Watching Thick White Wall Tires Bend Through An Autocross Is Deeply Fascinating

Gif: MrPizzaman09 (YouTube)

One of my favorite camera views in racing is the tire view that shows big Formula One tires flex and wobble through turns and over curbs. Thankfully, the amateur version of this is just as fascinating. Look at how much these Oldsmobile white walls flex at an autocross!

This is MrPizzaman08's splendid Oldsmobile Eighty-Eight, getting driven hard at an autocross at Lake Erie Speedway. Specifically, this is his period-appropriate white-wall tires flexing more than your roommate in the bathroom mirror every morning. (We see you, man. Stop skipping arm day and you’ll see better results.)

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If you’ve ever noticed some extra rubbing on the side of your tire after hooning around, it’s because tires aren’t just a big, static hunk of rubber. They bend and flex around the air in the middle. Sometimes the rim of the tire is further out than the outer tire rubber itself!

Adding more air in your tires can help reduce this effect. This is why autocrossers and rallycrossers tend to run higher air pressures for their runs. There isn’t enough time with those shorter runs to get much heat (and the higher air pressures heat gives you from expanding the air in your tires) in the tires, so the extra air firms up the tire and keeps the sidewall from flexing. In the case of the dirty stuff, more air added before short rallycross runs also helps prevent the tire from debeading. The more you know!

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It’s a fascinating view, because even my low-profile sticky meats do this to some extent. It’s just a lot more pronounced on these thick white walls. Autocross your land yachts, folks!

Moderator, OppositeLock. Former Staff Writer, Jalopnik. 1984 "Porschelump" 944 race car, 1971 Volkswagen 411 race car, 2010 Mitsubishi Lancer GTS.

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DISCUSSION

oldbarntom
heytherejunebug

For this car and these tires, yes it looks like they could use a few more pounds of air. But generally, lower pressures mean better grip for an autocrosser.

I always heard and read that about autocrossing, too - that you just add a bunch of pressure. Yea - if you’re going there with high profile all-season radials you’re going to need a few more pounds to reduce sidewall flex a bit. But most autocrossers run lower profile summer performance tires with inherently stiff sidewalls - so you don’t need the “extra” air to create a stiff balloon effect. After the first run, they’re usually letting out a few pounds, not adding. Further nerding this out, you DO add extra air to the back tires if your car is an understeering pig like mine - so that the back tires will slide (and to raise the center of gravity in the back).