I thought it did my homework. Did a lot of searching and found that the 12mm front / 15mm rear combo should put me flush with the fender lip running stock wheels and tire.
Nope!
The fronts with 12mm look perfect The rears with 15mm are way too wide. I remeasured and it looks like 5mm would make it flush just like the fronts. I've read there are some issues with the 5mm not having enough hubcentric support and really can't find any.
I thought it did my homework. Did a lot of searching and found that the 12mm front / 15mm rear combo should put me flush with the fender lip running stock wheels and tire.
Nope!
The fronts with 12mm look perfect The rears with 15mm are way too wide. I remeasured and it looks like 5mm would make it flush just like the fronts. I've read there are some issues with the 5mm not having enough hubcentric support and really can't find any.
As long as the car is not tracked or driven aggressively on the street, a 5 mm spacer—which by design cannot be fully hubcentric—will generally perform without issue.
When fitting the spacer, there remains a small portion of the 66 mm hub lip that still engages the wheel center bore, providing adequate centering assistance.
Be sure to use 34 mm long bolts and tighten them in two stages: first to 80 Nm, then to 180 Nm for final torque. This ensures full frictional contact between the wheel and the hub face. If the bolts are under-torqued or the wheel is not seated properly, micro-movement under load can occur, which may damage the hub lip, face or elongate the bolt holes over time.
10mm would work and not be excessively wide. Would that be a better, more durable choice?
The short answer is NO. The only spacers that can fit any of the GT, GTS, GTC or GTR ar non-hub-centric 5mm, or hub-centric 15mm or higher..
Here is the explanation:
There are no 10 mm or 12 mm hub-centric spacer that properly fits the 66.56 mm AMG GT hub, which has a nominal hub lip depth of approximately 13.5 mm.
The problem lies in the geometry: the hub’s lip is too deep relative to the spacer’s center bore recess. As a result, a 10 or 12mm spacers cannot fully seat against the hub face, leaving a small gap between the inner surface of the spacer and the hub flange—an unacceptable condition for proper load transfer and wheel centering.
Even a 15 mm spacer is somewhat marginal, as it provides only about 1.5 mm of material thickness to support the entire wheel load if it does not fully seat against the hub face.In the photos, the 10 mm spacer on the left and the 15 mm spacer on the right clearly show the difference in hub lip recess depth—the 10 mm unit has a noticeably shallower bore compared to the 15 mm, which allows slightly better seating but still leaves very limited structural engagement.
10mm on left and 15mm on right
In these photo below , you can see the result of what happens when a 15 mm spacer experiences impact loading. When the wheel hits a bump, the longer 44 mm bolts can flex slightly due to their increased length, which introduces micro-movement between the spacer and hub. Over time, this flex causes the spacer’s hub-centric ring to fracture.
This failure was not caused by a manufacturing defect, but by mechanical stress from insufficient surface friction between the hub flange, spacer, and wheel face. These lightweight, circuit-style spacers are designed for smooth track conditions, and when subjected to harsh public roads, the combination of impact forces and bolt flex can lead to cracking. Any spacer that is not in full, rigid contact with both mating surfaces is prone to the same issue.
Non-hubcentric spacers in 10 or 12 mm thickness will not function properly either, as there is insufficient hub lip engagement to stabilize the wheel. Without adequate hub-to-bore contact, even minor vibration forces can cause the wheel to shift slightly off-center, leading to imbalance under load.
A 5 mm spacer, however, still provides approximately 8.5 mm of hub engagement, which is generally enough to maintain proper centering and stability under typical road forces.
Everyone wants their car to look more aggressive and distinctive, and making aesthetic or performance modifications is part of the passion. Just remember that every change can have safety implications, and proper mechanical fitment should always take priority over appearance.
Do I recommend using spacers? Generally, no. The better approach is to select wheels with the correct offset to achieve the desired stance and fitment.
However, that option often comes with a significant cost, which is why many enthusiasts choose to make compromises using spacers instead.
It’s a balance between aesthetics, performance, and budget—but from a pure engineering standpoint, a properly sized wheel is always the preferred solution.
Thank you for the detailed response. I understand it. It would serm that if going with a non hubcentric spacer that having the absolute closest tolerances for the bolt holes would be optimal.
Thank you for the detailed response. I understand it. It would serm that if going with a non hubcentric spacer that having the absolute closest tolerances for the bolt holes would be optimal.
If you refer to a 5mm non–hub-centric spacer, yes.
However, for thicker non–hub-centric spacers, even with exceptionally tight bolt-hole tolerances, a non–hub-centric setup can never replicate the concentric precision or long-term stability of a properly engineered hub-centric interface. Over time, minor shifts inevitably occur due to vibration, impact loads, and thermal cycling.
Non-hub-centric spacers are primarily intended for standard passenger vehicles and are ill-suited for high-performance sports cars, where precise wheel alignment and load distribution are critical. While ensuring that the spacer’s bolt holes are machined to the closest possible tolerances can help maintain centering, it remains a mechanical compromise relative to a true hub-centric configuration.
The load integrity between the wheel and the hub depends on the combined support of the hub lip, the clamping friction of the wheel face, and the tension from the mounting bolts. Removing the hub lip from that equation reduces the system’s load-bearing capacity and compromises safety under dynamic conditions.
As previously noted, the only semi-safe non–hub-centric spacer for the AMG GT platform is a 5 mm spacer. A practical alternative to achieve a similar stance or fitment effect as a 10 mm spacer is to use a 5 mm spacer in conjunction with 325/30ZR20 rear tires, or to adjust the wheel offset directly for a more structurally sound solution.
