2008 Pontiac Grand Prix GXP
The 2008 Pontiac Grand Prix GXP tire size and wheel specifications below reflect standard OEM reference fitment data for this trim level.
Detailed tire and wheel breakdown for the 2008 Pontiac Grand Prix
Tire geometry â 255/45R18
The 255/45R18 fitted to the 2008 Pontiac Grand Prix has a section width of 255mm and an aspect ratio of 45%, mounted on a 18-inch rim. That gives a sidewall height of 114.8mm (4.52") and an overall outside diameter of 686.7mm (27.04"). At highway speed this tire completes roughly 464 revolutions per kilometre, which is what your speedometer and odometer are calibrated against.
Plus-sizing window
If you want to upsize wheels on the 2008 Pontiac Grand Prix while keeping the speedometer accurate, target a 265/39R19 (plus-one). For a softer ride or winter setup, a 245/52R17 (minus-one) keeps the overall diameter within Âą3% of stock, which is the industry tolerance for ABS and stability control to stay calibrated.
Wheel fitment specs
The 2008 Pontiac Grand Prix uses a 5x115 bolt pattern with a 70.3mm hub bore. Safe rim width range for the OEM tire is 7.5J â 8.5J, and offsets in the ET35 â ET45 window will clear suspension and fender without rubbing on most setups.
Staggered setup notes
The 2008 Pontiac Grand Prix ships staggered: 255/45R18 up front and 225/50R18 on the rear. That is a 225mm vs 255mm width difference â do not rotate front-to-rear, and replace tires in axle pairs to keep ABS and traction control balanced.
Tire pressure guidance
Manufacturer-recommended cold tire pressure for the 2008 Pontiac Grand Prix is printed on the driver-side door jamb sticker â always defer to that value, not to the maximum pressure printed on the tire sidewall. Check pressure monthly and before long trips; under-inflation by 20% can reduce tread life by 25%.
Fitment Specifications
| Engine & Trim | Tire Size | Rim Size | Offset (ET) |
|---|---|---|---|
| GXP | 255/45R18 Rear: 225/50R18 | 18" x 8.0 | ET40 |
Frequently Asked Questions
What tire size does the 2008 Pontiac Grand Prix GXP use?
The 2008 Pontiac Grand Prix GXP uses 255/45R18 tires as standard equipment.
What is the bolt pattern of the 2008 Pontiac Grand Prix GXP?
The 2008 Pontiac Grand Prix GXP has a 5x115 bolt pattern with a center bore of 70.3mm.
What is the wheel offset of the 2008 Pontiac Grand Prix GXP?
The 2008 Pontiac Grand Prix GXP has a wheel offset of ETET40.