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TECHNOLOGY – CONSULTANT


Back to school Q


Where to look first to improve your car’s general set up


I am an avid BMW CCA club racer. I have progressed quite far and have even won my championship a few times. However, there are still a couple of guys that I just can’t


catch. Other than money, I think one of the reasons they are beating me is set up. They are very good at nailing a set up for a given track. I have a good baseline for my car, which was given to me. I


soften it a bit for bumpy tracks like Mosport or Sebring, but otherwise pretty much stick to it. Once in a while, all the planets align and I set a lap record, but it’s always a surprise to me. I call this my little set up lottery.


apply to a wide variety of vehicles. For production-based cars with tightly regulated bodywork, it does get a little simpler than for winged cars, because at least we aren’t dealing with dramatic variations in the aero properties, but even then it isn’t simple. One universally applicable principle would be to know why


I


don’t see any way to reduce something this complex to a brief set of principles or rules, especially if those have to


you are trying a given set up change. What are the physics? What exactly are you trying to make the car do or not do? The basic idea of having a baseline set up and softening it a bit if the track is rough makes sense. Depending on the car and the rules, it is often necessary to use higher static ride heights for the softer set up. In addition to general


roughness of the track, factors that may influence set up include:


I am an engineer by schooling (electrical). I have come up


through the BMW and Porsche clubs where I have been instructing for years. I understand all the underlying principles and have read all the books. But I have no idea how to unite them all into a unified theory of suspension set up. In this respect, I am quite typical of club racers and probably a good chunk of your readers. Do you think you can give me some guidance toward


developing my set up skills? Where should I look? My car is a BMW E36 M3, 410bhp, 2200lb, Moton three-ways,


slicks etc.


• Dominant turn direction. Some tracks have most of their turns in the same direction


• One or two turns being more important to lap time or passing opportunities than the rest. Most commonly, such turns are at the beginning of major straightaways


• Predominance of tight turns or sweepers


Issues such as these become


particularly interesting if we have ballast we can move. Production-based cars may or may not have ballast, depending on the rules.


When one turn direction is


dominant, or when one turn is unusually important, sometimes it pays to move ballast toward the inside of such turns. It may cost us elsewhere in the lap, but we may come out ahead overall. When there are lots of short-


duration tight turns, braking before those turns and forward acceleration after them become more important, and mid-turn speed becomes less important. With rear-wheel drive, more rear percentage will help the car put power down, and will also shorten braking distances. When there are a lot of


sweeping turns, and few long straights and tight turns, it may pay to move ballast forward a bit more, to work the tyres more evenly in steady-state cornering. With live axle rear suspension, it can help to use a bit less than 50 per cent diagonal (meaning LR + RF) to compensate for torque wedge. If the turn before the most important straight is a tight right-hander, there is a case for being a bit more aggressive with the diagonal. But again, in all of this, it is of


The most important thing in any set up is to know what you are trying to achieve and how you expect to achieve it 48 www.racecar-engineering.com • January 2012


paramount importance to know what one is trying to achieve, and have a clear understanding of how one expects a set up change to accomplish that.


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