Piston Slap: Pounding the LaCrosse Super With Too Much Air?
Jim writes:
I just got new wheels and tires on my 2008 Buick LaCrosse Super, 245/45R19s to replace the stock 18s. The tire dealer put in 40 lbs of air, and when I said “is that a little high?” they pointed to the sidewall and said “look, it can take up to 51 lbs.” I’ve never run more than 36 lbs in my tires, but I’ve never had a profile this low before. Am I just behind the times?
Behind the times? You do own a Buick . . . but there’s an argument for displaced American muscle junkies (of all ages) needing a “Super” for their Yank-Tank fix with a new car warranty. If you believe in the latter, consider yourself off the hook. I agree with your conclusion, for two reasons. That wide of a tire with a 45-series sidewall is far from a rubber band donk-mobile, there’s enough cushion to merit conventional tire pressures.
Reason two: never, ever use the sidewall’s pressure for justification. That number is usually (always?) the maximum pressure allowed by the tire maker, with little relevance to the engineers who designed your car. If my knowledge of the LS4-powered Impala, Grand Prix and LaCrosse holds true, the staggered tire sizes and air pressures of the Pontiac and Buick came from extensive testing on how to put down massive power in a wrong-wheel drive application with less of the Impala’s drama. So don’t discount their calculations: it’s kind of a big deal.
Matter of fact, I suspect the Venn diagrams for tire maker/auto maker tire pressure ratings never overlap. Not that I’m gonna make one and find out, I’m just sayin’.
Sadly, I can’t find information on tire pressure changes for “+1”wheel and tire upgrades. This is what you really need. I’d recommend sticking with 1-2psi more than what the owner’s manual says, or follow GM’s recommendations as-is.
Bonus! A Piston Slap Nugget of Wisdom:
Automotive OCDs unite! If you measure air by “lbs” (pounds) and not “psi” (pounds per square inch), you’ll probably blow up the tire. Yeah, I know that “lbs” is in the American vernacular, but I didn’t ignore wild college parties and NCAA football for Mechanical Engineering homework for no reason. Believe that.
[Send your queries to mehta@ttac.com]
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So my little CUV calls for 26 psi cold. Unloaded. How much do I raise the tire pressures when it is fully loaded? Is there a sliding scale? Say max cargo weight means 32 psi. At half the max weight do I use 29 psi? FWIW I use about 2-3 psi more than the door jamb calls for. Rides a little better (tighter) and the fuel mileage is a little better. Tire wear is a little better because we aren't sawing the edges off of the tires from cornering.