2008 Pontiac Grand Prix — GXP
The 2008 Pontiac Grand Prix GXP shipped with 2 different factory tire sizes, depending on the wheel package it left the factory with (this can also reflect a staggered front/rear setup). Check your tire sidewall or door placard to confirm which one applies to your vehicle.
This trim shipped with more than one tire size (staggered fitment, front/rear, or optional wheel package). Confirm which one matches your vehicle by checking your tire sidewall or door placard.
255/45R18 (Front)
| Section width | 255 mm |
|---|---|
| Aspect ratio (sidewall height) | 45% (114.8 mm) |
| Rim diameter | 18" |
| Overall tire diameter | ~27" |
| Revolutions per mile | ~746 |
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225/50R18 (Rear)
| Section width | 225 mm |
|---|---|
| Aspect ratio (sidewall height) | 50% (112.5 mm) |
| Rim diameter | 18" |
| Overall tire diameter | ~26.9" |
| Revolutions per mile | ~751 |
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What this size means for your Pontiac Grand Prix
On the 2008 Pontiac Grand Prix GXP, the factory 255/45R18 measures about 27″ in overall diameter with a 114.8 mm (4.5″) sidewall, and completes roughly 746 revolutions per mile. Its 45-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 passenger (P-metric / Euro-metric) size.
This is a staggered setup: the front axle runs 255/45R18 and the rear runs 225/50R18. The two sizes are not interchangeable, so order each for its correct axle and don't rotate front-to-rear.
On a vehicle of this age, the Pontiac Grand Prix may have been refitted with a slightly different replacement size somewhere in its life, so check the current sidewall — not just the factory spec — before buying.
Other 2008 Pontiac Grand Prix trims
- Base Model 225/60R16 / 225/55R17
- GT 225/55R17
Pontiac Grand Prix tire sizes by year
- 2007 Pontiac Grand Prix 225/60R16 / 225/55R17
- 2006 Pontiac Grand Prix 225/60R16
- 2005 Pontiac Grand Prix 225/60R16
- 2004 Pontiac Grand Prix 225/60R16
- 2003 Pontiac Grand Prix 225/60R16
- 2002 Pontiac Grand Prix 225/60R16
- 2001 Pontiac Grand Prix 225/60R16
- 2000 Pontiac Grand Prix 225/60R16
- 1999 Pontiac Grand Prix 205/70R15 / 225/60R16
- 1998 Pontiac Grand Prix 205/70R15 / 225/60R16
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.