Q: Why do drivers drive over apex curbs?

Q: “I have seen on some racetracks sometimes driver skip the apex ‘kerb.’ I mean they do not go for those red and white kerb. Instead, they turn far away from the apex and quickly back to straight line. Does this supposed save time and make the car go faster? I have seen it in Formula One sometime as well. It might be in Hungary Grand Prix. Could you please clear the idea for me? Is it always necessary to touch the kerb in the middle of a corner (apex)?”

A: Clipping or driving right over the apex curbing (kerb) is a method of straightening the corner out as much as possible, making the radius as large as possible. The larger the radius of the line you drive through a corner, the faster you can go. That’s simple physics.

The tradeoff is that the curbing can upset the car, and cause it to have less grip. Less grip means you have to drive slower. So, there is a balance or compromise between maximizing the radius of the corners by driving over the curbs versus the curb upsetting the balance of the car. That’s why you’ll see some drivers running over some curbs, but not others. They’ve tested out which curbs can be used, and which ones can’t. Of course, a curb might be okay for one car with suspension that is more compliant, whereas another car with a stiffer setup might lose too much grip by driving over the same curb. So, it’s car-dependent.

8 Comments

  1. I have also found in a very stiff car you can break bearings if you use the FIA curbs as well, don’t ask me how I know….

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  2. “Kerb” is a new one on me. Is it a racing-related play on “curb” spelling?

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    • Kim, ‘kerb’ is British English while ‘curb’ is chiefly American.
      HTH! 😉

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  3. I was also thinking, are there instances when the apex has a bump or tends to be slippery so drivers decide to go around the outside? I know it may be true for wet conditions but does it also apply to dry racing?

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    • Yes, it all comes down to grip levels versus the benefit of the radius. If the curb has little grip, then the extra radius is not worth it; if it does have grip, then the trade-off is a good one. Usually, painted curbs are slippery in the rain. Some are good in the dry, and some are slippery in the wet. You have to test it out.

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    • They both are different condition. That is why there is a dry line and a wet one.

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  4. So here is my spin on “curbs”.

    I use them as markers. To hone my skills of being able to plan each corner, and place my car correctly and axactly where I planned to. I generally either “kiss” the cubs, or ride up on the 1st set of curbs on a corner. How far I drive through/up the curbs depends entirely on each curb. By that I mean; the consistency of the curbs, the actual angle of the curbs and how those angles affect the tire patches of the outside tires, the dangers to the inside of the curb e.g. ruts, mud, rocks, Armco, and finally the roughness of the curbs. As Karl Seger mentioned above, curbs can play havoc with suspension components. Is it worth it? Maybe only in a sanctioned race where there is something to really be gained by driving over the curbs. Otherwise “kissing” the curbs, just as I planned, is just as rewarding to me as climbing the curbs, and going for a 1/10 of a second lap advantage. It’s a very individual driver decision.

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  5. The curb can also efectively be used to help turn the car. A little bit of inside back wheel over the curb turns the car a little in tight corners, getting a straigter exit.

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