC+ system (multi-plate clutch pack in the transfer case with variable torque split, up to 100% rear bias) to tolerate this small mismatch plus normal tire wear.

Your proposed 2% delta is roughly double the stock mismatch but still falls within the commonly accepted 2–3% safe range for Mercedes 4MATIC/4MATIC+ vehicles (including AMG models). Multiple Mercedes owner forums, mechanics, and technical discussions confirm: Differences under 2% are ideal and essentially problem-free.

Up to ~2.5–3% is generally tolerable (the system’s clutch pack and ESP can compensate without constant binding or codes).

Over 3% starts to risk overworking the transfer case, leading to heat buildup, fluid breakdown, and accelerated wear.

Real-world outcomes at ~2% (same brand/model tires): Not damaging in normal use — Many E63/E63 S owners run aftermarket staggered setups with 1.5–2.5% deltas (e.g., 265–285 front / 295–315 rear) without transfer case failure.

Possible long-term effects (if driven hard or for 50k+ miles): Slightly faster clutch pack wear, earlier fluid degradation, or need for more frequent transfer case fluid changes (Mercedes recommends ~40k-mile intervals; you might want to halve that).

No widespread reports of 2% deltas causing sudden failure, ESP/ABS faults, or binding on W213 E63s when tires are the same model.

Bottom Line & Recommendations

2% is acceptable and not damaging for your 2023 E63 4MATIC+ — especially since you’re using identical Continental ECS02 tires (same compound, tread, construction). It’s well within what the system was engineered to handle.

It is higher than stock, so it’s not “perfect,” but it won’t void warranties or grenade the transfer case.

The real-world probability of transfer case failure on a 2023 Mercedes-AMG E63 S 4MATIC+ specifically due to your proposed ~2% tire diameter/revs-per-mile mismatch (305/35R20 vs. 285/35R20 on Continental ECS02 tires) is low — likely in the range of 5% or less over 50,000–80,000 miles of mixed driving, assuming the tires remain at similar tread depths and you don't abuse the car constantly in extreme conditions.

 

And Google;


While some general tire guidelines mention 3% as a universal limit, 2% is considered risky and potentially unsafe for a Mercedes 4MATIC+ system. The 4MATIC+ system is highly sensitive to rotational speed differences, and most specialized recommendations for this drivetrain suggest staying within 1% to avoid damaging the differentials and transfer case.
Why 2% is generally discouraged:

• System Sensitivity: 4MATIC+ relies on precise wheel speed data for its performance-oriented torque distribution. A 2% difference can cause the system to "think" a wheel is slipping, leading to constant engagement of the center clutch or traction control.
• Drivetrain Stress: Operating at a 2% variance forces the differentials to work harder, which can lead to overheating the viscous fluid or premature wear on internal gears.
• Safety Systems: Larger differences (2% and above) can cause issues with ABS and Electronic Stability Control (ESC), as the vehicle's computer may misinterpret the rotational speeds during emergency maneuvers.

Recommended Limits for 4MATIC+: Metric Safe Limit Reason Rolling Diameter Under 1% Minimizes heat and stress on the 4MATIC+ transfer case. Tread Depth 2/32" to 3/32" Ensures all tires have nearly identical circumferences. Mix & Match None Even tires of the same size from different brands can vary in actual diameter. If your current or planned setup exceeds 1%, it is better to adjust the tire profile or width to bring the variance closer to 0%.

 

I've noticed the 4MATIC bias issue in my '22 C 63 and yeah, it's pretty annoying. I'm not sure if it's a hardware or software thing, but it's definitely more pronounced when the rear wheels are under heavy load, like when I'm accelerating out of a corner. Anyone have any insights on this?

 

The problem with AI is that will mostly just try to assume since it doesnt have any proper MB\AMG source, so ig only way of really knowing is asking some AMG techs?
But I dont see have 1% can be an issue when stock setups per you sheet exceeds that, surely there would be more common issue and afaik E63s dont have any common issue with diffs etc.

 

Another data point to consider is the OEM Winter Wheel setup is a 265/40R19 square setup... a 1.4% difference in the rear. Add in tire wear and/or environmental modifiers, I think it logical to assume a 2% buffer that'll still be within spec, no?

 

Well, square would be 0% difference front/rear well below any specified tolerance level, of which I can still find no documentation except "These are Mercedes Approved tire sizes, The End."

 

Here is a thread where eveyone says 3% and someone said they chatted MB who said 3% too.
I will try to chat MB!

https://mbworld.org/forums/w213-amg/...-help-plz.html

 

My favorite AI Meme so far:

 

Still no official answer from Mercedes and the only public definitive articles I can find are:
XDrive is 1%
Audi is 1%
Nissan GTR is 3%

I just ordered some tires to move from 2% to 1% difference to be safe.