2018 Mercedes-Benz GLS550 — 4MATIC
The 2018 Mercedes-Benz GLS550 4MATIC came from the factory equipped with 295/40R21 tires. If your vehicle has since been fitted with aftermarket or upsized wheels, your actual tire size may no longer match this factory spec — always confirm against your door placard before buying.
295/40R21
| Section width | 295 mm |
|---|---|
| Aspect ratio (sidewall height) | 40% (118 mm) |
| Rim diameter | 21" |
| Overall tire diameter | ~30.3" |
| Revolutions per mile | ~666 |
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What this size means for your Mercedes-Benz GLS550
On the 2018 Mercedes-Benz GLS550 4MATIC, the factory 295/40R21 measures about 30.3″ in overall diameter with a 118 mm (4.6″) sidewall, and completes roughly 666 revolutions per mile. Its 40-series aspect ratio gives a low-profile sidewall tuned for sharper handling, common on sport trims and larger-wheel packages. In tire terms it is a large-diameter fitment.
Mercedes-Benz GLS550 tire sizes by year
- 2019 Mercedes-Benz GLS550 295/40R21
- 2017 Mercedes-Benz GLS550 295/40R21
How to read a tire size
A tire size like 225/45R17 breaks down into three parts:
the first number is the section width in millimeters
(the tire's width from sidewall to sidewall), the second is the
aspect ratio — the sidewall's height as a percentage of
that width — and the number after the "R" is the rim
diameter in inches. A letter prefix (P or LT) indicates
Passenger or Light Truck construction; its absence usually means
Euro-metric sizing.
Some trucks and off-road tires instead use "flotation" sizing, like
37X12.50R17 — here the numbers are the tire's overall
diameter and width in inches directly, with the rim diameter last.
Always verify against the tire information placard on your driver's-side door jamb or your owner's manual before purchasing — tire size can vary by factory option package even within the same trim.