Posted by: drracing | April 4, 2010

The Beast!

I would like to introduce you to…The BEAST!! Actually our Chevrolet Lumina CR-8!

When they asked me to work on this car (and, in general, with touring cars) at the beginning i was not so sure that i would enjoy so much to do so. I had always worked on single seater till 2010 and to work on big heavy street cars converted to race on track..it didn’t seem so appealing. But i was wrong!

Frist of all…some informations about the rules. The championship is thought to make big V8 cars to compete in a nearly stockish configuration. But to prepare these cars to race on track, it’s not an easy task any way. There are a lot of things you have to do, keeping always fixed in your mind the obsession of all race car designer: WEIGHT!

Rules say you cannot modify nearly anything on suspension geometry and, if there isn’t any safety problem, you have to use street version parts, changing only bushings with ball joints. The engine is exactly the same than the road version or you have to change it with another from the same brand: you can only play a bit with electronics. You can change the gearbox (to use a sequential one) but shifting must be manual and you have to use always the same gear ratios, chosing only between two final ratios to adapt the car to very fast tracks like Monza. You can also change nearly all the bodywork with parts of exactly the same shape but made of light materials, like carbon fiber. Then, of course, you have to fit the car with a Roll Hoop which actually became the real chassis, providing a big improvement in torsional stiffness.

On the other hand, you have completely free choice on dampers, springs, antiroll bars, ride height (there is just a small restriction on minimum ride height) you can set the rear wing…so you can play a bit with setup!

Our Chevrolet Lumina CR8 use a huge 6.3 liters V8 engine with really a lot of torque and about 480 hp. The car with the driver weights about 1400 kg, it’s really heavy! Tires are the same front and rear and are Michelin 27-65/18 with a quite hard compound. Since the car is so heavy, tires lose a lot of grip after just a few laps, so the driver and the setup must act as a consequence of this. It’s also very important to avoid tire locking, because it can cause immediately problems like tire graining or tire blow up! To play properly with brake balance is very important, as well as to have a good balance of the car in braking. Moreover, the brakes are quite weak, so brakings are very long and driver can still play a big role. Actually you can see some very good racing, with a lot of fights and overtakings.

Cars are very wide as well (track are about 1.7 meter) and have very long wheelbase! They are like a rhinoceros! Very heavy, but they run very fast as well!

Our car, as the street version, use McPherson strut at the front suspension and double wishbone at the rear. To change camber and caster at the front you have to move damper axis. So, when you do so, you have a changing also on king pin as a consequence. Acutally, when you change one thing, you change also al the others. I dont’ like McPherson! Anyway…we use Ohlins Dampers…and i like them very much! You can do a lot of nice things with them!

I still had no time to explore our suspensions geometry. We cannot change it but i want to study all the stuff of the car the most i can anyway. To know what you are working on is one of the most important things at this game, in my opinion. But a lot of people, above all in Italy, don’t agree with that.

Also steering geometry is the same than the street version. It was the first time for me to measure a street car steering geometry. It is a pro ackermann geometry, with a quite high ackermann percentage. And i like it, also if Michelin tires usually want something different than this.

I manage to have also some data on tires. Normally it’s not so easy to have this kind of informations. Very often, a lot of people on the track don’t know anything about the tires they are using. They only go with their experience. Again, in this championship you cannot adapt the car so much on your tires because of the rules. But when you can, to have tire data is really an incomparable starting point in designing a car and, in particular, supensions. I will be back on this matter in future posts, about other projects.

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