10/15/2004
By: Roger Hewson
| Front-wheel-drive cars have come a long way in the last 15 years. It used to be a common belief 200 horsepower was the limit of a FWD platform. Engineers said wheel spin and torque steer were just the beginning of the problems that more power would bring. |
| That was until Cadillac, yes, our friends at the company that makes cars for silver haired bingo, mobsters and rap stars kicked the door for fwd performance wide open in 1993 with the 290-horse V8-powered Allante convertible and a year or so later, the 300 horsepower Seville and Eldorado. The engineers at Caddy even managed to make it work without the magic of traction control. The blue hair crew had never had it so good and you could hear them lighting the tires from Palm Springs to Orlando. |
|
What gives? Why can an OEM car like the 290-horse Allante or the 260-horse Acura TL/CL with a six-speed manual gearbox put the power to the ground so well while at the same time when you try to get 200 wheel horsepower to stick in a Civic all you get is big clouds of tire smoke in first and second plus another 300 dollar bill from the guy at the tire shop? One word: Engineering. The teams who designed those cars thought about things like weight distribution, gear ratios and tire size, just to name a few, so all the power could be put to good use. |
So what can you do with you do with your street car to help get the power to the ground without turning it into a tube frame racecar? It’s all pretty simple actually. Everything from shock valving to tire alignment plays a role in how your car gets moving when you push the pedal to the floor. “Finding traction is not a black art like some people think it is,” says Russ O’Blenes, a chassis engineer who works for GM Racing and just happens to be one of the brains behind the suspension used by Lisa Kubo and Nelson Hoyos. “You need to remember to look at the basics. Everything happens for a reason, you just need to sit back and think about what is causing whatever you are having a problem with.” |
|
After spending weeks researching the ins and outs of traction, we have discovered that it is a bunch of little things combined which can make a big difference in the available traction. |
|
Get Your Car Stiff A stiff spring rate in the rear suspension will limit weight transfer which means more weight hanging over the front of the car during acceleration. More weight over the front during the launch equals better 60-foot times in the world of FWD dragging. It’s a lot like when rear-wheel-drive cars have most of the weight over the rear tires during wheels-up launches, but only in reverse. The problem is because of the physics of a hard launch, the front still wants to rise, causing it to fight the rear. Unfortunately there is no fix with the remaining weight transfer, but stiff spring rates in the rear do help fight the transfer. |
|
Shocks Have Valves Too Shock valving is another often overlooked step to traction that the domestic crowd has been using since getting two miles to the gallon was cool. According to O’Blenes, you want lots of compression damping in the front shocks. What this does “push” the front tires into the ground when the front lifts to keep them firmly planted. Soft rebound damping in the front will allow the front to settle back down for aerodynamics. You’ll want the opposite effect happening in the rear. |
|
Baby’s Got Back Doesn’t Help in FWD Drag Racing You can also help the shocks and springs out manipulating the car’s weight distribution. GM has found that the ideal distribution is around 70/30, meaning 70 percent of the car’s weight in the front and 30 percent in the rear. Placement is not incredibly critical as long as that weight is kept low in the chassis. Keeping the center of gravity low is more important than putting weight on the front tires. When the weight is low in the chassis it reduces the pitching of the weight rearward under acceleration leaving more weight on the front tires. Another trick is trying to keep weight closer to the center of the car. This also reduces the pitching of weight rearward by giving the front of the car less leverage when you accelerate. |
| Flex Your Way to Traction
“You want to reduce flex as much as possible in the rear suspension of the car” says O’Blenes. Reducing flex in the rear suspension and in its joints like where the ball joints mount to the control arms, has the same effect as adding spring rate by reducing weight transfer and there is also an added bonus; it makes the car more consistent because the suspension mounting points are not squirming around. |
|
Point Your Toes Out One trick for a little more speed on the big end is to run a slight toe out in the alignment settings. “We see most people running toe in and it doesn’t make any sense because the wheels and suspension crawl forward during acceleration” says O’Blenes. Running toe in will scrub off speed during acceleration. The more toe in, the more speed gets scrubbed off. By toeing the car out the wheels crawl to a zero toe position so they do not lose any speed at all, allowing you to get a slightly more mph on the top end. How much toe you run depends on the suspension setup of your car. Some cars have a lot more suspension movement during acceleration than others do. One way to check it to watch your car on the dyno and see how much the wheels move. Play with different adjustments of toe out to see which yields the best performance. |
| Sorting out these issues on a street car will take some trial, error and a fair bit of planning on your part. Don’t get frustrated, the results in the end will be well worth it; you’ll be rewarded with a much more consistent, easier to launch car. In part two of the series we will tackle tires, limited slip differentials, and give you some ideas on how to execute the ideas we talked about here. Remember just because a car is front-wheel-drive doesn’t mean it is immune to the laws of physics; it’s still just a car. |