Piston Slap: Pounding the LaCrosse Super With Too Much Air?

Sajeev Mehta
by Sajeev Mehta

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?

Sajeev answers:

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]

Sajeev Mehta
Sajeev Mehta

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  • Joeaverage Joeaverage on Nov 03, 2009

    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.

  • Sajeev Mehta Sajeev Mehta on Nov 03, 2009
    joeaverage : 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. Since 26psi is pretty low by modern standards and you are enjoying 29-30 psi, I'd keep it there. Check tire wear over the course of years, not days or months to know for sure.
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  • Lou_BC "That’s expensive for a midsize pickup" All of the "offroad" midsize trucks fall in that 65k USD range. The ZR2 is probably the cheapest ( without Bison option).
  • Lou_BC There are a few in my town. They come out on sunny days. I'd rather spend $29k on a square body Chevy
  • Lou_BC I had a 2010 Ford F150 and 2010 Toyota Sienna. The F150 went through 3 sets of brakes and Sienna 2 sets. Similar mileage and 10 year span.4 sets tires on F150. Truck needed a set of rear shocks and front axle seals. The solenoid in the T-case was replaced under warranty. I replaced a "blend door motor" on heater. Sienna needed a water pump and heater blower both on warranty. One TSB then recall on spare tire cable. Has a limp mode due to an engine sensor failure. At 11 years old I had to replace clutch pack in rear diff F150. My ZR2 diesel at 55,000 km. Needs new tires. Duratrac's worn and chewed up. Needed front end alignment (1st time ever on any truck I've owned).Rear brakes worn out. Left pads were to metal. Chevy rear brakes don't like offroad. Weird "inside out" dents in a few spots rear fenders. Typically GM can't really build an offroad truck issue. They won't warranty. Has fender-well liners. Tore off one rear shock protector. Was cheaper to order from GM warehouse through parts supplier than through Chevy dealer. Lots of squeaks and rattles. Infotainment has crashed a few times. Seat heater modual was on recall. One of those post sale retrofit.Local dealer is horrific. If my son can't service or repair it, I'll drive 120 km to the next town. 1st and last Chevy. Love the drivetrain and suspension. Fit and finish mediocre. Dealer sucks.
  • MaintenanceCosts You expect everything on Amazon and eBay to be fake, but it's a shame to see fake stuff on Summit Racing. Glad they pulled it.