Written by Per Schroeder
From the Oct. 2010 issue
Posted in Suspension & Handling
One of the immutable laws of physics is that it takes force to accelerate mass. Whether you’re barreling down the drag strip, gunning it off an apex, or screeching to a halt, mass determines how much force you’ll need to get the job done. Reducing a car’s weight pays dividends in handling, acceleration and braking—as well as enhancing tire and brake life.
Want to make maximum power? A vital ingredient is getting the car down to minimum weight—whether that number is dictated by class rules or sheer functionality. Here are 10 steps for doing just that.
Know Where Your Weight Is
Access to a set of quality corner-weighting scales is key for any racer or serious enthusiast. If you can’t afford a set, find a buddy who has some.
These scales will show how your modifications are affecting your car’s weight as well as how it’s distributed. That second part is especially important. If you’re working on a car that has an uneven distribution of weight—like just about any front-drive car—you need to be mindful of how much you’re adding to already heavy areas.
Once you have your numbers, you can set about modifying the car—and driver—so that everything is as light as possible. Double-check your weights with official track scales every chance you get to ensure that they’re repeatable and accurate.
Consider the Talking Ballast
The driver is a significant portion of the overall weight of a car—sometimes as much as 20 or 30 percent depending on the size of the horse and jockey.
With our LeGrand project, for example, our primary wheelman is a little less than one quarter of the car’s minimum weight with driver. His goal is to lose 20 pounds before Nationals. Along with making him healthier, this will remove 2 percent of the weight from an already chunky side of the car.
Carry Just Enough Fuel
The fuel that a car carries makes up a surprisingly large percentage of the bottom line. With gasoline weighing 6.2 pounds per gallon, carrying unnecessary fuel can quickly add up.
In our autocross cars, we’ve placed fuel displacement blocks in our fuel cell to reduce the load. By placing these blocks in the front of the tank, we also moved the center of gravity rearward to the lighter end of the car.
Investigate Lightweight Batteries
Batteries offer another quick and easy opportunity to drop some weight. As long as you can meet the cranking amperage needs of your starting system and still have some reserve, a lightweight battery is a no-brainer.
We’ve had good luck with XS Power and Braille batteries. Our current Braille weighs just 6 pounds and helped us lose 15 pounds from our LeGrand.
The placement of the battery is also important, but sometimes relocation isn’t the best option. For example, while moving the battery to the back of the car can help weight distribution, the long cables required for that job can increase the curb weight. What’s the right answer? Ask the stopwatch.
Look Into Alternative Materials
Steel and iron have been replaced by aluminum, magnesium and plastic composites as demand for strong, lightweight materials has increased. A cubic foot of steel tips the scales at around 490 pounds, while a same-size chunk of aluminum weighs 165 pounds; magnesium is lighter still at 109 pounds. Carbon fiber composites are at the forefront of race car design, as they can be used to create structures that are half the weight of an aluminum counterpart.
When building components, consider your materials. For example, we recently replaced a 6-pound aluminum wing element with a carbon fiber piece that weighs just 3 pounds. That’s especially impressive considering that the wing is the highest point on the car, where every pound counts.
Shed Rotating Mass
This one can be a bit tricky to pick up on a chassis dyno, but it’s hard to argue with physics. Lightening components that rotate and move—wheels, clutches, pistons, driveshafts and the like—sheds weight and reduces the amount of energy needed to start and stop the car. For example, an engine can accelerate a lighter flywheel quicker than a heavier one.
Look beyond the obvious in your quest for more speed. How about upgrading to gun-drilled axles and lightweight brakes? There are also lightened CV joints that weigh 12 ounces less than a standard piece, saving a total of 3 pounds for the entire car.
Keep Repairs Light
Body panels made from fiberglass or carbon fiber are at their lightest the day they come out of the molds. While the final finishing, polyester fillers, primers and paints all add to the total weight of the piece, they hardly measure up to the excesses of hasty repairs.
We’ve seen fiberglass sports racer noses that have picked up 30 or 40 percent of their total weight from repair efforts: excess matting, reinforcements and epoxy. At some point, maybe it’s just easier—and lighter—to replace the entire panel.
We find ourselves obsessing about weight before we even plunk down our credit card for parts. Our newest project—a Mazda MX-5—has already lost 19.6 pounds since we replaced the stock exhaust with an aftermarket system supplied by Good-Win Racing.
But not all aftermarket parts are created equal. If hollow and solid anti-roll bars provide the same rate, which would you choose?
Take Advantage of the Rules
If the rules say you can change or modify something, why not use that as excuse to make your car as light as possible? Contributor Andy Hollis once used brake rotor allowances to shed 6 pounds of rotational weight from the front of his car.
Cutting the rotors to their minimum service width took them from 9 pounds each to 8. Swiss cheesing each disc shed another 2 pounds. “Of course, with the reduced heat sink, I could actually overheat the brakes on an autocross run,” he notes. “They lasted about a season of autocross and started cracking, and then the SCCA changed the rules to outlaw them.” We wouldn’t go that extreme on a street or track car.
You'll need to log in to post.
2 days ago in News
Find out in the next issue of Grassroots Motorsports.
5 days ago in News
Now is a great time to renew or start subscribing to our magazine.