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Meet Kenny Sapper: Rear Suspension Tech

Would you believe that a baking pan and a block of ice are two important tools used to work on NASCAR racecars? It’s true; just ask Kenny Sapper, the technician in charge of rear suspensions at Joe Gibbs Racing. Specifically, Kenny works on the rear-end housings that go into our Sprint Cup cars. He has been a team member for about 6 years and has celebrated 50 victories with JGR (at the time this article was written).

But, what exactly is a rear-end housing? In its most basic form, a rear-end housing is two hollow steel tubes that house the axles. Those tubes are connected to a center casing that houses the rear-end gears that spin the axles. The axles, of course, connect to the wheels of the racecar and get the power to the road. The rear-end housing is more than just a simple shell, however. You can adjust the housing to change the camber and toe of the rear wheels & tires. Camber is the way the top of the wheel leans (in towards the center of the car, or outwardly); Toe is the way the wheel points (the front or rear of the wheel pointing inwardly or outwardly). These two factors are vitally important to the way a car handles because they determine how well a tire makes contact with the track! If you are off in these areas, you probably won’t be winning the race.

Here’s the kicker – the rear-end housing is a solid piece of metal that stretches from one rear wheel to the other. There is no bolt or knob or spacer that allows crews to adjust camber and toe. That’s where Kenny comes in, he works on a molecular level. A torch is used in a specific spot to heat the metal, allowing it to bend ever so slightly. Then, Kenny goes to his trusty ice block in the baking┬ápan and rubs it against the heated area, causing the metal to contract and maintain form. We call this “heating & clenching.” You might ask yourself, “how can a crew adjust these things at the track?” The answer is, it is difficult and rarely done. That means Kenny must meet the crew chief’s and head mechanic’s specifications at the shop, before the housing is ever bolted onto a racecar. Tire data from Goodyear, simulations, and notes from past races provide a baseline for crew chiefs and engineers when determining ideal rear camber and toe. And we aren’t talking inches or tenths of an inch that Kenny has to worry about. We are working in thousandths of an inch (0.001)! He uses plates (acting as wheels) and precise calipers to make sure his metalwork is accurate as he measures the camber angles and toe. We have different rear-end housing setups for the different types of race tracks, be they road-courses, speedways, superspeedways, or short-tracks.

Those tiny thousandths of an inch mean major adjustments in the handling and tire grip on a racecar. NASCAR also has strict limits on the amount of camber and toe that can go into our cars. That’s why Kenny says precision and consistency are the two most important parts of his job. Like every other piece of the racecar, rear-end housings play an important role and Kenny must keep up with the shop schedule in order to get specific housings on their respective cars for a certain race. On race weekends, you won’t normally hear about the rear-end housing unless the car is in a wreck and the housing breaks loose from the car. This will cause the rear wheels to sway awkwardly beneath the car and make it crab-walk as it limps to pit road.

So, the next time you’re at your local Food Lion grocery store and you walk past the baking isle, think about Kenny and remember that those boring baking pans play an important role in the operations of a championship-winning NASCAR team!

Have more questions or comments about this part of the racecar? Leave them in the comments section below. Thanks for reading!


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Request (Keen collector)


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I’ve been curious about how you accommodate the camber and toe angles through the power transmission path. I’m guessing from one of the photos in Kenny Sapper’s explanation of how the rear end housing is “heated & clenched” (should that be quenched?), the adjustment is made near the center section rather than near the wheel end of the tube.
My question is, how do you accommodate the non-perpendicularity of the axle to the third member? Your hardware is so highly engineered that I can’t believe that the axle just flexes or you machine extra clearance in straight conventional splines.
Just a curious (engineer) fan.


Ray wrote on august 24th 2013 asking how camber (heat/quench of the axle housing) effects the perpendicularity of the axle to the third member splines. Is there enough clearance on the splines that it does not flex the live axle shaft?


I have the same question as Ray…

Lifetime mechanic and Fan

Tom Porzondek

I have the same question as Daryl and Ray (above) about the camber put into the rear axle housing. I am a former short track racer and Tool & Diemaker as well as a machinist, and I am having difficulty understanding the concept of rear axle camber. I do know that some guys used to lead the rear end (toe in the right rear) and that I can understand.
Lifetime race fan and former short tracker.


Probably set up with the toe in so the rear axle runs true under power, just as you would set up the front with toe in and the friction of the tires on the road push them out to run straight under power?