Friday, February 16, 2007

Cars too want to loose Weight!

Keywords: Traction, Emission, Balance, Weight Transfer

How does your car handle on slippery Ice? One of the factors is:[1] Front wheel drives handle better than rear wheel drives on slippery roads as the weight of the engine is on the drive wheels, which helps to improve traction. How does weight affect traction? Though we won't see the exact science of it, we can get a peek at the factors that play a role in the story behind traction.

Medium sized cars weigh approx 600 lbs less than 25 years ago. Mid-sized Cars now weigh around the ballpark of 3000 lb.

A debate carried in an article, carries the following points:

"vehicle quality is a better predictor of safety than weight" says an University of Michigan physicist Marc Ross. "It turns out that relatively inexpensive light cars do tend to be unsafe but more expensive light cars are much safer and are as safe as heavier cars and SUV (sports utility vehicle) models," said Ross. "Analyzing statistical things is sort of funny," Ross said. "If you choose categories so you get cheap cars in your category, then the death rates go up. What we found is that the price of a car is a much better predictor of risk in traffic accidents than the weight of the car."

"No matter what you do, you cannot repeal the laws of physics," spokesman for the Insurance Institute for Highway Safety, Russ Rader said. "A larger, heavier vehicle is always going to be safer than a smaller, lighter vehicle. If you're looking at small cars vs. larger cars, small cars have twice as many occupant deaths as large cars." He noted, however, SUVs have a higher rollover risk and are disproportionately involved in single vehicle crashes.

Reducing the weight also brings with it other benefits: “A 40% decrease in car weight can result in a tremendous reduction in CO2 emissions,” says Ignaas Verpoest of Belgium’s Katholieke Universiteit Leuven.

How does weight interplay with traction? While driving, if you change direction towards your left, you get pushed to the right. This push transfers the weight on the left tires to the right. Your car has 60% of its weight (1800 lb) on the front tires and 40% on the back (1200 lb). So the car is unevenly loaded. When you make such a turn this push has a chance of pushing you over. The best protection against this comes by adding weight to the car: the greater the weight, the harder it is to transfer any weight from one side to the other. Some recommendations that come your way suggest placing weight on the rear ends to balance weight between the tires. Using a front-drive car, so the higher load on the front tires can be effectively countered.

There are other suggestions: Increasing the distance between the right and left tires (a person is more stable standing in "at ease" posture than in the "attention" posture). Also, reducing the Center of Gravity of the vehicle, or the "center of balance" of the vehicle (a Sumo wrestler or a Football player buckles down before taking a hit from the opponent). For something to think about until the next blog:

***For slippery ice, there is a lot more at play, on how the steering is used along with brakes, keeping off the gas pedals, etc. But these are things you do independent of the design of the car.

related: European cars are doing much better than U.S cars in mileage standards.


Anonymous said...

Perhaps Americans should buy European cars which are much safer and eco-friendly!

bharath said...

yeah. agree. I finally found something to do a post about it.