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Mazda Tech Notes: 12H Sebring

SpeedSource Competition Director Jeff Braun describes engineering challenges for Sebring…

Photo: John Dagys

Photo: John Dagys

Jeff Braun, Competition Director at SpeedSource, the Florida-based factory Mazda team, describes the engineering challenge and the delicate compromises to prepare the race car properly for the Sebring track. Here are his quotes:

How low: “There are a number of challenges at Sebring with 17 turns, but it’s mainly the significant number of bumps. The engineers want the car to run as low to the track as possible, and a driver can feel the difference of as little as a two millimeter change to the ride height.

“The biggest limiting factor is the wooden skid plank under the car. It is 25 mm thick to begin, and it must measure 20 mm or more after the race. If you run the car too low, the plank hits the track at every bump and there’s no chance of it remaining legal at the end of 12 hours.”

How stiff: “To counter that, you can raise the ride height to protect the plank, but that results in much lower downforce figures. To try to regain downforce, you can choose very stiff springs to keep the car as low as possible.

“The trade-off with high rates of spring stiffness is that the spring isn’t able to absorb the bumps and the tires come right off the ground! Here at Sebring, that’s most common in the ‘old school’ corners, turns one and 17. Of course, anytime a tire loses contact with the track, it’s a huge loss of downforce and traction.”

How shocking: “The next phase is to find the best balance between the ride height and stiffness issues, and we do that primarily with the shock absorbers. Sebring is the track where the shock absorber specialists can have the biggest impact.

“Like a restrictor plate track in NASCAR, where the engine builder can really make a difference, it’s the shock specialist that makes it happen here. We have JF Chretien, who is an employee of Multimatic, who oversees the shocks on our cars. This is where he can shine.”

Simulations: “With so little track time this weekend before the race, you can’t possibly make a large number of changes on the car and test each one. It’s also cost prohibitive to run constant test sessions with the entire team and drivers, so we rely upon our in-house computer simulations.

“The software is improving all the time as we hone the mathematical model of the race car. Since Daytona, we used the software to run more than 400 different simulations. That’s 400 different combinations of settings (wing angles, ride height, and much more) that we tested. Based upon those simulations, we arrived at the track with what we believe is the best setup for our cars.”

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